Showing 1–50 of 127 results for author: Ryan, G

Eccentric Binaries Accreting from Thin Disks: Orbital Evolution

Authors: Alexander J. Dittmann, Geoffrey Ryan, Luciano Combi

Abstract: Circumbinary disks crucially affect the orbital and electromagnetic properties of binary systems across the universe, from stars in our galactic neighborhood to supermassive black hole binaries formed as the result of tumultuous galactic mergers. Previous simulations have focused nearly exclusively on thick accretion disks, appropriate for studying stellar binaries, and have found encouraging agre… ▽ More Circumbinary disks crucially affect the orbital and electromagnetic properties of binary systems across the universe, from stars in our galactic neighborhood to supermassive black hole binaries formed as the result of tumultuous galactic mergers. Previous simulations have focused nearly exclusively on thick accretion disks, appropriate for studying stellar binaries, and have found encouraging agreement with observations thereof. We present herein the first systematic study of eccentric binary systems accreting from thin disks, focusing on binary orbital evolution. Our main results are that (1) thinner disk not only drive binaries to rapidly inspiral, but also excite binary eccentricities at much higher rates; (2) while thick disks may drive binaries to a stable fixed point of $e\approx0.425$, thinner disks pump binary eccentricities to $e\gtrsim0.6$; (3) the range of near-zero eccentricities that are damped towards zero depends on both disk thickness and viscosity, thinner disks and those with $α$ viscosities driving binaries towards circularity over a much narrower range of eccentricities. These differences follow largely from the effects of pressure support on accretion streams and shocks within the inner regions of the accretion flow. Our results suggest that accreting binary black holes should have high eccentricities well into the frequency range probed by pulsar timing arrays and space-based gravitational wave interferometers, affecting the spectrum and isotropy of the gravitational wave background. Our results also suggest that circumbinary disks may play an important role in shaping the orbits of close binary stars, but much less so those of wider binaries. △ Less

Submitted 12 December, 2025; originally announced December 2025.

Comments: 20 pages, 11 figures. Comments welcome

The Advanced X-ray Imaging Satellite Community Science Book

Authors: Michael Koss, Nafisa Aftab, Steven W. Allen, Roberta Amato, Hongjun An, Igor Andreoni, Timo Anguita, Riccardo Arcodia, Thomas Ayres, Matteo Bachetti, Maria Cristina Baglio, Arash Bahramian, Marco Balboni, Ranieri D. Baldi, Solen Balman, Aya Bamba, Eduardo Banados, Tong Bao, Iacopo Bartalucci, Antara Basu-Zych, Rebeca Batalha, Lorenzo Battistini, Franz Erik Bauer, Andy Beardmore, Werner Becker , et al. (373 additional authors not shown)

Abstract: The AXIS Community Science Book represents the collective effort of more than 500 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24'… ▽ More The AXIS Community Science Book represents the collective effort of more than 500 scientists worldwide to define the transformative science enabled by the Advanced X-ray Imaging Satellite (AXIS), a next-generation X-ray mission selected by NASA's Astrophysics Probe Program for Phase A study. AXIS will advance the legacy of high-angular-resolution X-ray astronomy with ~1.5'' imaging over a wide 24' field of view and an order of magnitude greater collecting area than Chandra in the 0.3-12 keV band. Combining sharp imaging, high throughput, and rapid response capabilities, AXIS will open new windows on virtually every aspect of modern astrophysics, exploring the birth and growth of supermassive black holes, the feedback processes that shape galaxies, the life cycles of stars and exoplanet environments, and the nature of compact stellar remnants, supernova remnants, and explosive transients. This book compiles over 140 community-contributed science cases developed by five Science Working Groups focused on AGN and supermassive black holes, galaxy evolution and feedback, compact objects and supernova remnants, stellar physics and exoplanets, and time-domain and multi-messenger astrophysics. Together, these studies establish the scientific foundation for next-generation X-ray exploration in the 2030s and highlight strong synergies with facilities of the 2030s, such as JWST, Roman, Rubin/LSST, SKA, ALMA, ngVLA, and next-generation gravitational-wave and neutrino networks. △ Less

Submitted 31 October, 2025; originally announced November 2025.

Comments: 595 pages, 225 figures

AT2025ulz and S250818k: Deep X-ray and radio limits on off-axis afterglow emission and prospects for future discovery

Authors: Brendan O'Connor, Roberto Ricci, Eleonora Troja, Antonella Palmese, Yu-Han Yang, Geoffrey Ryan, Hendrik van Eerten, Muskan Yadav, Xander J. Hall, Ariel Amsellem, Rosa L. Becerra, Malte Busmann, Tomas Cabrera, Simone Dichiara, Lei Hu, Ravjit Kaur, Keerthi Kunnumkai, Ignacio Magana Hernandez

Abstract: The first joint electromagentic (EM) and gravitational wave (GW) detection, known as GW170817, marked a critical juncture in our collective understanding of compact object mergers. However, it has now been 8 years since this discovery, and the search for a second EM-GW detection has yielded no robust discoveries. Recently, on August 18, 2025, the LIGO-Virgo-KAGRA collaboration reported a low-signi… ▽ More The first joint electromagentic (EM) and gravitational wave (GW) detection, known as GW170817, marked a critical juncture in our collective understanding of compact object mergers. However, it has now been 8 years since this discovery, and the search for a second EM-GW detection has yielded no robust discoveries. Recently, on August 18, 2025, the LIGO-Virgo-KAGRA collaboration reported a low-significance (high false alarm rate) binary neutron star merger candidate S250818k. Rapid optical follow-up revealed a single optical candidate AT2025ulz ($z=0.08484$) that initially appeared consistent with kilonova emission. We quickly initiated a set of observations with \textit{Swift}, \textit{XMM-Newton}, \textit{Chandra}, and the Very Large Array to search for non-thermal afterglow emission. Our deep X-ray and radio search rules out that the optical rebrightening of AT2025ulz is related to the afterglow onset, reinforcing its classification as a stripped-envelope supernova (SN 2025ulz). We derive constraints on the afterglow parameters for a hypothetical binary neutron star merger at the distance of AT2025ulz ($\approx 400$ Mpc) based on our X-ray and radio limits. We conclude that our observational campaign could exclude a GW170817-like afterglow out to viewing angles of $θ_\textrm{v}\approx 12.5$ degrees. We briefly discuss the prospects for the future discovery of off-axis afterglows. △ Less

Submitted 29 October, 2025; v1 submitted 27 October, 2025; originally announced October 2025.

Comments: Accepted for publication in ApJL on 10/22/2025

Attribution Locus and the Timeliness of Long-lived Asset Write-downs

Authors: Yao-Lin Chang, Chun-Yang Lin, Chi-Chun Liu, Stephen G. Ryan

Abstract: We examine the relative timeliness with which write-downs of long-lived assets incorporate adverse macroeconomic and industry outcomes versus adverse firm-specific outcomes. We posit that users of financial reports are more likely to attribute adverse firm-specific outcomes to suboptimal managerial actions, which provide managers with more incentive to delay write downs. We provide evidence that,… ▽ More We examine the relative timeliness with which write-downs of long-lived assets incorporate adverse macroeconomic and industry outcomes versus adverse firm-specific outcomes. We posit that users of financial reports are more likely to attribute adverse firm-specific outcomes to suboptimal managerial actions, which provide managers with more incentive to delay write downs. We provide evidence that, controlling for other incentives to manage earnings, firms record write-downs in the current year that are driven by adverse macroeconomic and industry outcomes during both the current year and the next year, but they record write-downs driven by adverse firm-specific outcomes only in the current year. △ Less

Submitted 13 September, 2025; originally announced September 2025.

Radio observations point to a moderately relativistic outflow in the fast X-ray transient EP241021a

Authors: Muskan Yadav, Eleonora Troja, Roberto Ricci, Yu-Han Yang, Mark H. Wieringa, Brendan O'Connor, Yacheng Kang, Rosa L. Becerra, Geoffrey Ryan, Malte Busmann

Abstract: Fast X-ray transients (FXRTs) are short-lived X-ray outbursts with diverse progenitor scenarios, including compact object mergers, stellar core-collapses and tidal disruption events. The Einstein Probe (EP) has enabled the rapid discovery and follow-up of dozens of FXRTs, revealing that while some of them overlap with traditional gamma-ray bursts (GRBs), a larger fraction of FXRTs have no associat… ▽ More Fast X-ray transients (FXRTs) are short-lived X-ray outbursts with diverse progenitor scenarios, including compact object mergers, stellar core-collapses and tidal disruption events. The Einstein Probe (EP) has enabled the rapid discovery and follow-up of dozens of FXRTs, revealing that while some of them overlap with traditional gamma-ray bursts (GRBs), a larger fraction of FXRTs have no associated gamma-ray counterpart down to deep limits. The origin of these gamma-ray dark FXRTs and their connection to the diverse landscape of stellar explosions remains an open question, which can be tackled through the study of their multi-wavelength counterparts and environment. In this paper, we present long-term radio observations of the gamma-ray dark EP241021a, which exhibits sustained radio emission for over 100 days, placing it among the longest-lived radio afterglows. We detect signature of interstellar scintillation in early epochs, allowing us to constrain the angular size and Lorentz factor of the emitting region. Our observations point to an outflow that is at least mildly relativistic with Lorentz factor > 4. Afterglow modeling favors a moderately relativistic and collimated outflow interacting with a low-density interstellar medium. The derived beaming-corrected kinetic energy and low radiative efficiency are consistent with a standard relativistic explosion which did not produce bright gamma-rays. Alternatively, a highly-relativistic structured jet remains consistent with our observations if seen substantially off-axis. In the latter case, the initial X-ray flare detected by EP would be caused by the slower ejecta from the lateral wings intercepting our line of sight rather than by traditional prompt-emission mechanisms within the jet core. △ Less

Submitted 23 October, 2025; v1 submitted 13 May, 2025; originally announced May 2025.

Comments: 11 pages, 8 figures, comments welcome

The curious case of EP241021a: Unraveling the mystery of its exceptional rebrightening

Authors: Malte Busmann, Brendan O'Connor, Julian Sommer, Daniel Gruen, Paz Beniamini, Ramandeep Gill, Michael J. Moss, Antonella Palmese, Arno Riffeser, Yu-Han Yang, Eleonora Troja, Simone Dichiara, Roberto Ricci, Noel Klingler, Claus Gössl, Lei Hu, Arne Rau, Christoph Ries, Geoffrey Ryan, Michael Schmidt, Muskan Yadav, Gregory R. Zeimann

Abstract: Fast X-ray Transients (FXTs) are a rare and poorly understood phenomenon with a variety of possible progenitors. The launch of the Einstein Probe (EP) mission has facilitated a rapid increase in the real-time discovery and follow-up of FXTs. We focus on the recent EP discovered transient EP241021a, which shows a peculiar panchromatic behavior. We obtained optical and near-infrared multi-band imagi… ▽ More Fast X-ray Transients (FXTs) are a rare and poorly understood phenomenon with a variety of possible progenitors. The launch of the Einstein Probe (EP) mission has facilitated a rapid increase in the real-time discovery and follow-up of FXTs. We focus on the recent EP discovered transient EP241021a, which shows a peculiar panchromatic behavior. We obtained optical and near-infrared multi-band imaging and spectroscopy with the Fraunhofer Telescope at Wendelstein Observatory, the Hobby-Eberly Telescope, and the Very Large Telescope over the first 100 days of its evolution. EP241021a was discovered by EP as a soft X-ray trigger, but was not detected at gamma-ray frequencies. The observed soft X-ray prompt emission spectrum is consistent with non-thermal radiation, which requires at least a mildly relativistic outflow with bulk Lorentz factor $Γ\gtrsim 4$. The optical and near-infrared lightcurve has a two component behavior where an initially fading component $\sim t^{-1}$ turns to a rise steeper than $\sim t^{4}$ after a few days before peaking at $M_r\approx -21.8$ mag and quickly returning to the initial decay. The peak absolute magnitude is the most luminous optical emission associated to an FXT, superseding EP240414a. Standard supernova models are unable to reproduce either the absolute magnitude or rapid timescale ($<2$ d) of the rebrightening. The X-ray, optical and near-infrared spectral energy distributions display a red color $r-J\approx 0.8$ mag, and point to a non-thermal origin ($ν^{-1}$) for the broadband emission. By considering a gamma-ray burst as a plausible scenario, we favor a refreshed shock as the cause of the rebrightening. This is consistent with the inference of an at least mildly relativistic outflow based on the prompt trigger. Our results suggest a link between EP discovered FXTs and gamma-ray bursts. △ Less

Submitted 7 July, 2025; v1 submitted 18 March, 2025; originally announced March 2025.

