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New submissions for Mon, 6 Jan 20

[1]  arXiv:2001.00584 [pdf, other]

Title: Cosmological Angular Trispectra and Non-Gaussian Covariance

Authors: Hayden Lee, Cora Dvorkin

Comments: 53 pages, 12 figures, 3 tables

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

Angular cosmological correlators are infamously difficult to compute due to the highly oscillatory nature of the projection integrals. Motivated by recent development on analytic approaches to cosmological perturbation theory, in this paper we present an efficient method for computing cosmological four-point correlations in angular space, generalizing previous works on lower-point functions. This builds on the FFTLog algorithm that approximates the matter power spectrum as a sum over power-law functions, which makes certain momentum integrals analytically solvable. The computational complexity is drastically reduced for correlators in a "separable" form---we define a suitable notion of separability for cosmological trispectra, and derive formulas for angular correlators of different separability classes. As an application of our formalism, we compute the angular galaxy trispectrum at tree level, with and without primordial non-Gaussianity. This includes effects of redshift space distortion and bias parameters up to cubic order. We also compute the non-Gaussian covariance of the angular matter power spectrum due to the connected four-point function, beyond the Limber approximation. We demonstrate that, in contrast to the standard lore, the Limber approximation can fail for the non-Gaussian covariance computation even for large multipoles.

[2]  arXiv:2001.00587 [pdf, other]

Title: ZTF Early Observations of Type Ia Supernovae III: Early-Time Colors as a Test for Explosion Models and Multiple Populations

Authors: Mattia Bulla, Adam A. Miller, Yuhan Yao, Luc Dessart, Suhail Dhawan, Semeli Papadogiannakis, Rahul Biswas, Ariel Goobar, S. R. Kulkarni, Jakob Nordin, Peter Nugent, Abigail Polin, Jesper Sollerman, Eric C. Bellm, Michael W. Coughlin, Richard Dekany, V. Zach Golkhou, Matthew J. Graham, Mansi M. Kasliwal, Thomas Kupfer, Russ R. Laher, Frank J. Masci, Michael Porter, Ben Rusholme, David L. Shupe

Comments: 16 pages, 9 figures, 1 table; submitted to ApJ; comments are welcome

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Colors of Type Ia supernovae in the first few days after explosion provide a potential discriminant between different models. In this paper, we present $g-r$ colors of 38 Type Ia supernovae discovered within 3 days from first light by the Zwicky Transient Facility in 2018, a sample which is twice as large as that in the literature. We find that $g-r$ colors are intrinsically rather homogeneous at early phases, with about half of the dispersion in the first 5 days attributable to photometric uncertainties ($\sigma_\mathrm{noise}\sim\sigma_\mathrm{int}\sim0.25$ mag). Colors are nearly constant starting from 5 days after first light ($g-r\sim-0.15$ mag), while the time evolution at earlier epochs is characterized by a continuous range of slopes, from events rapidly transitioning from redder to bluer colors (slope of $\sim-0.25$ mag day$^{-1}$) to events with a flatter evolution. The continuum in the slope distribution is in good agreement both with models requiring some amount of $^{56}$Ni mixed in the outermost regions of the ejecta and with "double-detonation" models having thin helium layers ($M_\mathrm{He}=0.01\,M_\odot$) and varying carbon-oxygen core masses. At the same time, four events show evidence for a distinctive "red bump" signature predicted by "double-detonation" models with larger helium masses. We finally identify a significant correlation between the early-time $g-r$ slopes and supernova brightness, with brighter events associated to flatter color evolution (p-value=0.001). The distribution of slopes, however, is consistent with being drawn from a single population, with no evidence for two components as claimed in the literature.

[3]  arXiv:2001.00588 [pdf, other]

Title: The Gravitational Wave Treasure Map: A Tool to Coordinate, Visualize, and Assess the Electromagnetic Follow-Up of Gravitational Wave Events

Authors: Samuel D. Wyatt, Aaron Tohuvavohu, Iair Arcavi, Michael J. Lundquist, D. Andrew Howell, David J. Sand

Comments: 14 pages, 8 figures, Submitted to AAS Journals

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM)

We present the Gravitational Wave Treasure Map, a tool to coordinate, visualize, and assess the electromagnetic follow-up of gravitational wave (GW) events. With typical GW localization regions of hundreds to thousands of square degrees and dozens of active follow-up groups, the pursuit of electromagnetic (EM) counterparts is a challenging endeavor, but the scientific payoff for early discovery of any counterpart is clear. With this tool, we provide a website and API interface that allows users to easily see where other groups have searched and better inform their own follow-up search efforts. A strong community of Treasure Map users will increase the overall efficiency of EM counterpart searches and will play a fundamental role in the future of multi-messenger astronomy.

[4]  arXiv:2001.00590 [pdf, other]

Title: Effects of Stellar Feedback on Stellar and Gas Kinematics of Star-Forming Galaxies at 0.6<z<1.0

Authors: Debora Pelliccia, Bahram Mobasher, Behnam Darvish, Brian C. Lemaux, Lori M. Lubin, Jessie Hirtenstein, Lu Shen, Po-Feng Wu, Kareem El-Badry, Andrew Wetzel, Tucker Jones

Comments: 8 pages, 2 figures, 2 tables. Submitted to ApJL

Subjects: Astrophysics of Galaxies (astro-ph.GA)

Recent zoom-in cosmological simulations have shown that stellar feedback can flatten the inner density profile of the dark matter halo in low-mass galaxies. A correlation between the stellar/gas velocity dispersion ($\sigma_{star}$, $\sigma_{gas}$) and the specific star formation rate (sSFR) is predicted as an observational test of the role of stellar feedback in re-shaping the dark matter density profile. In this work we test the validity of this prediction by studying a sample of star-forming galaxies at $0.6<z<1.0$ from the \mbox{LEGA-C} survey, which provides high signal-to-noise measurements of stellar and gas kinematics. We find that a correlation between $\sigma_{star}$ (and $\sigma_{gas}$) and sSFR indeed exists for galaxies in the lowest mass bin (M$_\ast\sim10^{10}\,$M$_\odot$). This correlation holds for different tracers of star formation, and becomes stronger with redshift. This result generally agrees with the picture that at higher redshifts star formation rate was generally higher, and galaxies at M$_\ast\lesssim10^{10}\,$M$_\odot$ have not yet settled into a disk. As a consequence, they have shallower gravitational potentials more easily perturbed by stellar feedback. The observed correlation between $\sigma_{star}$ (and $\sigma_{gas}$) and sSFR supports the scenario predicted by cosmological simulations, in which feedback-driven outflows cause fluctuations in the gravitation potential which flatten the density profiles of low-mass galaxies.

[5]  arXiv:2001.00591 [pdf, other]

Title: A Compendium of Distances to Molecular Clouds in the Star Formation Handbook

Authors: Catherine Zucker, Joshua S. Speagle, Edward F. Schlafly, Gregory M. Green, Douglas P. Finkbeiner, Alyssa Goodman, João Alves

Comments: Accepted for publication in Astronomy & Astrophysics. Full catalog of distances available at this https URL or the CDS

Subjects: Astrophysics of Galaxies (astro-ph.GA)

Accurate distances to local molecular clouds are critical for understanding the star and planet formation process, yet distance measurements are often obtained inhomogeneously on a cloud-by-cloud basis. We have recently developed a method which combines stellar photometric data with Gaia DR2 parallax measurements in a Bayesian framework to infer the distances of nearby dust clouds to a typical accuracy of $\sim5\%$. After refining the technique to target lower latitudes and incorporating deep optical data from DECam in the southern Galactic plane, we have derived a catalog of distances to molecular clouds in Reipurth (2008, Star Formation Handbook, vols I and II) which contains a large fraction of the molecular material in the solar neighborhood. Comparison with distances derived from maser parallax measurements towards the same clouds shows our method produces consistent distances with $\lesssim10\%$ scatter for clouds across our entire distance spectrum (150 pc $-$ 2.5 kpc). We hope this catalog of homogeneous distances will serve as a baseline for future work.

[6]  arXiv:2001.00595 [pdf, other]

Title: Modeling the uncertainties of solar-system ephemerides for robust gravitational-wave searches with pulsar timing arrays

Authors: M. Vallisneri, S. R. Taylor, J. Simon, W. M. Folkner, R. S. Park, C. Cutler, J. A. Ellis, T. J. W. Lazio, S. J. Vigeland, K. Aggarwal, Z. Arzoumanian, P. T. Baker, A. Brazier, P. R. Brook, S. Burke-Spolaor, S. Chatterjee, J. M. Cordes, N. J. Cornish, F. Crawford, H. T. Cromartie, K. Crowter, M. DeCesar, P. B. Demorest, T. Dolch, R. D. Ferdman, E. C. Ferrara, E. Fonseca, N. Garver-Daniels, P. Gentile, D. Good, J. S. Hazboun, A. M. Holgado, E. A. Huerta, K. Islo, R. Jennings, G. Jones, M. L. Jones, D. L. Kaplan, L. Z. Kelley, J. S. Key, M. T. Lam, L. Levin, D. R. Lorimer, J. Luo, R. S. Lynch, D. R. Madison, M. A. McLaughlin, S. T. McWilliams6, C. M. F. Mingarelli, C. Ng, D. J. Nice, T. T. Pennucci, N. S. Pol, S. M. Ransom, P. S. Ray, X. Siemens, R. Spiewak, I. H. Stairs, D. R. Stinebring, K. Stovall, et al. (4 additional authors not shown)

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Instrumentation and Methods for Astrophysics (astro-ph.IM); General Relativity and Quantum Cosmology (gr-qc)

The regularity of pulsar emissions becomes apparent once we reference the pulses' times of arrivals to the inertial rest frame of the solar system. It follows that errors in the determination of Earth's position with respect to the solar-system barycenter can appear as a time-correlated bias in pulsar-timing residual time series, affecting the searches for low-frequency gravitational waves performed with pulsar timing arrays. Indeed, recent array datasets yield different gravitational-wave background upper limits and detection statistics when analyzed with different solar-system ephemerides. Crucially, the ephemerides do not generally provide usable error representations. In this article we describe the motivation, construction, and application of a physical model of solar-system ephemeris uncertainties, which focuses on the degrees of freedom (Jupiter's orbital elements) most relevant to gravitational-wave searches with pulsar timing arrays. This model, BayesEphem, was used to derive ephemeris-robust results in NANOGrav's 11-yr stochastic-background search, and it provides a foundation for future searches by NANOGrav and other consortia. The analysis and simulations reported here suggest that ephemeris modeling reduces the gravitational-wave sensitivity of the 11-yr dataset; and that this degeneracy will vanish with improved ephemerides and with the longer pulsar timing datasets that will become available in the near future.

