arXiv subjects

Adelle J. Goodwin

Publications and source records attributed to Adelle J. Goodwin.

At least 19 recordsLinked to original sources

arXiv2026

Constraining neutron-star properties with ensembles of thermonuclear bursts: application to SRGA J144459.2-604207

Deducing the properties of the host neutron stars from thermonuclear (type-I) X-ray bursts remains a challenge, due to incomplete data, multidimensional parameter space, and dearth of suitable models and analysis tools. Here we describe further development of the BEANSP package, with a new "ensemble" analysis mode utilising the consistent and regular "clocked" bursting exhibited by some sources. This mode requires only one model evaluation per epoch, and so is much more efficient than the previous "train" mode. We apply the code to the best-known source exhibiting "clocked" bursting, GS 1826-24, utilising a grid of KEPLER models pre-calculated for this purpose, and find good agreement with a previous study. We performed experiments on simulated data, and recovered input parameters related to the burst ignition with reasonable accuracy, but less so for the system distance, emission anisotropy and neutron star mass and radius. Finally, we assembled a set of 14 daily burst epochs covering the 2024 outburst of the accretion-powered millisecond pulsar SRGA J144459.2-604207, and attempted to constrain the system properties of this object by comparing to SETTLE model predictions. We find reasonably good agreement between the observations and model predictions for a mildly sub-solar fuel composition, with H-fraction $X\approx0.54$ and CNO metallicity $Z_{\rm CNO}\approx0.01$. However, we note that the inferred H-fraction is in excess of the limit of 0.4 established separately, and the adopted model may not provide sufficiently accurate predictions for this burst ignition regime. The inferred distance depends on assumptions about the system inclination and corresponding anisotropy of the persistent emission, and is likely in the range 6-11 kpc. Future applications with more physically realistic models are a promising avenue for this and other sources with H-rich bursts.

astro-ph.HE↗

arXiv2026

SKAO and Gamma-Ray Synergies

A wide variety of Galactic and extragalactic sources are known to emitradiation across the entire electromagnetic spectrum, including both transient and steady-state phenomena. A few hundred of these sources (~300) have been detected even at the highest energies, in the TeV range. The number of known TeV emitters is expected to increase substantially in the coming years with the operation of current and next-generation Cherenkov detectors, such as the Large High Altitude Air Shower Observatory (LHAASO) and the Cherenkov Telescope Array Observatory (CTAO). These sources typically exhibit broad, non-thermal, spectral energy distributions. Explaining such emission requires efficient particle acceleration mechanisms (e.g. Fermi processes, shock acceleration) and radiative processes involving magnetic fields (e.g. synchrotron and inverse Compton radiation), often accompanied by polarization signatures. However, the relative contribution of these emission mechanisms and the underlying physical processes are still debated. In this work, we present an overview of the scientific potential arising from the synergy between the Square Kilometre Array (SKA) and current and upcoming gamma-ray facilities. Combined observations across these energy bands will provide crucial insights into the physical mechanisms driving emission from GeV-TeV sources of both Galactic and extragalactic origin. These include transient events (e.g. gamma-ray bursts, supernovae, fast radio bursts, tidal disruption events, neutrino and gravitational-wave counterparts), variable sources (e.g. blazars, active galactic nuclei), and steady emitters (e.g. the Galactic centre, supernova remnants, radio galaxies, and galaxy clusters). We discuss the prospects for coordinated SKA-gamma-ray observations, including wide-field surveys, monitoring of variable sources, and target-of-opportunity follow-ups.

