61,646 research outputs found
Variation of the Amati Relation with the Cosmological Redshift: a Selection Effect or an Evolution Effect?
Because of the limit in the number of gamma-ray bursts (GRBs) with available
redshifts and spectra, all current investigations on the correlation among GRB
variables use burst samples with redshifts that span a very large range. The
evolution and selection effects have thus been ignored, which might have
important influence on the results. In this Letter, we divide the 48
long-duration GRBs in Amati (2006, 2007) into four groups with redshift from
low to high, each group contains 12 GRBs. Then we fit each group with the Amati
relation \log E_\iso = a + b \log E_\p, and check if the parameters and
evolve with the GRB redshift. We find that and vary with the mean
redshift of the GRBs in each group systematically and significantly.
Monte-Carlo simulations show that there is only percent of chance that
the variation is caused by the selection effect arising from the fluence limit.
Hence, our results may indicate that GRBs evolve strongly with the cosmological
redshift.Comment: 5 pages, including 5 figures. MNRAS Letters accepte
Search for strong gravitational lensing effect in the current GRB data of BATSE
Because gamma-ray bursts (GRBs) trace the high-z Universe, there is an
appreciable probability for a GRB to be gravitational lensed by galaxies in the
universe. Herein we consider the gravitational lensing effect of GRBs
contributed by the dark matter halos in galaxies. Assuming that all halos have
the singular isothermal sphere (SIS) mass profile in the mass range and all GRB samples follow
the intrinsic redshift distribution and luminosity function derived from the
Swift LGRBs sample, we calculated the gravitational lensing probability in
BATSE, Swift/BAT and Fermi/GBM GRBs, respectively. With an derived probability
result in BATSE GRBs, we searched for lensed GRB pairs in the BATSE 5B GRB
Spectral catalog. The search did not find any convincing gravitationally lensed
events. We discuss our result and future observations for GRB lensing
observation.Comment: 18 pages, 8 figure
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