arXiv subjects

Kunal Mooley

Publications and source records attributed to Kunal Mooley.

At least 19 recordsLinked to original sources

arXiv2026

Development and demonstration of a Modular Astrobiological Experiments (MAEx) payload for autonomous biological monitoring in Low Earth Orbit (LEO)

The spaceflight environment presents unique physicochemical conditions, including microgravity, ionizing radiation, altered fluid transport, and confined engineered habitats, which influence biological systems and biomolecular assembly processes. These conditions also provide opportunities for orbital biomanufacturing and autonomous biofabrication that are difficult to reproduce under terrestrial gravity, motivating the development of compact autonomous experimental platforms for spaceflight research. Here, we present the Modular Astrobiology Experiment (MAEx) platform, a compact 3U spaceflight-compatible payload designed for autonomous multimodal biological characterization under space-relevant conditions. MAEx was engineered to operate within the constraints of orbital deployment, including limited volume, low power consumption, thermal regulation, and autonomous data acquisition. To demonstrate platform versatility, representative biological systems, including the electroactive bacterium Shewanella oneidensis MR-1, the radiation-resistant fungus Ustilago maydis FB1, and the human eye lens protein {\gamma}D-crystallin, spanning cellular and molecular scales were incorporated. MAEx platform integrates imaging, absorption and fluorescence spectroscopy, and electrochemical sensing within a modular architecture, enabling simultaneous monitoring of microbial growth, extracellular electron transfer (EET), and protein aggregation dynamics.

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arXiv2025

Multi-messenger and time-domain astronomy in the 2040s

Multi-messenger astronomy will be transformed in the 2040s by an unprecedented volume of detections from next-generation gravitational wave, high-energy, and ultra-high energy neutrino, cosmic ray, and time domain observatories. This white paper, prepared for the European Southern Observatory (ESO) Expanding Horizons call, outlines the key science questions enabled by this emerging multi-messenger ecosystem, ranging from nucleosynthesis and dense matter physics to cosmology, fundamental physics, and the growth of black holes across cosmic time. We demonstrate that fully exploiting these discoveries requires a step change in optical to near infrared spectroscopic capability, including low latency response, high throughput, and flexible time domain operations across both hemispheres. We argue that without a dedicated large-aperture time domain facility, the scientific return of multi-messenger astronomy in the 2040s will be considerably limited.

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arXiv2025

Thermal electrons in the radio afterglow of relativistic tidal disruption event ZTF22aaajecp/AT2022cmc

A tidal disruption event (TDE) occurs when a star travels too close to a supermassive black hole. In some cases, accretion of the disrupted material onto the black hole launches a relativistic jet. In this paper, we present a long term observing campaign to study the radio and sub-millimeter emission associated with the fifth jetted/relativistic TDE: AT2022cmc. Our campaign reveals a long lived counterpart. We fit three different models to our data: a non-thermal jet, a spherical outflow consisting of both thermal and non-thermal electrons, and a jet with thermal and non-thermal electrons. We find that the data is best described by a relativistic spherical outflow propagating into an environment with a density profile following R^-1.8. Comparison of AT2022cmc to other TDEs finds agreement in the density profile of the environment but also that AT2022cmc is twice as energetic as the other well-studied relativistic TDE Swift J1644. Our observations of AT2022cmc allow a thermal electron population to be inferred for the first time in a jetted transient providing, new insights into the microphysics of relativistic transients jets.

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arXiv2023

The High Energy X-ray Probe (HEX-P): Sensitive broadband X-ray observations of transient phenomena in the 2030s

HEX-P will launch at a time when the sky is being routinely scanned for transient gravitational wave, electromagnetic and neutrino phenomena that will require the capabilities of a sensitive, broadband X-ray telescope for follow up studies. These include the merger of compact objects such as neutron stars and black holes, stellar explosions, and the birth of new compact objects. \hexp\ will probe the accretion and ejecta from these transient phenomena through the study of relativistic outflows and reprocessed emission, provide unique capabilities for understanding jet physics, and potentially revealing the nature of the central engine.

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arXiv2023

A Radio Flare in the Long-Lived Afterglow of the Distant Short GRB 210726A: Energy Injection or a Reverse Shock from Shell Collisions?

