arXiv subjects

Armin Rest

Publications and source records attributed to Armin Rest.

At least 109 records · Page 6Linked to original sources

arXiv2022

Toward automated detection of light echoes in synoptic surveys: considerations on the application of the Deep Convolutional Neural Networks

Light Echoes (LEs) are the reflections of astrophysical transients off of interstellar dust. They are fascinating astronomical phenomena that enable studies of the scattering dust as well as of the original transients. LEs, however, are rare and extremely difficult to detect as they appear as faint, diffuse, time-evolving features. The detection of LEs still largely relies on human inspection of images, a method unfeasible in the era of large synoptic surveys. The Vera C. Rubin Observatory Legacy Survey of Space and Time, LSST, will generate an unprecedented amount of astronomical imaging data at high spatial resolution, exquisite image quality, and over tens of thousands of square degrees of sky: an ideal survey for LEs. However, the Rubin data processing pipelines are optimized for the detection of point-sources and will entirely miss LEs. Over the past several years, Artificial Intelligence (AI) object detection frameworks have achieved and surpassed real-time, human-level performance. In this work, we prepare a dataset from the ATLAS telescope and test a popular AI object detection framework, You Only Look Once, or YOLO, developed in the computer vision community, to demonstrate the potential of AI in the detection of LEs in astronomical images. We find that an AI framework can reach human-level performance even with a size- and quality-limited dataset. We explore and highlight challenges, including class imbalance and label incompleteness, and roadmap the work required to build an end-to-end pipeline for the automated detection and study of LEs in high-throughput astronomical surveys.

astro-ph.IM↗

arXiv2022

Weak Mass Loss from the Red Supergiant Progenitor of the Type II SN 2021yja

We present high-cadence optical, ultraviolet (UV), and near-infrared data of the nearby ($D\approx23$ Mpc) Type II supernova (SN) 2021yja. Many Type II SNe show signs of interaction with circumstellar material (CSM) during the first few days after explosion, implying that their red supergiant (RSG) progenitors experience episodic or eruptive mass loss. However, because it is difficult to discover SNe early, the diversity of CSM configurations in RSGs has not been fully mapped. SN 2021yja, first detected within ${\approx}5.4$ hours of explosion, shows some signatures of CSM interaction (high UV luminosity, radio and x-ray emission) but without the narrow emission lines or early light curve peak that can accompany CSM. Here we analyze the densely sampled early light curve and spectral series of this nearby SN to infer the properties of its progenitor and CSM. We find that the most likely progenitor was an RSG with an extended envelope, encompassed by low-density CSM. We also present archival Hubble Space Telescope imaging of the host galaxy of SN 2021yja, which allows us to place a stringent upper limit of ${\lesssim}9\ M_\odot$ on the progenitor mass. However, this is in tension with some aspects of the SN evolution, which point to a more massive progenitor. Our analysis highlights the need to consider progenitor structure when making inferences about CSM properties, and that a comprehensive view of CSM tracers should be made to give a fuller view of the last years of RSG evolution.

astro-ph.HE↗

arXiv2022

The origins of Calcium-rich supernovae from disruptions of CO white-dwarfs by hybrid He-CO white-dwarfs