[7]  arXiv:2001.00598 [pdf, other]

Title: ZTF Early Observations of Type Ia Supernovae II: First Light, the Initial Rise, and Time to Reach Maximum Brightness

Authors: A. A. Miller, Y. Yao, M. Bulla, E. C. Bellm, S. B. Cenko, R. Dekany, C. Fremling, M. J. Graham, T. Kupfer, R. R. Laher, A. A. Mahabal, F. J. Masci, P. E. Nugent, R. Riddle, B. Rusholme, R. M. Smith, D. L. Shupe, J. van Roestel, S. R. Kulkarni

Comments: 29 pages, 16 figures; submitted to ApJ; comments are welcome

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

While it is clear that Type Ia supernovae (SNe) are the result of thermonuclear explosions in C/O white dwarfs (WDs), a great deal remains uncertain about the binary companion that facilitates the explosive disruption of the WD. Here, we present a comprehensive analysis of a unique, and large, data set of 127 SNe Ia with exquisite coverage by the Zwicky Transient Facility (ZTF). High-cadence (6 observations per night) ZTF observations allow us to measure the SN rise time and examine its initial evolution. We develop a Bayesian framework to model the early rise as a power-law in time, which enables the inclusion of priors in our model. For a volume-limited subset of normal SNe Ia, we find the mean power-law index is consistent with 2 in the $r_\mathrm{ztf}$-band ($\alpha_r = 2.01\pm0.02$), as expected in the expanding fireball model. There are, however, individual SNe that are clearly inconsistent with $\alpha_r=2$. We estimate a mean rise time of 18.5$\,$d (with a range extending from $\sim$15$-$22$\,$d), though this is subject to the adopted prior. We identify an important, previously unknown, bias whereby the rise times for higher redshift SNe within a flux-limited survey are systematically underestimated. This effect can be partially alleviated if the power-law index is fixed to $\alpha=2$, in which case we estimate a mean rise time of 21.0$\,$d (with a range from $\sim$18$-$23$\,$d). The sample includes a handful or rare and peculiar SNe Ia. Finally, we conclude with a discussion of lessons learned from the ZTF sample that can eventually be applied to Large Synoptic Survey Telescope observations.

[8]  arXiv:2001.00601 [pdf, other]

Title: The Molecular Gas in the NGC 6240 Merging Galaxy System at the Highest Spatial Resolution

Authors: E. Treister (1), H. Messias (2), G. C. Privon (3), N. Nagar (4), A. M. Medling (5), V. U. (6), F. E. Bauer (1), C. Cicone (7), L. Barcos Munoz (8), A. S. Evans (8,9), F. Muller-Sanchez (10), J. M. Comerford (11), L. Armus (12), C. Chang (2), M. Koss (13), G. Venturi (1), K. Schawinski (14), C. Casey (15), C. M. Urry (16), D. B. Sanders (17), N. Scoville (12), K. Sheth (18) ((1) Instituto de Astrofisica, Pontificia Universidad Catolica, Chile, (2) Joint ALMA Observatory, (3) U. of Florida, (4) U. de Concepcion, Chile, (5) U. of Toledo, (6) U. of California, Irvine, (7) University of Oslo, Norway, (8) NRAO, (9) U. of Virginia, (10) U. of Memphis, (11) U. of Colorado, (12) Caltech, (13) Eureka Scientific, (14) Modulus AG, Switzerland, (15) U. of Texas Austin, (16) Yale U., (17) U. of Hawaii, (18) NASA Headquarters)

Comments: 27 pages, 13 figures, accepted for publication by The Astrophysical Journal

Subjects: Astrophysics of Galaxies (astro-ph.GA)

We present the highest resolution --- 15 pc (0.03'') --- ALMA $^{12}$CO(2-1) line emission and 1.3mm continuum maps, tracers of the molecular gas and dust, respectively, in the nearby merging galaxy system NGC 6240, that hosts two supermassive black holes growing simultaneously. These observations provide an excellent spatial match to existing Hubble optical and near-infrared observations of this system. A significant molecular gas mass, $\sim$9$\times$10$^9$M$_\odot$, is located in between the two nuclei, forming a clumpy stream kinematically dominated by turbulence, rather than a smooth rotating disk as previously assumed from lower resolution data. Evidence for rotation is seen in the gas surrounding the southern nucleus, but not in the northern one. Dynamical shells can be seen, likely associated with nuclear supernovae remnants. We further detect the presence of significant high velocity outflows, some of them reaching velocities $>$500 km/s, affecting a significant fraction, $\sim$11\% of the molecular gas in the nuclear region. Inside the spheres of influence of the northern and southern supermassive black holes we find molecular masses of 7.4$\times$10$^8$M$_\odot$ and 3.3$\times$10$^9$M$_\odot$, respectively. We are thus directly imaging the reservoir of gas that can accrete onto each supermassive black hole. These new ALMA maps highlight the critical need for high resolution observations of molecular gas in order to understand the feeding of supermassive black holes and its connection to galaxy evolution in the context of a major galaxy merger.

[9]  arXiv:2001.00642 [pdf, other]

Title: The (re)appearance of NGC 925 ULX-3, a new transient ULX

Authors: Hannah P. Earnshaw, Marianne Heida, Murray Brightman, Felix Fürst, Fiona A. Harrison, Amruta Jaodand, Matthew J. Middleton, Timothy P. Roberts, Rajath Sathyaprakash, Daniel Stern, Dominic J. Walton

Comments: 9 pages, 3 figures, 1 table. Submitted to ApJ

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We report the discovery of a third ULX in NGC 925 (ULX-3), detected in November 2017 by Chandra at a luminosity of $L_{\rm X} = (7.8\pm0.8)\times10^{39}$ erg s$^{-1}$. Examination of archival data for NGC 925 reveals that ULX-3 was detected by Swift at a similarly high luminosity in 2011, as well as by XMM-Newton in January 2017 at a much lower luminosity of $L_{\rm X} = (3.8\pm0.5)\times10^{38}$ erg s$^{-1}$. With an additional Chandra non-detection in 2005, this object demonstrates a high dynamic range of flux of factor >26. In its high-luminosity detections, ULX-3 exhibits a hard power-law spectrum with $\Gamma=1.6\pm0.1$, whereas the XMM-Newton detection is slightly softer, with $\Gamma=1.8^{+0.2}_{-0.1}$ and also well-fitted with a broadened disc model. The long-term light curve is sparsely covered and could be consistent either with the propeller effect or with a large-amplitude superorbital period, both of which are seen in ULXs, in particular those with neutron star accretors. Further systematic monitoring of ULX-3 will allow us to determine the mechanism by which ULX-3 undergoes its extreme variability and to better understand the accretion processes of ULXs.

[10]  arXiv:2001.00648 [pdf, other]

Title: Shock-breakout and central engine activities in H.E.S.S. detected GRB 190829A

Authors: Vikas Chand, Ankush Banerjee, Rahul Gupta, Dimple, Partha Sarathi Pal, Jagdish C. Joshi, Bin-Bin Zhang, R. Basak, P. H. T. Tam, Vidushi Sharma, S. B. Pandey, Amit Kumar, Yi-Si Yang

Comments: Submitted for publication in ApJL

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present the results of a detailed investigation of the prompt and afterglow emission in the H.E.S.S. detected GRB 190829A. Swift and Fermi observations of the prompt phase of this GRB reveal two isolated sub-bursts or episodes, separated by a quiescent phase. The energetic and the spectral properties of the first episode are in stark contrast to the second. The first episode, which has a higher spectral peak $\sim 120 \keV$ and a low isotropic energy $\sim 10^{50}\erg$ is an outlier to the Amati correlation and marginally satisfies the Yonetoku correlation. However, the energetically dominant second episode has a lower peak energy and is well consistent with both the correlations. We compared this GRB to other low luminosity GRBs. A fundamental correlation predicts a duration that makes the first episode consistent with a shock breakout. Additionally, peculiar central engine activities are observed during the afterglow phase. This includes a long-lasting flare in X-rays and optical emission that requires the central engine to be active for a long duration ($\sim 10^4 \s$). We analyzed the late time Fermi-LAT emission that encapsulates the H.E.S.S. detection. Some of the LAT photons are likely to be associated with the source and might have inverse Compton origin as seen in previously detected TeV-GRBs. All the above observational facts suggest GRB 190819A is a peculiar low luminosity GRB that is initially powered by shock breakout followed by central engine activities. Furthermore, our results show that TeV energy photons seem common in both high and low luminosity GRBs.

