Gokul P. Srinivasaragavan
A5017540414- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- X-ray Spectroscopy and Fluorescence Analysis
- Solar and Space Plasma Dynamics
- Astronomy and Astrophysical Research
- Geophysics and Gravity Measurements
- Dark Matter and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Radioactivity and Radon Measurements
- Methane Hydrates and Related Phenomena
- Planetary Science and Exploration
- Radiation Therapy and Dosimetry
- Digital Radiography and Breast Imaging
- Astro and Planetary Science
- Neutrino Physics Research
- Atmospheric and Environmental Gas Dynamics
- Optical Imaging and Spectroscopy Techniques
- Astronomical Observations and Instrumentation
- Nuclear Physics and Applications
- Medical Imaging Techniques and Applications
- Atomic and Subatomic Physics Research
University of Maryland, College Park
2021-2025
Goddard Space Flight Center
2023-2025
Deleted Institution
2023-2025
Joint Space Science Institute
2023-2025
California Institute of Technology
2020-2022
Long-duration gamma-ray bursts (GRBs) are powerful cosmic explosions, signaling the death of massive stars. Among them, GRB 221009A is by far brightest burst ever observed. Because its enormous energy (Eiso ≈ 1055 erg) and proximity (z 0.15), an exceptionally rare event that pushes limits our theories. We present multiwavelength observations covering first 3 months afterglow evolution. The x-ray brightness decays as a power law with slope ≈t-1.66, which not consistent standard predictions...
Abstract We present the results of our multiwavelength (X-ray to radio) follow-up campaign Einstein Probe transient EP240408a. The initial 10 s trigger displayed bright soft X-ray (0.5–4 keV) radiation with peak luminosity L X ≳ 49 (10 50 ) erg −1 for an assumed redshift z 0.5 (2.0). Neil Gehrels Swift Observatory and Neutron star Interior Composition ExploreR discovered a fading counterpart lasting ∼5 days (observer frame), which showed long-lived (∼4 days) plateau-like emission ( t −0.5...
Abstract One of the open questions following discovery GW170817 is whether neutron star (NS) mergers are only astrophysical sites capable producing r -process elements. Simulations have shown that 0.01–0.1 M ⊙ material could be generated in outflows originating from accretion disk surrounding rapidly rotating black hole forms as a remnant to both NS and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature nucleosynthesis binary merger...
Abstract We report observations of the optical counterpart long gamma-ray burst GRB 221009A. Due to extreme rarity being both nearby ( z = 0.151) and highly energetic E γ ,iso ≥ 10 54 erg), 221009A offers a unique opportunity probe connection between massive star core collapse relativistic jet formation across very broad range -ray properties. Adopting phenomenological power-law model for afterglow host galaxy estimates from high-resolution Hubble Space Telescope imaging, we use Bayesian...
Abstract We report observations of the optical counterpart long gamma-ray burst (GRB) GRB 230812B and its associated supernova (SN) SN 2023pel. The proximity ( z = 0.36) high energy E γ ,iso ∼ 10 53 erg) make it an important event to study as a probe connection between massive star core collapse relativistic jet formation. With phenomenological power-law model for afterglow, we find late-time flattening consistent with presence SN. 2023pel has absolute peak r -band magnitude M −19.46 ± 0.18...
Abstract Gamma-ray Bursts (GRBs) are the most explosive phenomena in universe after big bang. A large fraction of GRB lightcurves (LCs) shows X-ray plateaus. We perform comprehensive analysis all GRBs (with known and unknown redshifts) with plateau emission observed by The Neil Gehrels Swift Observatory from its launch until 2019 August. fit 455 LCs showing a explore whether these follow closure relations, relations between temporal spectral indices afterglow, corresponding to two distinct...
The Large Area Telescope (LAT) on board the Fermi Gamma-ray Space (Fermi) shows long-lasting high-energy emission in many gamma-ray bursts (GRBs), similar to X-ray afterglows observed by Neil Gehrels Swift Observatory (Swift). Some LAT light curves (LCs) show a late-time flattening reminiscent of plateaus. We explore presence plateaus temporally extended analyzing GRBs from second Fermi-LAT GRB Catalog 2008 2016 May with known redshifts, and check whether they follow closure relations...