Calcium-rich (SN 2005E-like) explosions are very faint (typical -15.5, type I supernovae (SNe) showing strong Ca-lines, mostly observed in old stellar environments. Several models for such SNe had been explored and debated, but non were able to consistently reproduce the observed properties of Ca-rich SNe, nor their rates and host-galaxy distributions. Here we show that the disruptions of low-mass carbon-oxygen (CO) white dwarfs (WDs) by hybrid Helium-CO (HeCO) WDs during their merger could explain the origin and properties of such SNe. We make use of detailed multi-dimensional hydrodynamical-thermonuclear (FLASH) simulations models of HeCO-CO WD-WD mergers to characterize such explosions. We find that the accretion of CO material onto a HeCO-WD heats its He-shell and eventually leads to its "weak" detonation and ejection and the production of a sub-energetic $\sim10^{49}$erg Ca-rich SN, while leaving the CO core of the HeCO-WD intact as a hot remnant white dwarf, possibly giving rise to X-ray emission as it cools down. We model the detailed light-curve and spectra of such explosions to find an excellent agreement with observations of Ia/c Ca-rich SNe. In these models most of the He is burned, producing Ia/c Ca-rich SNe but higher He-enrichment levels might potentially also explain the Ib Ca-rich SNe. We thereby provide a viable, consistent model for the origins of Ca-rich. These findings can shed new light on the role of Ca-rich in the chemical evolution of galaxies and the intra-cluster medium, and their contribution to the observed 511 kev signal in the Galaxy originating from positrons produced from ${}^{44}\textrm{Ti}$ decay. Finally, the origins of such SNe points to the key-role of HeCO WDs as SN progenitors, and their potential role as progenitors of other thermonuclear SNe including normal type Ia SNe.

astro-ph.HE↗

arXiv2022

Searching for a Hypervelocity White Dwarf Companion: A Proper Motion Survey of SN 1006

Type Ia Supernovae (SNe Ia) are securely understood to come from the thermonuclear explosion of a white dwarf as a result of binary interaction, but the nature of that binary interaction and the secondary object is uncertain. Recently, a double white dwarf model known as the dynamically driven double-degenerate double-detonation (D6) model has become a promising explanation for these events. One realization of this scenario predicts that the companion may survive the explosion and reside within the remnant as a fast moving ($V_{peculiar} >1000$ km s$^{-1}$), overluminous ($L > 0.1 L_\odot$) white dwarf. Recently, three objects which appear to have these unusual properties have been discovered in the Gaia survey. We obtained photometric observations of the SN Ia remnant SN 1006 with the Dark Energy Camera over four years to attempt to discover a similar star. We present a deep, high precision astrometric proper motion survey of the interior stellar population of the remnant. We rule out the existence of a high proper motion object consistent with our tested realization of the D6 scenario ($V_{transverse} > 600$ km s$^{-1}$ with $m_r < 21$ corresponding to an intrinsic luminosity of $L > 0.0176 L_\odot$). We conclude that such a star does not exist within the remnant, or is hidden from detection by either strong localized dust or the unlikely possibility of ejection from the binary system near parallel to the line of sight.

astro-ph.SR↗

arXiv2022

SOAR/Goodman Spectroscopic Assessment of Candidate Counterparts of the LIGO-Virgo Event GW190814

On 2019 August 14 at 21:10:39 UTC, the LIGO/Virgo Collaboration (LVC) detected a possible neutron star-black hole merger (NSBH), the first ever identified. An extensive search for an optical counterpart of this event, designated GW190814, was undertaken using the Dark Energy Camera (DECam) on the 4m Victor M. Blanco Telescope at the Cerro Tololo Inter-American Observatory. Target of Opportunity interrupts were issued on 8 separate nights to observe 11 candidates using the 4.1m Southern Astrophysical Research (SOAR) telescope's Goodman High Throughput Spectrograph in order to assess whether any of these transients was likely to be an optical counterpart of the possible NSBH merger. Here, we describe the process of observing with SOAR, the analysis of our spectra, our spectroscopic typing methodology, and our resultant conclusion that none of the candidates corresponded to the gravitational wave merger event but were all instead other transients. Finally, we describe the lessons learned from this effort. Application of these lessons will be critical for a successful community spectroscopic follow-up program for LVC observing run 4 (O4) and beyond.

astro-ph.HE↗

arXiv2022

Target of Opportunity Observations of Gravitational Wave Events with Vera C. Rubin Observatory