[11]  arXiv:2001.00671 [pdf, other]

Title: New fully evolutionary models for asteroseismology of ultra-massive white dwarf stars

Authors: A. H. Córsico, F. C. De Gerónimo, M. E. Camisassa, L. G. Althaus

Comments: 4 pages, 2 tables, 2 figures, poster contribution at the conference "Stars and their variability observed from space - Celebrating the 5th anniversary of BRITE-Constellation", Vienna, Austria, August 19 - 23, 2019. Eds: C. Neiner, W. Weiss, D. Baade, E. Griffin, C. Lovekin, A. Moffat

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

Ultra-massive hydrogen-rich (DA spectral type) white dwarf (WD) stars ($M_{\star} > 1M_{\odot}$) coming from single-star evolution are expected to harbor cores made of $^{16}$O and $^{20}$Ne, resulting from semi-degenerate carbon burning when the progenitor star evolves through the super asymptotic giant branch (S-AGB) phase. These stars are expected to be crystallized by the time they reach the ZZ Ceti instability strip ($T_{\rm eff} \sim 12\,500$ K). Theoretical models predict that crystallization leads to a separation of $^{16}$O and $^{20}$Ne in the core of ultra-massive WDs, which impacts their pulsational properties. This property offers a unique opportunity to study the processes of crystallization. Here, we present the first results of a detailed asteroseismic analysis of the best-studied ultra-massive ZZ Ceti star BPM~37093. As a second step, we plan to repeat this analysis using ultra-massive DA WD models with C/O cores in order to study the possibility of elucidating the core chemical composition of BPM~37093 and shed some light on its possible evolutionary origin. We also plan to extend this kind of analyses to other stars observed from the ground and also from space missions like Kepler and TESS.

[12]  arXiv:2001.00674 [pdf]

Title: Reframing astronomical research through an anticolonial lens -- for TMT and beyond

Authors: Chanda Prescod-Weinstein, Lucianne M. Walkowicz, Sarah Tuttle, Brian Nord, Hilding R. Neilson

Comments: 8 pages, APC (State of the Profession) White Paper submitted to the Astro2020 Decadal Survey

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

This white paper explains that professional astronomy has benefited from settler colonial white supremacist patriarchy. We explicate the impact that this has had on communities which are not the beneficiaries of colonialism and white supremacy. We advocate for astronomers to reject these benefits in the future, and we make proposals regarding the steps involved in rejecting colonialist white supremacy's benefits. We center ten recommendations on the timely issue of what to do about the Thirty Meter Telescope (TMT) on Maunakea in Hawaii. This paper is written in solidarity with and support of efforts by Native Hawaiian scientists (e.g. Kahanamoku et al. 2019).

[13]  arXiv:2001.00675 [pdf, ps, other]

Title: Curvature induced polarization and spectral index behavior for PKS 1502+106

Authors: Xi Shao, Yunguo Jiang, Xu Chen

Comments: 13 pages, 8 figures

Journal-ref: Published in ApJ, 2019, 884, 15

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

A comprehensive study of multifrequency correlations can shed light on the nature of variation for blazars. In this work, we collect the long-term radio, optical and $\gamma$-ray light curves of PKS 1502+106. After performing the localized cross-correlation function analysis, we find that correlations between radio and $\gamma$-ray or $V$ band are beyond the $3\sigma$ significance level. The lag of the $\gamma$-ray relative to 15 GHz is $-60^{+5}_{-10}$ days, translating to a distance $3.18^{+0.50}_{-0.27}$ parsec (pc) between them. Within uncertainties, the locations of the $\gamma$-ray and optical emitting regions are roughly the same, and are away from the jet base within $1.2$ pc. The derived magnetic field in optical and $\gamma$-ray emitting regions is about $0.36$ G. The logarithm of $\gamma$-ray flux is significantly linearly correlated with that of $V$ band fluxes, which can be explained by the synchrotron self-Compton (SSC) process, the external Compton (EC) processes, or the combination of them. We find a significant linear correlation in the plot of $\log\prod$ (polarization degree) versus $\log \nu F_{\nu}$ at $V$ band, and use the empirical relation $\Pi \sim \sin^n \theta'$ ($\theta'$ is the observing angle in the comoving frame blob) to explain it. The behaviors of color index (generally redder when brighter at the active state) and $\gamma$-ray spectral index (softer when brighter) could be well explained by the twisted jet model. These findings suggest that the curvature effect (mainly due to the change of the viewing angle) is dominant in the variation phenomena of fluxes, spectral indices, and polarization degrees for PKS 1502+106.

[14]  arXiv:2001.00679 [pdf, ps, other]

Title: Five Stellar Populations in M22 (NGC 6656)

Authors: Jae-Woo Lee

Comments: Astrophysical Journal Letters, 2020, 888, 6

Subjects: Astrophysics of Galaxies (astro-ph.GA); Solar and Stellar Astrophysics (astro-ph.SR)

We present the Ca-CN-CH photometry of the metal-complex globular cluster (GC) M22 (NGC 6656). Our photometry clearly shows the discrete double CN-CH anticorrelations in M22 red giant branch (RGB) stars, due to the difference in the mean metallicity. The populational number ratio between the two main groups is n(G1):n(G2) = 63:37(+/-3), with the G1 being more metal-poor. Furthermore, the G1 can be divided into two subpopulations with the number ratio of n(CN-w):n(CN-s) = 51:49 (+/-4), while the G2 can be divided into three subpopulations with n(CN-w):n(CN-i):n(CN-s) = 24:32:44 (+/-5). The proper motion of individual stars in the cluster shows an evidence of internal rotation, showing the G2 with a faster rotation, confirming our previous results from radial velocities. The cumulative radial distributions (CRDs) of individual subpopulations are intriguing in the following aspects: (1) In both main groups, the CRDs of the CN-s subpopulations are more centrally concentrated than other subpopulations. (2) The CRDs of the the G1 CN-s and the G2 CN-s are very similar. (3) Likewise, the G1 CN-w and the G2 CN-w and CN-i have almost identical CRDs. We also estimate the relative helium abundance of individual subpopulations by comparing their RGB bump magnitudes, finding that no helium abundance variation can be seen in the G1, while significant helium enhancements by Delta Y = 0.03 ~ 0.07 are required in the G2. Our results support the idea that M22 formed via a merger of two GCs.

[15]  arXiv:2001.00695 [pdf, other]

Title: Evidence against Ryskin's model of cosmic acceleration

Authors: Joseph Ryan

Comments: Submitted to Astroparticle Physics

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

In this paper I examine how well Ryskin's model of emergent cosmic acceleration fits several sets of cosmological observations. I find that while Ryskin's model is somewhat compatible with the standard model of cosmological acceleration ($\Lambda$CDM) for low redshift (z < 1) measurements, its predictions diverge considerably from those of the standard model for measurements made at high redshift (for which z > 1), and it is therefore not a compelling substitute for the standard model.

[16]  arXiv:2001.00713 [pdf, ps, other]

Title: Disappearance of the Fe K$α$ emission line in Ultra Compact X-ray Binaries 4U 1543-624 and Swift J1756.9-2508

Authors: Filippos Koliopanos, Georgios Vasilopoulos, Sebastien Guillot, Natalie Webb

Comments: submitted to MNRAS, comments and suggestions encouraged and appreciated. 12 pages 8 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We investigate the long-term variability of the K$\alpha$ line of iron in the spectra of two Ultra Compact X-ray Sources (UCXBs) with C/O-rich donors. We revisit archival observations by five different X-ray telescopes, over a ~twenty year period. Adopting physically motivated models for the spectral continuum, we probe the long-term evolution of the source emission in a self-consistent manner enabling physical interpretation of potential variability in the primary X-ray emission continuum and/or any emission lines from reflection off the accretion disk. We find that the spectral shape and flux of the source emission (for both objects) has remained almost constant throughout all the observations, displaying only minor variability in some spectral parameters and the source flux (largest variation is a ~25% drop in the flux of Swift J1756.9-2508). We note a striking variability of the Fe K$\alpha$ line which fluctuates from a notable equivalent width of ~66-100 eV in 4U 1543-624 and ~170 eV in Swift J1756.9-2508, to non-detections with upper limits of 2-8 eV. We argue that the disappearance of the iron line is due to the screening of the Fe K$\alpha$ line by the overabundant oxygen in the C/O-rich UCXBs. This effect is cancelled when oxygen becomes fully ionized in the inner disk region, resulting in the variability of the Fe K$\alpha$ line in an otherwise unaltered spectral shape. This finding supports earlier predictions on the consequences of H-poor, C/O-rich accretion disk on reflection induced fluorescent lines in the spectra of UCXBs.

[17]  arXiv:2001.00716 [pdf, other]

Title: The chemical composition of the accretion disk and donor star in Ultra Compact X-ray Binaries: A comprehensive X-ray analysis

Authors: Filippos Koliopanos, Mathias Peault, Georgios Vasilopoulos, Natalie Webb

Comments: submitted to MNRAS, comments and suggestions encouraged and appreciated. 17 pages 21 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We have analyzed the X-ray spectra of all known Ultra Compact X-ray Binaries (UCXBs), with the purpose of constraining the chemical composition of their accretion disk and donor star. Our investigation was focused on the presence (or absence) of the Fe K${\alpha}$ emission line, which was used as the probe of chemical composition of the disk, based on previously established theoretical predictions for the reflection of X-ray radiation off the surface of C/O-rich or He-rich accretion disks in UCXBs. We have contrasted the results of our spectral analysis to the history of type I X-ray bursts from these systems, which can also indicate donor star composition. We found that UCXBs with prominent and persistent iron K${\alpha}$ emission also featured repeat bursting activity. On the other hand, the UCXBs for which no iron line was detected, appear to have few or no type I X-ray bursts detected over more than a decade of monitoring. Based on Monte Carlo simulations, demonstrating a strong correlation between the Fe K${\alpha}$ line strength and the abundance of C and O in the accretion disk material and given the expected correlation between the H/He abundance and the recurrence rate of type I X-ray bursts, we propose that there is a considerable likelihood that UCXBs with persistent iron emission have He-rich donors, while those that do not, likely have C/O or O/Ne/Mg-rich donors. Our results strongly advocate for the development of more sophisticated simulations of X-ray reflection from hydrogen-poor accretion disks.