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arXiv2026

VLA Observations Confirm AT 2023mfm as an Off-nuclear Tidal Disruption Event

We report new radio observations of the tidal disruption event (TDE) AT 2023mfm, which we identified as a high-confidence candidate in a systematic search for off-nuclear TDEs. High-resolution NSF Karl G. Jansky Very Large Array C-band (6 GHz) imaging resolves two radio sources: one consistent with the host-galaxy nucleus and one offset by $0.651\pm0.036^{\prime\prime}$ ($1.06\pm0.06$ kpc), consistent with the Zwicky Transient Facility and Pan-STARRS1 positions of AT 2023mfm. These observations confirm the off-nuclear nature of AT 2023mfm, demonstrating the power of high-resolution radio imaging to validate off-nuclear TDE candidates and reveal hidden off-nuclear massive black holes.

astro-ph.HE↗

arXiv2026

Resolving the sub-parsec circumnuclear density profiles of quiescent galaxies: Evidence for Bondi accretion flows in tidal disruption event hosts

The sub-parsec circumnuclear density profiles of galaxies represent a key element in our understanding of the accretion history and fuel availability of supermassive black holes (SMBHs). Observations that directly resolve sub-parsec scales in galaxies require extremely high resolution and generally hot (bright) environments, making this impossible in all but the nearest active galaxies. Transient accretion events onto previously quiescent SMBHs, such as a tidal disruption event (TDE), offer a new avenue to understand SMBHs and their environments. Radio-bright outflows from TDEs directly probe the ambient density at $10^{-3}-1$ pc scales, allowing direct constraints on the circumnuclear density of TDE host galaxies (i.e., quiescent galaxies). Here we present, using radio observations of a sample of 11 TDE hosts, a new methodology for fitting observed TDE radio emission to constrain their sub-parsec circumnuclear density profiles. Our findings reveal that TDE host galaxies exhibit circumnuclear density profiles remarkably consistent with the expectations of a simple Bondi accretion flow ($n_e\propto R^{-3/2}$). Under the assumption of a Bondi profile, we present a new method to jointly fit the outflow mass and ambient densities, in order to constrain the Bondi accretion rate and temperature. For the TDE host galaxies in our sample, we constrain a sample average Bondi accretion rate Eddington fraction of $\log_{10}f_{\rm{Edd}} = -3.96^{+0.30}_{-0.38}$ (as well as individual fits to each host). This work provides a methodology by which radio observations of TDEs can provide powerful constraints on the sub-parsec density distribution of quiescent SMBHs -- well inside the Bondi sphere. This opens up a new observational avenue to constrain sub-parsec gas distributions in a broad range of galaxies.

astro-ph.GA↗

arXiv2026

A universal critical accretion rate for black hole jet formation

It has long been suspected that black hole accretion-outflow coupling is invariant from the stellar to supermassive scales. Stellar mass black hole accretion flows are known to launch jets and outflows as they transition through critical accretion rate thresholds, with values well constrained observationally owing to their short evolutionary timescales. In contrast, accretion flows in typical supermassive black hole (SMBH) systems (those in active galactic nuclei) evolve over thousands of years, making the critical transitions at which jets are launched impossible to constrain in individual systems. Tidal disruption events (TDEs) provide the unique opportunity to witness the birth and evolution of an accretion flow onto a SMBH which evolves on timescales of years. Here we show that TDEs launch outflows during a super-Eddington accretion phase and a second, physically distinct outflow, at a critical accretion rate of $L_{\rm crit} \approx0.02$ $L_{\rm Edd}$, the same as the critical accretion rate for state transitions observed in accreting stellar mass black holes. This work naturally explains the mechanism, observed properties, and detection rate for prompt and delayed outflows observed in TDEs, which until now have been open problems. More broadly, we demonstrate that SMBHs exhibit the same accretion-outflow coupling as stellar mass black holes and that the critical low accretion rate threshold for jet formation in black holes is scale invariant.

astro-ph.HE↗

arXiv2026

First Results from the PanRadio Gamma-Ray Burst Collaboration: The 400-day Afterglow of GRB 230815A

