We gratefully acknowledge support from
the Simons Foundation and Leiden University.

Astrophysics

New submissions

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New submissions for Wed, 25 Mar 20

[1]  arXiv:2003.10447 [pdf, ps, other]
Title: GRB Prompt Emission Spectra: The Synchrotron Revenge
Authors: Maria Edvige Ravasio (1, 2) ((1) University of Milano-Bicocca, (2) INAF - Astronomical Observatory of Brera-Merate)
Comments: 4 pages, 2 figures, Proceeding of the Yamada Conference LXXI: Gamma-ray Bursts in the Gravitational Wave Era 2019
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

After more than 40 years from their discovery, the long-lasting tension between predictions and observations of GRBs prompt emission spectra starts to be solved. We found that the observed spectra can be produced by the synchrotron process, if the emitting particles do not completely cool. Evidence for incomplete cooling was recently found in Swift GRBs spectra with prompt observations down to 0.5 keV (Oganesyan et al. 2017, 2018), characterized by an additional low-energy break. In order to search for this break at higher energies, we analysed the 10 long and 10 short brightest GRBs detected by the Fermi satellite in over 10 years of activity. We found that in 8/10 long GRBs there is compelling evidence of a low energy break (below the peak energy) and the photon indices below and above that break are remarkably consistent with the values predicted by the synchrotron spectrum (-2/3 and -3/2, respectively). None of the ten short GRBs analysed shows a break, but the low energy spectral slope is consistent with -2/3. Within the framework of the GRB standard model, these results imply a very low magnetic field in the emission region, at odds with expectations. I also present the spectral evolution of GRB 190114C, the first GRB detected with high significance by the MAGIC Telescopes, which shows the compresence (in the keV-MeV energy range) of the prompt and of the afterglow emission, the latter rising and dominating the high energy part of the spectral energy range.

[2]  arXiv:2003.10450 [pdf, other]
Title: An Isolated White Dwarf with 317-Second Rotation and Magnetic Emission
Comments: 11 pages, 6 figures, 3 tables. Accepted for publication in ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP)

We report the discovery of short-period photometric variability and modulated Zeeman-split hydrogen emission in SDSSJ125230.93-023417.72 (EPIC 228939929), a variable white dwarf star observed at long cadence in \textit{K2} Campaign 10. The behavior is associated with a magnetic ($B=5.0$ MG) spot on the stellar surface, making the $317.278$-second period a direct measurement of the stellar rotation rate. This object is therefore the fastest-rotating apparently isolated (without a stellar companion) white dwarf yet discovered, and the second found to exhibit chromospheric Balmer emission after GD 356, in which the emission has been attributed to a unipolar inductor mechanism driven by a possible rocky planet. We explore the properties and behavior of this object, and consider whether its evolution may hold implications for white dwarf mergers and their remnants.

[3]  arXiv:2003.10451 [pdf, other]
Title: The TESS-Keck Survey I: A Warm Sub-Saturn-Mass Planet and a Caution about Stray Light in TESS Cameras
Comments: 17 pages, 9 figures, 4 tables. Resubmitted to AAS Journals following a positive referee report
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)

We report the detection of a Saturn-size exoplanet orbiting HD 332231 (TOI 1456) in light curves from the Transiting Exoplanet Survey Satellite ($\textit{TESS}$). HD 332231, an F8 dwarf star with a V-band magnitude of 8.56, was observed by $\textit{TESS}$ in Sector 14 and 15. We detect a single-transit event in the Sector 15 presearch data conditioning (PDC) light curve. We obtain spectroscopic follow-up observations of HD 332231 with the Automated Planet Finder (APF), Keck-I, and SONG telescopes. The orbital period we infer from the radial velocity (RV) observations leads to the discovery of another transit in Sector 14 that was masked by PDC due to scattered light contamination. A joint analysis of the transit and RV data confirms the planetary nature of HD 332231 b, a Saturn-size ($0.867^{+0.027}_{-0.025} \; R_{\rm J}$), sub-Saturn mass ($0.244\pm0.021 \; M_{\rm J}$) exoplanet on a 18.71-day circular orbit. The low surface gravity of HD 332231 b along with the relatively low stellar flux it receives makes it a compelling target for transmission spectroscopy. Also, the stellar obliquity is likely measurable via the Rossiter-McLaughlin effect, an exciting prospect given the 0.14-au orbital separation of HD 332231 b. The spectroscopic observations do not provide substantial evidence for any additional planets in the HD 332231 system, but continued RV monitoring is needed to further characterize this system. We also predict that the frequency and duration of masked data in the PDC light curves for $\textit{TESS}$ Sectors 14-16 could hide transits of some exoplanets with orbital periods between 10.5 and 17.5 days.

[4]  arXiv:2003.10453 [pdf, ps, other]
Title: Limited Modified Gravity
Authors: Eric V. Linder
Comments: 8 pages, 7 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

We systematically assess several limiting cases of modified gravity, where particular theoretical or observational conditions hold. This framework includes the well known scalar-tensor gravity and No Slip Gravity and No Run Gravity, and we extend it to three new limits: Only Run, Only Light, and Only Growth Gravities. These limits give simplifications that allow deeper understanding of modified gravity, including demonstration that gravitational effects on light and matter can have opposite signs in their deviation from general relativity. We also show observational predictions for the different cosmic structure growth rates $f\sigma_8$ and the ratio of gravitational wave standard siren luminosity to photon standard candle luminosity distance relations, defining a new statistic $D_G$ that emphasizes their complementarity and ability to distinguish models.

[5]  arXiv:2003.10454 [pdf, other]
Title: The impact of spectroscopic incompleteness in direct calibration of redshift distributions for weak lensing surveys
Comments: 19 pages, 12 figures. Our main result is shown in Fig. 6. Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Obtaining accurate distributions of galaxy redshifts is a critical aspect of weak lensing cosmology experiments. One of the methods used to estimate and validate redshift distributions is apply weights to a spectroscopic sample so that their weighted photometry distribution matches the target sample. In this work we estimate the \textit{selection bias} in redshift that is introduced in this procedure. We do so by simulating the process of assembling a spectroscopic sample (including observer-assigned confidence flags) and highlight the impacts of spectroscopic target selection and redshift failures. We use the first year (Y1) weak lensing analysis in DES as an example data set but the implications generalise to all similar weak lensing surveys. We find that using colour cuts that are not available to the weak lensing galaxies can introduce biases of $\Delta~z\sim0.015$ in the weighted mean redshift of different redshift intervals. To assess the impact of incompleteness in spectroscopic samples, we select only objects with high observer-defined confidence flags and compare the weighted mean redshift with the true mean. We find that the mean redshift of the DES Y1 weak lensing sample is typically biased at the $\Delta~z=0.005-0.05$ level after the weighting is applied. The bias we uncover can have either sign, depending on the samples and redshift interval considered. For the highest redshift bin, the bias is larger than the uncertainties in the other DES Y1 redshift calibration methods, justifying the decision of not using this method for the redshift estimations. We discuss several methods to mitigate this bias.

[6]  arXiv:2003.10455 [pdf, other]
Title: Gravitational Wave Production right after Primordial Black Hole Evaporation
Comments: 23 pages, 11 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

We discuss the footprint of evaporation of primordial black holes (PBHs) on stochastic gravitational waves (GWs) induced by scalar perturbations. We consider the case where PBHs once dominate the Universe but eventually evaporate before the big bang nucleosynthesis. The reheating through the PBH evaporation could end with a sudden change in the equation of state of the Universe compared to the conventional reheating caused by particle decay. We show that this "sudden reheating" by the PBH evaporation enhances the induced GWs, whose amount depends on the length of the PBH-dominated era and the width of the PBH mass function. We explore the possibility to constrain the primordial abundance of the evaporating PBHs by observing the induced GWs. We find that the abundance parameter $\beta \gtrsim 10^{-5} - 10^{-8}$ for $\mathcal{O}(10^3 - 10^5) \, \text{g}$ PBHs can be constrained by future GW observations if the width of the mass function is smaller than about a hundredth of the mass.

[7]  arXiv:2003.10456 [pdf, other]
Title: Fornax 3D project: automated detection of planetary nebulae in the centres of early-type galaxies and first results
Comments: 20 pages, 17 figures. Accepted for publication in Astronomy and Astrophysics Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Extragalactic Planetary Nebulae (PNe) are detectable via relatively strong nebulous [OIII] emission, acting as direct probes into the local stellar population. Due to an apparently universal, invariant magnitude cut-off, PNe are also considered to be a remarkable standard candle for distance estimation. Through detecting PNe within the galaxies, we aim to connect the relative abundances of PNe to the properties of their host galaxy stellar population. By removing the stellar background components from FCC 167 and FCC 219, we aim to produce PN Luminosity Functions (PNLF) of those galaxies, and therefore also estimate the distance modulus to those two systems. Finally, we test the reliability and robustness of our novel detection and analysis method. It detects the presence of unresolved point sources via their [OIII] 5007{\AA} emission, within regions previously unexplored. We model the [OIII] emissions in both the spatial and spectral dimensions together, as afforded to us by the Multi Unit Spectroscopic Explorer (MUSE) and drawing on data gathered as part of the Fornax3D survey. For each source, we inspect the properties of the nebular emission lines present to remove other sources, that could hinder the safe construction of the PNLF, such as supernova remnants and HII regions. As a further step, we characterise any potential limitations and draw conclusions about the reliability of our modelling approach via a set of simulations. Through the application of this novel detection and modelling approach to IFU observations, we report for both galaxies: distance estimates, luminosity specific PNe frequency values. Furthermore, we include an overview into source contamination, galaxy differences and how they may affect the PNe populations in the dense stellar environments.