Abstract We present multi-wavelength analysis of ZTF23abelseb (AT 2023sva), an optically discovered fast-fading (Δmr = 2.2 mag in Δt 0.74 days), luminous (Mr ∼ −30.0 mag) and red (g − r 0.50 transient at z 2.28 with accompanying radio emission. AT 2023sva does not possess a γ-ray burst (GRB) counterpart to isotropic equivalent energy limit Eγ, iso < 1.6 × 1052 erg, determined through searching satellite archives between the last non-detection first detection, making it sixth example...
We present the optical discovery and multiwavelength follow-up observations of AT2024kmq, a likely tidal disruption event (TDE) associated with supermassive ($M_{\rm BH}\sim 10^{8} M_\odot$) black hole in massive galaxy at $z=0.192$. The light curve AT2024kmq exhibits two distinct peaks: an early fast (timescale 1 d) luminous ($M\approx-20$ mag) red peak, then slower month) blue peak higher luminosity ($M\approx-22$ featureless spectra. second component is similar to spectroscopic class...
Abstract The Neil Gehrels Swift observatory observes gamma-ray burst (GRB) plateaus in X-rays. We test the reliability of closure relations through fireball model when dealing with GRB plateau emissions. analyze 455 X-ray light curves collected by from 2005 January until 2019 August for which redshifts are either known or unknown using phenomenological Willingale 2007 model. Using these fits, we emission mechanisms and astrophysical environments GRBs within time interval emission. Finally,...
Abstract The dividing line between gamma-ray bursts (GRBs) and ordinary stripped-envelope core-collapse supernovae (SNe) is yet to be fully understood. Observationally mapping the variety of ejecta outcomes (ultrarelativistic, mildly relativistic, or nonrelativistic) in SNe Type Ic with broad lines (Ic-BL) can provide a key test stellar explosion models. However, this requires large samples rare SN Ic-BL events follow-up observations radio, where fast probed largely free geometry viewing...
Eruptive mass loss of massive stars prior to supernova (SN) explosion is key understanding their evolution and end fate. An observational signature pre-SN the detection an early, short-lived peak radioactive-powered in lightcurve SN. This usually attributed SN shock passing through extended envelope or circumstellar medium (CSM). Such early common for double-peaked Type IIb SNe with Hydrogen but uncommon normal Ibc very compact progenitors. In this paper, we systematically study a sample 14...
During the first half of fourth observing run (O4a) International Gravitational Wave Network (IGWN), Zwicky Transient Facility (ZTF) conducted a systematic search for kilonova (KN) counterparts to binary neutron star (BNS) and star-black hole (NSBH) merger candidates. Here, we present comprehensive study five high-significance (FAR < 1 per year) BNS NSBH candidates in O4a. Our follow-up campaigns relied on both target-of-opportunity observations (ToO) re-weighting nominal survey schedule...
Abstract The Galactic magnetar SGR 1935+2154 has been reported to produce the first example of a bright millisecond-duration radio burst (FRB 200428) similar cosmological population fast bursts (FRBs). detection coincident X-ray represents observed multiwavelength counterpart an FRB. However, search for emission at optical wavelengths hampered by high inferred extinction on line sight. Here, we present results from second-timescale source near-infrared (NIR) using Palomar Gattini-IR...
Abstract We present the discovery and multiwavelength characterization of SRGA J181414.6-225604, a Galactic hard X-ray transient discovered during ongoing SRG/ART-XC sky survey. Using data from Palomar Gattini-IR survey, we identify spatially temporally coincident variable infrared (IR) source, IRAS 18111-2257, classify it as very-late-type (M7–M8), long-period (1502 ± 24 days), luminous ( M K ≈ −9.9 0.2) O-rich Mira donor star located at distance ≈14.6 +2.9 −2.3 kpc. Combining multicolor...