Comments: Accepted in A&A

Multi-Wavelength Analysis of AT 2023sva: a Luminous Orphan Afterglow With Evidence for a Structured Jet

Authors: Gokul P. Srinivasaragavan, Daniel A. Perley, Anna Y. Q. Ho, Brendan O'Connor, Antonio de Ugarte Postigo, Nikhil Sarin, S. Bradley Cenko, Jesper Sollerman, Lauren Rhodes, David A. Green, Dmitry S. Svinkin, Varun Bhalerao, Gaurav Waratkar, A. J. Nayana, Poonam Chandra, M. Coleman Miller, Daniele B. Malesani, Geoffrey Ryan, Suryansh Srijan, Eric C. Bellm, Eric Burns, David J. Titterington, Maria B. Stone, Josiah Purdum, Tomás Ahumada , et al. (28 additional authors not shown)

Abstract: We present multi-wavelength analysis of ZTF23abelseb (AT 2023sva), an optically discovered fast-fading ($Δm_r = 2.2$ mag in $Δt = 0.74 $ days), luminous ($M_r \sim -30.0$ mag) and red ($g-r = 0.50$ mag) transient at $z = 2.28$ with accompanying luminous radio emission. AT 2023sva does not possess a $γ$-ray burst (GRB) counterpart to an isotropic equivalent energy limit of… ▽ More We present multi-wavelength analysis of ZTF23abelseb (AT 2023sva), an optically discovered fast-fading ($Δm_r = 2.2$ mag in $Δt = 0.74 $ days), luminous ($M_r \sim -30.0$ mag) and red ($g-r = 0.50$ mag) transient at $z = 2.28$ with accompanying luminous radio emission. AT 2023sva does not possess a $γ$-ray burst (GRB) counterpart to an isotropic equivalent energy limit of $E_{\rm{γ, \, iso}} < 1.6 \times 10^{52}$ erg, determined through searching $γ$-ray satellite archives between the last non-detection and first detection, making it the sixth example of an optically-discovered afterglow with a redshift measurement and no detected GRB counterpart. We analyze AT 2023sva's optical, radio, and X-ray observations to characterize the source. From radio analyses, we find the clear presence of strong interstellar scintillation (ISS) 72 days after the initial explosion, allowing us to place constraints on the source's angular size and bulk Lorentz factor. When comparing the source sizes derived from ISS of orphan events to those of the classical GRB population, we find orphan events have statistically smaller source sizes. We also utilize Bayesian techniques to model the multi-wavelength afterglow. Within this framework, we find evidence that AT 2023sva possesses a shallow power-law structured jet viewed slightly off-axis ($θ_{\rm{v}} = 0.07 \pm 0.02$) just outside of the jet's core opening angle ($θ_{\rm{c}} = 0.06 \pm 0.02$). We determine this is likely the reason for the lack of a detected GRB counterpart, but also investigate other scenarios. AT 2023sva's evidence for possessing a structured jet stresses the importance of broadening orphan afterglow search strategies to a diverse range of GRB jet angular energy profiles, to maximize the return of future optical surveys. △ Less

Submitted 6 January, 2025; originally announced January 2025.

Comments: 22 pages, 14 Figures, Submitted to MNRAS

GRB$\,$220831A: a hostless, intermediate Gamma-ray burst with an unusual optical afterglow

Authors: James Freeburn, Brendan O'Connor, Jeff Cooke, Dougal Dobie, Anais Möller, Nicolas Tejos, Jielai Zhang, Paz Beniamini, Katie Auchettl, James DeLaunay, Simone Dichiara, Wen-fai Fong, Simon Goode, Alexa Gordon, Charles D. Kilpatrick, Amy Lien, Cassidy Mihalenko, Geoffrey Ryan, Karelle Siellez, Mark Suhr, Eleonora Troja, Natasha Van Bemmel, Sara Webb

Abstract: GRB$\,$220831A is a gamma-ray burst (GRB) with a duration and spectral peak energy that places it at the interface between the distribution of long-soft and short-hard GRBs. In this paper, we present the multi-wavelength follow-up campaign to GRB$\,$220831A and its optical, near-infrared, X-ray and radio counterparts. Our deep optical and near-infrared observations do not reveal an underlying host… ▽ More GRB$\,$220831A is a gamma-ray burst (GRB) with a duration and spectral peak energy that places it at the interface between the distribution of long-soft and short-hard GRBs. In this paper, we present the multi-wavelength follow-up campaign to GRB$\,$220831A and its optical, near-infrared, X-ray and radio counterparts. Our deep optical and near-infrared observations do not reveal an underlying host galaxy, and establish that GRB$\,$220831A is observationally hostless to depth, $m_i\gtrsim26.6$ AB mag. Based on the Amati relation and the non-detection of an accompanying supernova, we find that this GRB is most likely to have originated from a collapsar at $z>2$, but it could also possibly be a compact object merger at $z<0.4$ with a large separation distance from its host galaxy. Regardless of its origin, we show that its optical and near-infrared counterpart departs from the evolution expected from a forward shock dominated synchrotron afterglow, exhibiting a steep post-break temporal powerlaw index of $-3.83^{+0.62}_{-0.79}$, too steep to be the jet-break. By analysing a range of models, we find that the observed steep departure from forward shock closure relations is likely due to an internal process producing either a flare or a plateau. △ Less

Submitted 22 January, 2025; v1 submitted 22 November, 2024; originally announced November 2024.

Comments: 17 pages, 14 figures, 7 tables, accepted for publication in MNRAS

$^{11}$B states above the $α$-decay threshold studied via $^{10}$B$(d,p){}^{11}$B

Authors: A. N. Kuchera, G. Ryan, G. Selby, D. Snider, S. Anderson, S. Almaraz-Calderon, L. T. Baby, B. A. Brown, K. Hanselman, E. Lopez-Saavedra, K. T. Macon, G. W. McCann, K. W. Kemper, M. Spieker, I. Wiedenhöver

Abstract: The resonance region of $^{11}$B covering excitation energies from 8.4 MeV to 13.6 MeV was investigated with the $(d,p)$ reaction performed on an enriched $^{10}$B target at the Florida State University Super-Enge Split-Pole Spectrograph of the John D. Fox Superconducting Linear Accelerator Laboratory. Complementary measurements were performed with a target enriched in $^{11}$B to identify possibl… ▽ More The resonance region of $^{11}$B covering excitation energies from 8.4 MeV to 13.6 MeV was investigated with the $(d,p)$ reaction performed on an enriched $^{10}$B target at the Florida State University Super-Enge Split-Pole Spectrograph of the John D. Fox Superconducting Linear Accelerator Laboratory. Complementary measurements were performed with a target enriched in $^{11}$B to identify possible $^{12}$B contaminants in the $(d,p)$ reaction. Four strongly populated $^{11}$B states were observed above the $α$-decay threshold. Angular distributions were measured and compared to DWBA calculations to extract angular momentum transfers and $^{10}\mathrm{B}\left(3^+\right)+n$ spectroscopic factors. The recently observed and heavily discussed resonance at 11.4 MeV in $^{11}$B was not observed in this work. This result is consistent with the interpretation that it is predominantly a $^{10}\mathrm{Be}\left(0^+\right)+p$ resonance with a possible additional $^{7}\mathrm{Li}+α$ contribution. The predicted $^{10}\mathrm{B}\left(3^+\right)+n$ resonance at 11.6 MeV, analogous to the 11.4-MeV proton resonance, was not observed either. Upper limits for the $^{10}\mathrm{B}\left(3^+\right)+n$ spectroscopic factors of the 11.4-MeV and 11.6-MeV states were determined. In addition, supporting configuration interaction shell model calculations with the effective WBP interaction are presented. △ Less

Submitted 14 November, 2024; originally announced November 2024.

Comments: 7 pages, 3 figures, accepted for publication in Physical Review C as regular article

The Nature of Optical Afterglows Without Gamma-ray Bursts: Identification of AT2023lcr and Multiwavelength Modeling

Authors: Maggie L. Li, Anna Y. Q. Ho, Geoffrey Ryan, Daniel A. Perley, Gavin P. Lamb, A. J. Nayana, Igor Andreoni, G. C. Anupama, Eric C. Bellm, Edo Berger, Joshua S. Bloom, Eric Burns, Ilaria Caiazzo, Poonam Chandra, Michael W. Coughlin, Kareem El-Badry, Matthew J. Graham, Mansi Kasliwal, Garrett K. Keating, S. R. Kulkarni, Harsh Kumar, Frank J. Masci, Richard A. Perley, Josiah Purdum, Ramprasad Rao , et al. (7 additional authors not shown)

Abstract: In the past few years, the improved sensitivity and cadence of wide-field optical surveys have enabled the discovery of several afterglows without associated detected gamma-ray bursts (GRBs). We present the identification, observations, and multiwavelength modeling of a recent such afterglow (AT2023lcr), and model three literature events (AT2020blt, AT2021any, and AT2021lfa) in a consistent fashio… ▽ More In the past few years, the improved sensitivity and cadence of wide-field optical surveys have enabled the discovery of several afterglows without associated detected gamma-ray bursts (GRBs). We present the identification, observations, and multiwavelength modeling of a recent such afterglow (AT2023lcr), and model three literature events (AT2020blt, AT2021any, and AT2021lfa) in a consistent fashion. For each event, we consider the following possibilities as to why a GRB was not observed: 1) the jet was off-axis; 2) the jet had a low initial Lorentz factor; and 3) the afterglow was the result of an on-axis classical GRB (on-axis jet with physical parameters typical of the GRB population), but the emission was undetected by gamma-ray satellites. We estimate all physical parameters using afterglowpy and Markov Chain Monte Carlo methods from emcee. We find that AT2023lcr, AT2020blt, and AT2021any are consistent with on-axis classical GRBs, and AT2021lfa is consistent with both on-axis low Lorentz factor ($Γ_0 \approx 5 - 13$) and off-axis ($θ_\text{obs}=2θ_\text{jet}$) high Lorentz factor ($Γ_0 \approx 100$) jets. △ Less

Submitted 31 March, 2025; v1 submitted 12 November, 2024; originally announced November 2024.

Comments: Accepted for publication in ApJ, 40 pages, 18 figures, 20 tables

Characterization of a peculiar Einstein Probe transient EP240408a: an exotic gamma-ray burst or an abnormal jetted tidal disruption event?

Authors: B. O'Connor, D. Pasham, I. Andreoni, J. Hare, P. Beniamini, E. Troja, R. Ricci, D. Dobie, J. Chakraborty, M. Ng, N. Klingler, V. Karambelkar, S. Rose, S. Schulze, G. Ryan, S. Dichiara, I. Monageng, D. Buckley, L. Hu, G. Srinivasaragavan, G. Bruni, T. Cabrera, S. B. Cenko, H. van Eerten, J. Freeburn , et al. (8 additional authors not shown)

Abstract: We present the results of our multi-wavelength (X-ray to radio) follow-up campaign of the Einstein Probe transient EP240408a. The initial 10 s trigger displayed bright soft X-ray (0.5-4 keV) radiation with peak luminosity $L_\textrm{X} \gtrsim 10^{49}$ ($10^{50}$) erg s$^{-1}$ for an assumed redshift z>0.5 (2.0). The Neil Gehrels Swift Observatory and Neutron star Interior Composition ExploreR dis… ▽ More We present the results of our multi-wavelength (X-ray to radio) follow-up campaign of the Einstein Probe transient EP240408a. The initial 10 s trigger displayed bright soft X-ray (0.5-4 keV) radiation with peak luminosity $L_\textrm{X} \gtrsim 10^{49}$ ($10^{50}$) erg s$^{-1}$ for an assumed redshift z>0.5 (2.0). The Neil Gehrels Swift Observatory and Neutron star Interior Composition ExploreR discovered a fading X-ray counterpart lasting for $\sim$5 d (observer frame), which showed a long-lived (~4 d) plateau-like emission ($t^{-0.5}$) before a sharp powerlaw decline ($t^{-7}$). The plateau emission was in excess of $L_\textrm{X} \gtrsim 10^{46}$ ($10^{47}$) erg s$^{-1}$ at z>0.5 (2.0). Deep optical and radio observations resulted in non-detections of the transient. Our observations with Gemini South revealed a faint potential host galaxy ($r \approx 24$ AB mag) near the edge of the X-ray localization. The faint candidate host, and lack of other potential hosts ($r \gtrsim 26$ AB mag; $J \gtrsim 23$ AB mag), implies a higher redshift origin (z>0.5), which produces extreme X-ray properties that are inconsistent with many known extragalactic transient classes. In particular, the lack of a bright gamma-ray counterpart, with the isotropic-equivalent energy ($10 - 10,000$ keV) constrained by GECam and Konus-Wind to $E_{γ,\textrm{iso}} \lesssim 4\times10^{51}$ ($6\times10^{52}$) erg at z>0.5 (2.0), conflicts with known gamma-ray bursts (GRBs) of similar X-ray luminosities. We therefore favor a jetted tidal disruption event (TDE) as the progenitor of EP240408a at z>1.0, possibly caused by the disruption of a white dwarf by an intermediate mass black hole. The alternative is that EP240408a may represent a new, previously unknown class of transient. △ Less

Submitted 11 January, 2025; v1 submitted 28 October, 2024; originally announced October 2024.

