S. Razzaque
A5072732961- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Neutrino Physics Research
- Dark Matter and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Pulsars and Gravitational Waves Research
- Particle physics theoretical and experimental studies
- Particle Detector Development and Performance
- Astrophysical Phenomena and Observations
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Particle Accelerators and Free-Electron Lasers
- Solar and Space Plasma Dynamics
- Cosmology and Gravitation Theories
- Astro and Planetary Science
- Nuclear Physics and Applications
- SAS software applications and methods
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Gyrotron and Vacuum Electronics Research
- Radiation Detection and Scintillator Technologies
- Scientific Research and Discoveries
- Statistical and numerical algorithms
- Atomic and Subatomic Physics Research
- Geophysics and Gravity Measurements
George Washington University
2022-2025
University of Johannesburg
2015-2024
Aryabhatta Research Institute of Observational Sciences
2021-2024
Centre National de la Recherche Scientifique
2016-2024
National Institute for Theoretical Physics
2022-2024
École Nationale Supérieure d'Ingénieurs de Caen
2024
Normandie Université
2024
Laboratoire de Physique Corpusculaire de Caen
2024
Université de Caen Normandie
2024
Université Paris Cité
2019-2023
The dwarf spheroidal satellite galaxies of the Milky Way are some most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack astrophysical backgrounds, widely considered be among promising targets for indirect detection via $\ensuremath{\gamma}$ rays. Here we report on $\ensuremath{\gamma}$-ray observations 25 based 4 years Fermi Large Area Telescope (LAT) data. None significantly detected in rays, present flux upper limits between 500 MeV GeV. We...
The extragalactic background light (EBL) from the far infrared through visible and extending into ultraviolet is thought to be dominated by starlight, either direct emission or absorption reradiation dust. This most important energy range for absorbing $\g$-rays distant sources such as blazars gamma-ray bursts producing electron positron pairs. In previous work we presented EBL models in optical consistently taking account star formation rate (SFR), initial mass function (IMF) dust...
On 2015 June 16, Fermi-LAT observed a giant outburst from the flat spectrum radio quasar 3C 279 with peak $>100$ MeV flux of $\sim3.6\times10^{-5}\;{\rm photons}\;{\rm cm}^{-2}\;{\rm s}^{-1}$ averaged over orbital period intervals. It is historically highest $\gamma$-ray source including past EGRET observations, isotropic luminosity reaching $\sim10^{49}\;{\rm erg}\;{\rm s}^{-1}$. During outburst, Fermi spacecraft, which has an 95.4 min, was operated in special pointing mode to optimize...
Abstract The Large Area Telescope (LAT) aboard the Fermi spacecraft routinely observes high-energy emission from gamma-ray bursts (GRBs). Here we present second catalog of LAT-detected GRBs, covering first 10 yr operations, 2008 to 2018 August 4. A total 186 GRBs are found; these, 91 show in range 30–100 MeV (17 which seen only this band) and 169 detected above 100 MeV. Most these sources were discovered by other instruments ( /GBM, Swift /BAT, AGILE, INTEGRAL ) or reported Interplanetary...
Abstract We present a search for spatial extension in high-latitude ( ) sources recent Fermi point source catalogs. The result is the High-Latitude Extended Sources Catalog, which provides extensions (or upper limits thereof) and likelihood profiles suite of tested morphologies. find 24 extended sources, 19 were not previously characterized as extended. These include that are potentially associated with supernova remnants star-forming regions. also found γ -ray emission vicinity Cen A radio...
The Fermi Large Area Telescope (LAT) light curve repository (LCR) is a publicly available, continually updated library of gamma-ray curves variable Fermi-LAT sources generated over multiple timescales. LCR aims to provide publication-quality binned on timescales 3 days, 7 and 30 days for 1525 deemed in the source catalog first 10 years observations. consists through full likelihood analyses that model surrounding region, providing fluxes photon indices each time bin. intended as resource...
Abstract The preliminary detections of the gamma-ray burst 221009A up to 18 TeV by LHAASO and 251 Carpet 2 have been reported through Astronomer’s Telegrams Gamma-ray Coordination Network circulars. Since this is at redshift z = 0.1505, these photons may first seem a low probability avoid pair production off background radiation fields survive reach detectors on Earth. By extrapolating 0.1–1.0 GeV Fermi Large Area Telescope spectrum from higher energies using limit intrinsic burst, we show...
GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments Large Area (LAT) and Burst Monitor (GBM). The burst consisted of one major emission episode which lasted for ~24.5 seconds (in GBM) had a peak flux 5.7\pm0.2 x 10^{-5} erg/s/cm^2. time-resolved spectrum is best modeled with combination Band function blackbody spectrum. energy component initially 15\pm2 MeV, highest value ever detected in GRB. This measurement made possible combining GBM/BGO data LAT Low...
Recent claims that the strength BIGMF of intergalactic magnetic field (IGMF) is ≳ 10−15 G are based on upper limits to expected cascade flux in GeV band produced by blazar TeV photons absorbed extragalactic background light. This limit depends an assumption mean remains constant timescales 2(BIGMF/10−18G)2/(E/10 GeV)2 yr for IGMF coherence length ≈1 Mpc, where E measured photon energy. Restricting activity 1ES 0229+200 ≈3–4 years during which source has been observed leads a more robust...
Current theories predict relativistic hadronic particle populations in clusters of galaxies addition to the already observed leptons. In these scenarios interactions give rise neutral pions which decay into γ rays that are potentially observable with Large Area Telescope (LAT) on board Fermi space telescope. We present a joint likelihood analysis searching for spatially extended γ-ray emission at locations 50 galaxy four years Fermi-LAT data under assumption universal cosmic-ray (CR) model...