The discovery of the electromagnetic counterpart to the binary neutron star merger GW170817 has opened the era of gravitational-wave multi-messenger astronomy. Rapid identification of the optical/infrared kilonova enabled a precise localization of the source, which paved the way to deep multi-wavelength follow-up and its myriad of related science results. Fully exploiting this new territory of exploration requires the acquisition of electromagnetic data from samples of neutron star mergers and other gravitational wave sources. After GW170817, the frontier is now to map the diversity of kilonova properties and provide more stringent constraints on the Hubble constant, and enable new tests of fundamental physics. The Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) can play a key role in this field in the 2020s, when an improved network of gravitational-wave detectors is expected to reach a sensitivity that will enable the discovery of a high rate of merger events involving neutron stars (about tens per year) out to distances of several hundred Mpc. We design comprehensive target-of-opportunity observing strategies for follow-up of gravitational-wave triggers that will make the Rubin Observatory the premier instrument for discovery and early characterization of neutron star and other compact object mergers, and yet unknown classes of gravitational wave events.

astro-ph.HE↗

arXiv2022

The Circumstellar Environments of Double-Peaked, Calcium-strong Supernovae 2021gno and 2021inl

We present panchromatic observations and modeling of calcium-strong supernovae (SNe) 2021gno in the star-forming host galaxy NGC 4165 (D = 30.5 Mpc) and 2021inl in the outskirts of elliptical galaxy NGC 4923 (D = 80 Mpc), both monitored through the Young Supernova Experiment (YSE) transient survey. The multi-color light curves of both SNe show two peaks, the former peak being derived from shock cooling emission (SCE) and/or shock interaction with circumstellar material (CSM). The primary peak in SN 2021gno is coincident with luminous, rapidly decaying X-ray emission ($L_x = 5 \times 10^{41}$ erg s$^{-1}$) detected by Swift-XRT at $δt = 1$ day after explosion, this observation being the second ever detection of X-rays from a calcium-strong transient. We interpret the X-ray emission from SN 2021gno in the context of shock interaction with dense CSM that extends to $r < 3 \times 10^{14}$ cm. Based on modeling of the SN 2021gno X-ray spectrum, we calculate a CSM mass range of $M_{\rm CSM} = (0.3 - 1.6) \times 10^{-3}$ M$_{\odot}$ and particle densities of $n = (1-4) \times 10^{10}$ cm$^{-3}$. Radio non-detections of SN 2021gno indicate a low-density environment at larger radii ($r > 10^{16}$ cm) and a progenitor mass loss rate of $\dot{M} < 10^{-4}$ M$_{\odot}$ yr$^{-1}$, for $v_w = 500$ km s$^{-1}$. For radiation derived from SCE, modeling of the primary light curve peak in both SNe indicates an extended progenitor envelope mass and radius of $M_e = 0.02 - 0.05$ M$_{\odot}$ and $R_e = 30 - 230$ R$_{\odot}$. The explosion properties of SNe 2021gno and 2021inl suggest progenitor systems containing either a low-mass massive star or a white dwarf (WD), the former being unlikely for either object given the lack of star formation at both explosion sites. Furthermore, the progenitor environments of both SNe are consistent with explosion models for low-mass hybrid He/C/O WD + C/O WD binaries.

astro-ph.HE↗

arXiv2022

The Candidate Progenitor Companion Star of the Type Ib/c SN 2013ge

This Letter presents the detection of a source at the position of the Type Ib/c supernova (SN) 2013ge more than four years after the radioactive component is expected to have faded. This source could mark the first post-SN direct detection of a surviving companion to a stripped-envelope Type Ib/c explosion. We test this hypothesis and find the shape of the source's spectral energy distribution is most consistent with that of a B5 I supergiant. While binary models tend to predict OB-type stars for stripped-envelope companions, the location of the source on a color-magnitude diagram (CMD) places it redward of its more likely position on the main sequence (MS). The source may be temporarily out of thermal equilibrium, or a cool and inflated non-MS companion, which is similar to the suggested companion of Type Ib SN 2019yvr that was constrained from pre-SN imaging. We also consider other possible physical scenarios for the source, including a fading SN, circumstellar shock interaction, line of site coincidence, and an unresolved host star cluster, all of which will require future observations to more definitively rule out. Ultimately, the fraction of surviving companions ("binary fraction") will provide necessary constraints on binary evolution models and the underlying physics.

