A5100325652- Gamma-ray bursts and supernovae
- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Aluminum Alloys Composites Properties
- Transition Metal Oxide Nanomaterials
- Gas Sensing Nanomaterials and Sensors
- ZnO doping and properties
- Advanced Machining and Optimization Techniques
- Stellar, planetary, and galactic studies
- Aluminum Alloy Microstructure Properties
- Advanced Welding Techniques Analysis
- Quantum Dots Synthesis And Properties
- Relativity and Gravitational Theory
- Astronomical and nuclear sciences
- Additive Manufacturing and 3D Printing Technologies
- Inorganic Chemistry and Materials
- Nonlinear Optical Materials Research
- Magnesium Alloys: Properties and Applications
- Quantum and electron transport phenomena
- Catalysis and Oxidation Reactions
- Semiconductor Quantum Structures and Devices
- Advanced Surface Polishing Techniques
- Metal Alloys Wear and Properties
Technical University of Darmstadt
2024
GSI Helmholtz Centre for Heavy Ion Research
2024
Social Service Sericulture Project Trust
2022-2024
The University of Texas at Austin
2003-2021
AAA College of Engineering and Technology
2020-2021
Hindu College of Pharmacy
2011
National College
2011
Pennsylvania State University
2006
Institute for Advanced Study
2000-2002
We extend our calculation of physical parameters gamma-ray burst (GRB) jets by modeling the broadband emission afterglows 970508, 980519, 991208, 000926, 000418, and 010222. Together with 990123, 990510, 991216, 000301c, there are 10 well-observed for which initial opening angle GRB jet can be constrained. The energies (after phase) obtained this set within one decade around 5 × 1050 ergs. With exception requires a wider than rad, half-angle in other cases ranges from 2° to 20°. find that...
Assuming an adiabatic evolution of a gamma-ray burst (GRB) remnant interacting with external medium, we calculate the injection, cooling, and absorption break frequencies afterglow flux for plausible orderings observing frequencies. The analytical calculations are restricted to relativistic and, in case collimated ejecta, phase where there is insignificant lateral expansion. Results given both homogeneous medium wind ejected by GRB progenitor. We compare emission at different frequencies,...
Abstract Observations of gamma-ray bursts by the Fermi satellite, capable detecting photons in a very broad energy band: 8keV to >300GeV, have opened new window for study these enigmatic explosions. It is widely assumed that larger than 100 MeV are produced same source generated lower – at least whenever shape spectrum Band function. We report here surprising result data bright burst, GRB 080916C, unambiguously shows high-energy (≳102MeV) were external shock via synchrotron process,...
We model the radio, optical, and X-ray emission for afterglows of GRB 980703, 990123, 990510, 991216, within framework relativistic jets, to determine their physical parameters. The models that yield acceptable fits data have jet energies mostly between 1050 1051 ergs initial opening angles 1° 4°. external medium density is uncertain by at least 1 order magnitude in each case, being around 10-3 cm-3 980703 ~10-1 ~3 991216. If jets are uniform (i.e., there no angular gradients energy per...
This present investigation focusing on preparation of Al-based hybrid composites in which Al6082 is engaged as the main alloy reinforced with two reinforcements ZrSiO₄/TiC. The combination stir-squeeze process helps to make different specimen by change four parameters such stir speed, time, reinforcements, and squeeze pressure. In this process, are reserved constant about 7.5 wt%. levels each parameter speed (300, 400, 500, 600 rpm), time (10, 15, 20, 25 min), reinforcement (2.5, 5, 7.5, 10...
This study explained about machining parameters of Al5086/Flyash/Sic hybrid metal matrix composites by the Taguchi technique. Al5086 reinforced in SiC (5–10 wt %) and 8% weight flyash are retained as constants. The specimens prepared with help stir casting method. material removal rate was examined electrochemical under various such feed (0.15–0.30 mm/min), voltage (10–20 V), electrolyte concentration (20–35 g/litre). Taguchi’s L16 orthogonal array selected for design experiments (DOEs), 16...
We present the results from a Hubble Space Telescope ACS search for supernovae associated with X-ray flashes 020903, 040701, 040812, and 040916. find strong evidence that XRF 020903 (z = 0.25) was SN 1998bw-like supernova confirm this using optical spectroscopy at t ~ 25 days. no evidence, however, other three events. In case of 040701 0.21), we rule out even faint similar to 2002ap, template light curves several local Type Ic supernovae. For two cases in which redshift is not known, XRFs...
It is widely believed that the maximum energy of synchrotron photons when electrons are accelerated in shocks via Fermi process about 50 MeV (in plasma comoving frame). We show under certain conditions, which expected to be realized relativistic gamma-ray bursts, much larger than (comoving frame) can produced. The requirement magnetic field should decay downstream shock front on a length scale small compared with distance traveled by highest before they lose half their energy; produced close...