[18]  arXiv:2001.00717 [pdf, ps, other]

Title: Superhydrogenated Polycyclic Aromatic Hydrocarbon Molecules: Vibrational Spectra in the Infrared

Authors: X.J. Yang, Aigen Li, R. Glaser

Comments: 49 pages, 26 figures; accepted for publication in The Astrophysical Journal Supplement Series

Subjects: Astrophysics of Galaxies (astro-ph.GA); Atomic and Molecular Clusters (physics.atm-clus)

Superhydrogenated polycyclic aromatic hydrocarbons (PAHs) may be present in H-rich and ultraviolet-poor benign regions. The addition of excess H atoms to PAHs converts the aromatic bonds into aliphatic bonds, the strongest of which falls near 3.4 $\mu$m. Therefore, superhydrogenated PAHs are often hypothesized as a carrier of the 3.4 $\mu$m emission feature which typically accompanies the stronger 3.3 $\mu$m aromatic C--H stretching feature. To assess this hypothesis, we use density function theory to compute the IR vibrational spectra of superhydrogenated PAHs and their ions of various sizes (ranging from benzene, naphthalene to perylene and coronene) and of various degrees of hydrogenation (ranging from minimal hydrogenation to heavy hydrogenation). For each molecule, we derive the intrinsic oscillator strengths of the 3.3 $\mu$m aromatic C--H stretch ($A_{3.3}$) and the 3.4 $\mu$m aliphatic C--H stretch ($A_{3.4}$). By comparing the computationally-derived mean ratio of $\langle A_{3.4}/A_{3.3}\rangle\sim1.98$ with the mean ratio of the observed intensities $\langle I_{3.4}/I_{3.3}\rangle\sim0.12$, we find that the degree of superhydrogenation --- the fraction of C atoms attached with excess H atoms --- is only $\sim2.2\%$ for neutral PAHs which predominantly emit the 3.3 and 3.4 $\mu$m features. We also determine for each molecule the intrinsic band strengths of the 6.2 $\mu$m aromatic C--C stretch ($A_{6.2}$) and the 6.85 $\mu$m aliphatic C--H deformation ($A_{6.85}$). We derive the degree of superhydrogenation from the mean ratio of the observed intensities $\langle I_{6.85}/I_{6.2}\rangle\sim0.10$ and $\langle A_{6.85}/A_{6.2}\rangle\sim1.53$ for neutrals and $\langle A_{6.85}/A_{6.2}\rangle\sim1.23$ for cations to be $\lesssim 3.1\%$ for neutrals and $\lesssim 8.6\%$ for cations. We conclude that astrophysical PAHs are primarily aromatic and are only marginally superhydrogenated.

[19]  arXiv:2001.00721 [pdf, other]

Title: A phase shift of gravitational waves induced by aberration

Authors: Alejandro Torres-Orjuela, Xian Chen, Pau Amaro-Seoane

Comments: 5 pages, 5 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc)

The velocity of a gravitational wave (GW) source provides crucial information about its formation and evolution processes. Previous studies considered the Doppler effect on the phase of GWs as a potential means to detect a time-dependent velocity of the source. However, the Doppler shift only accounts for the time component of the wave vector, and in principle motion also affects the spatial components. The latter effect, known as "aberration'' for light, is analyzed in this Letter for GWs and applied to the waveform modeling of an accelerating source. We show that the additional aberrational phase shift could be detectable in two astrophysical scenarios, namely, a recoiling binary black hole (BBH) due to GW radiation and a BBH in a triple system. Our results suggest that adding the aberrational phase shift in the waveform templates could significantly enhance the detectability of moving sources.

[20]  arXiv:2001.00723 [pdf, ps, other]

Title: NuSTAR X-ray spectrum of Be-X-ray pulsar Swift J1845.7-0037: Bulk and thermal Comptonization of cyclotron seed photons in the accretion column

Authors: Filippos Koliopanos, Georgios Vasilopoulos, Michael T. Wolff

Comments: submitted to A&A, comments and suggestions appreciated. 7 pages, 9 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Aims: Spectral and temporal analysis of the NuSTAR observation Galactic Be-XRB Swift J1845.7-0037. during its recent outburst. Methods: For the spectral analysis we use both phenomenological and physics-based models. We employ an often used empirical model to identify the main characteristics of the spectral shape in relation to nominal spectral characteristics of X-ray pulsars. Additionally, we used the latest version of Bulk \& Thermal comptonization model (BW), to assess the validity of the spectral components required by the empirical model and to investigate the origin of the hard X-ray emission. We also analyzed the source light-curve, studying the pulse shape at different energy ranges and tracking the spectral evolution with pulse phase by using the model independent hardness ratio (HR). Results: We find that while both the empirical and physical (BW) spectral models can produce good spectral fits, the BW model returns physically plausible best-fit values for the source parameters and does not require any additional spectral components to the non-thermal, accretion column emission. The BW model also yielded an estimation of the neutron star magnetic field placing it in the 10^12G range. Conclusions: Our results, show that the spectral and temporal characteristics of the source emission are consistent with the scattering processes expected for radiation dominated shocks within the accretion column of highly magnetized accreting neutron stars. We further indicate that physically-derived spectral models such as BW, can be used to tentatively infer fundamental source parameters, in the absence of more direct observational signatures.

[21]  arXiv:2001.00754 [pdf, other]

Title: Blazhko effect in the Galactic bulge fundamental mode RR~Lyrae stars II: Modulation shapes, amplitudes and periods

Authors: M. Skarka, Z. Prudil, J. Jurcsik

Comments: 12 pages, 14 figures, 2 tables. Submitted to MNRAS

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

The number of stars observed by the Optical Gravitational Lensing Experiment (OGLE) project in the Galactic bulge offers an invaluable chance to study RR Lyrae stars in a statistical manner. We used data of 3141 fundamental-mode RR Lyrae stars showing the Blazhko effect observed in OGLE-IV to investigate a possible connection between modulation amplitudes and periods, light curve and pulsation characteristics. We found that there is no simple monotonic correlation of any combination of two parameters concerning the Blazhko and pulsation amplitudes, periods and the shape of the light curves. There are only systematic limits. There is a bottom limit of the modulation period with respect to the pulsation period. We also found that the possible range of modulation amplitudes decreases with increasing pulsation period which could point towards that the Blazhko effect is suppressed in cooler, larger, more luminous and less metal abundant bulge RR Lyrae stars. We identified six modulation types showing similar modulation envelopes. Basically, every Blazhko star can be assigned to one of these six classes. Further, our investigation revealed two possible populations of stars that have mean modulation periods of 48 and 186 days. Double modulation was found in 25 per cent of the studied stars. It was found that only 6.3 per cent of modulated stars belongs to the Oosterhoff group II. The asymmetry of the amplitudes of the side peaks around the basic pulsation frequency suggests that in 70 per cent of stars the phase difference between amplitude and phase modulation is $\pi<\phi_{\rm m}<2\pi$.

[22]  arXiv:2001.00755 [pdf, other]

Title: Unveiling the temporal properties of MAXI J1820+070 throughAstroSatobservations

Authors: Sneha Prakash Mudambi, Bari Maqbool, Ranjeev Misra, Sabhya Hebbar, J. S. Yadav, Shivappa B. Gudennavar, Bubbly S. G

Comments: 8 pages, 4 figures and 1 Table

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present here the results of the first broadband simultaneous spectral and temporal studies of the newly detected black hole binary MAXI J1820+070 as seen by SXT and LAXPC on-board AstroSat.The observed combined spectra in the energy range 0.7 -80 keV were well modeled using disk black-body emission, thermal Comptonization and a reflection component. The spectral analysis revealed that the source was in its hard spectral state (Gamma = 1.61) with a cool disk (kTin= 0.22 keV). We report the energy dependent time-lag and root mean squared (rms) variability at different frequencies in the energy range 3-80 keV using LAXPC data. We also modeled the flux variability using a single zone stochastic propagation model to quantify the observed energy dependence of time-lag and fractional rms variability and then compared the results with that of Cygnus X-1. Additionally, we confirm the detection of a quasi-periodic oscillation with the centroid frequency at 47.7 mHz.

[23]  arXiv:2001.00768 [pdf, other]

Title: High-energy neutrinos from cosmic ray interactions in the Local Bubble

Authors: M. Bouyahiaoui, M. Kachelriess, D.V. Semikoz

Comments: 8 pages, 9 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

A surprisingly large flux of extraterrestrial high-energy neutrinos was discovered by the IceCube experiment. While the flux of muon neutrinos with energies $E>100$ TeV is consistent with the extragalactic gamma-ray background (EBL) determined by Fermi-LAT, the softer component of the cascade neutrino flux at $E<100$ TeV is larger than expected. Moreover, a gamma-ray excess at high Galactic latitudes at energies $E>300$ GeV was found in the data of Fermi-LAT. The gamma-ray excess at TeV energies and the neutrino excess at $E<100$ TeV may have a common Galactic origin. In this work, we study the possibility that both excesses are caused by interactions of cosmic rays (CRs) with energies up to PeV in the wall of the Local Bubble. Source of these CRs may be a recent nearby source like Vela. We show that such a scenario can explain the observed CR flux around the knee, while CR interactions in the bubble wall can generate a substantial fraction of the observed astrophysical high-energy neutrino flux below $\sim {\rm few} \times 100$ TeV.

[24]  arXiv:2001.00789 [pdf]

Title: Polarimetric properties of asteroid 3200 Phaethon

Authors: L. F. Golubeva, D.I. Shestopalov, O. I. Kvaratskhelia

Comments: 26 pages, 7 figures, 2 tables

Subjects: Earth and Planetary Astrophysics (astro-ph.EP)

The polarimetric observations of asteroid 3200 Phaethon, the target of international observation campaign, did not cover a proper phase angle interval to provide estimating all the attributes of the asteroid polarization curve. Based on present discrete observation data for Phaethon, its full polarimetric curves in BVRI bandpasses were reproduced. The polarimetric properties of the asteroid correspond to a notion on surface structure as thermally altered regolith particles mixed with lager rock fragments like a coarse pebble.