[8]  arXiv:2003.10457 [pdf, other]
Title: Dark Energy Survey Identification of A Low-Mass ActiveGalactic Nucleus at Redshift 0.823 from Optical Variability
Comments: 13 pages, 8 figures, 1 table, submitted to MNRAS, comments are welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We report the identification of a low-mass AGN, DES J0218$-$0430, in a redshift $z = 0.823$ galaxy in the Dark Energy Survey (DES) Supernova field. We select DES J0218$-$0430 as an AGN candidate by characterizing its long-term optical variability alone based on DES optical broad-band light curves spanning $\sim$6 years. An archival optical spectrum from the fourth phase of the Sloan Digital Sky Survey shows both broad Mg II and broad H$\beta$ lines, confirming its nature as a broad-line AGN. Archival XMM-Newton X-ray observations suggest an intrinsic hard X-ray luminosity of $L_{{\rm 2-12\,keV}}\sim7.6\pm0.4\times10^{43}$ erg s$^{-1}$, which exceeds those of the most X-ray luminous starburst galaxies, in support of an AGN driving the optical variability. Based on the broad H$\beta$ from SDSS spectrum, we estimate a virial BH mass of $M_{\bullet}\sim10^{6.4\pm0.1}M_{\odot}$ (with the error denoting 1$\sigma$ statistical uncertainties only), consistent with the estimation from OzDES, making it the lowest mass AGN with redshift $>$ 0.4 detected in optical. We estimate the host galaxy stellar mass to be $M_{\ast}\sim10^{10.5\pm0.3}M_{\odot}$ based on modeling the multi-wavelength spectral energy distribution. DES J0218$-$0430 extends the $M_{\bullet}$-$M_{\ast}$ relation observed in luminous AGNs at $z\sim1$ to masses lower than being probed by previous work. Our work demonstrates the feasibility of using optical variability to identify low-mass AGNs at higher redshift in deeper synoptic surveys with direct implications for the upcoming Legacy Survey of Space and Time at Vera C. Rubin Observatory.

[9]  arXiv:2003.10458 [pdf, ps, other]
Title: Spinning Bar and a Star-formation Inefficient Repertoire: Turbulence in Hickson Compact Group NGC7674
Comments: 16 pages, 7 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The physics regulating star formation (SF) in Hickson Compact Groups (HCG) has thus far been difficult to describe, due to their unique kinematic properties. In this study we expand upon previous works to devise a more physically meaningful SF relation able to better encompass the physics of these unique systems. We combine CO(1--0) data from the Combined Array from Research in Millimeter Astronomy (CARMA) to trace the column density of molecular gas $\Sigma_\mathrm{gas}$ and deep H$\alpha$ imaging taken on the Southern Astrophysical Research (SOAR) Telescope tracing $\Sigma_\mathrm{SFR}$ to investigate star formation efficiency across face-on HCG, NGC7674. We find a lack of universality in star formation, with two distinct sequences present in the $\Sigma_\mathrm{gas}-\Sigma_\mathrm{SFR}$ plane; one for inside and one for outside the nucleus. We devise a SF relation based on the multi-freefall nature of gas and the critical density, which itself is dependent on the virial parameter $\alpha_{\mathrm{vir}}$, the ratio of turbulent to gravitational energy. We find that our modified SF relation fits the data and describes the physics of this system well with the introduction of a virial parameter of about 5--10 across the galaxy. This $\alpha_{\mathrm{vir}}$ leads to an order-of-magnitude reduction in SFR compared to $\alpha_{\mathrm{vir}}\approx 1$ systems.

[10]  arXiv:2003.10459 [pdf, ps, other]
Title: VLBI observations of the H2O gigamaser in TXS2226-184
Comments: 13 pages, 10 figures, 3 tables, accepted for publication by Astronomy & Astrophysics
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Outside the Milky Way, the most luminous H2O masers at 22 GHz, called 'megamasers' because of their extreme luminosity with respect to the Galactic and extragalactic H2O masers associated with star formation, are mainly detected in active galactic nuclei. In the case of the H2O maser detected in the nuclear region of the galaxy TXS2226-184 for the first time the term 'gigamaser' was used. However, the origin of this very luminous H2O maser emission has never been investigated into details. We study the nature of the H2O gigamaser in TXS2226-184 by measuring for the first time its absolute position at mas resolution, by comparing the morphology and characteristics of the maser emission at the VLBI scales after about 20 years, and by trying to detect its polarized emission. We observed the maser emission towards TXS2226-184 three times: the very first one with the VLBA (epoch 2017.45) and the next two times with the EVN (epochs 2017.83 and 2018.44). The first two epochs were observed in phase-reference mode, while the last epoch was observed in full-polarization mode but not in phase-reference mode to increase the on-source integration time. We also retrieved and analyzed the VLBA archival data at 22 GHz of TXS2226-184 observed in 1998.40. We detected 6 H2O maser features in epoch 2017.45 (VLBA), one in epoch 2017.83 (EVN), and two in epoch 2018.44 (EVN). All of them but one are red-shifted with respect to the systemic velocity of TXS2226-184, we detected only one blue-shifted maser feature and it is the weakest one. For the first time, we were able to measure the absolute position of the H2O maser features with errors below 1 mas. No linear and circular polarization was detected. We were able to associate the H2O maser features in TXS2226-184 with the most luminous radio continuum clump reported in the literature.

[11]  arXiv:2003.10460 [pdf, ps, other]
Title: Proton Synchrotron $γ$-rays and the Energy Crisis in Blazars
Comments: 8 pages, 4 figures, accepted for publication in the Astrophysical Journal Letters
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The origin of high-energy emission in blazars jets (i.e., leptonic versus hadronic) has been a long-standing matter of debate. Here, we focus on one variant of hadronic models where proton synchrotron radiation accounts for the observed steady $\gamma$-ray blazar emission. Using analytical methods, we derive the minimum jet power ($P_{j,\min}$) for the largest blazar sample analyzed to date (145 sources), taking into account uncertainties of observables and jet's physical parameters. We compare $P_{j,\min}$ against three characteristic energy estimators for accreting systems, i.e., the Eddington luminosity, the accretion disk luminosity, and the power of the Blandford-Znajek process, and find that $P_{j,\min}$ is about 2 orders of magnitude higher than all energetic estimators for the majority of our sample. The derived magnetic field strengths in the emission region require either large amplification of the jet's magnetic field (factor of 30) or place the $\gamma$-ray production site at sub-pc scales. The expected neutrino emission peaks at $\sim 0.1-10$ EeV, with typical peak neutrino fluxes $\sim 10^{-4}$ times lower than the peak $\gamma$-ray fluxes. We conclude that if relativistic hadrons are present in blazar jets, they can only produce a radiatively subdominant component of the overall spectral energy distribution of the blazar's steady emission.

[12]  arXiv:2003.10461 [pdf, ps, other]
Title: The clustering of X-ray AGN at 0.5 < z < 4.5: host galaxies dictate dark matter halo mass
Comments: 13 pages, 10 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present evidence that AGN do not reside in ``special'' environments, but instead show large-scale clustering determined by the properties of their host galaxies. Our study is based on an angular cross-correlation analysis applied to X-ray selected AGN in the COSMOS and UDS fields, spanning redshifts from $z\sim4.5$ to $z\sim0.5$. Consistent with previous studies, we find that AGN at all epochs are on average hosted by galaxies in dark matter halos of $10^{12}-10^{13}$ M$_{\odot}$, intermediate between star-forming and passive galaxies. We find, however, that the same clustering signal can be produced by inactive (i.e. non-AGN) galaxies closely matched to the AGN in spectral class, stellar mass and redshift. We therefore argue that the inferred bias for AGN lies in between the star-forming and passive galaxy populations because AGN host galaxies are comprised of a mixture of the two populations. Although AGN hosted by higher mass galaxies are more clustered than lower mass galaxies, this stellar mass dependence disappears when passive host galaxies are removed. The strength of clustering is also largely independent of AGN X-ray luminosity. We conclude that the most important property that determines the clustering in a given AGN population is the fraction of passive host galaxies. We also infer that AGN luminosity is likely not driven by environmental triggering, and further hypothesise that AGN may be a stochastic phenomenon without a strong dependence on environment.

[13]  arXiv:2003.10465 [pdf, other]
Title: Effective photon mass and (dark) photon conversion in the inhomogeneous Universe
Comments: 29 pages, 17 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Photons traveling cosmological distances through the inhomogeneous Universe experience a great variation in their in-medium induced effective mass. Using the EAGLE suite of hydrodynamical simulations, we infer the free electron distribution and thereby the effective photon mass after reionization. We use this data to study the inter-conversion of kinetically mixed photons and dark photons, which may occur at a great number of resonance redshifts, and obtain the "optical depth" against conversion along random lines-of-sight. Using COBE/FIRAS, Planck, and SPT measurements, we constrain the dark photon parameter space from the depletion of CMB photons into dark photons that causes both spectral distortions and additional anisotropies in the CMB. Finally, we also consider the conversion of sub-eV dark radiation into ordinary photons. We make the line-of-sight distributions of both, free electrons and dark matter, publicly available.

[14]  arXiv:2003.10467 [pdf, ps, other]
Title: On Monolithic Supermassive Stars
Comments: 9 pages, 6 figures, 1 table, MNRAS accepted
Subjects: Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Supermassive stars have been proposed as the progenitors of the massive ($\sim 10^{9}\,\rm{M}_{\odot}$) quasars observed at $z\sim7$. Prospects for directly detecting supermassive stars with next-generation facilities depend critically on their intrinsic lifetimes, as well as their formation rates. We use the 1D stellar evolution code Kepler to explore the theoretical limiting case of zero-metallicity, non-rotating stars, formed monolithically with initial masses between $10\,\rm{kM}_{\odot}$ and $190\,\rm{kM}_{\odot}$. We find that stars born with masses between $\sim60\,\rm{kM}_{\odot}$ and $\sim150\,\rm{kM}_{\odot}$ collapse at the end of the main sequence, burning stably for $\sim1.5\,\rm{Myr}$. More massive stars collapse directly through the general relativistic instability after only a thermal timescale of $\sim3\,\rm{kyr}$--$4\,\rm{kyr}$. The expected difficulty in producing such massive, thermally-relaxed objects, together with recent results for currently preferred rapidly-accreting formation models, suggests that such ``truly direct'' or ``dark'' collapses may not be typical for supermassive objects in the early Universe. We close by discussing the evolution of supermassive stars in the broader context of massive primordial stellar evolution and the possibility of supermassive stellar explosions.

[15]  arXiv:2003.10489 [pdf, ps, other]
Title: Spitzer's perspective of polycyclic aromatic hydrocarbons in galaxies
Authors: Aigen Li
Comments: 14 pages, 6 figures, Nature Astronomy (2020 April issue); I dedicate this invited review article to the 60th anniversary of the Department of Astronomy of Beijing Normal University, the 2nd astronomy program in the modern history of China
Subjects: Astrophysics of Galaxies (astro-ph.GA); Atomic and Molecular Clusters (physics.atm-clus); Chemical Physics (physics.chem-ph)

Polycyclic aromatic hydrocarbon (PAH) molecules, as revealed by the distinctive set of emission bands at 3.3, 6.2, 7.7, 8.6, 11.3 and 12.7 $\mu$m characteristic of their vibrational modes, are abundant and widespread throughout the Universe. They are ubiquitously seen in a wide variety of astrophysical regions, ranging from planet-forming disks around young stars to the interstellar medium (ISM) of the Milky Way and external galaxies out to high redshifts at z>4. PAHs profoundly influence the thermal budget and chemistry of the ISM by dominating the photoelectric heating of the gas and controlling the ionization balance.
Here, we review the current state of knowledge of the astrophysics of PAHs, focusing on their observational characteristics obtained from the Spitzer Space Telescope and their diagnostic power for probing the local physical and chemical conditions and processes. Special attention is paid to the spectral properties of PAHs and their variations revealed by the Infrared Spectrograph (IRS) on board Spitzer across a much broader range of extragalactic environments (e.g., distant galaxies, early-type galaxies, galactic halos, active galactic nuclei, and low-metallicity galaxies) than was previously possible with the Infrared Space Observatory (ISO) or any other telescope facilities. Also highlighted is the relation between the PAH abundance and the galaxy metallicity established for the first time by Spitzer.