Comments: Accepted in ApJL. Minor revisions. Appendices from previous version combined with main text

A fast, flexible simulation framework for Bayesian adaptive designs -- the R package BATSS

Authors: Dominique-Laurent Couturier, Rainer Puhr, Stephane Heritier, Thomas Jaki, Elizabeth G Ryan

Abstract: The use of Bayesian adaptive designs for randomised controlled trials has been hindered by the lack of software readily available to statisticians. We have developed a new software package (Bayesian Adaptive Trials Simulator Software - BATSS for the statistical software R, which provides a flexible structure for the fast simulation of Bayesian adaptive designs for clinical trials. We illustrate ho… ▽ More The use of Bayesian adaptive designs for randomised controlled trials has been hindered by the lack of software readily available to statisticians. We have developed a new software package (Bayesian Adaptive Trials Simulator Software - BATSS for the statistical software R, which provides a flexible structure for the fast simulation of Bayesian adaptive designs for clinical trials. We illustrate how the BATSS package can be used to define and evaluate the operating characteristics of Bayesian adaptive designs for various different types of primary outcomes (e.g., those that follow a normal, binary, Poisson or negative binomial distribution) and can incorporate the most common types of adaptations: stopping treatments (or the entire trial) for efficacy or futility, and Bayesian response adaptive randomisation - based on user-defined adaptation rules. Other important features of this highly modular package include: the use of (Integrated Nested) Laplace approximations to compute posterior distributions, parallel processing on a computer or a cluster, customisability, adjustment for covariates and a wide range of available conditional distributions for the response. △ Less

Submitted 2 October, 2025; v1 submitted 2 October, 2024; originally announced October 2024.

Single-Neutron Adding on $^{34}$S

Authors: A. N. Kuchera, C. R. Hoffman, G. Ryan, I. B. D'Amato, O. M. Guarinello, P. S. Kielb, R. Aggarwal, S. Ajayi, A. L. Conley, I. Conroy, P. D. Cottle, J. C. Esparza, S. Genty, K. Hanselman, M. Heinze, D. Houlihan, B. Kelly, M. I. Khawaja, E. Lopez-Saavedra, G. W. McCann, A. B. Morelock, L. A. Riley, A. Sandrik, V. Sitaraman, M. Spieker , et al. (3 additional authors not shown)

Abstract: Purpose: Single-neutron adding data was collected in order to determine the distribution of the single-neutron strength of the $0f_{7/2}$, $1p_{3/2}$, $1p_{1/2}$ and $0f_{5/2}$ orbitals outside of $Z=16, N=18$, $^{34}$S. Methods: The $^{34}$S($d$,$p$)$^{35}$S reaction has been measured at 8 MeV/u to investigate cross sections to excited states in $^{35}$S. Outgoing proton yields and momenta were… ▽ More Purpose: Single-neutron adding data was collected in order to determine the distribution of the single-neutron strength of the $0f_{7/2}$, $1p_{3/2}$, $1p_{1/2}$ and $0f_{5/2}$ orbitals outside of $Z=16, N=18$, $^{34}$S. Methods: The $^{34}$S($d$,$p$)$^{35}$S reaction has been measured at 8 MeV/u to investigate cross sections to excited states in $^{35}$S. Outgoing proton yields and momenta were analyzed by the Super-Enge Split-Pole Spectrograph in conjunction with the CeBrA demonstrator located at the John D. Fox Laboratory at Florida State University. Angular distributions were compared with Distorted Wave Born Approximation calculations in order to extract single-neutron spectroscopic overlaps. Results: Spectroscopic overlaps and strengths were determined for states in $^{35}$S up through 6 MeV in excitation energy. Each orbital was observed to have fragmented strength where a single level carried the majority. The single-neutron centroids of the $0f_{7/2}$, $1p_{3/2}$, $1p_{1/2}$ and $0f_{5/2}$ orbitals were determined to be $2360^{+90}_{-40}$ keV, $3280^{+80}_{-50}$ keV, $4780^{+60}_{-40}$ keV, and $\gtrsim7500$ keV, respectively. Conclusion: A previous discrepancy in the literature with respect to distribution of the neutron $1p_{1/2}$ strength was resolved. The integration of the normalized spectroscopic strengths, up to 5.1 MeV in excitation energy, revealed fully-vacant occupancies for the $0f_{7/2}$, $1p_{3/2}$, and $1p_{1/2}$ orbitals, as expected. The spacing in the single-neutron energies highlighted a reduction in the traditional $N=28$ shell-gap, relative to both the $1p$ spin-orbit energy difference ($N=32$) and the lower limit on the $N=34$ shell spacing. △ Less

Submitted 30 July, 2024; v1 submitted 8 July, 2024; originally announced July 2024.

Comments: Updated draft

Be careful in multi-messenger inference of the Hubble constant: A path forward for robust inference

Authors: Michael Müller, Suvodip Mukherjee, Geoffrey Ryan

Abstract: Multi-messenger observations of coalescing binary neutron stars (BNSs) are a direct probe of the expansion history of the universe and carry the potential to shed light on the disparity between low- and high-redshift measurements of the Hubble constant $H_0$. To measure the value of $H_0$ with such observations requires pristine inference of the luminosity distance and the true source redshift wit… ▽ More Multi-messenger observations of coalescing binary neutron stars (BNSs) are a direct probe of the expansion history of the universe and carry the potential to shed light on the disparity between low- and high-redshift measurements of the Hubble constant $H_0$. To measure the value of $H_0$ with such observations requires pristine inference of the luminosity distance and the true source redshift with minimal impact from systematics. In this analysis, we carry out joint inference on mock gravitational wave (GW) signals and their electromagnetic (EM) afterglows from BNS coalescences and find that the inclination angle inferred from the afterglow light curve and apparent superluminal motion can be precise, but need not be accurate and is subject to systematic uncertainty that could be as large as $1.5σ$. This produces a disparity between the EM and GW inferred inclination angles, which if not carefully treated when combining observations can bias the inferred value of $H_0$. We also find that already small misalignments of $3^{\circ}-6^{\circ}$ between the inherent system inclinations for the GW and EM emission can bias the inference by $\mathcal{O}(1-2σ)$ if not taken into account. As multi-messenger BNS observations are rare, we must make the most out of a small number of events and harness the increased precision, while avoiding reduced accuracy. We demonstrate how to mitigate these potential sources of bias by jointly inferring the mismatch between the GW- and EM-based inclination angles and $H_0$. △ Less

Submitted 31 October, 2024; v1 submitted 17 June, 2024; originally announced June 2024.

Comments: 21 pages, 10 figures, accepted in ApJL on October 24, 2024

Accretion onto supermassive black hole binaries

Authors: Eduardo M. Gutiérrez, Luciano Combi, Geoffrey Ryan

Abstract: In this chapter, we give an overview of our current understanding of the physics of accreting massive black hole binaries (MBHBs), with a special focus on the latest developments in numerical simulations and General-Relativistic Magnetohydrodynamics (GRMHD) simulations in particular. We give a self-contained global picture of how to model accretion onto MBHBs, analyzing different aspects of the sy… ▽ More In this chapter, we give an overview of our current understanding of the physics of accreting massive black hole binaries (MBHBs), with a special focus on the latest developments in numerical simulations and General-Relativistic Magnetohydrodynamics (GRMHD) simulations in particular. We give a self-contained global picture of how to model accretion onto MBHBs, analyzing different aspects of the system such as the dynamics of the circumbinary disk, mini-disks, outflows, the role of magnetic fields, and electromagnetic signatures. We discuss important questions and open problems related to these systems, what are the advantages and disadvantages of the different numerical approaches, and what robust knowledge we have built from simulations. △ Less

Submitted 23 May, 2024; originally announced May 2024.

Comments: Invited chapter for the edited book "New Frontiers in GRMHD Simulations" (Eds. C. Bambi, Y. Mizuno, S. Shashank and F. Yuan, Springer Singapore, expected in 2024)

The Santa Barbara Binary-Disk Code Comparison

Authors: Paul C. Duffell, Alexander J. Dittmann, Daniel J. D'Orazio, Alessia Franchini, Kaitlin M. Kratter, Anna B. T. Penzlin, Enrico Ragusa, Magdalena Siwek, Christopher Tiede, Haiyang Wang, Jonathan Zrake, Adam M. Dempsey, Zoltan Haiman, Alessandro Lupi, Michal Pirog, Geoffrey Ryan

Abstract: We have performed numerical calculations of a binary interacting with a gas disk, using eleven different numerical methods and a standard binary-disk setup. The goal of this study is to determine whether all codes agree on a numerically converged solution, and to determine the necessary resolution for convergence and the number of binary orbits that must be computed to reach an agreed-upon relaxed… ▽ More We have performed numerical calculations of a binary interacting with a gas disk, using eleven different numerical methods and a standard binary-disk setup. The goal of this study is to determine whether all codes agree on a numerically converged solution, and to determine the necessary resolution for convergence and the number of binary orbits that must be computed to reach an agreed-upon relaxed state of the binary-disk system. We find that all codes can agree on a converged solution (depending on the diagnostic being measured). The zone spacing required for most codes to reach a converged measurement of the torques applied to the binary by the disk is roughly 1% of the binary separation in the vicinity of the binary components. For our disk model to reach a relaxed state, codes must be run for at least 200 binary orbits, corresponding to about a viscous time for our parameters, $0.2 (a^2 Ω_B /ν)$ binary orbits, where $ν$ is the kinematic viscosity. We did not investigate dependence on binary mass ratio, eccentricity, disk temperature, or disk viscosity; therefore, these benchmarks may act as guides towards expanding converged solutions to the wider parameter space but might need to be updated in a future study that investigates dependence on system parameters. We find the most major discrepancies between codes resulted from the dimensionality of the setup (3D vs 2D disks). Beyond this, we find good agreement in the total torque on the binary between codes, although the partition of this torque between the gravitational torque, orbital accretion torque, and spin accretion torque depends sensitively on the sink prescriptions employed. In agreement with previous studies, we find a modest difference in torques and accretion variability between 2D and 3D disk models. We find cavity precession rates to be appreciably faster in 3D than in 2D. △ Less

Submitted 20 June, 2024; v1 submitted 20 February, 2024; originally announced February 2024.

Comments: ApJ Accepted

Code-Aware Prompting: A study of Coverage Guided Test Generation in Regression Setting using LLM

Authors: Gabriel Ryan, Siddhartha Jain, Mingyue Shang, Shiqi Wang, Xiaofei Ma, Murali Krishna Ramanathan, Baishakhi Ray

Abstract: Testing plays a pivotal role in ensuring software quality, yet conventional Search Based Software Testing (SBST) methods often struggle with complex software units, achieving suboptimal test coverage. Recent works using large language models (LLMs) for test generation have focused on improving generation quality through optimizing the test generation context and correcting errors in model outputs,… ▽ More Testing plays a pivotal role in ensuring software quality, yet conventional Search Based Software Testing (SBST) methods often struggle with complex software units, achieving suboptimal test coverage. Recent works using large language models (LLMs) for test generation have focused on improving generation quality through optimizing the test generation context and correcting errors in model outputs, but use fixed prompting strategies that prompt the model to generate tests without additional guidance. As a result LLM-generated testsuites still suffer from low coverage. In this paper, we present SymPrompt, a code-aware prompting strategy for LLMs in test generation. SymPrompt's approach is based on recent work that demonstrates LLMs can solve more complex logical problems when prompted to reason about the problem in a multi-step fashion. We apply this methodology to test generation by deconstructing the testsuite generation process into a multi-stage sequence, each of which is driven by a specific prompt aligned with the execution paths of the method under test, and exposing relevant type and dependency focal context to the model. Our approach enables pretrained LLMs to generate more complete test cases without any additional training. We implement SymPrompt using the TreeSitter parsing framework and evaluate on a benchmark challenging methods from open source Python projects. SymPrompt enhances correct test generations by a factor of 5 and bolsters relative coverage by 26% for CodeGen2. Notably, when applied to GPT-4, SymPrompt improves coverage by over 2x compared to baseline prompting strategies. △ Less

Submitted 2 April, 2024; v1 submitted 31 January, 2024; originally announced February 2024.

