Abstract
The detection of an astrophysical source of Ultra High Energy (& 1 PeV) neutrinos and Ultra
High Energy Cosmic Rays (UHECRs) would be a great achievement in the field of Neutrino
Astronomy. The interaction of UHECRs with photons produce neutrinos. The detection
of these neutrinos can lead us to the detection of an astrophysical source of neutrinos and
UHECRs simultaneously.
The Gamma Ray Burst (GRB) blastwave is expected to be an excellent site for the relativistic
acceleration of Cosmic Rays (CRs). The Ultra High Energy Cosmic Rays (UHECRs),
which are expected to be produced during the burst, interacts with the low energy afterglow
photons to produce ultra high energy neutrinos. The gamma rays and UHE neutrinos are
messengers which can carry direct information about the underlying physical phenomena of
astrophysical sources of cosmic rays to the detectors on earth.
Long duration GRBs are a well-motivated source of UHECRs which in turn is the source
of UHE neutrinos. The expected neutrino flux from the GRB afterglows, can be modelled
by the synchrotron spectrum modelling of the afterglow photons from the blastwave. The
synchrotron modelling of low energy afterglow photons has been done from a well-defined
set of 17 long nearby GRBs having a redshift within 0.5. These are the most promising ones
to calculate the expected UHE neutrinos.
The synchrotron modelling of an afterglow spectrum, has been done for the selected sample
of GRBs, which varies as a single power law distribution of electrons in the shock front.
The modelling has been done in both a fast cooling regime where all electrons radiate away
their energy within the dynamic time and in the slow cooling regime where only the electrons
above a certain energy can radiate away their energy within the dynamic time scale. The synchrotron
modelling of Spectral Energy Distributions (SEDs) at different time intervals and
temporal evolution of the flux, the light curves, at different frequencies are done by fitting the
available afterglow data in multi-wavelength (radio, optical, UV, X-ray and ! rays) with the...
Ph.D. (Physics)