We introduce the PanRadio Gamma-ray Burst (GRB) program carried out on the Australia Telescope Compact Array: a systematic, multi-year, radio survey of all southern $\textit{Swift}$ GRB events, comprehensively following the multi-frequency evolution of their afterglows from within an hour to years post-burst. We present the results of the 400-day observing campaign following the afterglow of the long-duration (collapsar) GRB 230815A, the first one detected through this program. Typically, GRB 230815A would not otherwise receive traditional radio follow-up, given it has no known redshift and lacks comprehensive multi-wavelength follow-up due to its high line-of-sight extinction with $A_V=2.3$. We found its early X-ray jet break at ${\sim}0.1$ days post-burst to be at odds with the evolution of the multi-frequency radio light curves that were traced over an unusually long duration of $400$ days. The radio light curves approximately evolved (with minor deviations) according to the standard self-similar expansion for a relativistic blast wave in a homogeneous environment prior to the jet break, showing no evidence for evolutions of the microphysical parameters describing the electron acceleration processes. We reconcile these features by proposing a two-component jet: the early X-ray break originates from a narrow component with a half-opening angle ${\sim}2.1^{\circ}$, while the evolution of the radio afterglow stems from a wider component with a half-opening angle of $\gtrapprox 35^{\circ}$. The PanRadio GRB program will establish a sample of comprehensively followed GRBs, where a rigorous inspection of their microphysical and dynamical parameters can be performed, thereby revealing the diversity of features in their outflows and environments.

astro-ph.HE↗

arXiv2025

The 6 year radio lightcurve of the tidal disruption event AT2019azh

Analysis of radio emission from tidal disruption events allows for detailed constraints on the properties of ejected outflows and the host environment surrounding the black hole. However, the late-time radio behaviour of tidal disruption events is not well-studied due to a lack of observations. In this work we present long-term radio monitoring observations of the tidal disruption event AT2019azh spanning 1167-2159 days post disruption. We fit a physically motivated synchrotron model to the radio spectra at each epoch, and model the decay of the light curve under the assumption that the outflow transitions into the non-relativistic Sedov-Taylor regime at late times. Through this modelling we obtain strong constraints on the density profile of the circumnuclear medium, finding an unusually flat density profile proportional to $r^{0.24^{+0.11}_{-0.15}}$. Overall we find that unlike some tidal disruption events, AT2019azh does not show late time re-brightening up to 6 years post-disruption. The Sedov-Taylor light curve decay model provides a good fit to the data, motivating the assumption that the outflow was produced by a single ejection of material close to the time of stellar disruption. From forward modelling the evolution of the radio light curve decay we predict that the radio afterglow from AT2019azh should be detectable for decades at its current rate of evolution.

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arXiv2025

Dichotomy in Long-Lived Radio Emission from Tidal Disruption Events AT 2020zso and AT 2021sdu: Multi-Component Outflows vs. Host Contamination

We present a detailed radio study of the tidal disruption events (TDEs) AT 2020zso and AT 2021sdu. Both exhibit transient radio emission beginning shortly after optical discovery and persisting for several years. For AT 2020zso, we identify two distinct radio flares. The first arises soon after the optical peak, reaching a maximum $\sim1$ year post-discovery before fading. The second flare appears $\sim800$ days after discovery and results in the brief presence of two distinct components in the radio spectra, providing strong evidence for physically separate outflows. Both flares are consistent with non-relativistic outflows, with velocities $v\approx0.1-0.2c$ and energies $E\sim10^{49}$ erg, propagating through a Bondi-like circumnuclear medium. Our analysis supports a scenario in which the first outflow is accretion-driven, launched while the TDE disk is accreting at a relatively high Eddington fraction, whereas the second outflow is associated with a transition to an advection-dominated accretion flow. In contrast, the radio emission from AT 2021sdu is best explained by a slower ($v\approx0.03c$), less energetic outflow ($E\sim10^{48}$ erg), combined with diffuse, non-variable host emission that becomes dominant $\sim500$ days after discovery. Assuming free expansion, we infer an outflow launch date preceding the optical discovery date. This suggests that the outflow may originate from either the unbound stellar debris ejected during disruption or, alternatively, from a decelerating outflow. Our findings demonstrate the diversity of outflow properties in TDEs and highlight the observational challenges of interpreting late-time radio variability in the presence of host galaxy contamination.