The CeBrA demonstrator for particle-$γ$ coincidence experiments at the FSU Super-Enge Split-Pole Spectrograph

Authors: A. L. Conley, B. Kelly, M. Spieker, R. Aggarwal, S. Ajayi, L. T. Baby, S. Baker, C. Benetti, I. Conroy, P. D. Cottle, I. B. D`Amato, P. DeRosa, J. Esparza, S. Genty, K. Hanselman, I. Hay, M. Heinze, D. Houlihan, M. I. Khawaja, P. S. Kielb, A. N. Kuchera, G. W. McCann, A. B. Morelock, E. Lopez-Saavedra, R. Renom , et al. (8 additional authors not shown)

Abstract: We report on a highly selective experimental setup for particle-$γ$ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University (FSU) using fast CeBr$_3$ scintillators for $γ$-ray detection. Specifically, we report on the results of characterization tests for the first five CeBr$_3$ scintill… ▽ More We report on a highly selective experimental setup for particle-$γ$ coincidence experiments at the Super-Enge Split-Pole Spectrograph (SE-SPS) of the John D. Fox Superconducting Linear Accelerator Laboratory at Florida State University (FSU) using fast CeBr$_3$ scintillators for $γ$-ray detection. Specifically, we report on the results of characterization tests for the first five CeBr$_3$ scintillation detectors of the CeBr$_3$ Array (CeBrA) with respect to energy resolution and timing characteristics. We also present results from the first particle-$γ$ coincidence experiments successfully performed with the CeBrA demonstrator and the FSU SE-SPS. We show that with the new setup, $γ$-decay branching ratios and particle-$γ$ angular correlations can be measured very selectively using narrow excitation energy gates, which are possible thanks to the excellent particle energy resolution of the SE-SPS. In addition, we highlight that nuclear level lifetimes in the nanoseconds regime can be determined by measuring the time difference between particle detection with the SE-SPS focal-plane scintillator and $γ$-ray detection with the fast CeBrA detectors. Selective excitation energy gates with the SE-SPS exclude any feeding contributions to these lifetimes. △ Less

Submitted 1 November, 2023; originally announced November 2023.

Scaling relations for gamma-ray burst afterglow light curves and centroid motion independent of jet structure and dynamics

Authors: Hendrik van Eerten, Geoffrey Ryan

Abstract: Models for gamma-ray burst afterglow dynamics and synchrotron spectra are known to exhibit various scale invariances, owing to the scale-free nature of fluid dynamics and the power-law shape of synchrotron spectra. Since GRB 170817A, off-axis jet models including a lateral energy structure in the initial outflow geometry have gained in prominence. Here we demonstrate how the scale-invariance for a… ▽ More Models for gamma-ray burst afterglow dynamics and synchrotron spectra are known to exhibit various scale invariances, owing to the scale-free nature of fluid dynamics and the power-law shape of synchrotron spectra. Since GRB 170817A, off-axis jet models including a lateral energy structure in the initial outflow geometry have gained in prominence. Here we demonstrate how the scale-invariance for arbitrary jet structure and dynamical stage can be expressed locally as a function of jet temporal light curve slope. We provide afterglow flux expressions and demonstrate their use to quickly assess the physical implications of observations. We apply the scaling expressions to the Swift XRT sample, which shows a spread in observed fluxes, binned by light curve slope at time of observation, that increases with increasing light curve slope. According to the scaling relations, this pattern is inconsistent with a large spread in environment densities if these were the dominant factor determining the variability of light curves. We further show how the late Deep Newtonian afterglow stage remains scale-invariant but adds distinct spectral scaling regimes. Finally, we show that for given jet structure a universal curve can be constructed of the centroid offset, image size and ellipticity (that can be measured using very-large baseline interferometry) versus observer angle, in a manner independent of explosion energy and circumburst density. Our results apply to any synchrotron transient characterized by a release of energy in an external medium, including supernova remnants, kilonova afterglows and soft gamma-repeater flares. △ Less

Submitted 25 April, 2024; v1 submitted 13 October, 2023; originally announced October 2023.

Comments: MNRAS accepted version. 13 pages, 6 figures, 4 tables. Changes during peer-review: added further context status of field, expanded scale-invariance VLBI discussion to include image size and ellipticity and added an extended application of scale-invariance for arbitrary light curve slope to the Swift XRT sample

The Evolution of Accreting Binaries: from Brown Dwarfs to Supermassive Black Holes

Authors: Alexander J. Dittmann, Geoffrey Ryan

Abstract: Circumbinary accretion occurs throughout the universe, from the formation of stars and planets to the aftermath of major galactic mergers. We present an extensive investigation of circumbinary accretion disks, studying circular binaries with mass ratios ($q\equiv M_2/M_1$) from 0.01 to 1 and at each mass ratio probing the effects of disk thickness and viscosity. We study disks with aspect ratios… ▽ More Circumbinary accretion occurs throughout the universe, from the formation of stars and planets to the aftermath of major galactic mergers. We present an extensive investigation of circumbinary accretion disks, studying circular binaries with mass ratios ($q\equiv M_2/M_1$) from 0.01 to 1 and at each mass ratio probing the effects of disk thickness and viscosity. We study disks with aspect ratios $H/r\in\{0.1, 0.05, 0.033\}$, and vary both the magnitude and spatial dependance of viscosity. Although thin accretion disks have previously been found to promote rapid inspirals of equal-mass binaries, we find that gravitational torques become weaker at lower mass ratios and most binaries with $0.01\leq q\leq0.04$ outspiral, which may delay the coalescence of black hole binaries formed from minor mergers and cause high-mass exoplanets to migrate outwards. However, in a number of cases, the disks accreting onto binaries with mass ratios $\sim 0.07$ fail to develop eccentric modes, leading to extremely rapid inspirals. Variability in black hole accretion correlates with disk eccentricity, and we observe variability above the $\sim10\%$ level even for mass ratios of $0.01$. We demonstrate that the spatial dependence of the viscosity (e.g. $α$ vs constant-$ν$) significantly affects the degree of preferential accretion onto the secondary, resolving discrepancies between previous studies. Colder circumbinary disks remain eccentric even at $q\sim0.01$ and sustain deep, asymmetric cavities. △ Less

Submitted 11 October, 2023; originally announced October 2023.

Comments: 23 pages, 17 figures. Comments welcome

Modelling of Long-Term Afterglow Counterparts to Gravitational Wave Events: The Full View of GRB 170817A

Authors: Geoffrey Ryan, Hendrik van Eerten, Eleonora Troja, Luigi Piro, Brendan O'Connor, Roberto Ricci

Abstract: The arrival of gravitational wave astronomy and a growing number of time-domain focused observatories are set to lead to a increasing number of detections of short gamma-ray bursts (GRBs) launched with a moderate inclination to Earth. Being nearby events, these are also prime candidates for very long-term follow-up campaigns and very-long-baseline interferometry (VLBI), which has implications for… ▽ More The arrival of gravitational wave astronomy and a growing number of time-domain focused observatories are set to lead to a increasing number of detections of short gamma-ray bursts (GRBs) launched with a moderate inclination to Earth. Being nearby events, these are also prime candidates for very long-term follow-up campaigns and very-long-baseline interferometry (VLBI), which has implications for multi-messenger modelling, data analysis, and statistical inference methods applied to these sources. Here we present a comprehensive modelling update that directly incorporates into afterglowpy astrometric observations of the GRB position, Poissonian statistics for faint sources, and modelling of a trans-relativistic population of electrons. We use the revolutionary event GW170817 to demonstrate the impact of these extensions both for the best-fit physics parameters and model selection methods that assess the statistical significance of additional late-time emission components. By including in our analysis the latest Chandra X-ray observations of GRB 170817A, we find only weak evidence (less than two sigma) for a new emission component at late times, which makes for a slightly more natural fit to the centroid evolution and prediction for the external medium density. △ Less

Submitted 3 October, 2023; originally announced October 2023.

Comments: 23 pages, 12 figures, submitted to ApJ

Potential biases and prospects for the Hubble constant estimation via electromagnetic and gravitational-wave joint analyses

Authors: Giulia Gianfagna, Luigi Piro, Francesco Pannarale, Hendrik Van Eerten, Fulvio Ricci, Geoffrey Ryan

Abstract: GW170817 is a binary neutron star merger that exhibited a gravitational wave (GW) and a gamma-ray burst, followed by an afterglow. In this work, we estimate the Hubble constant ($H_0$) using broad-band afterglow emission and relativistic jet motion from the Very Long Baseline Interferometry and Hubble Space Telescope images of GW170817. Compared to previous attempts, we combine these messengers wi… ▽ More GW170817 is a binary neutron star merger that exhibited a gravitational wave (GW) and a gamma-ray burst, followed by an afterglow. In this work, we estimate the Hubble constant ($H_0$) using broad-band afterglow emission and relativistic jet motion from the Very Long Baseline Interferometry and Hubble Space Telescope images of GW170817. Compared to previous attempts, we combine these messengers with GW in a simultaneous Bayesian fit. We probe the $H_0$ measurement robustness depending on the data set used, the assumed jet model, the possible presence of a late time flux excess. Using the sole GW leads to a $20\%$ error ($77^{+21}_{-10}$ km/s/Mpc, medians, 16th-84th percentiles), because of the degeneracy between viewing angle ($θ_v$) and luminosity distance ($d_L$). The latter is reduced by the inclusion in the fit of the afterglow light curve, leading to $H_0=96^{+13}_{-10}$ km/s/Mpc, a large value, caused by the fit preference for high viewing angles due to the possible presence of a late-time excess in the afterglow flux. Accounting for the latter by including a constant flux component at late times brings $H_0=78.5^{+7.9}_{-6.4}$ km/s/Mpc. Adding the centroid motion in the analysis efficiently breaks the $d_L-θ_v$ degeneracy and overcome the late-time deviations, giving $H_0 = 69.0^{+4.4}_{-4.3}$ km/s/Mpc (in agreement with Planck and SH0ES measurements) and $θ_v = 18.2^{+1.2}_{-1.5}$ deg. This is valid regardless of the jet structure assumption. Our simulations show that for next GW runs radio observations are expected to provide at most few other similar events. △ Less

Submitted 24 January, 2024; v1 submitted 29 September, 2023; originally announced September 2023.

Comments: 14 pages, 10 figures. Accepted for publication in MNRAS

Evidence for a luminosity-decay correlation in GRB GeV light curves

Authors: K. R. Hinds, S. R. Oates, M. Nicholl, J. Patel, N. Omodei, B. Gompertz, J. L. Racusin, G. Ryan

Abstract: Correlations between intrinsic properties of gamma-ray burst (GRB) light curves provide clues to the nature of the central engine, the jet, and a possible means to standardise GRBs for cosmological use. Here we report on the discovery of a correlation between the intrinsic early time luminosity, $L_{G,\rm 10s}$, measured at rest frame 10s, and the average decay rate measured from rest frame 10s on… ▽ More Correlations between intrinsic properties of gamma-ray burst (GRB) light curves provide clues to the nature of the central engine, the jet, and a possible means to standardise GRBs for cosmological use. Here we report on the discovery of a correlation between the intrinsic early time luminosity, $L_{G,\rm 10s}$, measured at rest frame 10s, and the average decay rate measured from rest frame 10s onward, $α_{G,\rm avg>10s}$, in a sample of 13 Fermi Large Array Telescope (LAT) long GRB light curves. We note that our selection criteria, in particular the requirement for a redshift to construct luminosity light curves, naturally limits our sample to energetic GRBs. A Spearman's rank correlation gives a coefficient of -0.74, corresponding to a confidence level of 99.6%, indicating that brighter afterglows decay faster than less luminous ones. Assuming a linear relation with $\log(L_{G,\rm 10s})$, we find $α_{G,\rm avg>10s} = -0.31_{-0.09}^{+0.12}\log(L_{G,\rm 10s}) + 14.43_{-5.97}^{+4.55}$. The slope of -0.31 is consistent at $1σ$ with previously identified correlations in the optical/UV and X-ray light curves. We speculate that differences in the rate at which energy is released by the central engine or differences in observer viewing angle may be responsible for the correlation. △ Less

Submitted 15 September, 2023; originally announced September 2023.

Comments: 8 pages, 4 figures, accepted for publication in MNRAS

A lanthanide-rich kilonova in the aftermath of a long gamma-ray burst

Authors: Yu-Han Yang, Eleonora Troja, Brendan O'Connor, Chris L. Fryer, Myungshin Im, Joe Durbak, Gregory S. H. Paek, Roberto Ricci, Clécio R. De Bom, James H. Gillanders, Alberto J. Castro-Tirado, Zong-Kai Peng, Simone Dichiara, Geoffrey Ryan, Hendrik van Eerten, Zi-Gao Dai, Seo-Won Chang, Hyeonho Choi, Kishalay De, Youdong Hu, Charles D. Kilpatrick, Alexander Kutyrev, Mankeun Jeong, Chung-Uk Lee, Martin Makler , et al. (2 additional authors not shown)

Abstract: Kilonovae are a rare class of astrophysical transients powered by the radioactive decay of nuclei heavier than iron, synthesized in the merger of two compact objects. Over the first few days, the kilonova evolution is dominated by a large number of radioactive isotopes contributing to the heating rate. On timescales of weeks to months, its behavior is predicted to differ depending on the ejecta co… ▽ More Kilonovae are a rare class of astrophysical transients powered by the radioactive decay of nuclei heavier than iron, synthesized in the merger of two compact objects. Over the first few days, the kilonova evolution is dominated by a large number of radioactive isotopes contributing to the heating rate. On timescales of weeks to months, its behavior is predicted to differ depending on the ejecta composition and merger remnant. However, late-time observations of known kilonovae are either missing or limited. Here we report observations of a luminous red transient with a quasi-thermal spectrum, following an unusual gamma-ray burst of long duration. We classify this thermal emission as a kilonova and track its evolution up to two months after the burst. At these late times, the recession of the photospheric radius and the rapidly-decaying bolometric luminosity ($L_{\rm bol}\propto t^{-2.7\pm 0.4}$) support the recombination of lanthanide-rich ejecta as they cool. △ Less

Submitted 2 August, 2023; v1 submitted 1 August, 2023; originally announced August 2023.