Abstract We study a magnitude-limited sample of 36 broad-lined type Ic supernovae (SNe Ic-BL) from the Zwicky Transient Facility Bright Survey (detected between 2018 March and 2021 August), which is largest systematic SNe Ic-BL done in literature thus far. present light curves (LCs) for each analyze shape LCs to derive empirical parameters, along with explosion epochs every event. The has an average absolute peak magnitude r band <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"...
Eruptive mass loss of massive stars prior to supernova (SN) explosion is key understanding their evolution and end fate. An observational signature pre-SN the detection an early, short-lived peak radioactive-powered in lightcurve SN. This usually attributed SN shock passing through extended envelope or circumstellar medium (CSM). Such early common for double-peaked Type IIb SNe with Hydrogen but uncommon normal Ibc very compact progenitors. In this paper, we systematically study a sample 14...
One of the open questions following discovery GW170817 is whether neutron star mergers are only astrophysical sites capable producing $r$-process elements. Simulations have shown that 0.01-0.1M$_\odot$ material could be generated in outflows originating from accretion disk surrounding rapidly rotating black hole forms as a remnant to both and collapsing massive stars associated with long-duration gamma-ray bursts (collapsars). The hallmark signature nucleosynthesis binary merger was its...
Abstract The nova rate in the Milky Way remains largely uncertain, despite its vital importance constraining models of Galactic chemical evolution as well understanding progenitor channels for Type Ia supernovae. has been previously estimated to be range ≈10–300 yr −1 , either based on extrapolations from a handful very bright optical novae or rates nearby galaxies; both methods are subject debatable assumptions. total discovery much smaller (≈5–10 ) than these estimates, even with advent...
Multi-Messenger observations and theory of astrophysical objects is fast becoming a critical research area in the astrophysics scientific community. In particular, point-like like that BL Lac, flat spectrum radio quasars (FSRQ), blazar candidates uncertain type (BCU) are distinct interest among those who look at synchrotron, Compton, neutrino, cosmic ray emissions sourced from compact objects. Notably, there also much correlation between multi-frequency blazars neutrino surveys on source...
Multi-messenger observations and theories of astrophysical objects are rapidly becoming a critical research area in the astrophysics scientific community. In particular, point-like such as BL Lacertae (BL Lac) objects, flat-spectrum radio quasars (FSRQs), blazar candidates uncertain type (BCUs) distinct interest to researchers studying synchrotron, Compton, neutrino, cosmic ray emissions sourced from compact objects. Notably, there is also much correlation between multi-frequency blazars...
The cores of stars are the cosmic furnaces where light elements fused into heavier nuclei. fusion hydrogen to helium initially powers all stars. ashes reactions then predicted serve as fuel in a series stages, eventually transforming massive structure concentric shells. These composed natal on outside, and consecutively compositions inside, be dominated by helium, carbon/oxygen, oxygen/neon/magnesium, oxygen/silicon/sulphur. Silicon sulphur inert iron, leading collapse core either supernova...
We study a magnitude-limited sample of 36 Broad-lined Type Ic Supernovae (SNe Ic-BL) from the Zwicky Transient Facility Bright Survey, detected between March 2018 and August 2021. present light curves (LCs) for each SNe, analyze shape LCs to derive empirical parameters, along with explosion epochs every event. The has an average absolute peak magnitude in r band $M_r^{max}$ = -18.51 $\pm$ 0.15 mag. Using spectra obtained around light, we compute expansion velocities Fe II 5169 Angstrom line...
In the past few years, improved sensitivity and cadence of wide-field optical surveys have enabled discovery several afterglows without associated detected gamma-ray bursts (GRBs). We present identification, observations, multiwavelength modeling a recent such afterglow (AT2023lcr), model three literature events (AT2020blt, AT2021any, AT2021lfa) in consistent fashion. For each event, we consider following possibilities as to why GRB was not observed: 1) jet off-axis; 2) had low initial...