astro-ph.HE↗

arXiv2022

The Pantheon+ Analysis: The Full Dataset and Light-Curve Release

Here we present 1701 light curves of 1550 spectroscopically confirmed Type Ia supernovae (SNe Ia) that will be used to infer cosmological parameters as part of the Pantheon+ SN analysis and the SH0ES (Supernovae and H0 for the Equation of State of dark energy) distance-ladder analysis. This effort is one part of a series of works that perform an extensive review of redshifts, peculiar velocities, photometric calibration, and intrinsic-scatter models of SNe Ia. The total number of light curves, which are compiled across 18 different surveys, is a significant increase from the first Pantheon analysis (1048 SNe), particularly at low redshift ($z$). Furthermore, unlike in the Pantheon analysis, we include light curves for SNe with $z<0.01$ such that SN systematic covariance can be included in a joint measurement of the Hubble constant (H$_0$) and the dark energy equation-of-state parameter ($w$). We use the large sample to compare properties of 151 SNe Ia observed by multiple surveys and 12 pairs/triplets of "SN siblings" - SNe found in the same host galaxy. Distance measurements, application of bias corrections, and inference of cosmological parameters are discussed in the companion paper by Brout et al. (2022b), and the determination of H$_0$ is discussed by Riess et al. (2022). These analyses will measure w with $\sim3\%$ precision and H$_0$ with 1 km/s/Mpc precision.

astro-ph.CO↗

arXiv2022

Locating the CSM Emission within the Type Ia Supernova Remnant N103B

We present results from deep Chandra observations of the young Type Ia supernova remnant (SNR) 0509-68.7, also known as N103B, located in the Large Magellanic cloud (LMC). The remnant displays an asymmetry in brightness, with the western hemisphere appearing significantly brighter than the eastern half. Previous multi-wavelength observations have attributed the difference to a density gradient and suggested circumstellar material origins, drawing similarities to Kepler's SNR. We apply a clustering technique combined with traditional imaging analysis to spatially locate various emission components within the remnant. We find that O and Mg emission is strongest along the blast wave, and coincides with Spitzer observations of dust emission and optical emission from the non-radiative shocks. The abundances of O and Mg in these regions are enhanced relative to the average LMC abundances and appear as a distinct spatial distribution compared to the ejecta products, supporting the circumstellar medium (CSM) interpretation. We also find that the spatial distribution of Cr is identical to that of Fe in the interior of the remnant, and does not coincide at all with the O and Mg emission.

astro-ph.HE↗

arXiv2021

SN 2018agk: A Prototypical Type Ia Supernova with a Smooth Power-law Rise in Kepler (K2)

We present the 30-min cadence Kepler/K2 light curve of the Type Ia supernova (SN Ia) SN 2018agk, covering approximately one week before explosion, the full rise phase and the decline until 40 days after peak. We additionally present ground-based observations in multiple bands within the same time range, including the 1-day cadence DECam observations within the first $\sim$5 days after the first light. The Kepler early light curve is fully consistent with a single power-law rise, without evidence of any bump feature. We compare SN 2018agk with a sample of other SNe~Ia without early excess flux from the literature. We find that SNe Ia without excess flux have slowly-evolving early colors in a narrow range ($g-i\approx -0.20\pm0.20$ mag) within the first $\sim 10$ days. On the other hand, among SNe Ia detected with excess, SN 2017cbv and SN 2018oh tend to be bluer, while iPTF16abc's evolution is similar to normal SNe Ia without excess in $g-i$. We further compare the Kepler light curve of SN 2018agk with companion-interaction models, and rule out the existence of a typical non-degenerate companion undergoing Roche-lobe overflow at viewing angles smaller than $45^{\circ}$.

astro-ph.HE↗

arXiv2021

A Carbon/Oxygen-dominated Atmosphere Days After Explosion for the "Super-Chandrasekhar" Type Ia SN 2020esm