We present the discovery of the radio afterglow of the short $\gamma$-ray burst (GRB) 210726A, localized to a galaxy at a photometric redshift of $z\sim 2.4$. While radio observations commenced $\lesssim 1~$day after the burst, no radio emission was detected until $\sim11~$days. The radio afterglow subsequently brightened by a factor of $\sim 3$ in the span of a week, followed by a rapid decay (a "radio flare"). We find that a forward shock afterglow model cannot self-consistently describe the multi-wavelength X-ray and radio data, and underpredicts the flux of the radio flare by a factor of $\approx 5$. We find that the addition of substantial energy injection, which increases the isotropic kinetic energy of the burst by a factor of $\approx 4$, or a reverse shock from a shell collision are viable solutions to match the broad-band behavior. At $z\sim 2.4$, GRB 210726A is among the highest redshift short GRBs discovered to date as well as the most luminous in radio and X-rays. Combining and comparing all previous radio afterglow observations of short GRBs, we find that the majority of published radio searches conclude by $\lesssim 10~$days after the burst, potentially missing these late rising, luminous radio afterglows.

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arXiv2023

Chemical Distribution of the Dynamical Ejecta in the Neutron Star Merger GW170817

GW170817 and its associated electromagnetic counterpart AT2017gfo continue to be a treasure trove as observations and modeling continue. Recent precision astrometry of AT2017gfo with the Hubble Space Telescope combined with previous constraints from Very Long Baseline Interferometry (VLBI) constraints narrowed down the inclination angle to 19-25 deg (90\% confidence). This paper explores how the inclusion of precise inclination information can reveal new insights about the ejecta properties, in particular, about the composition of the dynamical ejecta of AT2017gfo. Our analysis relies on updated kilonova modeling, which includes state-of-the-art heating rates, thermalization efficiencies, and opacities and is parameterized by $\bar{Y}_{\rm e,dyn}$, the average electron fraction of the dynamical ejecta component. Using this model, we incorporate the latest inclination angle constraint of AT2017gfo into a light curve fitting framework to derive updated parameter estimates. Our results suggest that the viewing angle of the observer is pointed towards the lanthanide-poor ($Y_{\rm e,dyn}\gtrsim0.25$), squeezed polar dynamical ejecta component, which can explain the early blue emission observed in the light curve of AT2017gfo. In contrast to a recent claim of spherical ejecta powering AT2017gfo, our study indicates that the composition of the dynamical ejecta has a strong angular dependence, with a lanthanide-rich ($Y_{\rm e,dyn}\lesssim0.25$), tidal component distributed around the merger plane with a half-opening angle of $35^\circ$. The inclination angle constraint reduces $\bar{Y}_{\rm e,dyn}$ from $0.24$ to $0.22$, with values $0.17\lesssim Y_{\rm e, dyn} \lesssim0.41$ enabling the robust production of $r$-process elements up to the $3^{\rm rd}$ peak in the tidal dynamical ejecta.

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arXiv2022

A very luminous jet from the disruption of a star by a massive black hole

Tidal disruption events (TDEs) are bursts of electromagnetic energy released when supermassive black holes (SMBHs) at the centers of galaxies violently disrupt a star that passes too close. TDEs provide a new window to study accretion onto SMBHs; in some rare cases, this accretion leads to launching of a relativistic jet, but the necessary conditions are not fully understood. The best studied jetted TDE to date is Swift J1644+57, which was discovered in gamma-rays, but was too obscured by dust to be seen at optical wavelengths. Here we report the optical discovery of AT2022cmc, a rapidly fading source at cosmological distance (redshift z=1.19325) whose unique lightcurve transitioned into a luminous plateau within days. Observations of a bright counterpart at other wavelengths, including X-rays, sub-millimeter, and radio, supports the interpretation of AT2022cmc as a jetted TDE containing a synchrotron "afterglow", likely launched by a SMBH with spin $a \gtrsim 0.3$. Using 4 years of Zwicky Transient Facility (ZTF) survey data, we calculate a rate of $0.02 ^{+ 0.04 }_{- 0.01 }$ Gpc$^{-3}$ yr$^{-1}$ for on-axis jetted TDEs based on the luminous, fast-fading red component, thus providing a measurement complementary to the rates derived from X-ray and radio observations. Correcting for the beaming angle effects, this rate confirms that about 1% of TDEs have relativistic jets. Optical surveys can use AT2022cmc as a prototype to unveil a population of jetted TDEs.