[16]  arXiv:2003.10503 [pdf, other]
Title: A relativistic outflow from the energetic, fast-rising blue optical transient CSS161010 in a dwarf galaxy
Comments: Submitted to ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present X-ray and radio observations of the Fast Blue Optical Transient (FBOT) CRTS-CSS161010 J045834-081803 (CSS161010 hereafter) at t=69-531 days. CSS161010 shows luminous X-ray ($L_x\sim5\times 10^{39}\,\rm{erg\,s^{-1}}$) and radio ($L_{\nu}\sim10^{29}\,\rm{erg\,s^{-1}Hz^{-1}}$) emission. The radio emission peaked at ~100 days post transient explosion and rapidly decayed. We interpret these observations in the context of synchrotron emission from an expanding blastwave. CSS161010 launched a relativistic outflow with velocity $\Gamma\beta c\ge0.55c$ at ~100 days. This is faster than the non-relativistic AT2018cow ($\Gamma\beta c\sim0.1c$) and closer to ZTF18abvkwla ($\Gamma\beta c\ge0.3c$ at 63 days). The inferred initial kinetic energy of CSS161010 ($E_k\gtrsim10^{51}$ erg) is comparable to that of long Gamma Ray Bursts (GRBs), but the ejecta mass that is coupled to the relativistic outflow is significantly larger ($\sim0.01-0.1\,M_{\odot}$). This is consistent with the lack of observed $\gamma$-rays. The luminous X-rays were produced by a different emission component to the synchrotron radio emission. CSS161010 is located at ~150 Mpc in a dwarf galaxy with stellar mass $M_{*}\sim10^{7}\,\rm{M_{\odot}}$ and specific star formation rate 0.3 $Gyr^{-1}$. This mass is among the lowest inferred for host-galaxies of explosive transients from massive stars. Our observations of CSS161010 are consistent with an engine-driven aspherical explosion from a rare evolutionary path of a H-rich stellar progenitor, but we cannot rule out a stellar tidal disruption event on a centrally-located intermediate mass black hole. Regardless of the physical mechanism, CSS161010 establishes the existence of a new class of rare (rate <0.25% the core-collapse supernova rate at z~0.2) H-rich transients that can launch relativistic outflows.

[17]  arXiv:2003.10505 [pdf, other]
Title: Simulating Solar Flare Irradiance with Multithreaded Models of Flare Arcades
Comments: Submitted to ApJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Understanding how energy is released in flares is one of the central problems of solar and stellar astrophysics. Observations of high temperature flare plasma hold many potential clues as to the nature of this energy release. It is clear, however, that flares are not composed of a few impulsively heated loops, but are the result of heating on many small-scale threads that are energized over time, making it difficult to compare observations and numerical simulations in detail. Several previous studies have shown that it is possible to reproduce some aspects of the observed emission by considering the flare as a sequence of independently heated loops, but these studies generally focus on small-scale features while ignoring the global features of the flare. In this paper, we develop a multithreaded model that encompasses the time-varying geometry and heating rate for a series of successively-heated loops comprising an arcade. To validate, we compare with spectral observations of five flares made with the MinXSS CubeSat as well as light curves measured with GOES/XRS and SDO/AIA. We show that this model can successfully reproduce the light curves and quasi-periodic pulsations in GOES/XRS, the soft X-ray spectra seen with MinXSS, and the light curves in various AIA passbands. The AIA light curves are most consistent with long duration heating, but elemental abundances cannot be constrained with the model. Finally, we show how this model can be used to extrapolate to spectra of extreme events that can predict irradiance across a wide wavelength range including unobserved wavelengths.

[18]  arXiv:2003.10533 [pdf, other]
Title: Formation of the first stars and black holes
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Solar and Stellar Astrophysics (astro-ph.SR)

We review the current status of knowledge concerning the early phases of star formation during cosmic dawn. This includes the first generations of stars forming in the lowest mass dark matter halos in which cooling and condensation of gas with primordial composition is possible at very high redshift ($z > 20$), namely metal-free Population III stars, and the first generation of massive black holes forming at such early epochs, the so-called black hole seeds. The formation of black hole seeds as end states of the collapse of Population III stars, or via direct collapse scenarios, is discussed. In particular, special emphasis is given to the physics of supermassive stars as potential precursors of direct collapse black holes, in light of recent results of stellar evolution models, and of numerical simulations of the early stages of galaxy formation. Furthermore, we discuss the role of the cosmic radiation produced by the early generation of stars and black holes at high redshift in the process of reionization.

[19]  arXiv:2003.10542 [pdf, other]
Title: Source Depth of Three-minute Umbral Oscillations
Comments: Accepted for publication in ApJL
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We infer the depth of the internal sources giving rise to three-minute umbral oscillations. Recent observations of ripple-like velocity patterns of umbral oscillations supported the notion that there exist internal sources exciting the umbral oscillations. We adopt the hypothesis that the fast magnetohydrodynamic (MHD) waves generated at a source below the photospheric layer propagate along different paths, reach the surface at different times, and excited slow MHD waves by mode conversion. These slow MHD waves are observed as the ripples that apparently propagate horizontally. The propagation distance of the ripple given as a function of time is strongly related to the depth of the source. Using the spectral data of the Fe I 5435A line taken by the Fast Imaging Solar Spectrograph of the Goode Solar Telescope at Big Bear Solar Observatory, we identified five ripples and determined the propagation distance as a function of time in each ripple. From the model fitting to these data, we obtained the depth between 1000 km and 2000 km. Our result will serve as an observational constraint to understanding the detailed processes of magnetoconvection and wave generation in sunspots.

[20]  arXiv:2003.10544 [pdf, other]
Title: A Multiple Power Law Distribution for Initial Mass Functions
Authors: Christopher Essex (1), Shantanu Basu (1), Janett Prehl (2), Karl Heinz Hoffmann (2) ((1) University of Western Ontario, (2) Technische Universitat Chemnitz)
Comments: 8 pages, 6 figures, to appear in MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We introduce a new multi-power-law distribution for the Initial Mass Function (IMF) to explore its potential properties. It follows on prior work that introduced mechanisms accounting for mass accretion in star formation, developed within the framework of general evolution equations for the mass distribution of accreting and non-accreting (proto)stars. This paper uses the same fundamental framework to demonstrate that the interplay between a mass-dependent and a time-dependent step-like dropout rate from accretion leads to IMFs that exhibit multiple power laws for an exponential mass growth. While the mass-dependent accretion and its dropout is intrinsic to each star, the time-dependent dropout might be tied to a specific history such as the rapid consumption of nebular material by nearby stars or the sweeping away of some material by shock waves. The time-dependent dropout folded into the mass-dependent process of star formation is shown to have a significant influence on the IMFs.

[21]  arXiv:2003.10545 [pdf]
Title: Potassium Isotope Compositions of Carbonaceous and Ordinary Chondrites: Implications on the Origin of Volatile Depletion in the Early Solar System
Comments: 71 pages, 2 tables, 9 figures
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

Solar system materials are variably depleted in moderately volatile elements (MVEs) relative to the proto-solar composition. To address the origin of this MVE depletion, we conducted a systematic study of high-precision K isotopic composition on 16 carbonaceous chondrites (CCs) of types CM1-2, CO3, CV3, CR2, CK4-5 and CH3 and 28 ordinary chondrites (OCs) covering petrological types 3 to 6 and chemical groups H, L, and LL. We observed significant overall K isotope (delta41K) variations (-1.54 to 0.70 permil). The K isotope compositions of CCs are largely higher than the Bulk Silicate Earth (BSE) value, whereas OCs show typically lower values than BSE. Neither CCs nor OCs show resolvable correlations between K isotopes and chemical groups, petrological types, shock levels, exposure ages, fall or find occurrence, or terrestrial weathering. The lack of a clear trend between K isotopes and K content indicates that the K isotope fractionations were decoupled from the relative elemental K depletions. The range of K isotope variations in the CCs is consistent with a four-component (chondrule, refractory inclusion, matrix and water) mixing model that is able to explain the bulk elemental and isotopic compositions of the main CC groups, but requires a fractionation in K isotopic compositions in chondrules. We propose that the major control of the isotopic compositions of group averages is condensation or vaporization in nebular environments that is preserved in the compositional variation of chondrules. Parent-body processes (aqueous alteration, thermal metamorphism, and metasomatism) can mobilize K and affect the K isotopes in individual samples. In the case of the OCs, the full range of K isotopic variations can only be explained by the combined effects of the size and relative abundances of chondrules, parent-body aqueous and thermal alteration.

[22]  arXiv:2003.10573 [pdf, ps, other]
Title: Small-Scale Dynamical Coherence Accompanied with Galaxy Conformity
Comments: 8 pages, 5 figures, accepted for publication in The Astrophysical Journal
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The discovery of the coherence between galaxy rotation and neighbor motion in 1-Mpc scales has been reported recently. Following up the discovery, we investigate whether the neighbors in such dynamical coherence also present galaxy conformity, using the Calar Alto Legacy Integral Field Area Survey (CALIFA) data and the NASA-Sloan Atlas (NSA) catalog. We measure the correlation coefficient of g - r colors between the CALIFA galaxies and their neighbors, as a quantitative indicator of galaxy conformity. The neighbors are divided into coherently moving and anti-coherently moving ones, the correlation coefficients from which are compared with each other, in various bins of relative luminosity and projected distance. In most cases, the CALIFA galaxies and their neighbors show positive correlation coefficients in g - r color, even for the anti-coherent neighbors. However, we find statistically significant (2.6-sigma) difference between coherent and anti-coherent neighbors, when the neighbor galaxies are bright (Delta Mr <= -1.0) and close (D <= 400 kpc). That is, when they are bright and close to the CALIFA galaxies, the coherently moving neighbors show stronger conformity with the CALIFA galaxies than the anti-coherently moving neighbors. This result supports that the small-scale dynamical coherence may originate from galaxy interactions as galaxy conformity is supposed to do, which agrees with the conclusion of the previous study.