Comments: 47 pages, 14 figures, 9 tables; submitted; a minor typo fixed

The Decoupling of Binaries from Their Circumbinary Disks

Authors: Alexander J. Dittmann, Geoffrey Ryan, M. Coleman Miller

Abstract: We have investigated, both analytically and numerically, accreting supermassive black hole binaries as they inspiral due to gravitational radiation to elucidate the decoupling of binaries from their disks and inform future multi-messenger observations of these systems. Our numerical studies evolve equal-mass binaries from initial separations of $100 GM/c^2$ until merger, resolving scales as small… ▽ More We have investigated, both analytically and numerically, accreting supermassive black hole binaries as they inspiral due to gravitational radiation to elucidate the decoupling of binaries from their disks and inform future multi-messenger observations of these systems. Our numerical studies evolve equal-mass binaries from initial separations of $100 GM/c^2$ until merger, resolving scales as small as $\sim0.04 GM/c^2$, where $M$ is the total binary mass. Our simulations accurately capture the point at which the orbital evolution of each binary decouples from that of their circumbinary disk, and precisely resolve the flow of gas throughout the inspiral. We demonstrate analytically and numerically that timescale-based predictions overestimate the binary separations at which decoupling occurs by factors of $\sim3$, and illustrate the utility of a velocity-based decoupling criterion. High-viscosity ($ν\gtrsim0.03 GM/c$) circumbinary systems decouple late ($a_b\lesssim 15 GM/c^2$) and have qualitatively similar morphologies near merger to circumbinary systems with constant binary separations. Lower-viscosity circumbinary disks decouple earlier and exhibit qualitatively different accretion flows, which lead to precipitously decreasing accretion onto the binary. If detected, such a decrease may unambiguously identify the host galaxy of an ongoing event within a LISA error volume. We illustrate how accretion amplitude and variability evolve as binaries gradually decouple from their circumbinary disks, and where decoupling occurs over the course of binary inspirals in the LISA band. We show that, even when dynamically negligible, gas may leave a detectable imprint on the phase of gravitational waves. △ Less

Submitted 3 May, 2023; v1 submitted 28 March, 2023; originally announced March 2023.

Comments: 10 pages, 5 figures. Submitted to ApJL, comments welcome

A Critique of the Spite Plateau, and the Astration of Primordial Lithium

Authors: J. E. Norris, D. Yong, A. Frebel, S. G. Ryan

Abstract: We investigate the distribution of the lithium abundances, A(Li), of metal-poor dwarf and subgiant stars within the limits 5500 K < Teff < 6700 K, -6.0 < [Fe/H] < -1.5, and logg > ~3.5 (a superset of parameters first adopted by Spite and Spite), using literature data for some 200 stars. We address the problem of the several methods that yield Teff differences up to 350 K, and hence uncertainties o… ▽ More We investigate the distribution of the lithium abundances, A(Li), of metal-poor dwarf and subgiant stars within the limits 5500 K < Teff < 6700 K, -6.0 < [Fe/H] < -1.5, and logg > ~3.5 (a superset of parameters first adopted by Spite and Spite), using literature data for some 200 stars. We address the problem of the several methods that yield Teff differences up to 350 K, and hence uncertainties of 0.3 dex in [Fe/H] and A(Li), by anchoring Teff to the Infrared Flux Method. We seek to understand the behaviour of A(Li) as a function of [Fe/H] -- small dispersion at highest [Fe/H], ``meltdown'' at intermediate values (i.e. large spread in Li below the Spite Plateau), and extreme variations at lowest [Fe/H]. Decreasing A(Li) is accompanied by increasing dispersion. Insofar as [Fe/H] increases as the universe ages, the behavior of A(Li) reflects chaotic star formation involving destruction of primordial Li, which settles to the classic Spite Plateau, with A(Li) ~2.3, by the time the Galactic halo reaches [Fe/H] ~ -3.0. We consider three phases: (1) first star formation in C-rich environments ([C/Fe] > 2.3), with depleted Li; (2) silicates-dominated star formation and destruction of primordial Li during pre-main-sequence evolution; and (3) materials from these two phases co-existing and coalescing to form C-rich stars with A(Li) below the Spite Plateau, leading to a toy model with the potential to explain the ``meltdown''. We comment on the results of Mucciarelli et al. on the Lower RGB, and the suggestion of Aguado et al. favouring a lower primordial lithium abundance than generally accepted. △ Less

Submitted 20 March, 2023; originally announced March 2023.

Comments: MNRAS in press (see source file for full versions of long tables)

NFL Career Success as Predicted by NFL Scouting Combine

Authors: Brian Szekely, Christian Sinnott, Savannah Halow, Gregory Ryan

Abstract: The National Football League (NFL) Scouting Combine serves as a tool to evaluate the skills of prospective players and assess their readiness to play in the NFL. The development of machine learning brings new opportunities in assessing the utility of the Scouting Combine. Using machine and statistical learning, it may be possible to predict future success of prospective athletes, as well as predic… ▽ More The National Football League (NFL) Scouting Combine serves as a tool to evaluate the skills of prospective players and assess their readiness to play in the NFL. The development of machine learning brings new opportunities in assessing the utility of the Scouting Combine. Using machine and statistical learning, it may be possible to predict future success of prospective athletes, as well as predict which Scouting Combine tests are the most important. Results from statistical learning research have been contradicting whether the Scouting combine is a useful metric for player success. In this study, we investigate if machine learning can be used to determine matriculation and future success in the NFL. Using Scouting Combine data, we evaluate six different algorithms' ability to predict whether a potential draft pick will play a single NFL snap (matriculation). If a player is drafted, we predict how many snaps they go on to play (success). We are able to predict matriculation with 83% accuracy; however, we are unable to predict later success. Our best performing algorithm returns large error and low explained variance (RMSE=1,210 snaps; ${R}^2$=0.17). These findings indicate that while the Scouting Combine can predict NFL matriculation, it may not be a reliable predictor of long-term player success. △ Less

Submitted 10 March, 2023; originally announced March 2023.

Comments: 16 pages, 2 figures, 1 table

A structured jet explains the extreme GRB 221009A

Authors: B. O'Connor, E. Troja, G. Ryan, P. Beniamini, H. van Eerten, J. Granot, S. Dichiara, R. Ricci, V. Lipunov, J. H. Gillanders, R. Gill, M. Moss, S. Anand, I. Andreoni, R. L. Becerra, D. A. H. Buckley, N. R. Butler, S. B. Cenko, A. Chasovnikov, J. Durbak, C. Francile, E. Hammerstein, A. J. van der Horst, M. Kasliwal, C. Kouveliotou , et al. (7 additional authors not shown)

Abstract: Long duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars. Among them, GRB 221009A is by far the brightest burst ever observed. Due to its enormous energy ($E_\textrm{iso}\!\approx$10$^{55}$ erg) and proximity ($z\!\approx$0.15), GRB 221009A is an exceptionally rare event that pushes the limits of our theories. We present multi-wavelength observatio… ▽ More Long duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars. Among them, GRB 221009A is by far the brightest burst ever observed. Due to its enormous energy ($E_\textrm{iso}\!\approx$10$^{55}$ erg) and proximity ($z\!\approx$0.15), GRB 221009A is an exceptionally rare event that pushes the limits of our theories. We present multi-wavelength observations covering the first three months of its afterglow evolution. The X-ray brightness decays as a power-law with slope $\approx\!t^{-1.66}$, which is not consistent with standard predictions for jetted emission. We attribute this behavior to a shallow energy profile of the relativistic jet. A similar trend is observed in other energetic GRBs, suggesting that the most extreme explosions may be powered by structured jets launched by a common central engine. △ Less

Submitted 15 February, 2023; originally announced February 2023.

Comments: Submitted version. 53 pages, 9 figures, 6 tables

Joint analysis of gravitational-wave and electromagnetic data of mergers: breaking an afterglow model degeneracy in GW170817 and in future events

Authors: Giulia Gianfagna, Luigi Piro, Francesco Pannarale, Hendrik Van Eerten, Fulvio Ricci, Geoffrey Ryan, Eleonora Troja

Abstract: On August 17, 2017, Advanced LIGO and Virgo observed GW170817, the first gravitational-wave (GW) signal from a binary neutron star merger. It was followed by a short-duration gamma-ray burst, GRB 170817A, and by a non-thermal afterglow emission. In this work, a combined simultaneous fit of the electromagnetic (EM, specifically, afterglow) and GW domains is implemented, both using the posterior dis… ▽ More On August 17, 2017, Advanced LIGO and Virgo observed GW170817, the first gravitational-wave (GW) signal from a binary neutron star merger. It was followed by a short-duration gamma-ray burst, GRB 170817A, and by a non-thermal afterglow emission. In this work, a combined simultaneous fit of the electromagnetic (EM, specifically, afterglow) and GW domains is implemented, both using the posterior distribution of a GW standalone analysis as prior distribution to separately process the EM data, and fitting the EM and GW domains simultaneously. These approaches coincide mathematically, as long as the actual posterior of the GW analysis, and not an approximation, is used as prior for the EM analysis. We treat the viewing angle, $θ_v$, as shared parameter across the two domains. In the afterglow modelling with a Gaussian structured jet this parameter and the jet core angle, $θ_c$, are correlated, leading to high uncertainties on their values. The joint EM+GW analysis relaxes this degeneracy, reducing the uncertainty compared to an EM-only fit. We also apply our methodology to hypothetical GW170817-like events occurring in the next GW observing run at $\sim$140 and 70 Mpc. At 70 Mpc the existing EM degeneracy is broken, thanks to the inclusion of the GW domain in the analysis. At 140 Mpc, the EM-only fit cannot constrain $θ_v$ nor $θ_c$ because of the lack of detections in the afterglow rising phase. Folding the GW data into the analysis leads to tighter constraints on $θ_v$, still leaving $θ_c$ unconstrained, requiring instruments with higher sensitivities, such as Athena. △ Less

Submitted 6 June, 2023; v1 submitted 2 December, 2022; originally announced December 2022.

Comments: 15 pages, 10 figures. Accepted for publication in MNRAS

A nearby long gamma-ray burst from a merger of compact objects

Authors: E. Troja, C. L. Fryer, B. O'Connor, G. Ryan, S. Dichiara, A. Kumar, N. Ito, R. Gupta, R. Wollaeger, J. P. Norris, N. Kawai, N. Butler, A. Aryan, K. Misra, R. Hosokawa, K. L. Murata, M. Niwano, S. B. Pandey, A. Kutyrev, H. J. van Eerten, E. A. Chase, Y. -D. Hu, M. D. Caballero-Garcia, A. J. Castro-Tirado

Abstract: Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts of long (>2 s) duration are produced by the core-collapse of massive stars, those of short (< 2 s) duration by the merger of two neutron stars (NSs). A third class of events with hybrid high-energy properties was identified, but never conclusively linked to a stellar progenitor. The lack o… ▽ More Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts of long (>2 s) duration are produced by the core-collapse of massive stars, those of short (< 2 s) duration by the merger of two neutron stars (NSs). A third class of events with hybrid high-energy properties was identified, but never conclusively linked to a stellar progenitor. The lack of bright supernovae rules out typical core-collapse explosions, but their distance scales prevent sensitive searches for direct signatures of a progenitor system. Only tentative evidence for a kilonova has been presented. Here we report observations of the exceptionally bright GRB211211A that classify it as a hybrid event and constrain its distance scale to only 346 Mpc. Our measurements indicate that its lower-energy (from ultraviolet to near-infrared) counterpart is powered by a luminous (~1E42 erg/s) kilonova possibly formed in the ejecta of a compact binary merger. △ Less

Submitted 11 December, 2022; v1 submitted 7 September, 2022; originally announced September 2022.

Comments: final version, including supplementary methods

Journal ref: Nature, volume 612, pages 228-231 (2022)

A Survey of Disc Thickness and Viscosity in Circumbinary Accretion: Binary Evolution, Variability, and Disc Morphology

Authors: Alexander J. Dittmann, Geoffrey Ryan

Abstract: Much of the parameter space relevant to the evolution of astrophysical circumbinary accretion discs remains unexplored. We have carried out a suite of circumbinary disc simulations surveying both disc thickness and kinematic viscosity, using both constant-$ν$ and constant-$α$ prescriptions. We focus primarily on disc aspect ratios between $0.1$ and $0.033$, and on viscosities between $ν=0.0005$ an… ▽ More Much of the parameter space relevant to the evolution of astrophysical circumbinary accretion discs remains unexplored. We have carried out a suite of circumbinary disc simulations surveying both disc thickness and kinematic viscosity, using both constant-$ν$ and constant-$α$ prescriptions. We focus primarily on disc aspect ratios between $0.1$ and $0.033$, and on viscosities between $ν=0.0005$ and $ν=0.008$ (in units of binary semi-major axis and orbital frequency), and specialise to circular equal-mass binaries. Both factors strongly influence the evolution of the binary semi-major axis: at $ν=0.0005,$ inspirals occur at aspect ratios $\lesssim0.059$, while at $ν=0.004$ inspirals occur only at aspect ratios $\lesssim0.04$. Inspirals occur largely because of the increasingly strong negative torque on the binary by streams of material which lag the binary, with negligible contributions from resonant torques excited in the circumbinary disc. We find that reductions in accretion rate occur when simulations are initialised too far from the eventual quasi-steady state driven by interaction with the binary, rather than being intrinsically linked to the disc aspect ratio. We find not only that the cavity size increases as viscosity is decreased, but that thinner circumbinary discs become more eccentric. Our results suggest that supermassive black hole binaries should be driven, more rapidly than previous estimates, from $\sim$parsec separations to distances where gravitational waves drive their inspiral, potentially reducing the number of binaries observable by pulsar timing arrays. △ Less

Submitted 6 June, 2022; v1 submitted 19 January, 2022; originally announced January 2022.