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arXiv2022

Studies on slow radio transients

We present a brief overview of a very extensive studies of the group of active galactic nuclei (AGNs) that transitioned to radio-loud state over the past few decades. The sample consists of twelve sources, both quasars and galaxies, showing the characteristics of gigahertz-peaked spectrum (GPS) objects undergoing relatively rapid changes, due to the evolution of their newly-born radio jets. Discussed objects also show a wide range of physical parameters such as bolometric luminosity, black hole mass and jet power, suggesting a great diversity among young active galactic nuclei and their hosts. Furthermore, we introduce a new observational project, the aim of which will be to investigate and gain a more in-depth understanding of the phenomenon of slow radio transients.

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arXiv2021

A transient radio source consistent with a merger-triggered core collapse supernova

A core-collapse supernova occurs when exothermic fusion ceases in the core of a massive star, typically due to exhaustion of nuclear fuel. Theory predicts that fusion could be interrupted earlier, by merging of the star with a compact binary companion. We report a luminous radio transient, VT J121001+495647, found in the Very Large Array Sky Survey. The radio emission is consistent with supernova ejecta colliding with a dense shell of material, potentially ejected by binary interaction in the centuries prior to explosion. We associate the supernova with an archival X-ray transient, which implies a relativistic jet was launched during the explosion. The combination of an early relativistic jet and late-time dense interaction is consistent with expectations for a merger-driven explosion.

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arXiv2021

An early peak in the radio light curve of short-duration Gamma-Ray Burst 200826A

We present the results of radio observations from the eMERLIN telescope combined with X-ray data from Swift for the short-duration Gamma-ray burst (GRB) 200826A, located at a redshift of 0.71. The radio light curve shows evidence of a sharp rise, a peak around 4-5 days post-burst, followed by a relatively steep decline. We provide two possible interpretations based on the time at which the light curve reached its peak. (1) If the light curve peaks earlier, the peak is produced by the synchrotron self-absorption frequency moving through the radio band, resulting from the forward shock propagating into a wind medium and (2) if the light curve peaks later, the turn over in the light curve is caused by a jet break. In the former case, we find a minimum equipartition energy of ~3x10^47 erg and bulk Lorentz factor of ~5, while in the latter case we estimate the jet opening angle of ~9-16 degrees. Due to the lack of data, it is impossible to determine which is the correct interpretation, however, due to its relative simplicity and consistency with other multi-wavelength observations which hint at the possibility that GRB 200826A is in fact a long GRB, we prefer scenario one over scenario two.

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arXiv2021

A luminous X-ray transient in SDSS J143359.16+400636.0: a likely tidal disruption event

We present the discovery of a luminous X-ray transient, serendipitously detected by Swift's X-ray Telescope (XRT) on 2020 February 5, located in the nucleus of the galaxy SDSS J143359.16+400636.0 at z=0.099 (luminosity distance $D_{\rm L}=456$ Mpc). The transient was observed to reach a peak luminosity of $\sim10^{44}$ erg s$^{-1}$ in the 0.3--10 keV X-ray band, which was $\sim20$ times more than the peak optical/UV luminosity. Optical, UV, and X-ray lightcurves from the Zwicky Transient Facility (ZTF) and Swift show a decline in flux from the source consistent with $t^{-5/3}$, and observations with NuSTAR and Chandra show a soft X-ray spectrum with photon index $Γ=2.9\pm0.1$. The X-ray/UV properties are inconsistent with well known AGN properties and have more in common with known X-ray tidal disruption events (TDE), leading us to conclude that it was likely a TDE. The broadband spectral energy distribution (SED) can be described well by a disk blackbody model with an inner disk temperature of $7.3^{+0.3}_{-0.8}\times10^{5}$ K, with a large fraction ($>40$%) of the disk emission up-scattered into the X-ray band. An optical spectrum taken with Keck/LRIS after the X-ray detection reveals LINER line ratios in the host galaxy, suggesting low-level accretion on to the supermassive black hole prior to the event, but no broad lines or other indications of a TDE were seen. The stellar velocity dispersion implies the mass of the supermassive black hole powering the event is log($M_{\rm BH}$/$M_{\odot}$)$=7.41\pm0.41$, and we estimate that at peak the Eddington fraction of this event was $\sim$50%. This likely TDE was not identified by wide-field optical surveys, nor optical spectroscopy, indicating that more events like this would be missed without wide-field UV or X-ray surveys.