An incremental version of the fourth catalog active galactic nuclei (AGNs) detected by Fermi-Large Area Telescope is presented. This (4LAC-DR3) derives from third data release 4FGL based on 12 years E>50 MeV gamma-ray data, where spectral parameters, energy distributions (SEDs), yearly light curves, and associations have been updated for all sources. The new reported AGNs include 587 blazar candidates four radio galaxies. We describe properties sample outline changes affecting previously...
The All-sky Medium Energy Gamma-ray Observatory eXplorer (AMEGO-X) is designed to identify and characterize gamma rays from extreme explosions accelerators. main science themes include: supermassive black holes their connections neutrinos cosmic rays; binary neutron star mergers the relativistic jets they produce; ray particle acceleration sources including Galactic supernovae; continuous monitoring of other astrophysical events over full sky in this important energy range. AMEGO-X will...
The brightest long gamma-ray burst detected so far by the Swift-BAT and Fermi-GBM telescopes, GRB~221009A, provides an unprecedented opportunity for understanding high-energy processes in extreme transient phenomena. We find that conventional leptonic models, synchrotron synchrotron-self-Compton, afterglow emission from this source have difficulties explaining observation of $\gtrsim 10$ TeV $\gamma$ rays, LHAASO detector, extending up to 18 energies. model $\gamma$-ray spectrum estimated...
Neutrinos at energies above TeV can serve as probes of the stellar progenitor and jet dynamics gamma ray bursts arising from core collapses. They also probe collapses which do not lead to rays, may be much more numerous. We calculate detailed neutrino spectra shock accelerated protons in jets just below outer envelope, before their emergence. present flux estimates such preburst for two different massive models. These should distinguishable by IceCube, we discuss implications.
The origin of the ultrahigh-energy (UHE) cosmic rays (CRs) from second knee ($\ensuremath{\sim}6\ifmmode\times\else\texttimes\fi{}{10}^{17}\text{ }\text{ }\mathrm{eV}$) above in CR spectrum is still unknown. Recently, there has been growing evidence that a peculiar type supernovae, called hypernovae, are associated with subenergetic gamma-ray bursts, such as SN1998bw/GRB980425 and SN2003lw/GRB031203. Such hypernovae appear to have high (up mildly relativistic) velocity ejecta, which may be...
The Auger Collaboration reports that the arrival directions of >60 EeV ultra-high energy cosmic rays (UHECRs) cluster along supergalactic plane and correlate with active galactic nuclei (AGN) within ~100 Mpc. association several events nearby radio galaxy Centaurus A supports paradigm UHECRs are powered by supermassive black-hole engines accelerated to energies in shocks formed variable plasma winds inner jets galaxies. GZK horizon length 75 UHECR protons is Mpc, so results consistent an...
The center of the Milky Way is a host to energetic phenomena across many electromagnetic wave bands and now possibly high-energy neutrinos. We show that 5 out 21 IceCube showerlike events, including PeV event, likely originated from Galactic Center region. A hard spectrum flux inferred these events are inconsistent with atmospheric neutrinos consistent an extrapolation gamma-ray measured by Fermi-LAT inner This indicates common hadronic origin both, powered supernovae. Three other spatially...
We discuss the possibility that IceCube neutrino telescope might be observing Fermi bubbles. If bubbles discovered in gamma rays originate from accelerated protons, they should strong emitters of high energy ($\ensuremath{\gtrsim}\mathrm{GeV}$) neutrinos. These neutrinos are detectable as showerlike or tracklike events at a ${\mathrm{Km}}^{3}$ observatory. For primary cosmic ray flux with spectrum $\ensuremath{\propto}{E}^{\ensuremath{-}2.1}$ and cutoff above 10 PeV, bubble substantially...
We present the first Fermi - Large Area Telescope (LAT) solar flare catalog covering 24 th cycle. This contains 45 -LAT flares (FLSFs) with emission in gamma-ray energy band (30 MeV 10 GeV) detected a significance greater than 5 sigma over years 2010-2018. A subsample containing 37 of these exhibit delayed beyond prompt-impulsive hard X-ray phase 21 showing lasting more two hours. No is four flares. also this observations GeV from 3 originating Active Regions located behind limb (BTL)...
Abstract While the available set of Gamma-ray Burst (GRB) data with known redshift is currently limited, a much larger GRB without from different instruments. This includes well-measured prompt gamma-ray flux and spectral information. We estimate selection these GRBs detected by Fermi-GBM Konus-Wind using Machine Learning techniques that are based on parameters. find Deep Neural Networks Random Forest models employing non-linear relations among input parameters can reasonably reproduce...
We have calculated the opacities and secondary production mechanisms of high energy photons arising in gamma-ray burst internal shocks, using exact cross-sections for relevant processes. find that reasonable choices parameters, range 10's to 100's GeV may be emitted prompt phase. Photons above this are subject electron-positron pair with fireball would absent from spectrum escaping burst. that, such cases, becomes optically thin again at ultra-high energies ($\gtrsim$ PeV). On other hand,...
A fraction of core-collapse supernovae type Ib/c are associated with gamma-ray bursts, which thought to produce highly relativistic jets. Recently, it has been hypothesized that a larger slower jets, may contribute the disruption and ejection supernova envelope, explain unusually energetic hypernovae. We explore TeV neutrino signatures expected from such calculate detection rates upcoming Gigaton Cherenkov experiments. conclude individual jetted be detectable nearby galaxies.