Seeing pristine material from the donor star in a Type Ia supernova (SN Ia) explosion can reveal the nature of the binary system. In this paper, we present photometric and spectroscopic observations of SN 2020esm, one of the best-studied SNe of the class of "super-Chandrasekhar" SNe Ia (SC SNe Ia), with data obtained $-12$ to +360 days relative to peak brightness, obtained from a variety of ground- and space-based telescopes. Initially misclassified as a Type II supernova, SN 2020esm peaked at $M_{B} = -19.9$ mag, declined slowly ($Δm_{15}(B) = 0.92$ mag), and had particularly blue UV and optical colors at early times. Photometrically and spectroscopically, SN 2020esm evolved similarly to other SC SNe Ia, showing the usual low ejecta velocities, weak intermediate mass elements (IMEs), and the enhanced fading at late times, but its early spectra are unique. Our first few spectra (corresponding to a phase of $\gtrsim$10~days before peak) reveal a nearly-pure carbon/oxygen atmosphere during the first days after explosion. This composition can only be produced by pristine material, relatively unaffected by nuclear burning. The lack of H and He may further indicate that SN 2020esm is the outcome of the merger of two carbon/oxygen white dwarfs (WDs). Modeling its bolometric light curve, we find a $^{56}$Ni mass of $1.23^{+0.14}_{-0.14}$ M$_{\odot}$ and an ejecta mass of $1.75^{+0.32}_{-0.20}$ M$_{\odot}$, in excess of the Chandrasekhar mass. Finally, we discuss possible progenitor systems and explosion mechanisms of SN 2020esm and, in general, the SC SNe Ia class.

astro-ph.HE↗

arXiv2021

Final Moments I: Precursor Emission, Envelope Inflation, and Enhanced Mass loss Preceding the Luminous Type II Supernova 2020tlf

We present panchromatic observations and modeling of supernova (SN) 2020tlf, the first normal type II-P/L SN with confirmed precursor emission, as detected by the Young Supernova Experiment transient survey with the Pan-STARRS1 telescope. Pre-explosion emission was detected in $riz-$bands at 130 days prior to SN 2020tlf and persisted at relatively constant flux until first light. Soon after discovery, "flash" spectroscopy of SN 2020tlf revealed prominent narrow symmetric emission lines ($v_w < 300$ km s$^{-1}$) that resulted from the photo-ionization of unshocked circumstellar material (CSM) shedded in progenitor mass loss episodes in the final weeks to months before explosion. Surprisingly, this novel display of pre-SN emission and associated mass loss occurred in a RSG progenitor with ZAMS mass of only 10-12 M$_{\odot}$, as inferred from nebular spectra. Modeling of the light curve and multi-epoch spectra with the non-LTE radiative transfer code CMFGEN and radiation-hydrodynamical (RHD) code HERACLES suggests a dense CSM limited to $r \approx 10^{15}$ cm, and mass loss rate of $10^{-2}$ M$_{\odot}$ yr$^{-1}$. The subsequent luminous light-curve plateau and persistent blue excess indicates an extended progenitor, compatible with a RSG model with $R_{\star} = 1100$ R$_{\odot}$. Inferences from the limits on the shock-powered X-ray and radio luminosity are consistent with these conclusions and suggest a CSM density of $ρ< 2 \times 10^{-16}$ g cm$^{-3}$ for distances of $r \approx 5 \times 10^{15}$ cm, as well as a mass loss rate of $\dot M<1.3 \times 10^{-5}\,\rm{M_{\odot}\,yr^{-1}}$ at larger distances. A promising power source for the observed precursor emission is the ejection of stellar material following energy disposition into the stellar envelope as a result of gravity waves emitted during either neon/oxygen burning or a nuclear flash from silicon combustion.

astro-ph.HE↗

arXiv2021

Updated Photometry of the Yellow Supergiant Progenitor and Late-time Observations of the Type IIb Supernova 2016gkg