astro-ph.HE↗

arXiv2025

The First Radio-Bright Off-Nuclear TDE 2024tvd Reveals the Fastest-Evolving Double-Peaked Radio Emission

We present the first multi-epoch broadband radio and millimeter monitoring of an off-nuclear TDE using the VLA, ALMA, ATA, AMI-LA, and the SMA. The off-nuclear TDE 2024tvd exhibits double-peaked radio light curves and the fastest evolving radio emission observed from a TDE to date. With respect to the optical discovery date, the first radio flare rises faster than $F_{\rm ν} \sim t^{9}$ at $Δt = 88-131$ days, and then decays as fast as $F_{\rm ν} \sim t^{-6}$. The emergence of a second radio flare is observed at $Δt \approx 194$ days with an initial fast rise of $F_{\rm ν} \sim t^{18}$, and an optically thin decline of $F_{\rm ν} \sim t ^{-12}$. We interpret these observations in the context of a self-absorbed and free-free absorbed synchrotron spectrum, while accounting for both synchrotron and external inverse-Compton cooling. We find that a single prompt outflow cannot easily explain these observations and it is likely that either there is only one outflow that was launched at $Δt \sim 80$ days, or two distinct outflows, with the second launched at $Δt \sim 170-190$ days. The nature of these outflows, whether sub-, mildly-, or ultra-relativistic, is still unclear, and we explore these different scenarios. Finally, we find a temporal coincidence between the launch time of the first radio-emitting outflow and the onset of a power-law component in the X-ray spectrum, attributed to inverse-Compton scattering of thermal photons.

astro-ph.HE↗

arXiv2025

A new Bowen Fluorescence Flare and Extreme Coronal Line Emitter discovered by SRG/eROSITA

The nuclear transient eRASSt J012026.5-292727 (J012026 hereafter) was discovered in the second SRG/eROSITA all-sky survey (eRASS2). The source appeared more than one order of magnitude brighter than the eRASS1 upper limits (peak eRASS2 0.2-2.3 keV flux of 1.14 x 10^-12 erg cm^-2 s^-1), and with a soft X-ray spectrum (photon index Gamma = 4.3). Over the following months, the X-ray flux started decaying, with significant flaring activity on both hour- and year-timescales. By inspecting the multiwavelength light curves of time-domain wide-field facilities, we detected a strong mid-infrared flare, evolving over 2 years, and a weaker optical counterpart. Follow-up optical spectroscopy revealed transient features, including redshifted Balmer lines (FWHM ~1500 km/s), strong Fe II emission, He II and Bowen lines, and high-ionization iron coronal lines. One spectrum showed a triple-peaked H-beta line, consistent with emission from a face-on elliptical disk. The spectroscopic features and the slow evolution of the event place J012026 within the classifications of Bowen fluorescence flares (BFFs) and extreme coronal line emitters (ECLEs). BFFs have been associated with rejuvenated accreting SMBHs, although the mechanism triggering the onset of the new accretion flow is still unclear, while ECLEs have been linked to the disruption of stars in gas-rich environments. The association of J012026 to both classes, combined with the multi-wavelength information, suggests that BFFs could be, at least in some cases, due to tidal disruption events (TDEs). The observed X-ray variability, uncommon in standard TDEs, adds complexity to these families of nuclear transients. These results highlight the diverse phenomenology of nuclear accretion events and demonstrate the value of systematic X-ray surveys, such as eROSITA and Einstein Probe, for uncovering such transients and characterizing their physical origin.