[23]  arXiv:2003.10575 [pdf, other]
Title: A Random Forest Approach to Identifying Young Stellar Object Candidates in the Lupus Star-Forming Region
Authors: Elizabeth Melton
Comments: 31 pages, 14 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

The identification and characterization of stellar members within a star-forming region are critical to many aspects of star formation, including formalization of the initial mass function, circumstellar disk evolution and star-formation history. Previous surveys of the Lupus star-forming region have identified members through infrared excess and accretion signatures. We use machine learning to identify new candidate members of Lupus based on surveys from two space-based observatories: ESA's Gaia and NASA's Spitzer. Astrometric measurements from Gaia's Data Release 2 and astrometric and photometric data from the Infrared Array Camera (IRAC) on the Spitzer Space Telescope, as well as from other surveys, are compiled into a catalog for the Random Forest (RF) classifier. The RF classifiers are tested to find the best features, membership list, non-membership identification scheme, imputation method, training set class weighting and method of dealing with class imbalance within the data. We list 27 candidate members of the Lupus star-forming region for spectroscopic follow-up. Most of the candidates lie in Clouds V and VI, where only one confirmed member of Lupus was previously known. These clouds likely represent a slightly older population of star-formation.

[24]  arXiv:2003.10582 [pdf, other]
Title: Burst properties of the most recurring transient magnetar SGR J1935+2154
Comments: accepted for publication in The Astrophysical Journal
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present timing and time-integrated spectral analysis of 127 bursts from SGR J1935+2154. These bursts were observed with the Gamma-ray Burst Monitor on the Fermi Gamma-ray Space Telescope and the Burst Alert Telescope on the Neil Gehrels Swift Observatory during the source's four active episodes from 2014 to 2016. This activation frequency makes SGR J1935+2154 the most burst prolific transient magnetar. We find the average duration of all the detected bursts to be much shorter than the typical, anticipated value. We fit the burst time-integrated spectra with two black-body functions, a Comptonized model and three other simpler models. Bursts from SGR J1935+2154 exhibit similar spectral properties to other magnetars, with the exception of the power law index from the Comptonized model, which correlates with burst fluence. We find that the durations and both black-body temperatures of the bursts have significantly evolved across the four active episodes. We also find that the burst time history exhibits two trends, which are strongly correlated with the decay of the persistent emission in each outburst.

[25]  arXiv:2003.10583 [pdf, other]
Title: On rising magnetic flux tube and formation of sunspots in a deep domain
Authors: H. Hotta, H. Iijima
Comments: 17 pages, 24 figures. Accepted for publication by MNRAS
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

We investigate the rising flux tube and the formation of sunspots in an unprecedentedly deep computational domain that covers the whole convection zone with a radiative magnetohydrodynamics simulation. Previous calculations had shallow computational boxes (< 30 Mm) and convection zones at a depth of 200 Mm. By using our new numerical code R2D2, we succeed in covering the whole convection zone and reproduce the formation of the sunspot from a simple horizontal flux tube because of the turbulent thermal convection. The main findings are (1) The rising speed of the flux tube is larger than the upward convection velocity because of the low density caused by the magnetic pressure and the suppression of the mixing. (2) The rising speed of the flux tube exceeds 250 m/s at a depth of 18 Mm, while we do not see any clear evidence of the divergent flow 3 hr before the emergence at the solar surface. (3) Initially, the root of the flux tube is filled with the downflows and then the upflow fills the center of the flux tube during the formation of the sunspot. (4) The essential mechanisms for the formation of the sunspot are the coherent inflow and the turbulent transport. (5) The low-temperature region is extended to a depth of at least 40 Mm in the matured sunspot, with the high-temperature region in the center of the flux tube. Some of the findings indicate the importance of the deep computational domain for the flux emergence simulations.

[26]  arXiv:2003.10641 [pdf, other]
Title: The effect of surface gravity on line-depth ratios in the wavelength range 0.97-1.32 μm
Comments: 12 pages, 7 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

A line-depth ratio (LDR) of two spectral lines with different excitation potentials is expected to be correlated with the effective temperature ($T_\mathrm{eff}$). It is possible to determine $T_\mathrm{eff}$ of a star with a precision of tens of Kelvin if dozens or hundreds of tight LDR-$T_\mathrm{eff}$ relations can be used. Most of the previous studies on the LDR method were limited to optical wavelengths, but Taniguchi and collaborators reported 81 LDR relations in the $YJ$-band, 0.97-1.32 $\mu\mathrm{m}$, in 2018. However, with their sample of only 10 giants, it was impossible to account for the effects of surface gravity and metallicity on the LDRs well. Here we investigate the gravity effect based on $YJ$-band spectra of 63 stars including dwarfs, giants, and supergiants observed with the WINERED spectrograph. We found that some LDR-$T_\mathrm{eff}$ relations show clear offsets between the sequence of dwarfs and those of giants/supergiants. The difference between the ionization potentials of the elements considered in each line pair and the corresponding difference in the depths can, at least partly, explain the dependency of the LDR on the surface gravity. In order to expand the stellar parameter ranges that the LDR method can cover with high precision, we obtained new sets of LDR-$T_\mathrm{eff}$ relations for solar-metal G0-K4 dwarfs and F7-K5 supergiants, respectively. The typical precision that can be achieved with our relations is 10-30 K for both dwarfs and supergiants.

[27]  arXiv:2003.10646 [pdf, other]
Title: A new calibration method of sub-halo orbital evolution for semi-analytic models
Comments: 11 pages, 7 figures
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Understanding the non-linear dynamics of satellite halos (a.k.a. ``sub-halos'') is important for predicting the abundance and distribution of dark matter substructures and satellite galaxies, and for distinguishing among microphysical dark matter models using observations. Typically, modeling these dynamics requires large N-body simulations with high resolution. Semi-analytic models can provide a more efficient way to describe the key physical processes such as dynamical friction, tidal mass loss, and tidal heating, with only a few free parameters. In this work, we present a fast Monte Carlo Markov Chain fitting approach to explore the parameter space of such a sub-halo non-linear evolution model. We use the dynamical models described in an earlier work and calibrate the models to two sets of high-resolution cold dark matter N-body simulations, ELVIS and Caterpillar. Compared to previous calibrations that used manual parameter tuning, our approach provides a more robust way to determine the best-fit parameters and their posterior probabilities. We find that jointly fitting for the sub-halo mass and maximum velocity functions can break the degeneracy between tidal stripping and tidal heating parameters, as well as providing better constraints on the strength of dynamical friction. We show that our semi-analytic simulation can accurately reproduce N-body simulations statistics, and that the calibration results for the two sets of N-body simulations agree at 95% confidence level. Dynamical models calibrated in this work will be important for future dark matter substructure studies.

[28]  arXiv:2003.10672 [pdf, other]
Title: A frequency-dependent squeezed vacuum source for broadband quantum noise reduction in advanced gravitational-wave detectors
Comments: To be published in Phys. Rev. Lett
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Instrumentation and Detectors (physics.ins-det)

The astrophysical reach of current and future ground-based gravitational-wave detectors is mostly limited by quantum noise, induced by vacuum fluctuations entering the detector output port. The replacement of this ordinary vacuum field with a squeezed vacuum field has proven to be an effective strategy to mitigate such quantum noise and it is currently used in advanced detectors. However, current squeezing cannot improve the noise across the whole spectrum because of the Heisenberg uncertainty principle: when shot noise at high frequencies is reduced, radiation pressure at low frequencies is increased. A broadband quantum noise reduction is possible by using a more complex squeezing source, obtained by reflecting the squeezed vacuum off a Fabry-Perot cavity, known as filter cavity. Here we report the first demonstration of a frequency-dependent squeezed vacuum source able to reduce quantum noise of advanced gravitational-wave detectors in their whole observation bandwidth. The experiment uses a suspended 300 m long filter cavity, similar to the one planned for KAGRA, Advanced Virgo and Advanced LIGO, and capable of inducing a rotation of the squeezing ellipse below 100 Hz.

[29]  arXiv:2003.10691 [pdf, other]
Title: DFT study on interstellar PAH molecules with aliphatic side groups
Journal-ref: The Astrophysical Journal, 892:11 (11pp), 2020 March 20
Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

Polycyclic Aromatic Hydrocarbon (PAH) molecules have been long adjudged to contribute to the frequently detected distinct emission features at 3.3, 6.2, 7.7, 8.6, 11.2 and 12.7 {\mu}m with weaker and blended features distributed in the 3-20 {\mu}m region. The comparatively weaker 3.4 {\mu}m emission feature has been attributed to have an aliphatic origin as carrier. PAH with aliphatic functional group attached to it is one of the proposed potential candidate carriers for the 3.4 {\mu}m emission band, however, the assignment of carrier is still enigmatic. In this work, we employ Density Functional Theory (DFT) calculation on a symmetric and compact PAH molecule; coronene (C24H12) with aliphatic side group to investigate any spectral similarities with observed features at 3-4 {\mu}m. The side groups considered in this study are -H (hydrogenated), -CH3 (methyl), -CH2-CH3 (ethyl) and -CH=CH2 (vinyl) functional groups. Considering the possible presence of deuterium (D) in PAHs, we also include D in the aliphatic side group to study the spectral behavior. We present a detailed analysis of the IR spectra of these molecules and discuss possible astrophysical implications.

[30]  arXiv:2003.10693 [pdf, other]
Title: Evidence for magnetar precession in X-ray afterglows of gamma-ray bursts
Comments: 6 pages, 4 figures, 1 table. Accepted for publication in ApJL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Many gamma-ray bursts are followed by periods of extended emission. At least in some cases, the burst afterglow may be powered by a rapidly rotating, highly-magnetised neutron star, which spins down due to electromagnetic and gravitational wave emission. Such a remnant is likely to strongly precess in the early stages of its life, which would lead to modulations in the X-ray luminosity as the triaxiality of the system evolves over time. Using a radiation profile appropriate for a precessing, oblique rotator, we find that Swift-XRT data of a long (080602) and a short (090510) burst matches the model with significantly higher accuracy (mean-square residuals dropping by $\gtrsim 200 \%$ in the early stages of the extended emission) than for an orthogonal rotator. We interpret this as evidence for precession in newborn magnetars.