We present Hubble Space Telescope (HST) observations of the type IIb supernova (SN) 2016gkg at 652, 1698, and 1795 days with the Advanced Camera for Surveys (ACS) and Wide Field Camera 3 (WFC3). Comparing to pre-explosion imaging from 2001 obtained with the Wide Field Planetary Camera 2, we demonstrate that SN 2016gkg is now fainter than its candidate counterpart in the latest WFC3 imaging, implying that the counterpart has disappeared and confirming that it was the SN progenitor star. We show the latest light curve and Keck spectra of SN 2016gkg, which implies that SN 2016gkg is declining more slowly than the expected rate for ${}^{56}$Co decay during its nebular phase. We find that this emission is too luminous to be powered by other radioisotopes, thus we infer that SN 2016gkg is entering a new phase in its evolution where it is powered primarily by interaction with circumstellar matter. Finally, we re-analyze the progenitor star spectral energy distribution and late-time limits in the context of binary evolution models and including emission from a potential companion star and find that all companion stars would be fainter than our limiting magnitudes.

astro-ph.HE↗

arXiv2021

An Early-Time Optical and Ultraviolet Excess in the type-Ic SN 2020oi

We present photometric and spectroscopic observations of Supernova 2020oi (SN 2020oi), a nearby ($\sim$17 Mpc) type-Ic supernova (SN Ic) within the grand-design spiral M100. We undertake a comprehensive analysis to characterize the evolution of SN 2020oi and constrain its progenitor system. We detect flux in excess of the fireball rise model $δt \approx 2.5$ days from the date of explosion in multi-band optical and UV photometry from the Las Cumbres Observatory and the Neil Gehrels Swift Observatory, respectively. The derived SN bolometric luminosity is consistent with an explosion with $M_{\rm ej} = 0.81 \pm 0.03 M_{\odot}$, $E_{k}= 0.79 \pm 0.09 \times 10^{51} \rm{erg} \rm{s}^{-1}$, and $M_{\rm Ni56} = 0.08 \pm 0.02 M_{\odot}$. Inspection of the event's decline reveals the highest $Δm_{15,\rm{bol}}$ reported for a stripped-envelope event to date. Modeling of optical spectra near event peak indicates a partially mixed ejecta comparable in composition to the ejecta observed in SN 1994I, while the earliest spectrum shows signatures of a possible interaction with material of a distinct composition surrounding the SN progenitor. Further, Hubble Space Telescope (HST) pre-explosion imaging reveals a stellar cluster coincident with the event. From the cluster photometry, we derive the mass and age of the SN progenitor using stellar evolution models implemented in the BPASS library. Our results indicate that SN 2020oi occurred in a binary system from a progenitor of mass $M_{\rm ZAMS} \approx 9.5 \pm 1.0 M_{\odot}$, corresponding to an age of $27 \pm 7$ Myr. SN 2020oi is the dimmest SN Ic event to date for which an early-time flux excess has been observed, and the first in which an early excess is unlikely to be associated with shock-cooling.

astro-ph.HE↗

arXiv2021

Progenitor and Close-In Circumstellar Medium of Type II Supernova 2020fqv from High-Cadence Photometry and Ultra-Rapid UV Spectroscopy

We present observations of SN 2020fqv, a Virgo-cluster Type II core-collapse supernova (CCSN) with a high temporal resolution light curve from the Transiting Exoplanet Survey Satellite (TESS) covering the time of explosion; ultraviolet (UV) spectroscopy from the Hubble Space Telescope (HST) starting 3.3 days post-explosion; ground-based spectroscopic observations starting 1.1~days post-explosion; along with extensive photometric observations. Massive stars have complicated mass-loss histories leading up to their death as CCSNe, creating circumstellar medium (CSM) with which the SNe interact. Observations during the first few days post-explosion can provide important information about the mass-loss rate during the late stages of stellar evolution. Model fits to the quasi-bolometric light curve of SN 2020fqv reveal ~0.23 $M_{\odot}$ of CSM confined within ~1450 $R_{\odot}$ ($10^{14}$ cm) from its progenitor star. Early spectra (<4 days post-explosion), both from HST and ground-based observatories, show emission features from high-ionization metal species from the outer, optically thin part of this CSM. We find that the CSM is consistent with an eruption caused by the injection of $\sim$$5\times 10^{46}$ erg into the stellar envelope $\sim$300 days pre-explosion, potentially from a nuclear burning instability at the onset of oxygen burning. Light-curve fitting, nebular spectroscopy, and pre-explosion \textit{HST} imaging consistently point to a red supergiant (RSG) progenitor with $M_{\rm ZAMS}$$\approx$$13.5$--$15 \, M_{\odot}$, typical for SN~II progenitor stars. This finding demonstrates that a typical RSG, like the progenitor of SN 2020fqv, has a complicated mass-loss history immediately before core collapse.