[25]  arXiv:2001.00800 [pdf, other]

Title: Clusters of Galaxies: Structure and Dynamics in the Last 8 Gyr

Authors: A. Biviano (INAF-OATs)

Comments: Invited review contribution to the 2019 meeting of the Asociaci\'on Argentina de Astronom\'ia. To appear in BAAA, Vol. 61B, V\'asquez, Benaglia, Iglesias & Sgr\'o eds

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

Clusters of galaxies, being dark matter dominated, have long been and still are the ideal cosmological targets to study the nature of dark matter. Constraints on the nature of dark matter comes in particular from the observational determination of the distribution of total and baryonic mass in clusters, by comparison with results from cosmological numerical simulations. I present here past and recent results on this research topic.

[26]  arXiv:2001.00827 [pdf, ps, other]

Title: Resolving the Nuclear Radio Emission from M32 with Very Large Array

Authors: Sijia Peng, Zhiyuan Li, Loránt O. Sjouwerman, Yang Yang, Fuguo Xie, Feng Yuan

Comments: 12 peges, 3 figures, submitted to ApJ. Comments welcome

Subjects: Astrophysics of Galaxies (astro-ph.GA)

The Local Group dwarf elliptical galaxy M32 hosts one of the nearest and most under-luminous super-massive black holes (SMBHs) ever known, offering a rare opportunity to study the physics of accreting SMBHs at the most quiescent state. Recent Very Large Array (VLA) observations have detected a radio source at the nucleus of M32, which is suggested to be the radio counterpart of the SMBH. To further investigate the radio properties of this nuclear source, we have conducted follow-up, high-resolution VLA observations in four epochs between 2015--2017, each with dual frequencies. At 6 GHz, the nuclear source is resolved under an angular resolution of $\sim$0\farcs4, exhibiting a coreless, slightly lopsided morphology with a detectable extent of $\sim$2 \arcsec ($\sim$8 parsec). No significant variability can be found among the four epochs. At 15 GHz, no significant emission can be detected within the same region, pointing to a steep intrinsic radio spectrum (with a 3\,$\sigma$ upper limit of -1.46 for the spectral index). We discuss possible scenarios for the nature of this nuclear source and conclude that a stellar origin, in particular planetary nebulae, X-ray binaries, supernova remnants or diffuse ionized gas powered by massive stars, can be ruled out.Instead, the observed radio properties can be explained by synchrotron radiation from a hypothetical wind driven by the weakly accreting SMBH.

[27]  arXiv:2001.00833 [pdf, other]

Title: HIR4: cosmology from a simulated neutral hydrogen full sky using Horizon Run 4

Authors: Jacobo Asorey, David Parkinson, Feng Shi, Yong-Seon Song, Kyungjin Ahn, Juhan Kim, Jian Yao, Le Zhang, Shifan Zuo

Comments: 21 pages, 20 figures

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

The distribution of cosmological neutral hydrogen will provide a new window into the large-scale structure of the Universe with the next generation of radio telescopes and surveys. The observation of this material, through 21cm line emission, will be confused by foreground emission in the same frequencies. Even after these foregrounds are removed, the reconstructed map may not exactly match the original cosmological signal, which will introduce systematic errors and offset into the measured correlations. In this paper, we simulate future surveys of neutral hydrogen using the Horizon Run 4 (HR4) cosmological N-body simulation. We generate HI intensity maps from the HR4 halo catalogue, and combine with foreground radio emission maps from the Global Sky Model, to create accurate simulations over the entire sky. We simulate the HI sky for the frequency range 700-800 MHz, matching the sensitivity of the Tianlai pathfinder. We test the accuracy of the fastICA, PCA and log-polynomial fitting foreground removal methods to recover the input cosmological angular power spectrum and measure the parameters. We show the effect of survey noise levels and beam sizes on the recovered the cosmological constraints. We find that while the reconstruction removes power from the cosmological 21cm distribution on large-scales, we can correct for this and recover the input parameters in the noise-free case. However, the effect of noise and beam size of the Tianlai pathfinder prevents accurate recovery of the cosmological parameters when using only intensity mapping information.

[28]  arXiv:2001.00838 [pdf, other]

Title: Dynamical Simulations of the First Globular Clusters

Authors: Raymond G. Carlberg

Comments: AAS submitted

Subjects: Astrophysics of Galaxies (astro-ph.GA); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

Tidally limited star clusters are started on nearly circular orbits in the dark matter sub-halos present at high redshift and evolved with an n-body code augmented with gravitational interactions in the clusters. The tidally removed stars and the remaining high redshift clusters from a redshift 8 start are more concentrated than the dark matter, as expected. However, the subset of stars from the clusters that began in the lower mass sub-halos have a distribution somewhat more extended than the dark matter halo, with a mean galactic radius of about 60 kpc inside 150 kpc. The clusters from low mass sub-halos, those with a peak circular velocity of $ 12-18$ \kms, also produce most of the population's thin stellar streams. The dependence of the stellar population distribution on sub-halo mass is not seen in simulations that start clusters at lower redshift. The half mass radii of the clusters are set by the tidal fields of the initial cluster orbits, which leads to the average half mass radius decreasing with increased redshift of formation. Starting clusters at greater than redshift 4 leads to cluster half mass radii approximately as seen in the Milky Way, with lower redshifts leading to clusters that are too large. If extremely metal poor globular clusters were preferentially formed in high redshift, low mass, dwarf galaxies, then the clusters should be spread nearly uniformly over the dark halo, along with their tidally removed stars.

[29]  arXiv:2001.00844 [pdf, other]

Title: Modelling the strongest silicate emission features of local type 1 AGN

Authors: M. Martínez-Paredes, O. González-Martín, D. Esparza-Arredondo, M. Kim, A. Alonso-Herrero, Y. Krongold, T. Hoang, C. Ramos Almeida, I. Aretxaga, D. Dultzin, J. Hodgson

Comments: Accepted for publication in ApJ

Subjects: Astrophysics of Galaxies (astro-ph.GA)

We measure the 10 and $18\mu$m silicate features in a sample of 67 local ($z<0.1$) type 1 active galactic nuclei (AGN) with available {\it Spitzer} spectra dominated by non-stellar processes. We find that the $10\mu$m silicate feature peaks at $10.3^{+0.7}_{-0.9}\mu$m with a strength (Si$_{p}$ = ln f$_{p}$(spectrum)/f$_{p}$(continuum)) of $0.11^{+0.15}_{-0.36}$, while the $18\mu$m one peaks at $17.3^{+0.4}_{-0.7}\mu$m with a strength of $0.14^{+0.06}_{-0.06}$. We select from this sample sources with the strongest 10$\mu$m silicate strength ($\sigma_{Si_{10\mu m}}>0.28$, 10 objects). We carry out a detailed modeling of the IRS/{\it Spitzer} spectra by comparing several models that assume different geometries and dust composition: a smooth torus model, two clumpy torus models, a two-phase medium torus model, and a disk+outflow clumpy model. We find that the silicate features are well modeled by the clumpy model of Nenkova et al. 2008, and among all models those including outflows and complex dust composition are the best (Hoenig et al. 2017). We note that even in AGN-dominated galaxies it is usually necessary to add stellar contributions to reproduce the emission at the shortest wavelengths.

[30]  arXiv:2001.00855 [pdf, ps, other]

Title: Spiral Instabilities in N-body Simulations: Emergence from noise II

Authors: J. A. Sellwood (Steward Observatory)

Comments: Accepted to appear in MNRAS. 4 pages, 2 figures

Subjects: Astrophysics of Galaxies (astro-ph.GA)

An earlier paper presented the potentially significant discovery that disturbances in simplified simulations of a stellar disc model that was predicted to be stable in linear theory grew to large amplitude over a long period of time. The ultimate appearance of true instabilities was attributed to non-linear scattering by a succession of collective waves excited by shot noise from the finite number of particles. The paper concluded that no finite number of particles, however large, could mimic a smooth disc. As this surprising finding has been challenged as an artifact of the numerical scheme employed, we here present a new calculation of the same model using a different grid geometry that confirms the original behaviour.

[31]  arXiv:2001.00860 [pdf, other]

Title: A Simple Unified Spectroscopic Indicator of Stellar Luminosity: the Extended Flux Weighted Gravity-Luminosity Relationship

Authors: Rolf-Peter Kudritzki, Miguel A. Urbaneja, Hans-Walter Rix

Comments: Accepted for The Astrophysical Journal. 10 pages and 9 figures

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

We show that for a wide range of stellar masses, from 0.3 to 20 Msun, and for evolutionary phases from the main sequence to the beginning of the red giant stage, the stellar flux weighted gravity, g_F ~ g/Teff^4, is tightly correlated with absolute bolometric magnitude Mbol. Such a correlation is predicted by stellar evolution theory. We confirm this relation observationally, using a sample of 445 stars with precise stellar parameters. It holds over 17 stellar magnitudes from Mbol = 9.0 mag to -8.0 mag with a scatter of 0.17 mag above Mbol = -3.0 and 0.29 mag below this value. We then test the relation with 2.2 million stars with 6.5 mag > Mbol > 0.5 mag, where 'mass-produced' but robust log g, Teff and Mbol from LAMOST DR5 and Gaia DR2 are available. We find that the same relation holds with a scatter of ~0.2 mag for single stars offering a simple spectroscopic distance estimate good to ~10 percent.