[31]  arXiv:2003.10733 [pdf]
Title: Antenna design for the SKA1-LOW and HERA super radio telescopes
Comments: 4 pages
Journal-ref: 2018 International Conference on Electromagnetics in Advanced Applications (ICEAA)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

This paper summarizes the design process and metrics for the latest antenna design for 2 radio telescopes, SKALA4 for the SKA1-LOW instrument and the V-feed for the HERA telescope. In the paper we briefly describe the main features of the antenna element design and the most important figures of merit for both instruments. Finally, we show the response of both designs against some of these figures of merit.

[32]  arXiv:2003.10753 [pdf, other]
Title: Nebulosities of the Symbiotic Binary R Aquarii -- A Short Review
Comments: Conference proceeding, accepted for publication in PoS-SISSA
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)

In this proceeding, we present a short review of the fascinating nebulosities of symbiotic binary R Aquarii. The R Aquarii system, comprising the central binary and surrounding nebular material, has been the subject of near-continuous study since its discovery, with a few hundred papers listed in ADS. As such, it is impossible to provide here the comprehensive review that R Aquarii deserves, instead we chose to focus on the nebulosities -- covering both our own research and other relevant results from the literature.

[33]  arXiv:2003.10766 [pdf, other]
Title: PhotoWeb redshift: boosting photometric redshift accuracy with large spectroscopic surveys
Subjects: Astrophysics of Galaxies (astro-ph.GA)

Improving distance measurements in large imaging surveys is a major challenge to better reveal the distribution of galaxies on a large scale and to link galaxy properties with their environments. Photometric redshifts can be efficiently combined with the cosmic web (CW) extracted from overlapping spectroscopic surveys to improve their accuracy. We apply a similar method using a new generation of photometric redshifts based on a convolution neural network (CNN). The CNN is trained on the SDSS images with the main galaxy sample (SDSS-MGS, $r \leq 17.8$) and the GAMA spectroscopic redshifts up tor $\sim 19.8$. The mapping of the CW is obtained with 680,000 spectroscopic redshifts from the MGS and BOSS surveys. The redshift probability distribution functions (PDF), which are well calibrated (unbiased and narrow, $\leq 120$ Mpc), intercept a few CW structure along the line of sight. Combining these PDFs with the density field distribution provides new photometric redshifts, $z_{web}$, whose accuracy is improved by a factor of two (i.e.,${\sigma} \sim 0.004(1+z)$) for galaxies with $r \leq 17.8$. For half of them, the distance accuracy is better than 10 cMpc. The narrower the original PDF, the larger the boost in accuracy. No gain is observed for original PDFs wider than 0.03. The final $z_{web}$ PDFs also appear well calibrated. The method performs slightly better for passive galaxies than star-forming ones, and for galaxies in massive groups since these populations better trace the underlying large-scale structure. Reducing the spectroscopic sampling by a factor of 8 still improves the photometric redshift accuracy by 25%. Extending the method to galaxies fainter than the MGS limit still improves the redshift estimates for 70% of the galaxies, with a gain in accuracy of 20% at low $z$ where the resolution of the CW is the highest.

[34]  arXiv:2003.10777 [pdf, other]
Title: Low geo-effectiveness of fast halo CMEs related to the 12 X-class flares in 2002
Comments: 33 pages, 12 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)

It is generally accepted that extreme space weather events tend to be related to strong flares and fast halo coronal mass ejections CMEs. In the present paper, we carefully identify the chain of events from the Sun to the Earth induced by all 12 X-class flares that occurred in 2002. In this small sample, we find an unusual high rate (58\%) of solar sources with a longitude larger than 74 degrees. Yet, all 12 X-class flares are associated with at least one CME. The fast halo CMEs (50\% ) are related to interplanetary CMEs (ICMEs) at L1 and weak Dst minimum values ($> -51\;$nT); while 5 (41\%) of the 12 X-class flares are related to solar proton events (SPE). We conclude that: (i) All twelve analyzed solar events, even those associated with fast halo CMEs originating from the central disk region, and those ICMEs and SPEs were not very geo-effective. This unexpected result demonstrates that the suggested events in the chain (fast halo CME, X-class flares, central disk region, ICME, SPE) are not infallible proxies for geo-effectiveness. (ii) The low value of integrated and normalized southward component of the IMF ($B^*_z$) may explain the low geo-effectiveness for this small sample. In fact, $B^*_z$ is well correlated to the weak Dst and low auroral electrojet (AE) activity. Hence, the only space weather impact at Earth in 2002 we can explain is based on $B^*_z$ at L1.

[35]  arXiv:2003.10792 [pdf, ps, other]
Title: Evolving grain-size distributions embedded in gas flows
Comments: 11 pages, 8 figures, accepted for publication in Monthly Notices of the Royal Astronomical Society
Subjects: Astrophysics of Galaxies (astro-ph.GA); Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

We present a numerical approach for accurately evolving a dust grain-size distribution undergoing number-conserving (such as sputtering) and/or mass-conserving (such as shattering) processes. As typically observed interstellar dust distributions follow a power-law, our method adopts a power-law discretisation and uses both the grain mass and number densities in each bin to determine the power-law parameters. This power-law method is complementary to piecewise-constant and linear methods in the literature. We find that the power-law method surpasses the other two approaches, especially for small bin numbers. In the sputtering tests the relative error in the total grain mass remains below 0.01% independent of the number of bins N, while the other methods only achieve this for N > 50 or higher. Likewise, the shattering test shows that the method also produces small relative errors in the total grain numbers while conserving mass. Not only does the power-law method conserve the global distribution properties, it also preserves the inter-bin characteristics so that the shape of the distribution is recovered to a high degree. This does not always happen for the constant and linear methods, especially not for small bin numbers. Implementing the power-law method in a hydrodynamical code thus minimises the numerical cost whilst maintaining high accuracy. The method is not limited to dust grain distributions, but can also be applied to the evolution of any distribution function, such as a cosmic-ray distribution affected by synchrotron radiation or inverse-Compton scattering.

[36]  arXiv:2003.10850 [pdf, other]
Title: Gadget3 on GPUs with OpenACC
Comments: 10 pages, 4 figures, printed by ParCo 2019 (at IOS Advances in Parallel Computing, Volume 36, pages 209 - 218, ISBN 978-1-64368-070-5)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Performance (cs.PF)

We present preliminary results of a GPU porting of all main Gadget3 modules (gravity computation, SPH density computation, SPH hydrodynamic force, and thermal conduction) using OpenACC directives. Here we assign one GPU to each MPI rank and exploit both the host and accellerator capabilities by overlapping computations on the CPUs and GPUs: while GPUs asynchronously compute interactions between particles within their MPI ranks, CPUs perform tree-walks and MPI communications of neighbouring particles. We profile various portions of the code to understand the origin of our speedup, where we find that a peak speedup is not achieved because of time-steps with few active particles. We run a hydrodynamic cosmological simulation from the Magneticum project, with $2\cdot10^{7}$ particles, where we find a final total speedup of $\approx 2.$ We also present the results of an encouraging scaling test of a preliminary gravity-only OpenACC porting, run in the context of the EuroHack17 event, where the prototype of the porting proved to keep a constant speedup up to $1024$ GPUs.

[37]  arXiv:2003.10851 [pdf, other]
Title: Proton-proton collisional age to order solar wind types
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Space Physics (physics.space-ph)

The properties of a solar wind stream are determined by its source region and by transport effects. Independently of the solar wind type, the solar wind measured in situ is always affected by both. We consider the proton-proton collisional age as an ordering parameter for the solar wind at 1AU and explore its relation to the solar wind classification scheme developed by Xu & Borovsky (2015). We use this to show that explicit magnetic field information is not required for this solar wind classification. Based on the observation that the three basic solar wind types from this categorization cover different regimes in terms of proton-proton collisional age $a_{col,p-p}$ , we propose a simplified solar wind classification scheme that is only based on the proton-proton collisional age. The resulting so-called PAC solar wind classifier is an alternative to the full Xu & Borovsky (2015) solar wind classification scheme and leads to a classification that is very similar to the full Xu & Borovsky (2015) scheme. The solar wind is well ordered by the proton-proton collisional age. This implies underlying intrinsic relationships between the plasma properties, in particular, proton temperature and magnetic field strength in each plasma regime. We argue that sector-reversal plasma is a combination of particularly slow and dense solar wind and most stream interaction boundaries. Most solar wind parameters (e.g., the magnetic field strength, B, and the oxygen charge state ratio $n_{O^{7+}}$ /$n_{O^{6+}}$) change with the solar activity cycle. Thus, all solar wind categorization schemes based on threshold values need to be adapted to the solar activity cycle as well.

[38]  arXiv:2003.10852 [pdf, other]
Title: TESS spots a hot Jupiter with an inner transiting Neptune
Comments: accepted by ApJL
Journal-ref: 2020ApJ...892L...7H
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Solar and Stellar Astrophysics (astro-ph.SR)

Hot Jupiters are rarely accompanied by other planets within a factor of a few in orbital distance. Previously, only two such systems have been found. Here, we report the discovery of a third system using data from the Transiting Exoplanet Survey Satellite (TESS). The host star, TOI-1130, is an 11th magnitude K-dwarf in the Gaia G band. It has two transiting planets: a Neptune-sized planet ($3.65\pm 0.10$ $R_E$) with a 4.1-day period, and a hot Jupiter ($1.50^{+0.27}_{-0.22}$ $R_J$) with an 8.4-day period. Precise radial-velocity observations show that the mass of the hot Jupiter is $0.974^{+0.043}_{-0.044}$ $M_J$. For the inner Neptune, the data provide only an upper limit on the mass of 0.17 $M_J$ (3$\sigma$). Nevertheless, we are confident the inner planet is real, based on follow-up ground-based photometry and adaptive optics imaging that rule out other plausible sources of the TESS transit signal. The unusual planetary architecture of and the brightness of the host star make TOI-1130 a good test case for planet formation theories, and an attractive target for future spectroscopic observations.

