Ramandeep Gill
A5037270880- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Astro and Planetary Science
- Solar and Space Plasma Dynamics
- Particle Detector Development and Performance
- Ionosphere and magnetosphere dynamics
- Atomic and Molecular Physics
- Nuclear Physics and Applications
- Geophysics and Gravity Measurements
- Dark Matter and Cosmic Phenomena
- High-pressure geophysics and materials
- Geomagnetism and Paleomagnetism Studies
- Astronomy and Astrophysical Research
- Cosmology and Gravitation Theories
- Magnetic confinement fusion research
- Stellar, planetary, and galactic studies
- Bipolar Disorder and Treatment
- Hydraulic and Pneumatic Systems
- Laser-Plasma Interactions and Diagnostics
- Radiation Therapy and Dosimetry
- Advanced MRI Techniques and Applications
- Pharmaceutical Practices and Patient Outcomes
- Historical Astronomy and Related Studies
Open University of Israel
2016-2024
Universidad Nacional Autónoma de México
2022-2024
George Washington University
2019-2022
Northeast Ohio Medical University
2021
Ben-Gurion University of the Negev
2017-2019
Goethe University Frankfurt
2019
James Cook University
2018
Stanford University
2017
Institut National de Physique Nucléaire et de Physique des Particules
2017
Université de Montpellier
2017
Abstract We report the discovery of GRB 221009A, highest flux gamma-ray burst (GRB) ever observed by Fermi Gamma-ray Burst Monitor (Fermi-GBM). This has continuous prompt emission lasting more than 600 s, which smoothly transitions to afterglow visible in Fermi-GBM energy range (8 keV–40 MeV), and total energetics higher any other sample. By using a variety new existing analysis techniques we probe spectral temporal evolution 221009A. find no prior trigger time ( t 0 ; 2022 October 9 at...
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...
The X-ray to radio afterglow emission of GRB 170817A/GW 170817 so far scales as $F_ν\proptoν^{-0.6}t^{0.8}$ with observed frequency and time, consistent a single power-law segment the synchrotron spectrum from external shock going into ambient medium. This requires effective isotropic equivalent energy in visible region increase $\sim t^{1.7}$. two main channels for such an are (i) \emph{radial}: more carried by slower material (in region) gradually catches up energizes it, (ii)...
The short-duration ($\lesssim2\;$s) GRB 170817A in the nearby ($D=40\;$Mpc) elliptical galaxy NGC 4993 is first electromagnetic counterpart of gravitational wave (GW) detection a binary neutron-star (NS-NS) merger. It was followed by optical, IR, and UV emission from half day up to weeks after event, as well late time X-ray radio emission. early UV, IR showed quasi-thermal spectrum suggestive radioactive-decay powered kilonova-like Comparison kilonova models favors formation short-lived...
ABSTRACT GRB 170817A/GW 170817 is the first gamma-ray burst (GRB) clearly viewed far from jet’s symmetry axis. Its afterglow was densely monitored over a wide range of frequencies and times. It has been modelled extensively, primarily numerically, although this endeavour very fruitful, many underlying model parameters remain undetermined. We provide analytic modelling afterglows observed off-axis, considering jets with narrow core (of half-opening angle θc) power-law wings in energy per unit...
ABSTRACT Exceptionally bright gamma-ray burst (GRB) afterglows can reveal the angular structure of their jets. GRB jets appear to have a narrow core (of half-opening angle θc), beyond which kinetic energy drops as power-law with θ from jet’s symmetry axis, $E_{\mathrm{ k},\rm iso}(\theta)\propto [1+(\theta /\theta _\mathrm{ c})^2]^{-a/2}$. The index reflects amount mixing between shocked jet and confining medium, depends on initial magnetization. Weakly magnetized undergo significant mixing,...
We present a complete analysis of Fermi Large Area Telescope (LAT) data GRB 221009A, the brightest Gamma-Ray Burst (GRB) ever detected. The burst emission above 30 MeV detected by LAT preceded 1 s low-energy (< 10 MeV) pulse that triggered Monitor (GBM), as has been observed in other GRBs. prompt phase 221009A lasted few hundred seconds. It was so bright we identify Bad Time Interval (BTI) 64 seconds caused extremely high flux hard X-rays and soft gamma rays, during which event...