Comments: 20 pages, 21 figures, published in MNRAS

The early afterglow of GRB 190829A

Authors: S. Dichiara, E. Troja, V. Lipunov, R. Ricci, S. R. Oates, N. R. Butler, E. Liuzzo, G. Ryan, B. O'Connor, S. B. Cenko, R. G. Cosentino, A. Y. Lien, E. Gorbovskoy, N. Tyurina, P. Balanutsa, D. Vlasenko, I. Gorbunov, R. Podesta, F. Podesta, R. Rebolo, M. Serra, D. A. H. Buckley

Abstract: GRB 190829A at z=0.0785 is the fourth closest long GRB ever detected by the Neil Gehrels Swift observatory, and the third confirmed case with a very high energy component. We present our multi-wavelength analysis of this rare event, focusing on its early stages of evolution, and including data from Swift, the MASTER global network of optical telescopes, ALMA, and ATCA. We report sensitive limits o… ▽ More GRB 190829A at z=0.0785 is the fourth closest long GRB ever detected by the Neil Gehrels Swift observatory, and the third confirmed case with a very high energy component. We present our multi-wavelength analysis of this rare event, focusing on its early stages of evolution, and including data from Swift, the MASTER global network of optical telescopes, ALMA, and ATCA. We report sensitive limits on the linear polarization of the optical emission, disfavouring models of off-axis jets to explain the delayed afterglow peak. The study of the multi-wavelength light curves and broadband spectra supports a model with at least two emission components: a bright reverse shock emission, visible at early times in the optical and X-rays and, later, in the radio band; and a forward shock component dominating at later times and lower radio frequencies. A combined study of the prompt and afterglow properties shows many similarities with cosmological long GRBs, suggesting that GRB 190829A is an example of classical GRBs in the nearby universe. △ Less

Submitted 16 February, 2022; v1 submitted 29 November, 2021; originally announced November 2021.

Comments: 13 pages, 8 figures, accepted for publication in MNRAS

Interpreting Machine Learning Models for Room Temperature Prediction in Non-domestic Buildings

Authors: Jianqiao Mao, Grammenos Ryan

Abstract: An ensuing challenge in Artificial Intelligence (AI) is the perceived difficulty in interpreting sophisticated machine learning models, whose ever-increasing complexity makes it hard for such models to be understood, trusted and thus accepted by human beings. The lack, if not complete absence, of interpretability for these so-called black-box models can lead to serious economic and ethical consequ… ▽ More An ensuing challenge in Artificial Intelligence (AI) is the perceived difficulty in interpreting sophisticated machine learning models, whose ever-increasing complexity makes it hard for such models to be understood, trusted and thus accepted by human beings. The lack, if not complete absence, of interpretability for these so-called black-box models can lead to serious economic and ethical consequences, thereby hindering the development and deployment of AI in wider fields, particularly in those involving critical and regulatory applications. Yet, the building services industry is a highly-regulated domain requiring transparency and decision-making processes that can be understood and trusted by humans. To this end, the design and implementation of autonomous Heating, Ventilation and Air Conditioning systems for the automatic but concurrently interpretable optimisation of energy efficiency and room thermal comfort is of topical interest. This work therefore presents an interpretable machine learning model aimed at predicting room temperature in non-domestic buildings, for the purpose of optimising the use of the installed HVAC system. We demonstrate experimentally that the proposed model can accurately forecast room temperatures eight hours ahead in real-time by taking into account historical RT information, as well as additional environmental and time-series features. In this paper, an enhanced feature engineering process is conducted based on the Exploratory Data Analysis results. Furthermore, beyond the commonly used Interpretable Machine Learning techniques, we propose a Permutation Feature-based Frequency Response Analysis (PF-FRA) method for quantifying the contributions of the different predictors in the frequency domain. Based on the generated reason codes, we find that the historical RT feature is the dominant factor that has most impact on the model prediction. △ Less

Submitted 23 November, 2021; originally announced November 2021.

Comments: 25 pages, 15 figures, 3 tables

MSC Class: I.2; H.4

Journal ref: Science and Technology for the Built Environment 29.7 (2023): 698-718

Resonant Shattering Flares in Black Hole-Neutron Star and Binary Neutron Star Mergers

Authors: Duncan Neill, David Tsang, Hendrik van Eerten, Geoffrey Ryan, William G. Newton

Abstract: Resonant Shattering flares (RSFs) are bursts of gamma-rays expected to be triggered by tidal resonance of a neutron star (NS) during binary inspiral. They are strongly dependent on the magnetic field strength at the surface of the NS. By modelling these flares as being the result of multiple colliding relativistic shells launched during the resonance window, we find that the prompt non-thermal gam… ▽ More Resonant Shattering flares (RSFs) are bursts of gamma-rays expected to be triggered by tidal resonance of a neutron star (NS) during binary inspiral. They are strongly dependent on the magnetic field strength at the surface of the NS. By modelling these flares as being the result of multiple colliding relativistic shells launched during the resonance window, we find that the prompt non-thermal gamma-ray emission may have luminosity up to a few $\times10^{48}\text{ erg/s}$, and that a broad-band afterglow could be produced. We compute the expected rates of detectable RSFs using the BPASS population synthesis code, with different assumptions about the evolution of surface magnetic field strengths before merger. We find the rate of detectable RSFs to be $\sim 0.0001-5$ per year for BHNS mergers and $\sim 0.0005-25$ per year for NSNS mergers, with the lower bound corresponding to surface-field decay consistent with magneto-thermal evolution in purely crustal fields, while the upper bounds are for systems which have longer-lived surface magnetic fields supported by flux frozen into the superconducting core. If some of the observed SGRB precursor flares are indeed RSFs, this suggests the presence of a longer-lived surface field for some fraction of the neutron star population, and that we could expect RSFs to be the most common detectable EM counterpart to GW detections of BHNS mergers. The non-detection of a RSF prior to GRB170817A provides an upper bound on the magnetic fields of the progenitor NSs of $B_{\rm surf}\sim 10^{13.5} \text{ G}$. △ Less

Submitted 10 June, 2022; v1 submitted 5 November, 2021; originally announced November 2021.

Comments: 19 pages, 12 figures, final version accepted by MNRAS

Multi-messenger-Athena Synergy White Paper

Authors: L. Piro, M. Ahlers, A. Coleiro, M. Colpi, E. de Oña Wilhelmi, M. Guainazzi, P. G. Jonker, P. Mc Namara, D. A. Nichols, P. O'Brien, E. Troja, J. Vink, J. Aird, L. Amati, S. Anand, E. Bozzo, F. J. Carrera, A. C. Fabian, C. Fryer, E. Hall, O. Korobkin, V. Korol, A. Mangiagli, S. Martínez-Núñez, S. Nissanke , et al. (8 additional authors not shown)

Abstract: In this paper we explore the scientific synergies between Athena and some of the key multi-messenger facilities that should be operative concurrently with Athena. These facilities include LIGO A+, Advanced Virgo+ and future detectors for ground-based observation of gravitational waves (GW), LISA for space-based observations of GW, IceCube and KM3NeT for neutrino observations, and CTA for very high… ▽ More In this paper we explore the scientific synergies between Athena and some of the key multi-messenger facilities that should be operative concurrently with Athena. These facilities include LIGO A+, Advanced Virgo+ and future detectors for ground-based observation of gravitational waves (GW), LISA for space-based observations of GW, IceCube and KM3NeT for neutrino observations, and CTA for very high energy observations. These science themes encompass pressing issues in astrophysics, cosmology and fundamental physics such as: the central engine and jet physics in compact binary mergers, accretion processes and jet physics in Super-Massive Binary Black Holes (SMBBHs) and in compact stellar binaries, the equation of state of neutron stars, cosmic accelerators and the origin of Cosmic Rays (CRs), the origin of intermediate and high-Z elements in the Universe, the Cosmic distance scale and tests of General Relativity and the Standard Model. Observational strategies for implementing the identified science topics are also discussed. A significant part of the sources targeted by multi-messenger facilities is of transient nature. We have thus also discussed the synergy of \textsl{Athena} with wide-field high-energy facilities, taking THESEUS as a case study for transient discovery. This discussion covers all the Athena science goals that rely on follow-up observations of high-energy transients identified by external observatories, and includes also topics that are not based on multi-messenger observations, such as the search for missing baryons or the observation of early star populations and metal enrichment at the cosmic dawn with Gamma-Ray Bursts (GRBs). △ Less

Submitted 29 October, 2021; originally announced October 2021.

Comments: White paper of the multi-messenger Athena synergy excersise

TOGA: A Neural Method for Test Oracle Generation

Authors: Elizabeth Dinella, Gabriel Ryan, Todd Mytkowicz, Shuvendu K. Lahiri

Abstract: Testing is widely recognized as an important stage of the software development lifecycle. Effective software testing can provide benefits such as bug finding, preventing regressions, and documentation. In terms of documentation, unit tests express a unit's intended functionality, as conceived by the developer. A test oracle, typically expressed as an condition, documents the intended behavior of a… ▽ More Testing is widely recognized as an important stage of the software development lifecycle. Effective software testing can provide benefits such as bug finding, preventing regressions, and documentation. In terms of documentation, unit tests express a unit's intended functionality, as conceived by the developer. A test oracle, typically expressed as an condition, documents the intended behavior of a unit under a given test prefix. Synthesizing a functional test oracle is a challenging problem, as it must capture the intended functionality rather than the implemented functionality. In this paper, we propose TOGA (a neural method for Test Oracle GenerAtion), a unified transformer-based neural approach to infer both exceptional and assertion test oracles based on the context of the focal method. Our approach can handle units with ambiguous or missing documentation, and even units with a missing implementation. We evaluate our approach on both oracle inference accuracy and functional bug-finding. Our technique improves accuracy by 33\% over existing oracle inference approaches, achieving 96\% overall accuracy on a held out test dataset. Furthermore, we show that when integrated with a automated test generation tool (EvoSuite), our approach finds 57 real world bugs in large-scale Java programs, including 30 bugs that are not found by any other automated testing method in our evaluation. △ Less

Submitted 20 April, 2022; v1 submitted 19 September, 2021; originally announced September 2021.

Comments: To appear in ICSE 2022

ACM Class: D.2.5; D.2.1

Discovery and confirmation of the shortest gamma ray burst from a collapsar

Authors: Tomas Ahumada, Leo P. Singer, Shreya Anand, Michael W. Coughlin, Mansi M. Kasliwal, Geoffrey Ryan, Igor Andreoni, S. Bradley Cenko, Christoffer Fremling, Harsh Kumar, Peter T. H. Pang, Eric Burns, Virginia Cunningham, Simone Dichiara, Tim Dietrich, Dmitry S. Svinkin, Mouza Almualla, Alberto J. Castro-Tirado, Kishalay De, Rachel Dunwoody, Pradip Gatkine, Erica Hammerstein, Shabnam Iyyani, Joseph Mangan, Dan Perley , et al. (32 additional authors not shown)

Abstract: Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe. The duration and hardness distribution of GRBs has two clusters, now understood to reflect (at least) two different progenitors. Short-hard GRBs (SGRBs; T90 <2 s) arise from compact binary mergers, while long-soft GRBs (LGRBs; T90 >2 s) have been attributed to the collapse of peculiar massive stars (collapsa… ▽ More Gamma-ray bursts (GRBs) are among the brightest and most energetic events in the universe. The duration and hardness distribution of GRBs has two clusters, now understood to reflect (at least) two different progenitors. Short-hard GRBs (SGRBs; T90 <2 s) arise from compact binary mergers, while long-soft GRBs (LGRBs; T90 >2 s) have been attributed to the collapse of peculiar massive stars (collapsars). The discovery of SN 1998bw/GRB 980425 marked the first association of a LGRB with a collapsar and AT 2017gfo/GRB 170817A/GW170817 marked the first association of a SGRB with a binary neutron star merger, producing also gravitational wave (GW). Here, we present the discovery of ZTF20abwysqy (AT2020scz), a fast-fading optical transient in the Fermi Satellite and the InterPlanetary Network (IPN) localization regions of GRB 200826A; X-ray and radio emission further confirm that this is the afterglow. Follow-up imaging (at rest-frame 16.5 days) reveals excess emission above the afterglow that cannot be explained as an underlying kilonova (KN), but is consistent with being the supernova (SN). Despite the GRB duration being short (rest-frame T90 of 0.65 s), our panchromatic follow-up data confirms a collapsar origin. GRB 200826A is the shortest LGRB found with an associated collapsar; it appears to sit on the brink between a successful and a failed collapsar. Our discovery is consistent with the hypothesis that most collapsars fail to produce ultra-relativistic jets. △ Less

Submitted 13 May, 2021; v1 submitted 11 May, 2021; originally announced May 2021.