[39]  arXiv:2003.10889 [pdf, ps, other]
Title: A search for prompt gamma-ray counterparts to fast radio bursts in the Insight-HXMT data
Comments: 15 pages, 3 figures, 6 tables, accepted by A&A
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

No robust detection of prompt electromagnetic counterparts to fast radio bursts (FRBs) has yet been obtained, in spite of several multi-wavelength searches carried out so far. Specifically, X/gamma-ray counterparts are predicted by some models. We planned on searching for prompt gamma-ray counterparts in the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) data, taking advantage of the unique combination of large effective area in the keV-MeV energy range and of sub-ms time resolution. We selected 39 FRBs that were promptly visible from the High-Energy (HE) instrument aboard Insight-HXMT. After calculating the expected arrival times at the location of the spacecraft, we searched for a significant excess in both individual and cumulative time profiles over a wide range of time resolutions, from several seconds down to sub-ms scales. Using the dispersion measures in excess of the Galactic terms, we estimated the upper limits on the redshifts. No convincing signal was found and for each FRB we constrained the gamma-ray isotropic-equivalent luminosity and the released energy as a function of emission timescale. For the nearest FRB source, the periodic repeater FRB180916.J0158+65, we find $L_{\gamma,iso}<5.5\times 10^{47}$ erg/s over 1 s, whereas $L_{\gamma,iso}<10^{49}-10^{51}$ erg/s for the bulk of FRBs. The same values scale up by a factor of ~100 for a ms-long emission. Even on a timescale comparable with that of the radio pulse itself no keV-MeV emission is observed. A systematic association with either long or short GRBs is ruled out with high confidence, except for subluminous events, as is the case for core-collapse of massive stars (long) or binary neutron star mergers (short) viewed off axis. Only giant flares from extra-galactic magnetars at least ten times more energetic than Galactic siblings are ruled out for the nearest FRB.

[40]  arXiv:2003.10912 [pdf, ps, other]
Title: On the Angular Momentum History of Galactic Disks
Authors: Alvio Renzini
Subjects: Astrophysics of Galaxies (astro-ph.GA)

The stellar mass, size and rotational velocity of galactic disks all grow from redshift ~2 to the present by amounts that are estimated from observationally derived scaling relations. The product of these three quantities, the angular momentum of stellar disks, is then estimated to grow by a remarkably large factor, between ~20 and ~50, whereas other evidences suggest a more moderate increase. This requires that the specific angular momentum of the accreted gas should systematically increase with time while remaining co-rotational with the disk over most of the last ~10 Gyr. Thus, the baryonic gas vorticity of the circumgalactic medium appears to emerge as a major driver in galaxy evolution, and this paper is meant to attract attention on the sheer size of the angular momentum increase and on the need to explore to which extent this can be observed in nature and/or in simulations.

[41]  arXiv:2003.10945 [pdf, ps, other]
Title: Swift Spectroscopy of the Accretion Disk Wind in the Black Hole GRO J1655-40
Authors: M. Balakrishnan (1), J. M. Miller (1), N. Trueba (1), M. Reynolds (1), J. Raymond (2), D. Proga (3), A. C. Fabian (4), T. Kallman (5), J. Kaastra (6) ((1) Univ. of Michigan, (2) SAO, (3) UNLV, (4) Univ. of Cambridge, (5) NASA/GSFC, (6) SRON)
Comments: Accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Chandra obtained two High Energy Transmission Grating (HETG) spectra of the stellar-mass black hole GRO J1655-40 during its 2005 outburst, revealing a rich and complex disk wind. Soon after its launch, the Neil Gehrels Swift Observatory began monitoring the same outburst. Some X-ray Telescope (XRT) observations were obtained in a mode that makes it impossible to remove strong Mn calibration lines, so the Fe K-alpha line region in the spectra was previously neglected. However, these lines enable a precise calibration of the energy scale, facilitating studies of the absorption-dominated disk wind and its velocity shifts. Here, we present fits to 15 Swift/XRT spectra, revealing variability and evolution in the outflow. The data strongly point to a magnetically driven disk wind: both the higher velocity (e.g., v ~ 10^4 km/s) and lower velocity (e.g., v ~ 10^3 km/s) wind components are typically much faster than is possible for thermally driven outflows (v < 200 km/s), and photoionization modeling yields absorption radii that are two orders of magnitude below the Compton radius that defines the typical inner extent of thermal winds. Moreover, correlations between key wind parameters yield an average absorption measure distribution (AMD) that is consistent with magnetohydrodynamic wind models. We discuss our results in terms of recent observational and theoretical studies of black hole accretion disks and outflows, and future prospects.

[42]  arXiv:2003.10946 [pdf, ps, other]
Title: Cluster membership for the long period Cepheid calibrator SV Vul
Authors: Ignacio Negueruela (Alicante), Ricardo Dorda (IAC), Amparo Marco (Alicante)
Comments: Accepted for publication in MNRAS, 9 pages, 10 figures
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

Classical Cepheids represent the first step of the distance scale ladder. Claims of tension between the locally calculated Hubble constant and the values deduced from $Planck$'s results have sparked new interest in these distance calibrators. Cluster membership provides an independent distance measurement, as well as astrophysical context for studies of their stellar properties. Here we report the discovery of a young open cluster in the vicinity of SV Vul, one of the most luminous Cephedis known in the Milky Way. $Gaia$ DR2 data show that SV Vul is a clear astrometric and photometric member of the new cluster, which we name Alicante 13. Although dispersed, Alicante 13 is moderately well populated, and contains three other luminous stars, one early-A bright giant and two low-luminosity red supergiants. The cluster is about 30 Ma old at a nominal distance of 2.5 kpc. With this age, SV Vul should have a mass around $10\:$M$_{\odot}$, in good accordance with its luminosity, close to the highest luminosity for Cepheids allowed by recent stellar models.

[43]  arXiv:2003.10947 [pdf, other]
Title: Thermal instabilities: Fragmentation and field misalignment of filament fine structure
Comments: 12 pages, 13 figures, accepted for publication, movies available upon request to the first author
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Prominences show a surprising amount of fine structure and it is widely believed that their threads, as seen in H$\alpha$ observations, provide indirect information concerning magnetic field topology. We investigate the spontaneous emergence and evolution of fine structure in high-density condensations formed through the process of thermal instability under typical solar coronal conditions. Our study reveals intricate multidimensional processes that occur through in situ condensations in a representative coronal volume in a low plasma beta regime. We performed 2D and 3D numerical simulations of interacting slow magnetohydrodynamic (MHD) wave modes when all relevant non-adiabatic effects are included.
We show that the interaction of multiple slow MHD wave modes in a regime unstable to the thermal mode leads to thermal instability. This initially forms pancake-like structures almost orthogonal to the local magnetic field, while low-pressure induced inflows of matter generate rebound shocks. This is succeeded by the rapid disruption of these pancake sheets through thin-shell instabilities evolving naturally from minute ram pressure imbalances. This eventually creates high-density blobs accompanied by thread-like features from shear flow effects. The further evolution of the blobs follows the magnetic field lines, such that a dynamical realignment with the background magnetic field appears. However, the emerging thread-like features are not at all field-aligned, implying only a very weak link between fine structure orientation and magnetic field topology which has far-reaching implications for field topology interpretations based on H$\alpha$ observations.

[44]  arXiv:2003.10949 [pdf, other]
Title: New ultracool dwarf neighbours within 20pc from Gaia DR2
Comments: accepted for publication in Astronomy and Astrophysics, 15 pages, 3 tables, 10 figures (reduced in size)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Earth and Planetary Astrophysics (astro-ph.EP); Astrophysics of Galaxies (astro-ph.GA)

The Gaia data release 2 (DR2) contains $>$6000 objects with parallaxes $(Plx+3\times{e\_Plx})>50$mas placing them within 20pc from the Sun. Since the expected numbers extrapolating the well-known 10pc census are much lower, nearby Gaia stars need a quality assessment. The 20pc sample of white dwarfs (WDs) had already been verified and completed with Gaia DR2. We aimed to check and complete the 20pc sample of ultracool dwarfs (UCDs) with spectral types $\gtrsim$M7 and given Gaia DR2 parallaxes. Dividing the Gaia DR2 20pc sample into subsamples of various astrometric and photometric quality, we studied their distribution on the sky, in the $M_G$ vs. $G$$-$$RP$ colour-magnitude diagram (CMD), and as a function of $G$ magnitude and total proper motion. After excluding 139 known WDs and 263 known UCDs from the CMD, we checked all remaining $\approx$3500 candidates with $M_G>14$mag (used to define UCDs in this study) for the correctness of their Gaia DR2 proper motions. For confirmed UCD candidates we estimated spectral types photometrically using Gaia and near-infrared absolute magnitudes and colours. We failed to confirm new WDs, but found 50 new UCD candidates not mentioned in three previous studies using Gaia DR2. They have relatively small proper motions and tangential velocities and are concentrated towards the Galactic plane. Half of them have spectral types in SIMBAD and/or previous non-Gaia distance estimates that placed them already within 20pc. For 20 of the 50 objects, we estimated photometric spectral types of M6-M6.5, slightly below the classical UCD spectral type limit. However, seven L4.5-L6.5, four L0-L1, five M8.5-M9.5, and three M7-M8 dwarfs can be considered as completely new UCDs discoveries within 20pc based on Gaia DR2. Four M6.5 and two L4.5 dwarfs have high membership probabilities (64%-99%) in the ARGUS, AB Doradus, or Carina Near young moving groups. (abbreviated)

[45]  arXiv:2003.10982 [pdf, other]
Title: Scientific prospects for a mini-array of ASTRI telescopes: a gamma-ray TeV data challenge
Comments: 14 pages, 11 figures, 1 table. Accepted in Journal of High Energy Astrophysics
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)

ASTRI is a project aiming at the realization of a gamma-ray imaging Cherenkov telescope that observes the sky in the TeV band. Recently, the development of a mini-array (MA) of ASTRI telescopes has been funded by the Istituto Nazionale di Astrofisica. The ASTRI Comprehensive Data Challenge (ACDC) project aims at optimizing the scientific exploitation and analysis techniques of the ASTRI MA, by performing a complete end-to-end simulation of a tentative scientific program, from the generation of suitable instrument response functions to the proposal, selection, analysis, and interpretation of the simulated data. We assumed that the MA will comprise nine ASTRI telescopes arranged in a (almost) square geometry (mean distance between telescopes of ~250m). We simulated three years of observations, adopting a realistic pointing plan that takes into account, for each field, visibility constraints for an assumed site in Paranal (Chile) and observational time slots in dark sky conditions. We simulated the observations of nineteen Galactic and extragalactic fields selected for their scientific interest, including several classes of objects (such as pulsar wind nebulae, supernova remnants, gamma-ray binaries etc), for a total of 81 point-like and extended sources. Here we present an overview of the ACDC project, providing details on the different software packages needed to carry out the simulated three-years operation of the ASTRI MA. We discuss the results of a systematic analysis applied on the whole simulated data, by making use of prototype science tools widely adopted by the TeV astronomical community. Furthermore, particular emphasis is also given to some targets used as benchmarks.