astro-ph.SR↗

arXiv2021

AT 2019qyl in NGC 300: Internal Collisions in the Early Outflow from a Very Fast Nova in a Symbiotic Binary

Nova eruptions, thermonuclear explosions on the surfaces of white dwarfs (WDs), are now recognized to be among the most common shock-powered astrophysical transients. We present the early discovery and rapid ultraviolet (UV), optical, and infrared (IR) temporal development of AT 2019qyl, a recent nova in the nearby Sculptor Group galaxy NGC 300. The light curve shows a rapid rise lasting $\lesssim 1$ day, reaching a peak absolute magnitude of $M_V = -9.2$ mag, and a very fast decline, fading by 2 mag over 3.5 days. A steep dropoff in the light curves after 71 days and the rapid decline timescale suggest a low-mass ejection from a massive WD with $M_{\rm WD} \gtrsim 1.2~M_{\odot}$. We present an unprecedented view of the early spectroscopic evolution of such an event. Three spectra prior to the peak reveal a complex, multicomponent outflow giving rise to internal collisions and shocks in the ejecta of an He/N-class nova. We identify a coincident IR-variable counterpart in the extensive preeruption coverage of the transient location and infer the presence of a symbiotic progenitor system with an O-rich asymptotic-giant-branch donor star, as well as evidence for an earlier UV-bright outburst in 2014. We suggest that AT 2019qyl is analogous to the subset of Galactic recurrent novae with red-giant companions such as RS Oph and other embedded nova systems like V407 Cyg. Our observations provide new evidence that internal shocks between multiple, distinct outflow components likely contribute to the generation of the shock-powered emission from such systems.

astro-ph.SR↗

arXiv2021

The Gravity Collective: A Search for the Electromagnetic Counterpart to the Neutron Star-Black Hole Merger GW190814

We present optical follow-up imaging obtained with the Katzman Automatic Imaging Telescope, Las Cumbres Observatory Global Telescope Network, Nickel Telescope, Swope Telescope, and Thacher Telescope of the LIGO/Virgo gravitational wave (GW) signal from the neutron star-black hole (NSBH) merger GW190814. We searched the GW190814 localization region (19 deg$^{2}$ for the 90th percentile best localization), covering a total of 51 deg$^{2}$ and 94.6% of the two-dimensional localization region. Analyzing the properties of 189 transients that we consider as candidate counterparts to the NSBH merger, including their localizations, discovery times from merger, optical spectra, likely host-galaxy redshifts, and photometric evolution, we conclude that none of these objects are likely to be associated with GW190814. Based on this finding, we consider the likely optical properties of an electromagnetic counterpart to GW190814, including possible kilonovae and short gamma-ray burst afterglows. Using the joint limits from our follow-up imaging, we conclude that a counterpart with an $r$-band decline rate of 0.68 mag day$^{-1}$, similar to the kilonova AT 2017gfo, could peak at an absolute magnitude of at most $-17.8$ mag (50% confidence). Our data are not constraining for ''red'' kilonovae and rule out ''blue'' kilonovae with $M>0.5 M_{\odot}$ (30% confidence). We strongly rule out all known types of short gamma-ray burst afterglows with viewing angles $<$17$^{\circ}$ assuming an initial jet opening angle of $\sim$$5.2^{\circ}$ and explosion energies and circumburst densities similar to afterglows explored in the literature. Finally, we explore the possibility that GW190814 merged in the disk of an active galactic nucleus, of which we find four in the localization region, but we do not find any candidate counterparts among these sources.

astro-ph.HE↗