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arXiv2020

Quasars That Have Transitioned from Radio-quiet to Radio-loud on Decadal Timescales Revealed by VLASS and FIRST

We have performed a search over 3440 deg$^2$ of Epoch 1 (2017-2019) of the Very Large Array Sky Survey to identify unobscured quasars in the optical ($0.2 < z < 3.2$) and obscured active galactic nuclei (AGN) in the infrared that have brightened dramatically in the radio over the past one to two decades. These sources would have been previously classified as "radio-quiet" quasars based on upper limits from the Faint Images of the Radio Sky at Twenty Centimeters survey (1993-2011), but they are now consistent with "radio-loud" quasars ($L_{\rm 3\,GHz} = 10^{40 - 42} \,\, {\rm erg} \,{\rm s}^{-1}$). A quasi-simultaneous, multiband ($\sim1-18$ GHz) follow-up study of 14 sources with the VLA has revealed compact sources ($<0.1^{\prime \prime}$ or $<1$ kpc) with peaked radio spectral shapes. The high-amplitude variability over decadal timescales at 1.5 GHz (100% to $>$2500%), but roughly steady fluxes over a few months at 3 GHz, are inconsistent with extrinsic variability due to propagation effects, thus favoring an intrinsic origin. We conclude that our sources are powerful quasars hosting compact/young jets. This challenges the generally accepted idea that "radio-loudness" is a property of the quasar/AGN population that remains fixed on human timescales. Our study suggests that frequent episodes of short-lived AGN jets that do not necessarily grow to large scales may be common at high redshift. We speculate that intermittent but powerful jets on subgalactic scales could interact with the interstellar medium, possibly driving feedback capable of influencing galaxy evolution.

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arXiv2020

Caltech-NRAO Stripe 82 Survey (CNSS). IV. The Birth of Radio-loud Quasar 013815+00

It is believed that the gas accretion onto the supermassive black holes (SMBHs) is the main process of powering its luminous emission, which occurs in optical, UV and X-ray regimes and less frequently in radio waves. The observational fact that only a few percent of quasars are radio-loud is still an unresolved issue concerning the understanding of the active galactic nucleus (AGN) population. Here we present a detection of a rapid transition from the radio-quiet to the radio-loud mode in quasar 013815+00 (z=0.94) which coincides with changes of its UV-optical continuum and the low ionization MgII broadline. We interpret this as an enhancement of accretion onto a central black hole of mass about 10^9 solar masses. As a consequence a new radio-loud AGN was born. Its spectral and morphological properties indicate that it went through the short gigahertz-peaked spectrum (GPS) phase at the beginning of its activity and has now stabilized its flux density at the level of a few mJy. The radio morphology of 013815+00 is very compact and we predict that with such short-term jet activity its development will be very slow. The observed luminosity changes of the accretion disk are shorter than the lifetime of the new radio phase in 013815+00.

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arXiv2020

Kilonova Luminosity Function Constraints based on Zwicky Transient Facility Searches for 13 Neutron Star Mergers

We present a systematic search for optical counterparts to 13 gravitational wave (GW) triggers involving at least one neutron star during LIGO/Virgo's third observing run. We searched binary neutron star (BNS) and neutron star black hole (NSBH) merger localizations with the Zwicky Transient Facility (ZTF) and undertook follow-up with the Global Relay of Observatories Watching Transients Happen (GROWTH) collaboration. The GW triggers had a median localization of 4480 deg^2, median distance of 267 Mpc and false alarm rates ranging from 1.5 to 1e-25 per yr. The ZTF coverage had a median enclosed probability of 39%, median depth of 20.8mag, and median response time of 1.5 hr. The O3 follow-up by the GROWTH team comprised 340 UVOIR photometric points, 64 OIR spectra, and 3 radio. We find no promising kilonova (radioactivity-powered counterpart) and we convert the upper limits to constrain the underlying kilonova luminosity function. Assuming that all kilonovae are at least as luminous as GW170817 at discovery (-16.1mag), we calculate our joint probability of detecting zero kilonovae is only 4.2%. If we assume that all kilonovae are brighter than -16.6mag (extrapolated peak magnitude of GW170817) and fade at 1 mag/day (similar to GW170817), the joint probability of zero detections is 7%. If we separate the NSBH and BNS populations, the joint probability of zero detections, assuming all kilonovae are brighter than -16.6mag, is 9.7% for NSBH and 7.9% for BNS mergers. Moreover, <57% (<89%) of putative kilonovae could be brighter than -16.6mag assuming flat (fading) evolution, at 90% confidence. If we further account for the online terrestrial probability for each GW trigger, we find that <68% of putative kilonovae could be brighter than -16.6mag. Comparing to model grids, we find that some kilonovae must have Mej < 0.03 Msun or Xlan>1e-4 or phi>30deg to be consistent with our limits. (Abridged)