Cross-lists for Wed, 25 Mar 20

[46]  arXiv:2003.08416 (cross-list from gr-qc) [pdf, other]
Title: Chiral Symmetry and the Cosmological Constant
Comments: 15 pages
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph); High Energy Physics - Theory (hep-th)

In this work we provide a link between a nearly vanishing cosmological constant and chiral symmetry. This is accomplished with a modification of General Relativity coupled to a topological field theory, namely BF theory by introducing fermions charged under the BF theory gauge group. We find that the cosmological constant sources a chiral anomaly for the fermions, providing a `technical naturalness' explanation for the smallness of the observed cosmological constant. Applied to the early universe, we show that production of fermions during inflation can provide all the dark matter in the universe today, in the form of superheavy dark baryons.

[47]  arXiv:2003.10437 (cross-list from eess.IV) [pdf]
Title: Rock Classification in Petrographic Thin Section Images Based on Concatenated Convolutional Neural Networks
Subjects: Image and Video Processing (eess.IV); Earth and Planetary Astrophysics (astro-ph.EP)

Rock classification plays an important role in rock mechanics, petrology, mining engineering, magmatic processes, and numerous other fields pertaining to geosciences. This study proposes a concatenated convolutional neural network (Con-CNN) method for classifying the geologic rock type based on petrographic thin sections. Herein, plane polarized light (PPL) and crossed polarized light (XPL) were used to acquire thin section images as the fundamental data. After conducting the necessary pre-processing analyses, the PPL and XPL images as well as their comprehensive image (CI) were incorporated in three convolutional neural networks (CNNs) comprising the same structure for achieving a preliminary classification; these images were developed by employing the fused principal component analysis (PCA). Subsequently, the results of the CNNs were concatenated by using the maximum likelihood detection to obtain a comprehensive classification result. Finally, a statistical revision was applied to fix the misclassification due to the proportion difference of minerals that were similar in appearance. In this study, 13 types of 92 rock samples, 196 petrographic thin sections, 588 images, and 63504 image patches were fabricated for the training and validation of the Con-CNN. The five-folds cross validation shows that the method proposed provides an overall accuracy of 89.97%, which facilitates the automation of rock classification in petrographic thin sections.

[48]  arXiv:2003.10498 (cross-list from gr-qc) [pdf, other]
Title: Analytic I-Love-C relations for realistic neutron stars
Authors: Nan Jiang, Kent Yagi
Comments: 11 pages, 8 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE)

Recent observations of neutron stars with radio, X-rays and gravitational waves have begun to constrain the equation of state for nuclear matter beyond the nuclear saturation density. To one's surprise, there exist approximate universal relations connecting certain bulk properties of neutron stars that are insensitive to the underlying equation of state and having important applications on probing fundamental physics including nuclear and gravitational physics. To date, analytic works on universal relations for realistic neutron stars are lacking, which may lead to a better understanding of the origin of the universality. Here, we focus on the universal relations between the compactness (C), the moment of inertia (I), and the tidal deformability (related to the Love number), and derive analytic, approximate I-Love-C relations. To achieve this, we construct slowly-rotating/tidally-deformed neutron star solutions analytically starting from an extended Tolman VII model that accurately describes non-rotating realistic neutron stars, which allows us to extract the moment of inertia and the tidal deformability on top of the compactness. We solve the field equations analytically by expanding them about the Newtonian limit and keeping up to 6th order in the stellar compactness. Based on these analytic solutions, we can mathematically demonstrate the O(10%) equation-of-state variation in the I-C and Love-C relations and the O(1%) variation in the I-Love relation that have previously been found numerically. Our new analytic relations agree more accurately with numerical results for realistic neutron stars (especially the I-C and Love-C ones) than the analytic relations for constant density stars derived in previous work. Our results provide a mathematical explanation of the amount of universality for realistic neutron stars in the above universal relations.

[49]  arXiv:2003.10516 (cross-list from gr-qc) [pdf, ps, other]
Title: Global asymptotic dynamics of Cosmological Einsteinian Cubic Gravity
Comments: 9 pages, 3 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

In this paper we investigate the cosmological dynamics of an up to cubic curvature correction to General Relativity (GR) known as Cosmological Einsteinian Cubic Gravity (CECG), whose vacuum spectrum consists of the graviton exclusively and its cosmology is well-posed as an initial value problem. We are able to uncover the global asymptotic structure of the phase space of this theory. It is revealed that an inflationary matter-dominated bigbang is the global past attractor which means that inflation is the starting point of any physically meaningful cosmic history. Given that higher order curvature corrections to GR are assumed to influence the cosmological dynamics at early times -- high energies/large curvature limit -- the late-time inflation can not be a consequence of the up to cubic order curvature modifications. We confirm this assumption by showing that late-time acceleration of the expansion in the CECG model is possible only if add a cosmological constant term.

[50]  arXiv:2003.10527 (cross-list from hep-ph) [pdf, other]
Title: Gravitational Waves and Possible Fast Radio Bursts from Axion Clumps
Comments: 8 pages, 7 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)

The axion objects such as axion mini-clusters and axion clouds around spinning black holes induce parametric resonances of electromagnetic waves through the axion-photon interaction. In particular, it has been known that the resonances from the axion with the mass around $10^{-6}$eV may explain the observed fast radio bursts (FRBs). Here we argue that similar bursts of high frequency gravitational waves, which we call the fast gravitational wave bursts (FGBs), are generated from axion clumps with the presence of gravitational Chern-Simons (CS) coupling. The typical frequency is half of the axion mass, which in general can range from kHz to GHz. We also discuss the secondary gravitational wave production associated with FRB, as well as the possible host objects of the axion clouds, such as primordial black holes with typical masses around $10^{-5}M_{\odot}$. Future detections of FGBs together with the observed FRBs are expected to provide more evidence for the axion.

[51]  arXiv:2003.10633 (cross-list from gr-qc) [pdf, other]
Title: Disformal invariance of cosmological observables
Comments: 28 pages, 1 figure
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

In this paper, we study the frame dependence/independence of cosmological observables under disformal transformations, extending the previous results regarding conformal transformations, and provide the correspondence between Jordan-frame and Einstein-frame variables. We consider quantities such as the gravitational constant in the Newtonian limit, redshift, luminosity and angular diameter distances, as well as the observed specific flux and intensity. Also, the distance-duality and reciprocity relation, the Boltzmann equation, and the adiabaticity condition are discussed. In particular, we show that the redshift is invariant and the distance-duality relation (the relation between the luminosity distance and the angular diameter distance) still holds in general spacetimes even though the reciprocity relation (the relation between two geometrical distances) is modified. Since the electromagnetic action changes under disformal transformations, photons in the Einstein frame no longer propagate along null geodesics. As a result, several quantities of cosmological interest are modified.

[52]  arXiv:2003.10686 (cross-list from gr-qc) [pdf, ps, other]
Title: Primordial tensor non-Gaussianities from general single-field inflation with non-Bunch-Davies initial states
Comments: 9 pages
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)

It has been found that the primordial non-Gaussianity of the curvature perturbation in the case of non-Bunch-Davies initial states can be enhanced compared with those in the case of the Bunch-Davies one due to the interactions among the perturbations on subhorizon scales. The purpose of the present paper is to investigate whether tensor non-Gaussianities can also be enhanced or not by the same mechanism. We consider general gravity theory in the presence of an inflaton, and evaluate the tensor auto-bispectrum and the cross-bispectrum involving one tensor and two scalar modes with the non-Bunch-Davies initial states for tensor modes. The crucial difference from the case of the scalar auto-bispectrum is that the tensor three-point function vanishes at the flattened momentum triangles. We point out that the cross-bispectrum can potentially be enhanced at non-trivial triangle shapes due to the non-Bunch-Davies initial states.

[53]  arXiv:2003.10781 (cross-list from gr-qc) [pdf, other]
Title: Tidal deformations of hybrid stars with sharp phase transitions and elastic crusts
Comments: 11 pages, 3 figures, submitted
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)

Gravitational wave astronomy is expected to provide independent constraints on neutron star properties, such as their dense matter equation of state. This is possible with the measurements of binary components' tidal deformability, which alter the point-particle gravitational waveforms of the late inspiral phase of neutron-star binaries. Although current gravitational wave detectors are not sensitive enough for a precise determination of the individual tidal deformations of the components, a large number of combined observations with future detectors will decrease uncertainties in this quantity. Here we provide a first study of the tidal deformability effects due to the elasticity of the crust in a hybrid neutron star, as well as the influence of a quark-hadronic phase density jump on tidal deformations. We employ the framework of nonradial perturbations with zero frequency and study hadronic phases presenting elastic aspects when perturbed (with the shear modulus approximately $1\%$ of the pressure). We find that the relative tidal deformation change in a hybrid star with a perfect-fluid quark phase and a hadronic phase presenting an elastic part is never larger than about $2-4\%$ (with respect to a perfect-fluid counterpart). These maximum changes occur when the elastic region of a hybrid star is larger than approximately $60\%$ of the star's radius, which may happen when its quark phase is small and the density jump is large enough, or even when a hybrid star has an elastic mixed phase. For other cases, the relative tidal deformation changes due to an elastic crust are negligible ($10^{-5}-10^{-1}\%$), therefore unlikely to be measured even with third generation detectors. Thus, only when the size of the elastic hadronic region of a hybrid star is over half of its radius, the effects of elasticity could have a noticeable impact on tidal deformations.

[54]  arXiv:2003.10859 (cross-list from gr-qc) [pdf, other]
Title: Photon surfaces as pure tension shells: Uniqueness of thin shell wormholes
Authors: Yasutaka Koga
Comments: 22 pages, 7 figures
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Theory (hep-th)

Thin shell wormholes are constructed by joining two asymptotically flat spacetimes along their inner boundaries. The junction conditions imposed on the spacetimes specify the EOS of the matter called thin shell distributed along the joined boundaries. Barcelo and Visser (2000) reported that spherically symmetric thin shell wormholes have their shells, namely the wormhole throats, on the photon spheres if the wormholes are $Z_2$-symmetric across the throats and the shells are of pure tension. In this paper, first, we consider general joined spacetimes (JSTs) and show that any $Z_2$-symmetric pure-tensional JST (Z2PTJST) of $\Lambda$-vacuum has its shell on a photon surface, a generalized object of photon spheres, without assuming any other symmetries. The class of Z2PTJSTs also includes, for example, brane world models with the shells being the branes we live in. Second, we investigate the shell stability of Z2PTJSTs by analyzing the stability of the corresponding photon surfaces. Finally, applying the uniqueness theorem of photon spheres by Cederbaum (2014), we establish the uniqueness theorem of static wormholes of Z2PTJST.