The energy release in gamma-ray bursts (GRBs) is one of the most useful clues to nature their "inner engines." We show that within framework relativistic external shock afterglow model, narrowness observed X-ray flux GRB afterglows implies jets, after early-afterglow phase, spans less than 1 order magnitude. This result not affected by uncertainties electron energy, magnetic field strength, or medium density. argue kinetic a factor 2 initial ejecta; therefore, output central engine...
In recent work, we suggested that photons of energy >100 MeV detected from gamma-ray bursts (GRBs) by the Fermi satellite are produced via synchrotron emission in external forward shock with a weak magnetic field – consistent shock-compressed upstream few tens μG. Here investigate whether electrons can be accelerated to energies such they radiate up about 10 GeV this particular scenario. We do using two methods: (i) check if these confined front; and (ii) calculate radiative losses while...
We calculate the reverse shock (RS) synchrotron emission in optical and radio wavelength bands from electron-positron pair enriched gamma-ray burst ejecta with goal of determining content GRBs using early time observations. take into account an extensive number physical effects that influence radiation reverse-shock heated GRB ejecta. find optical/IR flux depends very weakly on pairs ejecta, there is no unique signature enrichment if observations are confined to a single band. It may be...
Photons of energy larger than 100 MeV from long-GRBs arrive a few seconds after <10 photons do. We show that this delay is natural consequence magnetic dominated relativistic jet. The much slower acceleration jet with radius (compared hot baryonic outflow) results in high gamma-ray to be converted electron-positron pairs out whereas lower gamma-rays less ~10 can escape when the crosses Thomson-photosphere. resulting for arrival found similar value observed by Fermi satellite number GRBs. A...
We investigate analytically the effect of an anisotropic distribution kinetic energy within a relativistic fireball on decay afterglow emission, focusing axially symmetric fireballs with uniform core and power-law decrease angle outside core. The fall-off steepens after becomes fully visible. For observer directions core, simple formulae are derived for break, while off-core observers results shown graphically. Some criteria assessing from observations necessity angular structure and/or...
Abridged: The decay of half the GRB radio afterglows with long temporal monitoring is significantly slower than at optical frequencies, contrary to what expected in simplest fireball model. We investigate four ways decouple and decays: an evolving index power-law distribution shock-accelerated electrons, presence a spectral break between two domains, structured outflow, long-lived reverse shock contribution afterglow emission. [...] In fourth scenario, it assumed that emission arises...
Swift discovered GRB 050128 with the Burst Alert Telescope and promptly pointed its narrow field instruments to monitor afterglow. X-ray observations started 108 s after trigger time. The early decay of afterglow is relatively flat, a temporal modeled power-law index ~-0.3. A steepening occurs at later times (~1500 s) ~-1.3. During this transition, observed spectrum does not change. We interpret behavior as either an jet break or evidence transition from fast cooling regime slow in wind environment.
The known I π = 8 + 1 , Ex 2129-keV isomer in the semi-magic nucleus 130 Cd82 was populated projectile fission of a 238 U beam at Radioactive Isotope Beam Factory RIKEN.The high counting statistics accumulated data allowed to determine excitation energy, 2001.2(2)keV, and half-life, T 1/2 57(3) ns, 6 state based on γγ coincidence information.Furthermore, half-life state, 224(4) remeasured with precision.The new experimental information, combined available for 134 Sn large-scale shell model...
We describe our attempt to determine if gamma-ray burst (GRB) and afterglow emissions could both arise in external shocks for simple GRBs--bursts consisting of just a few peaks their lightcurves. calculate peak flux frequency during the ten well observed bursts using same set parameters that are determined from modeling emissions. find emission properties 970508 (which had single lightcurve) fit nicely with extrapolation its data, therefore this was likely produced shock. One can explain two...
We report on the temporal and spectral characteristics of early X-ray emission from Gamma Ray Bursts GRB050126 GRB050219A as observed by Swift . The light-curves these 2 bursts both show remarkably steep decays (), breaking to flatter slopes timescales a few hundred seconds. For burst shows no evidence evolution in 20–150 keV band, index γ-ray afterglows are significantly different suggesting separate origin. By contrast BAT spectrum displays significant evolution, becoming softer at later...
The prompt optical emission of GRB 990123 was uncorrelated to the gamma-ray light-curve and exhibited temporal properties similar those steeply-decaying, early X-ray observed by Swift at end many bursts. These facts suggest that counterpart large-angle released during (the second pulse of) burst. If emissions have, indeed, same origin then their require (i) synchrotron gamma-rays arose from inverse-Compton scatterings ("synchrotron self-Compton model"), (ii) peak-energy optical-synchrotron...