astro-ph.HE↗

arXiv2025

The population of tidal disruption events discovered with eROSITA

This paper presents a systematic study of X-ray-selected canonical tidal disruption events (TDEs) discovered in the western Galactic hemisphere of the first two eROSITA all-sky surveys (eRASS1 and eRASS2) performed between Dec 2019 and Dec 2020. We compiled a TDE sample from the catalog of eROSITA's extragalactic transients and variables eRO-ExTra, which includes X-ray sources with a variability significance and fractional amplitude over four between eRASS1 and eRASS2, not associated with known AGNs. Each X-ray source is associated with an optical counterpart from the Legacy Survey DR10. Canonical TDEs were selected based on their X-ray light-curve properties (single flare or decline), soft X-ray spectra ($Γ>3$), and the absence of archival X-ray variability and AGN signatures in their host photometry and spectroscopy. The sample includes 31 X-ray-selected TDE candidates with redshifts of $0.02< z<0.34$ and luminosities of $5.7 \times 10^{41}<L_X<5.3 \times 10^{44}$ erg/s in the 0.2-6.0 keV rest frame, of which 30 are canonical TDEs and one is an off-nuclear TDE candidate. The derived X-ray luminosity function is best fit by a double power law with a luminosity break at $10^{44}$ erg/s, corresponding to the Eddington-limiting prediction. This corresponds to a TDE volumetric rate of $ (2.3^{+1.2}_{-0.9})\times10^{-7}\,Mpc^{-3} yr^{-1}$ ($\approx1.2\times 10^{-5}$ events per galaxy per year). TDE host galaxies show a green-valley overdensity. In addition, 20%, 30%, and 15% of the sample exhibit flares in the optical, mid-infrared (mid-IR), or radio bands, respectively. We discuss the differences between X-ray, optical, and mid-IR TDE populations and the origins of multiwavelength flares in the context of the obscuring envelope and stream-stream collision models. Finally, we highlight TDE subpopulations that are not included in the canonical sample and should be explored in the future.

astro-ph.HE↗

arXiv2025

Spectral Insights and Evolutionary Pathways of Globular Cluster ULX in NGC 1399: A Two-Decade X-ray and Optical Study

We present new multi-wavelength observations of two ultraluminous X-ray sources (ULXs) hosted by globular clusters (GCs) in the giant elliptical NGC 1399, focusing on CXO J0338318-352604 (GCU7), only the second GC ULX known to have luminous optical emission lines. Notably, only NII and OIII emission is observed in the optical spectra, suggesting H-poor material. Previous work suggested the possibility that the properties of GCU7 could be explained by the tidal disruption of a horizontal branch star by an intermediate-mass black hole. We use new data to show that the lack of evolution in the X-ray or optical properties of the source over the last 20 years rules out this scenario. Instead, we use CLOUDY simulations to demonstrate that the optical emission lines are consistent with an outflow from an ultra-compact X-ray binary where a compact object - likely a neutron star (NS) - is accreting above the Eddington limit from a helium white dwarf (He WD). This binary would have dynamically formed from a direct collision between a NS and a red giant, or else via an exchange interaction. The ULX is predicted to evolve to lower mass transfer rates over time and eventually become a doppelganger to the well-studied ultra-compact X-ray binaries in Galactic GCs such as 4U 1820-30. These results show the utility of using extragalactic GCs to study short-lived phases in dynamical binary evolution that occur too rarely to be observed in Galactic clusters.

astro-ph.HE↗

arXiv2025

eRO-ExTra: eROSITA extragalactic non-AGN X-ray transients and variables in eRASS1 and eRASS2

(Abridged) While previous X-ray studies showed the dominance of regular active galactic nuclei (AGN) variability, a small fraction of sources arise from more exotic phenomena such as tidal disruption events (TDEs), quasi-periodic eruptions, or other short-lived events associated with supermassive black hole accretion. This paper describes the systematic selection of X-ray extragalactic transients found in the first two eROSITA all-sky surveys (eRASS) that are not associated with known AGN prior to eROSITA observations. We generated a variability sample from eRASS1 and eRASS2 (Dec. 2019-Dec. 2020), which includes sources with a variability significance and a fractional amplitude larger than four, located in the Legacy Survey DR10 (LS10) footprint. The properties of LS10 counterparts were used to exclude stars and known AGN. The sample was additionally cleaned using pre-eROSITA classifications, archival optical spectra, and archival X-ray data. The final catalog eRO-ExTra includes 304 extragalactic eROSITA transients and variables not associated with known AGN. More than 90% of sources have reliable LS10 optical counterparts. For each source, we provide archival X-ray data from Swift, ROSAT, and XMM-Newton; the eROSITA long-term light curve (2-2.5 years) with a light curve classification; as well as the best power law fit spectral results at the peak eROSITA epoch. Reliable spectroscopic and photometric redshifts are provided for more than 80% of the sample. Several sources in the catalog are known TDE candidates discovered by eROSITA. In addition, 31 sources are radio detected. The eRO-ExTra transients constitute a relatively clean parent sample of non-AGN variability phenomena associated with massive black holes. More than 95% of eRO-ExTra sources were discovered in X-rays with eROSITA for the first time, which makes it a valuable resource for studying unique nuclear transients.

