29 research outputs found
On the spherical-axial transition in supernova remnants
A new law of motion for supernova remnant (SNR) which introduces the quantity
of swept matter in the thin layer approximation is introduced. This new law of
motion is tested on 10 years observations of SN1993J. The introduction of an
exponential gradient in the surrounding medium allows to model an aspherical
expansion. A weakly asymmetric SNR, SN1006, and a strongly asymmetric SNR,
SN1987a, are modeled. In the case of SN1987a the three observed rings are
simulated.Comment: 19 figures and 14 pages Accepted for publication in Astrophysics &
Space Science in the year 201
Turbulence induced additional deceleration in relativistic shock wave propagation: implications for gamma-ray burst
The late afterglow of gamma-ray burst is believed to be due to progressive
deceleration of the forward shock wave driven by the gamma-ray burst ejecta
propagating in the interstellar medium. We study the dynamic effect of
interstellar turbulence on shock wave propagation. It is shown that the shock
wave decelerates more quickly than previously assumed without the turbulence.
As an observational consequence, an earlier jet break will appear in the light
curve of the forward shock wave. The scatter of the jet-corrected energy
release for gamma-ray burst, inferred from the jet-break, may be partly due to
the physical uncertainties in the turbulence/shock wave interaction. This
uncertainties also exist in two shell collisions in the well-known internal
shock model proposed for gamma-ray burst prompt emission. The large scatters of
known luminosity relations of gamma-ray burst may be intrinsic and thus
gamma-ray burst is not a good standard candle. We also discuss the other
implications.Comment: accepted for publication in Astrophysics and Space Scienc
On the sensitivity of the HAWC observatory to gamma-ray bursts
We present the sensitivity of HAWC to Gamma Ray Bursts (GRBs). HAWC is a very
high-energy gamma-ray observatory currently under construction in Mexico at an
altitude of 4100 m. It will observe atmospheric air showers via the water
Cherenkov method. HAWC will consist of 300 large water tanks instrumented with
4 photomultipliers each. HAWC has two data acquisition (DAQ) systems. The main
DAQ system reads out coincident signals in the tanks and reconstructs the
direction and energy of individual atmospheric showers. The scaler DAQ counts
the hits in each photomultiplier tube (PMT) in the detector and searches for a
statistical excess over the noise of all PMTs. We show that HAWC has a
realistic opportunity to observe the high-energy power law components of GRBs
that extend at least up to 30 GeV, as it has been observed by Fermi LAT. The
two DAQ systems have an energy threshold that is low enough to observe events
similar to GRB 090510 and GRB 090902b with the characteristics observed by
Fermi LAT. HAWC will provide information about the high-energy spectra of GRBs
which in turn could help to understanding about e-pair attenuation in GRB jets,
extragalactic background light absorption, as well as establishing the highest
energy to which GRBs accelerate particles
Observation of inverse Compton emission from a long Îł-ray burst.
Long-duration Îł-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission1,2. Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands1-6. The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock7-9. Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C10,11. Here we report multi-frequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 Ă 10-6 to 1012 electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs
The statistics of BAT-to-XRT flux ratio in GRBs: Evidence for a characteristic value and its implications
We present the statistics of the ratio, R, between the prompt and afterglow "plateau" fluxes of gamma-ray bursts (GRBs). We define this as the ratio of the mean prompt energy flux in Swift BAT and the Swift XRT one, immediately following the steep transition between these two states and the beginning of the afterglow stage referred to as the "plateau". Like the distribution of many other GRB observables, the histogram of R is log-normal with maximum at a value Rm â 2000, FWHM of about two decades, and with the entire distribution spanning about five decades in the value of R. We note that the peak of the distribution is close to the proton-to-electron mass ratio (Rm â mp/me = 1836), as proposed to be the case in an earlier publication, on the basis of a specific model of the GRB dissipation process. It therefore appears that, in addition to the values of the energy of peak luminosity Epk ⌠mec2, GRBs present us with one more quantity with an apparent characteristic value. The fact that the values of both these quantities (Epk and R) are consistent with the same specific model invoked to account for the efficient conversion of their relativistic proton energies to electrons argues favorably for its underlying assumptions. © 2015. The American Astronomical Society. All rights reserved
Observational evidence for magnetars powering GRBs
The coreâcollapse of a massive star may lead either to a black hole or a, possibly unstable, rapidlyârotating magnetar. A magnetar provides an potential additional source of rotational energy which is available to power emission during the burst. If the energy reservoir is used up the magnetar may then suffer gravitational collapse ending the emission period. We have carried out a systematic search for the signature of a spinningâdown magnetar in the long GRBs observed by the Swift satellite up to the end of 2008. We find 10 GRBs that have a featureâwhich we call an âinternal plateauââin their light curves that can be associated with the injection of energy into the jet by a magnetar. The duration and intensity of the internal plateau provides constraints on the initial spin period and magnetic field of the magnetar. The derived magnetic fields are large compared to those of longâlived galactic magnetars, but are within the most extreme values predicted for magnetars
GRB 070224: Swift detection of a burst
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GRB 070126: Swift detection of a possible burst
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