[32]  arXiv:2001.00868 [pdf, other]

Title: 3D Turbulent Reconnection: Theory, Tests and Astrophysical Implications

Authors: Alex Lazarian, Gregory L. Eyink, Amir Jafari, Grzegorz Kowal, Hui Li, Siyao Xu, Ethan T. Vishniac

Comments: 94 pages, 39 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Computational Physics (physics.comp-ph); Plasma Physics (physics.plasm-ph)

Magnetic reconnection, topological change in magnetic fields, is a fundamental process in magnetized plasmas. It is associated with energy release in regions of magnetic field annihilation, but this is only one facet of this process. Astrophysical flows normally have very large Reynolds numbers and are expected to be turbulent, in agreement with observations. In strong turbulence magnetic lines constantly reconnect everywhere at all scales, making magnetic reconnection an intrinsic part of turbulent cascade. We note that this is inconsistent with the usual practice of regarding magnetic lines as persistent dynamical elements. A number of theoretical, numerical, and observational studies, starting with Lazarian & Vishniac (1999), demonstrated that 3D turbulence makes magnetic reconnection fast and that these two processes are intrinsically connected. We discuss the dramatic violation of the textbook concept of magnetic flux-freezing in the presence of turbulence and demonstrate that in the presence of turbulence the plasma effects are subdominant to turbulence as far as the magnetic reconnection is concerned. This justifies an MHD-like treatment of magnetic reconnection at scales much larger than the relevant plasma scales. We discuss numerical and observational evidences supporting the turbulent reconnection model. In particular, we show that tearing reconnection is suppressed in 3D and, unlike the 2D case, the 3D reconnection induces turbulence that makes reconnection independent of resistivity. We show that turbulent reconnection dramatically affects the key astrophysical processes, e.g., star formation, turbulent dynamo, acceleration of cosmic rays. We provide criticism of the concept of "reconnection-mediated turbulence" and explain why turbulent reconnection is very different from enhanced turbulent resistivity and hyper-resistivity, and why the latter has fatal conceptual flaws.

[33]  arXiv:2001.00873 [pdf, other]

Title: Onset of Cosmic Reionization: Evidence of An Ionized Bubble Merely 680 Myrs after the Big Bang

Authors: V. Tilvi (ASU), S. Malhotra (NASA), J. E. Rhoads (NASA), A. Coughlin (Chandler Com College), Z. Zheng (Shanghai Obs.), S. L. Finkelstein (UT Austin), S. Veilleux (Univ. Maryland), B. Mobasher (UC Riverside), J. Wang (USTC), R. Probst (NOAO), R. Swaters (Univ Maryland), P. Hibon (ESO), B. Joshi (ASU) J. Zabl (Univ Lyon), T. Jiang (ASU), J. Pharo (ASU), H. Yang (ASU)

Subjects: Astrophysics of Galaxies (astro-ph.GA)

While most of the inter-galactic medium (IGM) today is permeated by ionized hydrogen, it was largely filled with neutral hydrogen for the first 700 million years after the Big Bang. The process that ionized the IGM (cosmic reionization) is expected to be spatially inhomogeneous, with fainter galaxies playing a significant role. However, we still have only a few direct constraints on the reionization process. Here we report the first spectroscopic confirmation of two galaxies and very likely a third galaxy in a group (hereafter EGS77) at redshift z = 7.7, merely 680 Myrs after the Big Bang. The physical separation among the three members is < 0.7 Mpc. We estimate the radius of ionized bubble of the brightest galaxy to be about 1.02 Mpc, and show that the individual ionized bubbles formed by all three galaxies likely overlap significantly, forming a large yet localized ionized region, which leads to the spatial inhomogeneity in the reionization process. It is striking that two of three galaxies in EGS77 are quite faint in the continuum, thanks to our selection of reionizing sources using their Lyman-alpha line emission. Indeed, one is the faintest spectroscopically confirmed galaxy yet discovered at such high redshifts. Our observations provide direct constraints in the process of cosmic reionization, and allow us to investigate the properties of sources responsible for reionizing the universe.

[34]  arXiv:2001.00877 [pdf, other]

Title: BAT AGN Spectroscopic Survey -- XV: The High Frequency Radio Cores of Ultra-hard X-ray Selected AGN

Authors: Krista Lynne Smith, Richard F. Mushotzky, Michael Koss, Claudio Ricci, O. Ivy Wong, Franz E. Bauer, Federica Ricci, Stuart Vogel, Daniel Stern, Meredith C. Powell, C. Meg Urry, Fiona Harrison, Julian Mejia-Restrepo, Kyuseok Oh, Junhyun Baek, Aeree Chung

Comments: 22 pages, 10 figures, 2 tables. Accepted for publication in MNRAS

Subjects: Astrophysics of Galaxies (astro-ph.GA)

We have conducted 22 GHz radio imaging at 1" resolution of 100 low-redshift AGN selected at 14-195 keV by the Swift-BAT. We find a radio core detection fraction of 96%, much higher than lower-frequency radio surveys. Of the 96 radio-detected AGN, 55 have compact morphologies, 30 have morphologies consistent with nuclear star formation, and 11 have sub-kpc to kpc-scale jets. We find that the total radio power does not distinguish between nuclear star formation and jets as the origin of the radio emission. For 87 objects, we use optical spectroscopy to test whether AGN physical parameters are distinct between radio morphological types. We find that X-ray luminosities tend to be higher if the 22 GHz morphology is jet-like, but find no significant difference in other physical parameters. We find that the relationship between the X-ray and core radio luminosities is consistent with the $L_R/L_X \sim 10^{-5}$ of coronally active stars. We further find that the canonical fundamental planes of black hole activity systematically over-predict our radio luminosities, particularly for objects with star formation morphologies.

[35]  arXiv:2001.00879 [pdf, other]

Title: The Robotilter: An Automated Lens / CCD Alignment System for the Evryscope

Authors: Jeffrey K. Ratzloff, Nicholas M. Law, Henry T. Corbett, Octavi Fors, Daniel del Ser

Comments: Accepted to JATIS, January 2020

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Camera lenses are increasingly used in wide-field astronomical surveys due to their high performance, wide field-of-view (FOV) unreachable from traditional telescope optics, and modest cost. The machining and assembly tolerances for commercially available optical systems cause a slight misalignment (tilt) between the lens and CCD, resulting in PSF degradation. We have built an automated alignment system (Robotilters) to solve this challenge, optimizing 4 degrees of freedom - 2 tilt axes, a separation axis (the distance between the CCD and lens), and the lens focus (the built-in focus of the lens by turning the lens focusing ring which moves the optical elements relative to one another) in a compact and low-cost package. The Robotilters remove tilt and optimize focus at the sub 10 micron level, are completely automated, take 2 hours to run, and remain stable for multiple years once aligned. The Robotilters were built for the Evryscope telescope (a 780 MPix 22-camera array with an 8150 sq.deg. field of view and continuous 2-minute cadence) designed to detect short timescale events across extremely large sky areas simultaneously. Variance in quality across the image field, especially the corners and edges compared to the center, is a significant challenge in wide-field astronomical surveys like the Evryscope. The individual star PSFs (which typically extend only a few pixels) are highly susceptible to slight increases in optical aberrations in this situation. The Robotilter solution resulted in a limiting magnitude improvement of .5 mag in the center of the image and 1.0 mag in the corners for typical Evryscope cameras, with less distorted and smaller PSFs (half the extent in the corners and edges in many cases). In this paper we describe the Robotilter mechanical and software design, camera alignment results, long term stability, and image improvement.

[36]  arXiv:2001.00899 [pdf, other]

Title: The Orion Protostellar Explosion and Runaway Stars Revisited: Stellar Masses, Disk Retention, and an Outflow from BN

Authors: John Bally, Adam Ginsburg, Jan Forbrich, Jaime Vargas-Gonzalez

Comments: 23 pages, 8 figures

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA)

The proper motions of the three stars ejected from Orion's OMC1 cloud core are combined with the requirement that their center of mass is gravitationally bound to OMC1 to show that radio source I (Src I) is likely to have a mass around 15 Solar masses consistent with recent measurements. Src I, the star with the smallest proper motion, is suspected to be either an AU-scale binary or a protostellar merger remnant produced by a dynamic interaction ~550 years ago. Near-infrared 2.2 um images spanning ~21 years confirm the ~55 km/s motion of `source x' (Src x) away from the site of stellar ejection and point of origin of the explosive OMC1 protostellar outflow. The radial velocities and masses of the Becklin-Neugebauer (BN) object and Src I constrain the radial velocity of Src x to be V_{LSR} = -28 +/-10 km/s . Several high proper-motion radio sources near BN, including Zapata 11 ([ZRK2004] 11) and a diffuse source near IRc 23, may trace a slow bipolar outflow from BN. The massive disk around Src I is likely the surviving portion of a disk that existed prior to the stellar ejection. Though highly perturbed, shocked, and re-oriented by the N-body interaction, enough time has elapsed to allow the disk to relax with its spin axis roughly orthogonal to the proper motion.

[37]  arXiv:2001.00903 [pdf, other]

Title: Characterizing the Uncertainty in Cluster Magnetic Fields derived from Rotation Measures

Authors: Andrew Johnson, Lawrence Rudnick, Thomas Jones, Peter Mendygral, Klaus Dolag

Comments: ApJ, in press

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Magnetic fields play vital roles in intracluster media (ICMs), but estimating their strengths and distributions from observations is a major challenge. Faraday rotation measures (RMs) are widely applied to this task, so it is critical to understand inherent uncertainties in RM analysis. In this paper, we seek to characterize those uncertainties given the types of information available today, independent of the specific technique used. We conduct synthetic RM observations through the ICM of a galaxy cluster drawn from an MHD cosmological simulation in which the magnetic field is known. We analyze the synthetic RM observations using an analytical formalism based on commonly used model assumptions allowing us to relate model physical variables to outcome uncertainties. Despite the simplicity of some assumptions, and unknown physical parameters, we are able to extract an approximate magnitude of the central magnetic field within an apparently irreducible uncertain factor approximately 3. Principal, largely irreducible, uncertainties come from the unknown depth along the line of sight of embedded polarized sources, the lack of robust coherence lengths from area-constrained polarization sampling, and the unknown scaling between ICM electron density and magnetic field strength. The RM-estimated central magnetic field strengths span more than an order of magnitude including the full range of synthetic experiments.