Comments: submitted to Nature Astronomy

Accurate flux calibration of GW170817: is the X-ray counterpart on the rise?

Authors: E. Troja, B. O'Connor, G. Ryan, L. Piro, R. Ricci, B. Zhang, T. Piran, G. Bruni, S. B. Cenko, H. van Eerten

Abstract: X-ray emission from the gravitational wave transient GW170817 is well described as non-thermal afterglow radiation produced by a structured relativistic jet viewed off-axis. We show that the X-ray counterpart continues to be detected at 3.3 years after the merger. Such long-lasting signal is not a prediction of the earlier jet models characterized by a narrow jet core and a viewing angle of about… ▽ More X-ray emission from the gravitational wave transient GW170817 is well described as non-thermal afterglow radiation produced by a structured relativistic jet viewed off-axis. We show that the X-ray counterpart continues to be detected at 3.3 years after the merger. Such long-lasting signal is not a prediction of the earlier jet models characterized by a narrow jet core and a viewing angle of about 20 deg, and is spurring a renewed interest in the origin of the X-ray emission. We present a comprehensive analysis of the X-ray dataset aimed at clarifying existing discrepancies in the literature, and in particular the presence of an X-ray rebrightening at late times. Our analysis does not find evidence for an increase in the X-ray flux, but confirms a growing tension between the observations and the jet model. Further observations at radio and X-ray wavelengths would be critical to break the degeneracy between models. △ Less

Submitted 27 April, 2021; originally announced April 2021.

Comments: 10 pages, 5 figures, submitted to MNRAS

Evidence of extended emission in GRB 181123B and other high-redshift short GRBs

Authors: S. Dichiara, E. Troja, P. Beniamini, B. O'Connor, M. Moss, A. Y. Lien, R. Ricci, L. Amati, G. Ryan, T. Sakamoto

Abstract: We study the high-energy properties of GRB 181123B, a short gamma-ray burst (sGRB) at redshift $z\approx$1.75. We show that, despite its nominal short duration with $T_{90}<$2 s, this burst displays evidence of a temporally extended emission (EE) at high energies and that the same trend is observed in the majority of sGRBs at $z\gtrsim$1. We discuss the impact of instrumental selection effects on… ▽ More We study the high-energy properties of GRB 181123B, a short gamma-ray burst (sGRB) at redshift $z\approx$1.75. We show that, despite its nominal short duration with $T_{90}<$2 s, this burst displays evidence of a temporally extended emission (EE) at high energies and that the same trend is observed in the majority of sGRBs at $z\gtrsim$1. We discuss the impact of instrumental selection effects on the GRB classification, stressing that the measured $T_{90}$ is not an unambiguous indicator of the burst physical origin. By examining their environment (e.g. stellar mass, star formation, offset distribution), we find that these high-$z$ sGRBs share many properties of long GRBs at a similar distance and are consistent with a short-lived progenitor system. If produced by compact binary mergers, these sGRBs with EE may be easier to localize at large distances and herald a larger population of sGRBs in the early universe. △ Less

Submitted 4 July, 2022; v1 submitted 3 March, 2021; originally announced March 2021.

Comments: 10 pages, 7 figures, 2 tables. ApJ Letters, in press

Preventing Anomalous Torques in Circumbinary Accretion Simulations

Authors: Alexander Dittmann, Geoffrey Ryan

Abstract: Numerical experiments are the primary method of studying the evolution of circumbinary disks due to the strong nonlinearities involved. Many circumbinary simulations also require the use of numerical mass sinks: source terms which prevent gas from unphysically accumulating around the simulated point masses by removing gas at a given rate. However, special care must be taken when drawing physical c… ▽ More Numerical experiments are the primary method of studying the evolution of circumbinary disks due to the strong nonlinearities involved. Many circumbinary simulations also require the use of numerical mass sinks: source terms which prevent gas from unphysically accumulating around the simulated point masses by removing gas at a given rate. However, special care must be taken when drawing physical conclusions from such simulations to ensure that results are not biased by numerical artifacts. We demonstrate how the use of improved sink methods reduces some of these potential biases in vertically-integrated simulations of aspect ratio 0.1 accretion disks around binaries with mass ratios between 0.1 and 1. Specifically, we show that sink terms that do not reduce the angular momentum of gas relative to the accreting object: 1) reduce the dependence on the sink rate of physical quantities such as the torque on the binary, distribution of accretion between binary components, and evolution of the binary semi-major axis; 2) reduce the degree to which the sink rate affects the structure of the accretion disks around each binary component; 3) alter the inferred variability of accretion onto the binary, making it more regular in time. We also investigate other potential sources of systematic error, such as the precise from of gravitational softening and previously employed simplifications to the viscous stress tensor. Because of the strong dependence of the orbital evolution of the binary on both the torque and distribution of mass between binary components, the sink methods employed can have a significant effect on the inferred orbital evolution of the binary. △ Less

Submitted 10 February, 2021; originally announced February 2021.

Comments: 16 pages, 10 figures, 2 tables. Submitted to ApJ

A tale of two mergers: constraints on kilonova detection in two short GRBs at z$\sim$0.5

Authors: B. O'Connor, E. Troja, S. Dichiara, E. A. Chase, G. Ryan, S. B. Cenko, C. L. Fryer, R. Ricci, F. Marshall, C. Kouveliotou, R. T. Wollaeger, C. J. Fontes, O. Korobkin, P. Gatkine, A. Kutyrev, S. Veilleux, N. Kawai, T. Sakamoto

Abstract: We present a detailed multi-wavelength analysis of two short Gamma-Ray Bursts (sGRBs) detected by the Neil Gehrels Swift Observatory: GRB 160624A at $z=0.483$ and GRB 200522A at $z=0.554$. These sGRBs demonstrate very different properties in their observed emission and environment. GRB 160624A is associated to a late-type galaxy with an old stellar population ($\approx$3 Gyr) and moderate on-going… ▽ More We present a detailed multi-wavelength analysis of two short Gamma-Ray Bursts (sGRBs) detected by the Neil Gehrels Swift Observatory: GRB 160624A at $z=0.483$ and GRB 200522A at $z=0.554$. These sGRBs demonstrate very different properties in their observed emission and environment. GRB 160624A is associated to a late-type galaxy with an old stellar population ($\approx$3 Gyr) and moderate on-going star formation ($\approx$1 $M_{\odot}$ yr$^{-1}$). Hubble and Gemini limits on optical/nIR emission from GRB 160624A are among the most stringent for sGRBs, leading to tight constraints on the allowed kilonova properties. In particular, we rule out any kilonova brighter than AT2017gfo, disfavoring large masses of wind ejecta ($\lesssim$0.03 $M_\odot$). In contrast, observations of GRB 200522A uncovered a luminous ($L_\textrm{F125W}\approx 10^{42}$ erg s$^{-1}$ at 2.3~d) and red ($r-H\approx 1.3$ mag) counterpart. The red color can be explained either by bright kilonova emission powered by the radioactive decay of a large amount of wind ejecta (0.03 $M_\odot$ $\lesssim$ $M$ $\lesssim$ 0.1 $M_\odot$) or moderate extinction, $E(B-V)\approx0.1-0.2$ mag, along the line of sight. The location of this sGRB in the inner regions of a young ($\approx$0.1 Gyr) star-forming ($\approx$2-6 $M_{\odot}$ yr$^{-1}$) galaxy and the limited sampling of its counterpart do not allow us to rule out dust effects as contributing, at least in part, to the red color. △ Less

Submitted 13 January, 2021; v1 submitted 30 November, 2020; originally announced December 2020.

Comments: MNRAS, In Press

Dynamically Tagged Groups of Very Metal-poor Halo Stars from the HK and Hamburg/ESO Surveys

Authors: Guilherme Limberg, Silvia Rossi, Timothy C. Beers, Hélio D. Perottoni, Angeles Pérez-Villegas, Rafael M. Santucci, Yuri Abuchaim, Vinicius M. Placco, Young Sun Lee, Norbert Christlieb, John E. Norris, Michael S. Bessell, Sean G. Ryan, Ronald Wilhelm, Jaehyon Rhee, Anna Frebel

Abstract: We analyze the dynamical properties of $\sim$1500 very metal-poor (VMP; [Fe/H] $\lesssim -2.0$) halo stars, based primarily on medium-resolution spectroscopic data from the HK and Hamburg/ESO surveys. These data, collected over the past thirty years, are supplemented by a number of calibration stars and other small samples, along with astrometric information from $Gaia$ DR2. We apply a clustering… ▽ More We analyze the dynamical properties of $\sim$1500 very metal-poor (VMP; [Fe/H] $\lesssim -2.0$) halo stars, based primarily on medium-resolution spectroscopic data from the HK and Hamburg/ESO surveys. These data, collected over the past thirty years, are supplemented by a number of calibration stars and other small samples, along with astrometric information from $Gaia$ DR2. We apply a clustering algorithm to the 4-D energy-action space of the sample, and identify a set of 38 Dynamically Tagged Groups (DTGs), containing between 5 and 30 member stars. Many of these DTGs can be associated with previously known prominent substructures such as $Gaia$-Sausage/Enceladus (GSE), Sequoia, the Helmi Stream (HStr), and Thamnos. Others are associated with previously identified smaller dynamical groups of stars and streams. We identify 10 new DTGs as well, many of which have strongly retrograde orbits. We also investigate possible connections between our DTGs and $\sim$300 individual $r$-process-enhanced (RPE) stars from a recent literature compilation. We find that several of these objects have similar dynamical properties to GSE (5), the HStr (4), Sequoia (1), and Rg5 (1), indicating that their progenitors might have been important sources of RPE stars in the Galaxy. Additionally, a number of our newly identified DTGs are shown to be associated with at least two RPE stars each (DTG-2: 3, DTG-7: 2; DTG-27: 2). Taken as a whole, these results are consistent with ultra-faint and/or dwarf spheroidal galaxies as birth environments in which $r$-process nucleosynthesis took place, and then were disrupted by the Milky Way. △ Less

Submitted 26 April, 2021; v1 submitted 16 November, 2020; originally announced November 2020.

Comments: Accepted for ApJ. Tables 5 and 6 available in the online journal. Minor typos fixed and references updated to match published version

Electromagnetic Emission from a Binary Black Hole Merger Remnant in Plasma: Field Alignment and Plasma Temperature

Authors: Bernard J. Kelly, Zachariah B. Etienne, Jacob Golomb, Jeremy D. Schnittman, John G. Baker, Scott C. Noble, Geoffrey Ryan

Abstract: Comparable-mass black-hole mergers generically result in moderate to highly spinning holes, whose spacetime curvature will significantly affect nearby matter in observable ways. We investigate how the moderate spin of a post-merger Kerr black hole immersed in a plasma with initially uniform density and uniform magnetic field affects potentially observable accretion rates and energy fluxes. Varying… ▽ More Comparable-mass black-hole mergers generically result in moderate to highly spinning holes, whose spacetime curvature will significantly affect nearby matter in observable ways. We investigate how the moderate spin of a post-merger Kerr black hole immersed in a plasma with initially uniform density and uniform magnetic field affects potentially observable accretion rates and energy fluxes. Varying the initial specific internal energy of the plasma over two decades, we find very little change in steady-state mass accretion rate or Poynting luminosity, except at the lowest internal energies, where fluxes do not exhibit steady-state behavior during the simulation timescale. Fixing the internal energy and varying the initial fixed magnetic-field amplitude and orientation, we find that the steady-state Poynting luminosity depends strongly on the initial field angle with respect to the black hole spin axis, while the matter accretion rate is more stable until the field angle exceeds $\sim 45\degree$. The proto-jet formed along the black hole spin-axis conforms to a thin, elongated cylinder near the hole, while aligning with the asymptotic magnetic field at large distances. △ Less

Submitted 26 March, 2021; v1 submitted 21 October, 2020; originally announced October 2020.