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arXiv2024

A Contact Binary Mis-Classified as an Ellipsoidal Variable: Complications for Detached Black Hole Searches

Identifying sources exhibiting ellipsoidal variability in large photometric surveys is becoming a promising method to search for candidate detached black holes in binaries. This technique aims to exploit the orbital-phase dependent modulation in optical photometry caused by the black hole distorting the shape of the luminous star to constrain the mass ratio of the binary. Without understanding if, or how much, contamination is present in the candidate black hole samples produced by this new technique it is hard to leverage them for black hole discovery. Here, we follow up one of the best candidates identified from Gaia Data Release 3, Gaia DR3 4042390512917208960, with a radial velocity campaign. Combined photometric and radial velocity modelling, along with spectral disentangling, suggests that the true mass ratio (mass of the unseen object divided by the mass of the luminous star) is an order of magnitude smaller than that inferred assuming the modulations arise from ellipsoidal variability. We therefore infer that this system is likely a contact binary, or on the boundary of both stars nearly filling their Roche lobes, however, further observations are required to confidently detect the secondary. We find that the well-known problem of discriminating between ellipsoidal and contact binary light curves results in a larger contamination from contact binaries than previously suggested. Until ellipsoidal variables can be reliably distinguished from contact binaries, samples of black hole candidates selected based on ellipsoidal variability are likely to be highly contaminated by contact binaries or similar systems.

astro-ph.SR↗

arXiv2024

Testing EMRI models for Quasi-Periodic Eruptions with 3.5 years of monitoring eRO-QPE1

Quasi-Periodic Eruptions (QPEs) are luminous X-ray outbursts recurring on hour timescales, observed from the nuclei of a growing handful of nearby low-mass galaxies. Their physical origin is still debated, and usually modeled as (a) accretion disk instabilities or (b) interaction of a supermassive black hole (SMBH) with a lower mass companion in an extreme mass-ratio inspiral (EMRI). EMRI models can be tested with several predictions related to the short- and long-term behavior of QPEs. In this study, we report on the ongoing 3.5-year NICER and XMM-Newton monitoring campaign of eRO-QPE1, which is known to exhibit erratic QPEs that have been challenging for the simplest EMRI models to explain. We report 1) complex, non-monotonic evolution in the long-term trends of QPE energy output and inferred emitting area; 2) the disappearance of the QPEs (within NICER detectability) in October 2023, then reappearance by January 2024 at a luminosity $\sim$100x fainter (and temperature $\sim$3x cooler) than initial discovery; 3) radio non-detections with MeerKAT and VLA observations partly contemporaneous with our NICER campaign (though not during outbursts); and 4) the presence of a possible $\sim$6-day modulation of the QPE timing residuals, which aligns with the expected nodal precession timescale of the underlying accretion disk. Our results tentatively support EMRI-disk collision models powering the QPEs, and we demonstrate that the timing modulation of QPEs may be used to jointly constrain the SMBH spin and disk density profile.