[38]  arXiv:2001.00922 [pdf, other]

Title: Mapping large-scale diffuse gamma-ray emission in 10-100 TeV band with Cherenkov telescopes

Authors: A.Neronov, D.Semikoz

Comments: 7 pages, 5 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

Measurement of diffuse gamma-ray emission from the Milky Way with Imaging Atmospheric Cherenkov Telescopes (IACT) is difficult because of high level of charged cosmic ray background and small field-of-view. We show that such a measurement is nevertheless possible in the energy band 10-100 TeV. The minimal charged particle background for IACTs is achieved in event selections used for the analyses of the cosmic ray electrons. Tight cuts on the event quality in these event selections allow to achieve the background level sufficiently low to allow the measurements of the diffuse Galactic gamma-ray flux above 10 TeV. We calculate the sensitivities of different types of IACT arrays for the Galactic diffuse emission measurements and compare them with the diffuse gamma-ray flux from different parts of the sky measured by the Fermi Large Area Telescope below 3 TeV and with the astrophysical neutrino signal measured by IceCube telescope. We show that deep exposure of existing IACT systems is sufficient for detection of the diffuse flux from all the Galactic Plane up to Galactic latitude |b|~ degrees. Medium Size Telescope array of CTA will be able to detect the diffuse flux up 30 degree Galactic latitude. Its sensitivity will be sufficient for detection of the gamma-ray counterpart of the Galactic component of the IceCube astrophysical neutrino signal above 10 TeV. We also propose that a dedicated IACT system composed of small but wide field-of-view telescopes could be used for mapping the 10-100 TeV the diffuse gamma-ray emission from across all the sky.

[39]  arXiv:2001.00923 [pdf, other]

Title: A Joint Fermi-GBM and LIGO/Virgo Analysis of Compact Binary Mergers From the First and Second Gravitational-wave Observing Runs

Authors: The Fermi Gamma-ray Burst Monitor Team, the LIGO Scientific Collaboration, the Virgo Collaboration: R. Hamburg, C. Fletcher, E. Burns, A. Goldstein, E. Bissaldi, M. S. Briggs, W. H. Cleveland, M. M. Giles, C. M. Hui, D. Kocevski, S. Lesage, B. Mailyan, C. Malacaria, S. Poolakkil, R. Preece, O. J. Roberts, P. Veres, A. von Kienlin, C. A. Wilson-Hodge, J. Wood, R. Abbott et. al

Comments: 11 pages, 4 figures

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

We present results from offline searches of Fermi Gamma-ray Burst Monitor (GBM) data for gamma-ray transients coincident with the compact binary coalescences observed by the gravitational-wave (GW) detectors Advanced LIGO and Advanced Virgo during their first and second observing runs. In particular, we perform follow-up for both confirmed events and low significance candidates reported in the LIGO/Virgo catalog GWTC-1. We search for temporal coincidences between these GW signals and GBM triggered gamma-ray bursts (GRBs). We also use the GBM Untargeted and Targeted subthreshold searches to find coincident gamma-rays below the on-board triggering threshold. This work implements a refined statistical approach by incorporating GW astrophysical source probabilities and GBM visibilities of LIGO/Virgo sky localizations to search for cumulative signatures of coincident subthreshold gamma-rays. All search methods recover the short gamma-ray burst GRB 170817A occurring ~1.7 s after the binary neutron star merger GW170817. We also present results from a new search seeking GBM counterparts to LIGO single-interferometer triggers. This search finds a candidate joint event, but given the nature of the GBM signal and localization, as well as the high joint false alarm rate of $1.1 \times 10^{-6}$ Hz, we do not consider it an astrophysical association. We find no additional coincidences.

[40]  arXiv:2001.00924 [pdf]

Title: Nucleosynthesis of "Light" Heavy Nuclei in Neutrino-driven Winds. Role of ($α,n$) reactions

Authors: Jorge Pereira, Almudena Arcones, Julia Bliss, Fernando Montes

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)

Neutrino-driven winds following core collapse supernovae have been proposed as a suitable site where the so-called light heavy elements (between Sr to Ag) can be synthetized. For moderately neutron-rich winds, ($\alpha,n$) reactions play a critical role in the weak r process, becoming the main mechanism to drive nuclear matter towards heavier elements. In this paper we summarize the sensitivity of network-calculated abundances to the astrophysical conditions, and to uncertainties in the ($\alpha,n$) reaction rates. A list of few ($\alpha,n$) reactions were identified to dominate the uncertainty in the calculated elemental abundances. Measurements of these reactions will allow to identify the astrophysical conditions of the weak r process by comparing calculated/observed abundances in r-limited stars.

[41]  arXiv:2001.00930 [pdf, other]

Title: High-energy astrophysical neutrinos are produced in central parsec-scale regions of radio-bright active galaxies

Authors: A.V. Plavin (ASC Lebedev, MIPT), Y.Y. Kovalev (ASC Lebedev, MIPT, MPIfR), Y.A. Kovalev (ASC Lebedev), S.V. Troitsky (INR)

Comments: 16 pages, 4 figures, 2 tables; submitted to ApJ

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Astrophysics of Galaxies (astro-ph.GA)

Observational information on high-energy astrophysical neutrinos is being continuously collected by the IceCube observatory. However, sources of the neutrinos are still unknown. In this paper we use radio very-long-baseline interferometry (VLBI) data for a complete VLBI-flux-density limited sample in a statistical manner in order to address the problem of the origin of astrophysical neutrinos with energies above 200 TeV. We find that active galactic nuclei (AGN) positionally associated with IceCube events have typically stronger parsec-scale cores than the rest of the sample, with the post-trial p-value of chance coincidence of p=0.2%. We select four strongest ones as highly probable associations: 3C 279, NRAO 530, PKS 1741-038, and 4C +06.69. Moreover, we find that the epochs of increase in radio emission at frequencies above 10 GHz coincide with neutrino arrival times for VLBI-selected AGN in IceCube error regions, the most pronounced example being PKS 1502+106. We conclude that AGN with bright Doppler-boosted jets constitute an important population of neutrino sources. High-energy neutrinos are produced in their central parsec-scale regions, probably in proton-photon interactions at or around the accretion disk. Radio-bright AGN likely associated with neutrinos have very diverse gamma-ray properties suggesting that gamma rays and neutrinos are produced in different regions of the AGN and are not directly related. A small viewing angle of the jet-disk axis is however required to detect either of them.

[42]  arXiv:2001.00931 [pdf, other]

Title: Asymmetric Drift of Andromeda Analogs in the Illustris Simulations

Authors: Amanda C. N. Quirk, Ekta Patel

Comments: 13 pages, 12 figures, submitted to MNRAS January 2, 2020

Subjects: Astrophysics of Galaxies (astro-ph.GA)

We analyze the kinematics as a function of stellar age for Andromeda (M31) mass analogs from the Illustris and Illustris TNG cosmological simulations. We divide the star particles into four age groups: < 1 Gyr, 1-5 Gyr, 5-10 Gyr, and >10 Gyr, and we compare the kinematics of these groups to that of the neutral gas cells. We calculate rotation curves for the stellar and gaseous components of each analog from 2 kpc to 20 kpc from the center of mass. We find that the lag, or asymmetric drift (AD), between the gas rotation curve and the stellar rotation curve on average increases with stellar age. This finding is consistent with observational measurements of AD in the disk of the Andromeda galaxy. When the M31 analogs are separated into groups based on merger history, we find that there is a difference in the AD of the analogs in the subgroup that corresponds to having had a 4:1 merger in a given time range compared to analogs that have not experienced a 4:1 merger in the same time frame. These differences are the most significant for recent 4:1 merger events (< 4 Gyr ago) and are therefore most visible in the 1-5 Gyr stellar age group where we find a difference in AD as large as 55 km/s. This subset of analogs that have had a 4:1 merger within the last 4 Gyr are also very consistent with AD measurements of stars in M31's disk, providing evidence that M31 may in fact have recently merged with a galaxy nearly 1/4 of its mass. Further work using high resolution zoom-in simulations is required to explore the contribution of internal heating to AD.

[43]  arXiv:2001.00932 [pdf, ps, other]

Title: The analogy of K-correction in the topic of gamma-ray bursts

Authors: Levente Borvák, Attila Mészáros, Jakub Řípa

Comments: 3 pages, 2 figures, published in Proceedings of the International Astronomical Union

Journal-ref: Proceedings of the International Astronomical Union, Symposium S346 (2019) 380-382

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

It is well-known that there are two types of gamma-ray bursts (GRBs): short/hard and long/soft ones, respectively. The long GRBs are coupled to supernovae, but the short ones are associated with the so called macronovae (also known as kilonovae), which can serve as the sources of gravitational waves as well. The kilonovae can arise from the merging of two neutron-stars. The neutron stars can be substituded by more massive black holes as well. Hence, the topic of gamma-ray bursts (mainly the topic of short ones) and the topic of massive binaries, are strongly connected.
In this contribution, the redshifts of GRBs are studied. The surprising result - namely that the apparently fainter GRBs can be in average at smaller distances - is discussed again. In essence, the results of M\'esz\'aros et al. (2011) are studied again using newer samples of GRBs. The former result is confirmed by the newer data.

[44]  arXiv:2001.00933 [pdf, ps, other]

Title: Gamma-ray bursts: A brief survey of the diversity

Authors: Attila Mészáros, Jakub Řípa

Comments: 5 pages, 2 figures, published in Proceedings of the International Astronomical Union

Journal-ref: Proceedings of the International Astronomical Union, Symposium S346 (2019) 383-387

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

The separation of the gamma-ray bursts (GRBs) into short/hard and long/soft subclasses, respectively, is well supported both theoretically and observationally. The long ones are coupled to supernovae type Ib/Ic - the short ones are connected to the merging of two neutron stars, where one or even both neutron stars can be substituted by black holes. These short GRBs - as merging binaries - can also serve as the sources of gravitation waves, and are observable as the recently detected macronovae. Since 1998 there are several statistical studies suggesting the existence of more than two subgroups. There can be a subgroup having an intermediate durations; there can be a subgroup with ultra-long durations; the long/soft subgroup itself can be divided into two subclasses with respect to the luminosity of GRBs. The authors with other collaborators provided several statistical studies in this topic. This field of the GRB-diversity is briefly surveyed in this contribution.