Comments: 13 pages, 14 figures. Minor changes to match published version

Journal ref: Phys. Rev. D 103, 063039 (2021)

GRB 160625B: Evidence for a Gaussian-Shaped Jet

Authors: Virginia Cunningham, S. Bradley Cenko, Geoffrey Ryan, Stuart N. Vogel, Alessandra Corsi, Antonino Cucchiara, Andrew S. Fruchter, Assaf Horesh, Tuomas Kangas, Daniel Kocevski, Daniel A. Perley, Judith Racusin

Abstract: We present multiwavelength modeling of the afterglow from the long gamma-ray burst GRB 160625B using Markov Chain Monte Carlo (MCMC) techniques of the afterglowpy Python package. GRB 160625B is an extremely bright burst with a rich set of observations spanning from radio to gamma-ray frequencies. These observations range from ~0.1 days to >1000 days, thus making this event extremely well-suited to… ▽ More We present multiwavelength modeling of the afterglow from the long gamma-ray burst GRB 160625B using Markov Chain Monte Carlo (MCMC) techniques of the afterglowpy Python package. GRB 160625B is an extremely bright burst with a rich set of observations spanning from radio to gamma-ray frequencies. These observations range from ~0.1 days to >1000 days, thus making this event extremely well-suited to such modeling. In this work we compare top-hat and Gaussian jet structure types in order to find best fit values for the GRB jet collimation angle, viewing angle, and other physical parameters. We find that a Gaussian-shaped jet is preferred (2.7-5.3 sigma) over the traditional top-hat model. Our estimate for the opening angle of the burst ranges from 1.26 to 3.90 degrees, depending on jet shape model. We also discuss the implications that assumptions on jet shape, viewing angle, and particularly the participation fraction of electrons have on the final estimation of GRB intrinsic energy release and the resulting energy budget of the relativistic outflow. Most notably, allowing the participation fraction to vary results in an estimated total relativistic energy of ~$10^{53}$ erg. This is two orders of magnitude higher than when the total fraction is assumed to be unity, thus this parameter has strong relevance for placing constraints on long GRB central engines, details of the circumburst media, and host environment. △ Less

Submitted 1 December, 2020; v1 submitted 1 September, 2020; originally announced September 2020.

Comments: 29 pages, 10 figures, accepted by ApJ

Journal ref: ApJ 904 (2020) 2

Global Impact of COVID-19 Restrictions on the Atmospheric Concentrations of Nitrogen Dioxide and Ozone

Authors: Christoph A. Keller, Mat. J. Evans, K. Emma Knowland, Christa A. Hasenkopf, Sruti Modekurty, Robert A. Lucchesi, Tomohiro Oda, Bruno B. Franca, Felipe C. Mandarino, M. Valeria Díaz Suárez, Robert G. Ryan, Luke H. Fakes, Steven Pawson

Abstract: Social-distancing to combat the COVID-19 pandemic has led to widespread reductions in air pollutant emissions. Quantifying these changes requires a business as usual counterfactual that accounts for the synoptic and seasonal variability of air pollutants. We use a machine learning algorithm driven by information from the NASA GEOS-CF model to assess changes in nitrogen dioxide (NO$_{2}$) and ozone… ▽ More Social-distancing to combat the COVID-19 pandemic has led to widespread reductions in air pollutant emissions. Quantifying these changes requires a business as usual counterfactual that accounts for the synoptic and seasonal variability of air pollutants. We use a machine learning algorithm driven by information from the NASA GEOS-CF model to assess changes in nitrogen dioxide (NO$_{2}$) and ozone (O$_{3}$) at 5,756 observation sites in 46 countries from January through June 2020. Reductions in NO$_{2}$ correlate with timing and intensity of COVID-19 restrictions, ranging from 60% in severely affected cities (e.g., Wuhan, Milan) to little change (e.g., Rio de Janeiro, Taipei). On average, NO$_{2}$ concentrations were 18% lower than business as usual from February 2020 onward. China experienced the earliest and steepest decline, but concentrations since April have mostly recovered and remained within 5% to the business as usual estimate. NO$_{2}$ reductions in Europe and the US have been more gradual with a halting recovery starting in late March. We estimate that the global NO$_{x}$ (NO+NO$_{2}$) emission reduction during the first 6 months of 2020 amounted to 2.9 TgN, equivalent to 5.1% of the annual anthropogenic total. The response of surface O$_{3}$ is complicated by competing influences of non-linear atmospheric chemistry. While surface O$_{3}$ increased by up to 50% in some locations, we find the overall net impact on daily average O$_{3}$ between February - June 2020 to be small. However, our analysis indicates a flattening of the O$_{3}$ diurnal cycle with an increase in night time ozone due to reduced titration and a decrease in daytime ozone, reflecting a reduction in photochemical production. The O$_{3}$ response is dependent on season, time scale, and environment, with declines in surface O$_{3}$ forecasted if NO$_{x}$ emission reductions continue. △ Less

Submitted 3 August, 2020; originally announced August 2020.

Comments: 32 pages, 17 figures

A thousand days after the merger: continued X-ray emission from GW170817

Authors: E. Troja, H. van Eerten, B. Zhang, G. Ryan, L. Piro, R. Ricci, B. O'Connor, M. H. Wieringa, S. B. Cenko, T. Sakamoto

Abstract: Recent observations with the Chandra X-ray telescope continue to detect X-ray emission from the transient GW170817. In a total exposure of 96.6 ks, performed between March 9 and March 16 2020 (935 d to 942 d after the merger), a total of 8 photons are measured at the source position, corresponding to a significance of about 5 sigma. Radio monitoring with the Australian Telescope Compact Array (ATC… ▽ More Recent observations with the Chandra X-ray telescope continue to detect X-ray emission from the transient GW170817. In a total exposure of 96.6 ks, performed between March 9 and March 16 2020 (935 d to 942 d after the merger), a total of 8 photons are measured at the source position, corresponding to a significance of about 5 sigma. Radio monitoring with the Australian Telescope Compact Array (ATCA) shows instead that the source has faded below our detection threshold (<33 uJy, 3 sigma). By assuming a constant spectral index beta=0.585, we derive an unabsorbed X-ray flux of approximately 1.4E-15 erg/cm^2/s, higher than earlier predictions, yet still consistent with a simple structured jet model. We discuss possible scenarios that could account for prolonged emission in X-rays. The current dataset appears consistent both with energy injection by a long-lived central engine and with the onset of a kilonova afterglow, arising from the interaction of the sub-relativistic merger ejecta with the surrounding medium. Long-term monitoring of this source will be essential to test these different models. △ Less

Submitted 1 June, 2020; originally announced June 2020.

Comments: 10 pages, 6 figures, 2 tables, submitted to MNRAS

Learning Nonlinear Loop Invariants with Gated Continuous Logic Networks (Extended Version)

Authors: Jianan Yao, Gabriel Ryan, Justin Wong, Suman Jana, Ronghui Gu

Abstract: Verifying real-world programs often requires inferring loop invariants with nonlinear constraints. This is especially true in programs that perform many numerical operations, such as control systems for avionics or industrial plants. Recently, data-driven methods for loop invariant inference have shown promise, especially on linear invariants. However, applying data-driven inference to nonlinear l… ▽ More Verifying real-world programs often requires inferring loop invariants with nonlinear constraints. This is especially true in programs that perform many numerical operations, such as control systems for avionics or industrial plants. Recently, data-driven methods for loop invariant inference have shown promise, especially on linear invariants. However, applying data-driven inference to nonlinear loop invariants is challenging due to the large numbers of and magnitudes of high-order terms, the potential for overfitting on a small number of samples, and the large space of possible inequality bounds. In this paper, we introduce a new neural architecture for general SMT learning, the Gated Continuous Logic Network (G-CLN), and apply it to nonlinear loop invariant learning. G-CLNs extend the Continuous Logic Network (CLN) architecture with gating units and dropout, which allow the model to robustly learn general invariants over large numbers of terms. To address overfitting that arises from finite program sampling, we introduce fractional sampling---a sound relaxation of loop semantics to continuous functions that facilitates unbounded sampling on real domain. We additionally design a new CLN activation function, the Piecewise Biased Quadratic Unit (PBQU), for naturally learning tight inequality bounds. We incorporate these methods into a nonlinear loop invariant inference system that can learn general nonlinear loop invariants. We evaluate our system on a benchmark of nonlinear loop invariants and show it solves 26 out of 27 problems, 3 more than prior work, with an average runtime of 53.3 seconds. We further demonstrate the generic learning ability of G-CLNs by solving all 124 problems in the linear Code2Inv benchmark. We also perform a quantitative stability evaluation and show G-CLNs have a convergence rate of $97.5\%$ on quadratic problems, a $39.2\%$ improvement over CLN models. △ Less

Submitted 25 June, 2020; v1 submitted 17 March, 2020; originally announced March 2020.

Journal ref: In Proceedings of the 41st ACM SIGPLAN Conference on Programming Language Design and Implementation, pp. 106-120. 2020

Gamma-Ray Burst Afterglows In The Multi-Messenger Era: Numerical Models and Closure Relations

Authors: Geoffrey Ryan, Hendrik van Eerten, Luigi Piro, Eleonora Troja

Abstract: Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a larger inclination than GRBs without gravitational wave detections. As demonstrated by the afterglow of GW170817, this requires an extension of the common GRB afterglow models which typically assume emission from an on-axis top hat jet. We present a characterization of the afterglows… ▽ More Gamma-ray bursts (GRBs) associated with gravitational wave events are, and will likely continue to be, viewed at a larger inclination than GRBs without gravitational wave detections. As demonstrated by the afterglow of GW170817, this requires an extension of the common GRB afterglow models which typically assume emission from an on-axis top hat jet. We present a characterization of the afterglows arising from structured jets, providing a framework covering both successful and choked jets. We compute new closure relations for structured jets and compare with the established relations for energy injection and refreshed shock models. The temporal slope before the jet break is found to be a simple function of the ratio between the viewing angle and effective opening angle of the jet. A numerical model to calculate synthetic light curves and spectra is publicly available as the open source Python package afterglowpy. △ Less

Submitted 25 September, 2019; originally announced September 2019.

Comments: 29 pages, 13 figures, submitted to ApJ

CLN2INV: Learning Loop Invariants with Continuous Logic Networks

Authors: Gabriel Ryan, Justin Wong, Jianan Yao, Ronghui Gu, Suman Jana

Abstract: Program verification offers a framework for ensuring program correctness and therefore systematically eliminating different classes of bugs. Inferring loop invariants is one of the main challenges behind automated verification of real-world programs which often contain many loops. In this paper, we present Continuous Logic Network (CLN), a novel neural architecture for automatically learning loop… ▽ More Program verification offers a framework for ensuring program correctness and therefore systematically eliminating different classes of bugs. Inferring loop invariants is one of the main challenges behind automated verification of real-world programs which often contain many loops. In this paper, we present Continuous Logic Network (CLN), a novel neural architecture for automatically learning loop invariants directly from program execution traces. Unlike existing neural networks, CLNs can learn precise and explicit representations of formulas in Satisfiability Modulo Theories (SMT) for loop invariants from program execution traces. We develop a new sound and complete semantic mapping for assigning SMT formulas to continuous truth values that allows CLNs to be trained efficiently. We use CLNs to implement a new inference system for loop invariants, CLN2INV, that significantly outperforms existing approaches on the popular Code2Inv dataset. CLN2INV is the first tool to solve all 124 theoretically solvable problems in the Code2Inv dataset. Moreover, CLN2INV takes only 1.1 seconds on average for each problem, which is 40 times faster than existing approaches. We further demonstrate that CLN2INV can even learn 12 significantly more complex loop invariants than the ones required for the Code2Inv dataset. △ Less

Submitted 17 October, 2019; v1 submitted 25 September, 2019; originally announced September 2019.

Fine Grained Dataflow Tracking with Proximal Gradients

Authors: Gabriel Ryan, Abhishek Shah, Dongdong She, Koustubha Bhat, Suman Jana

Abstract: Dataflow tracking with Dynamic Taint Analysis (DTA) is an important method in systems security with many applications, including exploit analysis, guided fuzzing, and side-channel information leak detection. However, DTA is fundamentally limited by the Boolean nature of taint labels, which provide no information about the significance of detected dataflows and lead to false positives/negatives on… ▽ More Dataflow tracking with Dynamic Taint Analysis (DTA) is an important method in systems security with many applications, including exploit analysis, guided fuzzing, and side-channel information leak detection. However, DTA is fundamentally limited by the Boolean nature of taint labels, which provide no information about the significance of detected dataflows and lead to false positives/negatives on complex real world programs. We introduce proximal gradient analysis (PGA), a novel, theoretically grounded approach that can track more accurate and fine-grained dataflow information. PGA uses proximal gradients, a generalization of gradients for non-differentiable functions, to precisely compose gradients over non-differentiable operations in programs. Composing gradients over programs eliminates many of the dataflow propagation errors that occur in DTA and provides richer information about how each measured dataflow effects a program. We compare our prototype PGA implementation to three state of the art DTA implementations on 7 real-world programs. Our results show that PGA can improve the F1 accuracy of data flow tracking by up to 33% over taint tracking (20% on average) without introducing any significant overhead (<5% on average). We further demonstrate the effectiveness of PGA by discovering 22 bugs (20 confirmed by developers) and 2 side-channel leaks, and identifying exploitable dataflows in 19 existing CVEs in the tested programs. △ Less

Submitted 24 February, 2021; v1 submitted 8 September, 2019; originally announced September 2019.

Comments: To appear in USENIX Security 2021