Abstract We analyzed broadband X-ray and radio data of the magnetar SGR J1935+2154 taken in aftermath its 2014, 2015, 2016 outbursts. The source soft spectrum <10 keV is well described with a blackbody+power-law (BB+PL) or 2BB model during all three Nuclear Spectroscopic Telescope Array observations revealed hard tail, PL photon index Γ = 0.9, extending up to 50 keV, flux comparable one detected keV. Imaging analysis Chandra did not reveal small-scale extended emission around source....
Abstract The first, long-awaited, detection of a gravitational-wave (GW) signal from the merger binary neutron star (NS–NS) system was finally achieved (GW170817) and also accompanied by an electromagnetic counterpart—the short-duration gamma-ray burst (GRB) 170817A. It occurred in nearby ( Mpc) elliptical galaxy NGC 4993 showed optical, IR, UV emission half day up to weeks after event, as well late-time X-ray (at days) radio emission. There delay between GW chirp prompt GRB onset, upper...
Abstract We report on the observations of gamma-ray burst (GRB) 190114C by Fermi Gamma-ray Space Telescope and Neil Gehrels Swift Observatory . The prompt emission was detected GRB Monitor (GBM), Large Area (LAT), Burst Alert (BAT) long-lived afterglow subsequently observed GBM, LAT, X-ray (XRT), UV Optical Telescope. early-time reveal multiple components that evolve independently, with a delayed power-law component exhibits significant spectral attenuation above 40 MeV in first few seconds...
Abstract We present Atacama Large Millimeter/submillimeter Array 97.5 GHz total intensity and linear polarization observations of the mm-band afterglow GRB 190114C spanning 2.2–5.2 hr after burst. detect at ≈5 σ level, decreasing from Π = (0.87 ± 0.13)% to (0.60 0.19)%, evolving in position angle (10 5)° (−44 12)° during course observations. This represents first detection measurement temporal evolution polarized radio/millimeter emission a γ -ray show that optical X-ray between 0.03 days...
Abstract The main hard pulse of prompt gamma-ray emission in GRB 170817A had a duration ∼0.5 s, and its onset was delayed with respect to the gravitational-wave chirp signal by <?CDATA ${t}_{\mathrm{del}}\approx 1.74\,{\rm{s}}$?> . Detailed follow-up subsequent broadband kilonova revealed two-component ejecta—a lanthanide-poor ejecta mass M ej,blue ≈ 0.025 ⊙ that powered early but rapidly fading blue lanthanide-rich ${M}_{\mathrm{ej},\mathrm{red}}\approx 0.04\,{M}_{\odot }$?> longer-lasting...
Gamma-ray burst afterglows arise from relativistic collisionless shocks in which the postshock tangled magnetic field $\vec{B}$ is produced by two-stream and/or Weibel instabilities on plasma skin-depth scales $(c/\omega_p)$. The expected to be oriented predominantly within shock plane ($B_{\perp}$; transverse normal, $\hat{n}_{\rm{sh}}$), and often approximated completely it ($B_\parallel\equiv\hat{n}_{\rm{sh}}\,\cdot\,\vec{B}=0$). Current 2D/3D particle-in-cell simulations are limited...
We perform three-dimensional (3D) general-relativistic magnetohydrodynamic simulations to model the jet break-out from ejecta expected be produced in a binary neutron-star merger. The structure of relativistic outflow 3D simulation confirms our previous results 2D simulations, namely, that magnetized breaking out merger exhibits hollow core $\theta_{\rm core}\approx4^{\circ}$, an opening angle jet}\gtrsim10^{\circ}$, and is accompanied by wind ejected matter will contribute kilonova...
Over half a century from the discovery of gamma-ray bursts (GRBs), dominant radiation mechanism responsible for their bright and highly variable prompt emission remains poorly understood. Spectral information alone has proven insufficient understanding composition main energy dissipation in GRB jets. High-sensitivity polarimetric observations upcoming instruments this decade may help answer such key questions physics. This article reviews current status polarization measurements provides...
