الفهرس يوجد فقط 14 صفحة متاحة للعرض العام
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المستخلص
Gamma Ray Bursts (GRBs) are a remarkable cosmic
phenomenon that occurs at a rate of approximately once a day.
They are intense flashes of high-energy radiations that last from a
few milliseconds to several minutes and take place at
cosmological distance, and therefore provide important insights
on the early universe. Gamma Ray Bursts come in two classes:
long bursts with duration longer than 2 s and short bursts with
duration less than 2 s. The two classes have distinct spectral and
timing properties and are observed to come from different
environments and thus are thought to originate from different
physical mechanisms. Long bursts are fairly understood as to
come from hypernovae (a special type of supernova) whereas
short bursts are believed to result from the collapse of a two
neutron star system or a neutron star-black hole system.
The SWIFT mission, a recent NASA observatory launched
in November of 2004 to study Gamma Ray Bursts, is designed to
answer open questions about GRBs. The key to the Swift mission
is its ability to detect and determine the location of a burst in the
sky and then autonomously point its X-ray and optical telescopes
at the burst position within seconds of the trigger. Among Swift’s
major contributions is the discovery of new sub-group of bursts
with short duration followed by extended emission named as
III
Short Gamma Ray Bursts with Extended Emission (SGRBEE)
that do not fit in the classification scheme mentioned above.
This dissertation aims to study the gamma-ray properties of
these bursts using SWIFT Burst Alert Telescope observations.
We performed spectral and temporal analysis that revealed the
new insights such as:
- The spike and the extended emission occupy different
regions in the flux, fluence, duration, and hardness
diagrams, and they show different trends of variation.
- The bulk of the fluence in most bursts is liberated in the
extended emission (EE).
- The ratio of the fluence of the extended emission to that
of the spike (Fl_EE/Fl_Sp) varies over a large range of
about two orders of magnitude (from 0.37 to 33.5).
- We find correlations between the Power-law Photon
Index and the Flux of the extended emission (EE) and the
spike (Sp). The spike is consistently harder than the
extended emission in all bursts.
- In the duration-hardness diagrams, the pattern of the
spikes is consistent with those measured for short bursts
without extended emission while the extended-emission
components form a tight cluster.
- We found that the light curve of the prompt spike
consists of a number of peaks
IV
- There is a wait time between the spike and the extended
emission that ranges from 4 to 10 s.
We confronted our results to various models and find agreements
with the Proto-Magnetar Spin-down model proposed by Metzger
et al. 2008. These include:
- Expected a large variation in the ratio between the
extended emission and the spike of the flux and fluence
plots.
- Existence of a delay time between the spike and the
extended emission.
- The bulk of the fluence is released during the extended
emission.
- Different Physical Origin for Spike & Extended
Emission, and hence different properties for the spike and
the extended emission.
- Existence of multi-peaked spike profile.
In addition our results bear new predictions concerning the
correlations between the spike and the extended emission and we
plan to pursue these trends in future work as new bursts of this
class become available.
Acknowledgeme