Issue |
A&A
Volume 385, Number 2, April II 2002
|
|
---|---|---|
Page(s) | 377 - 398 | |
Section | Cosmology (including clusters of galaxies) | |
DOI | https://doi.org/10.1051/0004-6361:20020038 | |
Published online | 15 April 2002 |
Temporal properties of gamma ray bursts as signatures of jets from the central engine
1
Department of Experimental Physics, University College Dublin, Dublin 4, Ireland
2
X-Ray Astronomy Group, Department of Physics and Astronomy, Leicester University, Leicester LE1 7RH, UK
Corresponding author: F. Quilligan, fquillig@bermuda.ucd.ie
Received:
31
July
2001
Accepted:
7
January
2002
A comprehensive temporal analysis has been performed
on the 319 brightest GRBs with s from the BATSE
current catalog. The GRBs were denoised using wavelets and
subjected to an automatic pulse selection algorithm as an
objective way of identifying pulses and quantifying the effects
of neighbouring pulses. The number of statistically significant
pulses selected from the sample was greater than 3000. The rise
times, fall times, full-widths at half-maximum (FWHM), pulse
amplitudes and pulse areas were measured and the frequency
distributions are presented here. All are consistent with
lognormal distributions provided the pulses are well separated.
The distribution of time intervals between pulses is not random
but compatible with a lognormal distribution when allowance was
made for the 64 ms time resolution and a small excess (5%) of
long duration intervals that is often referred to as a
Pareto-Lévy tail. The time intervals between pulses are most
important because they may be an almost direct measure of the
activity in the central engine. Lognormal distributions of time
intervals also occur in pulsars and SGR sources and therefore
provide indirect evidence that the time intervals between pulses
in GRBs are also generated by rotation powered
systems with super-strong magnetic fields.
A range of correlations are presented on pulse
and burst properties. The rise and fall times, FWHM and area of
the pulses are highly correlated with each other. The pulse
amplitudes are anticorrelated with the FWHM. The time intervals
between pulses and pulse amplitudes of neighbouring pulses are
correlated with each other. It was also found that the number of
pulses, N, in GRBs is strongly correlated with the fluence and
duration and that can explain the well known correlation between
duration and fluence. The GRBs were sorted into three categories
based on N i.e.
,
and
. The properties of pulses before and after the
strongest pulse were compared for three categories of bursts. No
major differences were found between the distributions of the
pulse properties before and after the strongest pulse in the GRB.
However there is a strong trend for pulses to have slower rise
times and faster fall times in the first half of the burst and
this pattern is strongest for category
. This
analysis revealed that the GRBs with large numbers of pulses
have narrower and faster pulses and also larger fluences, longer
durations and higher hardness ratios than the GRBs with smaller
numbers of pulses. These results may be explained by either
homogeneous or inhomogeneous jet models of GRBs. The GRBs with
larger number of pulses are closer to the axis if Γ varies
with the opening angle of the jet and the imprint of the jet is
preserved in the pulse structure of the burst. The distribution
of the number of pulses per GRB broadly reflects the beaming by
the jet.
Key words: gamma rays / bursts: gamma rays / observations: methods / data analysis: methods / statistical
© ESO, 2002
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.