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arXiv2019

An ASKAP search for a radio counterpart to the first high-significance neutron star-black hole merger LIGO/Virgo S190814bv

We present results from a search for a radio transient associated with the LIGO/Virgo source S190814bv, a likely neutron star-black hole (NSBH) merger, with the Australian Square Kilometre Array Pathfinder. We imaged a $30\,{\rm deg}^2$ field at $ΔT$=2, 9 and 33 days post-merger at a frequency of 944\,MHz, comparing them to reference images from the Rapid ASKAP Continuum Survey observed 110 days prior to the event. Each epoch of our observations covers $89\%$ of the LIGO/Virgo localisation region. We conducted an untargeted search for radio transients in this field, resulting in 21 candidates. For one of these, \object[AT2019osy]{AT2019osy}, we performed multi-wavelength follow-up and ultimately ruled out the association with S190814bv. All other candidates are likely unrelated variables, but we cannot conclusively rule them out. We discuss our results in the context of model predictions for radio emission from neutron star-black hole mergers and place constrains on the circum-merger density and inclination angle of the merger. This survey is simultaneously the first large-scale radio follow-up of an NSBH merger, and the most sensitive widefield radio transients search to-date.

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arXiv2019

Late-outburst radio flaring in SS Cyg and evidence for a powerful kinetic output channel in cataclysmic variables

Accreting white dwarfs in binary systems known as cataclysmic variables (CVs) have in recent years been shown to produce radio flares during outbursts, qualitatively similar to those observed from neutron star and black hole X-ray binaries, but their ubiquity and energetic significance for the accretion flow has remained uncertain. We present new radio observations of the CV SS Cyg with Arcminute Microkelvin Imager Large Array, which show for the second time late-ouburst radio flaring, in April 2016. This flaring occurs during the optical flux decay phase, about ten days after the well-established early-time radio flaring. We infer that both the early- and late-outburst flares are a common feature of the radio outbursts of SS Cyg, albeit of variable amplitudes, and probably of all dwarf novae. We furthermore present new analysis of the physical conditions in the best-sampled late-outburst flare, from Feb 2016, which showed clear optical depth evolution. From this we can infer that the synchrotron-emitting plasma was expanding at about 1% of the speed of light, and at peak had a magnetic field of order 1 Gauss and total energy content > 10^{33} erg. While this result is independent of the geometry of the synchrotron-emitting region, the most likely origin is in a jet carrying away a significant amount of the available accretion power.

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arXiv2017

Changing-look AGNs or short-lived radio sources?

The evolution of extragalactic radio sources has been a fundamental problem in the study of active galactic nuclei for many years. A standard evolutionary model has been created based on observations of a wide range of radio sources. In the general scenario of the evolution, the younger and smaller Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) sources become large-scale FRI and FRII objects. However, a growing number of observations of low power radio sources suggests that the model cannot explain all their properties and there are still some aspects of the evolutionary path that remain unclear. There are indications, that some sources may be short-lived objects on timescales of $10^4$ - $10^5$ years. Those objects represent a new population of active galaxies. Here, we present the discovery of several radio transient sources on timescales of 5-20 years, largely associated with renewed AGN (Active Galactic Nucleus) activity. These changing-look AGNs possibly represent behaviour typical for many active galaxies.

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arXiv2017

Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star

Every supernova hitherto observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining. Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95-130 solar masses, which experience the pulsational pair instability. That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.

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