astro-ph.HE↗

arXiv2023

An Observationally-Derived Kick Distribution for Neutron Stars in Binary Systems

Understanding the natal kicks received by neutron stars (NSs) during formation is a critical component of modelling the evolution of massive binaries. Natal kicks are an integral input parameter for population synthesis codes, and have implications for the formation of double NS systems and their subsequent merger rates. However, many of the standard observational kick distributions that are used are obtained from samples created only from isolated NSs. Kick distributions derived in this way overestimate the intrinsic NS kick distribution. For NSs in binaries, we can only directly estimate the effect of the natal kick on the binary system, instead of the natal kick received by the NS itself. Here, for the first time, we present a binary kick distribution for NSs with low-mass companions. We compile a catalogue of 145 NSs in low-mass binaries with the best available constraints on proper motion, distance, and systemic radial velocity. For each binary, we use a three-dimensional approach to estimate its binary kick. We discuss the implications of these kicks on system formation, and provide a parametric model for the overall binary kick distribution, for use in future theoretical modelling work. We compare our results with other work on isolated NSs and NSs in binaries, finding that the NS kick distributions fit using only isolated pulsars underestimate the fraction of NSs that receive low kicks. We discuss the implications of our results on modelling double NS systems, and provide suggestions on how to use our results in future theoretical works.

astro-ph.HE↗

arXiv2022

The most probable host of CHIME FRB 190425A, associated with binary neutron star merger GW190425, and a late-time transient search

The identification and localization of Fast Radio Bursts to their host galaxies has revealed important details about the progenitors of these mysterious, millisecond-long bursts of coherent radio emission. In this work we study the most probable host galaxy of the apparently non-repeating CHIME/FRB event FRB 20190425A -- a particularly high luminosity, low dispersion measure event that was demonstrated by Moroianu et al. 2022 to be temporally and spatially coincident with the LIGO-Virgo-KAGRA binary neutron star merger GW190425, suggesting an astrophysical association (p-value 0.0052). In this paper we remain agnostic to this result, and we confirm UGC10667 as the most probable host galaxy of FRB 20190425A, demonstrating that the host galaxies of low dispersion measure, one-off CHIME FRBs can be plausibly identified. We then perform multi-wavelength observations to characterize the galaxy and search for any afterglow emission associated with the FRB and its putative GW counterpart. We find no radio or optical transient emission in our observations $2.5\,\mathrm{yr}$ post-burst. UGC10667 is a spiral galaxy at $z\sim0.03$, dominated by an old stellar population. We find no evidence of a large population of young stars, with nebular emission dominated by star formation at a rate of $1-2\,\mathrm{M_\odot\,yr^{-1}}$. While we cannot rule out a young magnetar as the origin of FRB 20190425A, our observations are consistent with an origin in a long delay-time neutron star binary merger as posited by Moroianu et al. 2022.

astro-ph.HE↗

arXiv2022

Radio observations of the tidal disruption event AT2020opy: a luminous non-relativistic outflow encountering a dense circumnuclear medium

Tidal disruption events (TDEs) occur when a star passes too close to a supermassive black hole and is destroyed by tidal gravitational forces. Radio observations of TDEs trace synchrotron emission from outflowing material that may be ejected from the inner regions of the accretion flow around the SMBH or by the tidal debris stream. Radio detections of tidal disruption events are rare, but provide crucial information about the launching of jets and outflows from supermassive black holes and the circumnuclear environment in galaxies. Here we present the radio detection of the TDE AT2020opy, including three epochs of radio observations taken with the Karl G. Jansky's Very Large Array (VLA), MeerKAT, and upgraded Giant Metrewave Radio telescope. AT2020opy is the most distant thermal TDE with radio emission reported to date, and from modelling the evolving synchrotron spectra we deduce that the host galaxy has a more dense circumnuclear medium than other thermal TDEs detected in the radio band. Based on an equipartition analysis of the synchrotron spectral properties of the event, we conclude that the radio-emitting outflow was likely launched approximately at the time of, or just after, the initial optical flare. We find no evidence for relativistic motion of the outflow. The high luminosity of this event supports that a dense circumnuclear medium of the host galaxy produces brighter radio emission that rises to a peak more quickly than in galaxies with lower central densities.

astro-ph.HE↗