The ultra-relativistic outflows powering gamma-ray bursts (GRBs) acquire angular structure through their interaction with external material. They are often characterized by a compact, nearly uniform narrow core (with half-opening angle $\theta_{c,\{\epsilon,\Gamma\}}$) surrounded material energy per unit solid ($\epsilon=\epsilon_c\Theta_{\epsilon}^{-a}$, where $\Theta_{\{\epsilon,\Gamma\}}=[1+\theta^2/\theta_{c,\{\epsilon,\Gamma\}}^2]^{1/2}$) and initial specific kinetic...
ABSTRACT We report on the analysis of two deep XMM-Newton observations magnetar Swift J1834.9−0846 and its surrounding extended emission taken in 2014 March October, 2.5 3.1 yr after source went into outburst. The is only weakly detected first observation, with an absorption-corrected flux <?CDATA ${F}_{0.5-10\mathrm{keV}}\approx 4\times {10}^{-14}$?> erg s −1 cm −2 a $3\sigma $?> upper limit during second observation about 3 × 10 −14 . This level more than orders magnitude lower measured at...
Abstract Despite being hard to measure, GRB prompt γ-ray emission polarization is a valuable probe of the dominant mechanism and outflow’s composition angular structure. During outflow ultra-relativistic with Lorentz factors Γ ≫ 1. We describe in detail linear properties various mechanisms: synchrotron radiation from different magnetic field structures (ordered: toroidal Btor or radial B∥, random: normal direction B⊥), Compton drag, photospheric emission. calculate for jet (e.g. top-hat,...
Abstract We present the Fermi Large Area Telescope (LAT) observations of binary neutron star merger event GW170817 and associated short gamma-ray burst (SGRB) GRB 170817A detected by Gamma-ray Burst Monitor. The LAT was entering South Atlantic Anomaly at time LIGO/Virgo trigger ( t GW ) therefore cannot place constraints on existence high-energy E > 100 MeV) emission with moment coalescence. focus instead constraining longer timescales. No candidate electromagnetic counterpart timescales...
The observations of GW170817/GRB170817A have confirmed that the coalescence a neutron-star binary is progenitor short gamma-ray burst. In standard picture burst, collimated highly relativistic outflow launched after merger and it successfully breaks out from surrounding ejected matter. Using initial conditions inspired numerical-relativity simulations, we performed general-relativistic hydrodynamic (HD) magnetohydrodynamic (MHD) simulations in which jet propagates self-consistently. complete...
The afterglow of GRB$\,$170817A/GW$\,$170817 was very unusual, slowly rising as $F_\nu\propto{}t_{\rm{}obs}^{0.8}\nu^{-0.6}$, peaking at $t_{\rm{obs,pk}}\sim\,150\;$days, and sharply decaying $\sim{}t_{\rm{}obs}^{-2.2}$. VLBI observations revealed an unresolved radio image whose flux centroid moved superluminally with $v_{\rm{app}}\approx4c$, clearly indicating that the dominated by a relativistic jet's compact core. Different jet angular structures explained lightcurves: Gaussian steep...
The light pseudoscalar particle, dubbed the axion, borne out of Peccei-Quinn solution to strong $CP$ problem in QCD remains elusive. One avenue inferring its existence is through coupling electromagnetic radiation. So far, laboratory experiments have dedicated all efforts detect axion mass range ${10}^{\ensuremath{-}6}<{m}_{a}<{10}^{\ensuremath{-}3}\text{ }\text{ }\mathrm{eV}$ with a photon-axion strength ${g}_{a\ensuremath{\gamma}\ensuremath{\gamma}}<{10}^{\ensuremath{-}10}\text{...
We present the Fermi Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) observations of LIGO binary black hole merger event GW151226 candi- date LVT151012. No candidate electromagnetic counterparts were detected by either GBM or LAT. a detailed analysis LAT data over range timescales from seconds to years, using automated pipelines new techniques for char- acterizing upper limits across large area sky. Due partial coverage localization regions at trigger times both events, dif-...