Cross-lists for Mon, 6 Jan 20

[45]  arXiv:2001.00568 (cross-list from hep-ph) [pdf, other]

Title: Electroweak baryogenesis at high wall velocities

Authors: James M. Cline, Kimmo Kainulainen

Comments: 15 pages, 6 figures

Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

It is widely believed that electroweak baryogenesis should be suppressed in strong phase transitions with fast-moving bubble walls, but this effect has never been quantitatively studied. We rederive fluid equations describing transport of particle asymmetries near the bubble wall without making the small-wall-velocity approximation. We show that the suppression of the baryon asymmetry is a smooth function of the wall speed and that there is no special behavior when crossing the sound speed barrier. Electroweak baryogenesis can thus be efficient also with strong detonations, generically associated with models with observably large gravitational waves. We also make a systematic and critical comparison of our improved transport equations to another one commonly used in the literature, based on the VEV-insertion formalism.

[46]  arXiv:2001.00638 (cross-list from hep-th) [pdf, other]

Title: Nonsingular Ekpyrotic Cosmology with a Nearly Scale-Invariant Spectrum of Cosmological Perturbations and Gravitational Waves

Authors: Robert Brandenberger, Ziwei Wang (McGill University)

Comments: 9 pages

Subjects: High Energy Physics - Theory (hep-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

We propose a mechanism borrowed from string theory which yields a non-singular transition from a phase of Ekpyrotic contraction to the expanding phase of Standard Big Bang cosmology. The same mechanism converts the initial vacuum spectrum of cosmological fluctuations before the bounce into a scale-invariant one, and also changes the spectrum of gravitational waves into an almost scale-invariant one. The scalar and tensor tilts are predicted to be the same, in contrast to the predictions from the "String Gas Cosmology" scenario. The amplitude of the gravitational wave spectrum depends on the ratio of the string scale to the Planck scale and may be in reach of upcoming experiments.

[47]  arXiv:2001.00673 (cross-list from physics.pop-ph) [pdf]

Title: There's No Place Like Home (in Our Own Solar System): Searching for ET Near White Dwarfs

Authors: John Gertz

Comments: 22 pages, 0 figures, accepted for publication in the Journal of the British Interplanetary Society (JBIS), comments welcome

Subjects: Popular Physics (physics.pop-ph); Earth and Planetary Astrophysics (astro-ph.EP)

The preponderance of white dwarfs in the Milky Way were formed from the remnants of stars of the same or somewhat higher mass as the Sun, i.e., from G-stars. We know that life can exist around G-stars. Any technologically advanced civilization residing within the habitable zone of a G-star will face grave peril when its star transitions from the main sequence and successively enters sub-giant, red giant, planetary nebula, and white dwarf stages. In fact, if the civilization takes no action it will face certain extinction. The two alternatives to passive extinction are (a) migrate away from the parent star in order to colonize another star system, or (b) find a viable solution within one's own solar system. It is argued in this paper that migration of an entire biological population or even a small part of a population is virtually impossible, but in any event, far more difficult than remaining in one's home solar system where the problem of continued survival can best be solved. This leads to the conclusion that sub-giants, red giants, planetary nebula, and white dwarfs are the best possible candidate targets for SETI observations. Search strategies are suggested.

[48]  arXiv:2001.00821 (cross-list from gr-qc) [pdf, other]

Title: Echoes from the Abyss: A Status Update

Authors: Jahed Abedi (AEI, Hannover), Niayesh Afshordi (Waterloo/PI)

Comments: 8 pages, 6 figures, comments are welcome!

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE)

Gravitational wave echoes provide our most direct and surprising observational window into quantum nature of black holes. Three years ago, the first search for echoes from Planck-scale modifications of general relativity near black hole event horizons led to tentative evidence at false detection probability of 1\% arXiv:1612.00266 . The study introduced a naive phenomenological model and used the public data release by the Advanced LIGO gravitational wave observatory for the first observing run O1 (GW150914, GW151226, and LVT151012, now GW151012). Here, we provide a status update on various observational searches for echoes by independent groups, and argue that they can all be consistent if echoes are most prominent at lower frequencies and/or in binary mergers of more extreme mass ratio. We also point out that the only reported "detection" of echoes (with $>4\sigma$ confidence) at 1.0 second after the binary neutron star merger GW170817 arXiv:1803.10454 is coincident with the formation time of the black hole inferred from electromagnetic observations.

[49]  arXiv:2001.00863 (cross-list from gr-qc) [pdf, other]

Title: Astrophysical Constraints on Strong Modified Gravity

Authors: Daniela Pérez, Gustavo E. Romero

Comments: In: Topics on Strong Gravity: A Modern View on Theories and Experiments. C\'esar Augusto Zen Vasconcellos (Ed.). World Scientific, 2020, pp. 19-65

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

We offer a discussion on the strong field regime predictions of two families of theories that deviate from General Relativity in different aspects: $f(R)$-gravity and Scalar-Tensor-Vector Gravity (STVG). We discuss astrophysical effects in models based upon both matter and vacuum solutions of such theories. In particular, we analize neutron star structure and the constraints on the parameters of the theories introduced by the latest observations. We also review black hole solutions and several astrophysical consequences of them, including accretion disks and jets. Finally, we report on the implications of the detection of various gravitational wave events for these theories.

Replacements for Mon, 6 Jan 20

[50]  arXiv:1809.02127 (replaced) [pdf, other]

Title: Threshold for primordial black holes: Dependence on the shape of the cosmological perturbations

Authors: Ilia Musco

Comments: 18 pages, 5 figures. The paper has been selected by Physical Review D as an Editors' Suggestion

Journal-ref: Phys. Rev. D 100, 123524 (2019)

Subjects: General Relativity and Quantum Cosmology (gr-qc); Cosmology and Nongalactic Astrophysics (astro-ph.CO)

[51]  arXiv:1904.02333 (replaced) [pdf, other]

Title: Cosmic rays escaping from Galactic starburst-driven superbubbles

Authors: Zhaowei Zhang, Kohta Murase, Peter Mészáros

Comments: 11 pages, 3 figures, accepted by MNRAS

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE)

[52]  arXiv:1904.04260 (replaced) [pdf, other]

Title: Estimating the dark matter velocity anisotropy to the cluster edge

Authors: Jacob Svensmark, Steen H. Hansen, Davide Martizzi, Ben Moore, Romain Teyssier

Comments: 20 pages, 10 figures

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO)

[53]  arXiv:1907.06476 (replaced) [pdf, other]

Title: Solar photosphere magnetization

Authors: Véronique Bommier

Comments: 11 pages, 4 figures, resubmitted to Astronomy and Astrophysics, Section Astrophysical Processes

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

[54]  arXiv:1907.11671 (replaced) [pdf, other]

Title: Probing heavy dark matter decays with multi-messenger astrophysical data

Authors: Koji Ishiwata, Oscar Macias, Shin'ichiro Ando, Makoto Arimoto

Comments: 22 pages, 10 figures, V2: Minor changes to match JCAP published version

Journal-ref: JCAP01(2020)003

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Phenomenology (hep-ph)

[55]  arXiv:1910.06396 (replaced) [pdf, ps, other]

Title: Nebula-Relay theory: primitive life in nebula and the origin of life on the earth

Authors: Lei Feng (Purple Mountain Observatory)

Comments: 4 pages, 1 figure

Subjects: Popular Physics (physics.pop-ph); Earth and Planetary Astrophysics (astro-ph.EP)

[56]  arXiv:1910.08553 (replaced) [pdf, other]

Title: Breaking a dark degeneracy: The gamma-ray signature of early matter domination

Authors: M. Sten Delos, Tim Linden, Adrienne L. Erickcek

Comments: 16 pages plus appendices (25 total), 25 figures. Several references added; no other changes. Matches published version

Journal-ref: Phys. Rev. D 100, 123546 (2019)

Subjects: Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics - Phenomenology (hep-ph)

[57]  arXiv:1910.09460 (replaced) [pdf, other]

Title: Trans-Planckian censorship and single-field inflaton potential

Authors: Kenji Kadota, Chang Sub Shin, Takahiro Terada, Gansukh Tumurtushaa

Comments: 30 pages, 4 figures; published version (minor revision)

Journal-ref: JCAP01 (2020) 008

Subjects: High Energy Physics - Theory (hep-th); Cosmology and Nongalactic Astrophysics (astro-ph.CO); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics - Phenomenology (hep-ph)

[58]  arXiv:1912.04185 (replaced) [pdf, other]

Title: Not so fast: LB-1 is unlikely to contain a 70 $M_{\odot}$ black hole

Authors: Kareem El-Badry, Eliot Quataert

Comments: 5 pages, 4 figures. Accepted to MNRAS letters

Subjects: Solar and Stellar Astrophysics (astro-ph.SR); Astrophysics of Galaxies (astro-ph.GA); High Energy Astrophysical Phenomena (astro-ph.HE)

[59]  arXiv:1912.05309 (replaced) [pdf, other]

Title: Testing CIBER cosmic infrared background measurements and axionlike particles with observations of TeV blazars

Authors: G. B. Long, W. P. Lin, P. H. T. Tam, W. S. Zhu

Comments: 15 pages, 5 figure, Accepted for publication in PRD

Subjects: High Energy Astrophysical Phenomena (astro-ph.HE); Cosmology and Nongalactic Astrophysics (astro-ph.CO); Astrophysics of Galaxies (astro-ph.GA)

[60]  arXiv:1912.08338 (replaced) [pdf, other]

Title: A stripped helium star in the potential black hole binary LB-1

Authors: Andreas Irrgang, Stephan Geier, Simon Kreuzer, Ingrid Pelisoli, Ulrich Heber

Comments: Accepted for publication in A&A (Astronomy and Astrophysics)

Subjects: Solar and Stellar Astrophysics (astro-ph.SR)

• New submissions
• Cross-lists
• Replacements