2,018 research outputs found
Statistical Properties of Multiple Optical Emission Components in Gamma-Ray Bursts and Implications
Well-sampled optical lightcurves of 146 gamma-ray bursts (GRBs) are complied
from the literature. Multiple optical emission components are extracted with
power-law function fits to these lightcurves. We present a systematical
analysis for statistical properties and their relations to prompt gamma-ray
emission and X-ray afterglow for each component. We show that peak luminosity
in the prompt and late flares are correlated and the evolution of the peak
luminosity may signal the evolution of the accretion rate. No tight correlation
between the shallow decay phase/plateau and prompt gamma-ray emission is found.
Assuming that they are due to a long-lasting wind injected by a compact object,
we show that the injected behavior favors the scenarios of a long-lasting wind
after the main burst episode. The peak luminosity of the afterglow onset is
tightly correlated with Eiso, and it is dimmer as peaking later. Assuming that
the onset bump is due to the fireball deceleration by the external medium, we
examine the Gamma_0-Eiso relation and find that it is confirmed with the
current sample. Optical re-brightening is observed in 30 GRBs in our sample. It
shares the same relation between the width and the peak time as found in the
onset bump, but no clear correlation between the peak luminosity and Eiso as
observed in the onset bumps is found. Although its peak luminosity also decays
with time, the slope is much shallower than that of the onset peak. We get L
t^{-1}_{p}$, being consistent with off-axis observations to an expanding
external fireball in a wind-like circum medium. The late re-brightening may
signal another jet component. Mixing of different emission components may be
the reason for the observed chromatic breaks in different energy bands.Comment: 10 pages, 5 figures, to be published by IJMPD (Proceedings of "The
Third Galileo - Xu Guangqi meeting", Beijing, October 11-15, 2011
Enhance Primordial Black Hole Abundance through the Non-linear Processes around Bounce Point
The non-singular bouncing cosmology is an alternative paradigm to inflation,
wherein the background energy density vanishes at the bounce point, in the
context of Einstein gravity. Therefore, the non-linear effects in the evolution
of density fluctuations () may be strong in the bounce phase,
which potentially provides a mechanism to enhance the abundance of primordial
black holes (PBHs). This article presents a comprehensive illustration for PBH
enhancement due to the bounce phase. To calculate the non-linear evolution of
, the Raychaudhuri equation is numerically solved here. Since the
non-linear processes may lead to a non-Gaussian probability distribution
function for after the bounce point, the PBH abundance is
calculated in a modified Press-Schechter formalism. In this case, the criterion
of PBH formation is complicated, due to complicated non-linear evolutionary
behavior of during the bounce phase. Our results indicate that
the bounce phase indeed has potential to enhance the PBH abundance
sufficiently. Furthermore, the PBH abundance is applied to constrain the
parameters of bounce phase, providing a complementary to the surveys of cosmic
microwave background and large scale structure.Comment: 17 pages, 6 figure
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