1,217 research outputs found
The role of photon scattering in shaping the lightcurves and spectra of gamma-ray bursts
We analyze the power spectra of the lightcurves of long gamma-ray bursts,
dividing the sample in bins of luminosity, using the recently discovered
variability-luminosity correlation. We find that the value of the variability
parameter strongly correlates with the frequency that contains most of the
power in the burst comoving frame. We compute the average power spectra in
luminosity bins. The average power spectrum is well described by a broken
power-low and the break frequency is a function of the variability parameter,
while the two slopes are roughly constant. This allow us to conclude that
scattering processes do not play a relevant role in modelling the lightcurves.
We finally discuss in which conditions scattering may still play a relevant
role in shaping the spectra of GRBs.Comment: Minor changes according to referee comments. Accepted for publication
in MNRA
Gamma-Ray Burst Progenitors Confront Observations
The discovery of a supernova emerging at late times in the afterglow of GRB
030329 has apparently settled the issue on the nature of the progenitor of
gamma-ray bursts. We now know that at least a fraction of cosmological GRBs are
associated with the death of massive stars, and that the two explosions are
most likely simultaneous. Even though the association was already suggested for
GRB 980425, the peculiarity of that burst did not allow to extend the
association to all GRBs. The issue is now to understand whether GRB 030329 is a
"standard burst" or not. I will discuss some peculiarities of GRB 030329 and
its afterglow lightcurve showing how, rather than a classical cosmological GRB,
it looks more like a transition object linking weak events like GRB 980425 to
the classical long duration GRBs. I will also discuss the problems faced by the
Hypernova scenario to account for the X-ray features detected in several GRBs
and their afterglows.Comment: 17 pages, 9 postscript figures. Invited review at the Xth Marcel
Grossmann Meeting on General Relativity, Rio de Janeiro, Brazil, July 200
High-efficiency photospheric emission of long-duration gamma-ray burst jets: the effect of the viewing angle
We present the results of a numerical investigation of the spectra and light
curves of the emission from the photospheres of long-duration gamma-ray burst
jets. We confirm that the photospheric emission has high efficiency and we show
that the efficiency increases slightly with the off-axis angle. We show that
the peak frequency of the observed spectrum is proportional to the square root
of the photosphere's luminosity, in agreement with the Amati relation. However,
a quantitative comparison reveals that the thermal peak frequency is too small
for the corresponding total luminosity. As a consequence, the radiation must be
out of thermal equilibrium with the baryons in order to reproduce the
observations. Finally, we show that the spectrum integrated over the emitting
surface is virtually indistinguishable from a Planck law, and therefore an
additional mechanism has to be identified to explain the non-thermal behavior
of the observed spectra at both high and low frequencies.Comment: 6 pages, 8 figures, ApJ in press (few changes to figures
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