Replacements for Wed, 25 Mar 20

[55]  arXiv:1701.00526 (replaced) [pdf, other]
Title: Gaseous Dynamical Friction in Presence of Black Hole Radiative Feedback
Comments: 8 pages of published article in ApJ, 4 pages of Erratum attached
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[56]  arXiv:1705.04737 (replaced) [pdf, other]
Title: Field Theories and Fluids for an Interacting Dark Sector
Comments: Corrections made and typos fixed in Section 3 & 4
Journal-ref: Phys. Rev. D 97, 043508 (2018)
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[57]  arXiv:1811.11104 (replaced) [pdf, other]
Title: The role of leptons in electroweak baryogenesis
Comments: 36 pages
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[58]  arXiv:1904.07789 (replaced) [pdf, other]
Title: Constraining the masses of microlensing black holes and the mass gap with Gaia DR2
Comments: 12 pages, accepted for publication in A&A
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[59]  arXiv:1906.00666 (replaced) [pdf, other]
Title: Constraints on ultra-light axions from compact binary systems
Comments: 19 pages, 5 figures, 2 tables. Accepted in Phys. Rev. D
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
[60]  arXiv:1906.02197 (replaced) [pdf, other]
Title: Securing the legacy of TESS through the care and maintenance of TESS planet ephemerides
Comments: 16 pages, 10 figures, accepted to AJ; main changes are cross-checking results against the sample of real TOIs, and addressing the impact of the TESS extended mission
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
[61]  arXiv:1907.08066 (replaced) [pdf, ps, other]
Title: The blackholic quantum
Comments: European Physical Journal C, in press
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[62]  arXiv:1908.01419 (replaced) [pdf, other]
Title: Gradient sub-grid-scale model for relativistic MHD Large Eddy Simulations
Comments: 15 pages, 6 figures. Final version. arXiv admin note: text overlap with arXiv:1904.04099
Journal-ref: Phys. Rev. D 101, 063003 (2020)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[63]  arXiv:1908.01791 (replaced) [pdf, other]
Title: Plateau de Bure High-z Blue-Sequence Survey 2 (PHIBSS2): Search for Secondary Sources, CO Luminosity Functions in the Field, and the Evolution of Molecular Gas Density through Cosmic Time
Comments: 29 pages (including 9 appendix pages), 14 figures and 6 tables, submitted to ApJ, replaced with version accepted by ApJ
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[64]  arXiv:1908.02638 (replaced) [pdf, other]
Title: Spin-polarized neutron matter, the maximum mass of neutron stars, and GW170817
Authors: I. Tews, A. Schwenk
Comments: 10 pages, 3 figures, published version
Journal-ref: Astrophys. J. 892, 14 (2020)
Subjects: Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics - Phenomenology (hep-ph)
[65]  arXiv:1908.06832 (replaced) [pdf, other]
Title: The influence of a top-heavy integrated galactic IMF and dust on the chemical evolution of high-redshift starbursts
Comments: 21 pages, 14 Figures. Accepted for publication in MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)
[66]  arXiv:1908.09997 (replaced) [pdf, other]
[67]  arXiv:1908.10352 (replaced) [pdf, other]
Title: Stringent constraints on neutron-star radii from multimessenger observations and nuclear theory
Comments: 39 pages, 4 figures
Journal-ref: Nature Astronomy, 2020
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph); Nuclear Theory (nucl-th)
[68]  arXiv:1909.04836 (replaced) [pdf, ps, other]
Title: Topological theory of physical fields
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Mathematical Physics (math-ph); Dynamical Systems (math.DS)
[69]  arXiv:1909.08632 (replaced) [pdf, other]
Title: Direct detection and complementary constraints for sub-GeV dark matter
Comments: 39 pages, 7 figures; matches the published version
Journal-ref: JHEP 2020, 118 (2020)
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[70]  arXiv:1910.07974 (replaced) [pdf, other]
Title: Detection of pulses from the Vela pulsar at millimeter wavelengths with phased ALMA
Comments: 8 pages, 6 figures, published in ApJ letter
Journal-ref: The Astrophysical Journal Letters, Volume 885, Issue 1, article id. L10, 6 pp. (2019)
Subjects: Astrophysics of Galaxies (astro-ph.GA); Instrumentation and Methods for Astrophysics (astro-ph.IM)
[71]  arXiv:1910.11387 (replaced) [pdf, other]
Title: Proton acceleration in pulsar magnetospheres
Comments: 14 pages, 12 figures, 1 table; updated to match the published version
Journal-ref: A&A 635, A138 (2020)
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[72]  arXiv:1911.04830 (replaced) [pdf, other]
Title: Thermodynamics of $f(R)$ Theories of Gravity
Comments: 12 pages, 11 figures. Different value of the free parameter $\theta$ provides more robust results and thermodynamics closer to a van der Waals gas
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[73]  arXiv:1911.07885 (replaced) [pdf, other]
Title: On the Wondrous Stability of ALP Dark Matter
Comments: 20 pages, 3 figures. v2: some references added
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[74]  arXiv:1911.09110 (replaced) [pdf, other]
Title: Neutrino propagation hinders fast pairwise flavor conversions
Comments: Submitted to JCAP, 20 pages, 12 Figures. Supplementary material: this https URL
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)
[75]  arXiv:1911.09999 (replaced) [pdf, other]
Title: The properties of He II 1640 emitters at z ~ 2.5-5 from the VANDELS survey
Comments: 21 pages, 11 figures (including appendix), Accepted for publication in A&A
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[76]  arXiv:1912.00482 (replaced) [pdf, other]
Title: The NANOGrav 11-year Data Set: Constraints on Planetary Masses Around 45 Millisecond Pulsars
Comments: Revised and accepted by ApJ Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR)
[77]  arXiv:1912.02622 (replaced) [pdf, other]
Title: Science Case for the Einstein Telescope
Comments: 51 pages, 14 figures; v3: references added, various improvements. v4: minor changes. Version published in JCAP
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[78]  arXiv:1912.09096 (replaced) [pdf, other]
Title: Calibration of systematics in constraining modified gravity models with galaxy cluster mass profiles
Comments: V-2. 27 pages, 13 figures. Accepted for publication on JCAP
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc)
[79]  arXiv:1912.12249 (replaced) [pdf, other]
Title: A multi-wavelength search for intrinsic linear polarization in Wolf-Rayet winds
Comments: 28 pages, 8 figures, 4 machine-readable tables, 1 figure set (47 images). Accepted in AJ
Subjects: Solar and Stellar Astrophysics (astro-ph.SR)
[80]  arXiv:2002.06937 (replaced) [pdf, other]
Title: A Dark Matter Interpretation of Excesses in Multiple Direct Detection Experiments
Comments: 20 pages, 7 figures. Submitted to PRD
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Materials Science (cond-mat.mtrl-sci); High Energy Physics - Experiment (hep-ex); Instrumentation and Detectors (physics.ins-det)
[81]  arXiv:2002.08291 (replaced) [pdf, other]
Title: Extending the PyCBC search for gravitational waves from compact binary mergers to a global network
Comments: 12 pages, 6 figures
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[82]  arXiv:2002.10189 (replaced) [pdf, ps, other]
Title: Reconstructing the Fraction of Baryons in the Intergalactic Medium with Fast Radio Bursts via Gaussian Processes
Comments: 14 pages, 6 figures, revtex4; v2: discussions added, JCAP in press
Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)
[83]  arXiv:2002.10717 (replaced) [pdf, ps, other]
Title: ASASSN-16oh: A nova outburst with no mass ejection -- A new type of supersoft X-ray source in old populations
Comments: 21 pages, 10 figures, published in ApJ, 892, 15 (16pp)
Journal-ref: ApJ, 892, 15 (2020)
Subjects: Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE)
[84]  arXiv:2003.03431 (replaced) [pdf, other]
Title: Millimeter-wave Point Sources from the 2500-square-degree SPT-SZ Survey: Catalog and Population Statistics
Comments: 43 pages, 19 figures, 7 tables. Submitted to AAS Journals 03/05/2020. 03/23/2020 co-author affiliation and acknowledgments updated
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
[85]  arXiv:2003.06223 (replaced) [pdf, other]
Title: The Fraction of Gamma-ray Bursts with an Observed Photospheric Emission Episode
Comments: Accepted: ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[86]  arXiv:2003.07235 (replaced) [pdf, other]
Title: The X-ray outburst of the Galactic Center magnetar over six years of Chandra observations
Authors: N. Rea, F. Coti Zelati, D. Vigano' (CSIC, IEEC), A. Papitto (INAF), F. Baganoff (MIT), A. Borghese (CSIC, IEEC), S. Campana (INAF), P. Esposito (INAF, IUSS), D. Haggard (McGill), G.L. Israel, S. Mereghetti, R. Mignani (INAF), R. Perna (Stony Brook), J.A. Pons (U. Alicante), G. Ponti, L. Stella (INAF), D.F. Torres (ICREA, CSIC, IEEC), R. Turolla (U. Padova), S. Zane (MSSL)
Comments: 11 pages, 6 figures. Accepted by ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[87]  arXiv:2003.08244 (replaced) [pdf, ps, other]
Title: A comment on "Lense-Thirring frame dragging induced by a fast-rotating white dwarf in a binary pulsar system" by V. Venkatraman Krishnan et al
Authors: Lorenzo Iorio
Comments: LaTex2e, 20 pages, 3 figures, no tables. Due to arXiv's space limitations, low-resolution pictures have been upoloaded. Some stylistic changes made
Subjects: General Relativity and Quantum Cosmology (gr-qc); High Energy Astrophysical Phenomena (astro-ph.HE); Space Physics (physics.space-ph)
[88]  arXiv:2003.09639 (replaced) [pdf, other]
Title: Opportunities to Search for Extra-Terrestrial Intelligence with the Five-hundred-meter Aperture Spherical radio Telescope
Comments: 14 pages, 8 figures, Accepted by Research in Astron. Astrophys. (FAST special issue)
Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)
[89]  arXiv:2003.09818 (replaced) [pdf, ps, other]
Title: Emergent gravity fails to explain color-dependent galaxy-galaxy lensing signals from SDSS Dr7
Comments: 7 pages, 3 figures
Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)
[90]  arXiv:2003.10035 (replaced) [pdf, ps, other]
Title: Time Variability of Nonthermal X-ray Stripes in Tycho's Supernova Remnant with Chandra
Comments: 8 pages, 3 figures, 2 tables, accepted for publication in ApJ
Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)
[91]  arXiv:2003.10127 (replaced) [pdf, other]
Title: Model Comparison tests of modified gravity from the Eöt-Wash experiment
Comments: 6 pages, 1 figure. Link to analysis code available at this https URL
Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Instrumentation and Methods for Astrophysics (astro-ph.IM)
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