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Spectral Analysis of GRBs Observed by Swift and Fermi Satellites

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thesis
posted on 15.01.2020 by Eman M. A. Moneer
Gamma-ray bursts (GRBs) one of the most energetic phenomena in the Universe that have been observed in distant galaxies. For the short period of time generally less than 30s, GRB can release energy about 1054 erg. The intense radiation of most observed GRBs is thought to be released within a massive explosions ’supernovae’ that are associated with the most catastrophic stellar events that ever detected to form a neutron star or a black hole. Two types of GRBs (long/short) are associated with different emission processes. Studying the GRB spectral analysis of a joint fit time-integrated or time-resolved spectra assist to investigate further spectral properties, via two observatories Swift and Fermi. The thesis chapter outlines two different spectral joint fit analysis with the time-integrated and the time-resolved spectra as applied to two datasets. Two spectral models are used throughout this analysis, namely the low-energy power law with an exponential high-energy cutoff (CPL) and the Band function (Band). The joint-fit shows a significant difference in the spectral parameters compared to the GBM-only. Resulting that, adding Swift (BAT) data obtained a higher Epeak and a softer a than what it found when applying Fermi (GBM-only). The evolution of Epeak is discussed for the spectral joint-fit timeresolved spectra, and found that the Epeak evolution follow two trends; the hard-to-soft ratio and the intensity-tracking trend. A further interesting area of study is the Amati (Epeak,rest − Eiso,g) and Yonetoku (Epeak,rest − Liso,g) relations, which are examined to investigate whether these two relations are in general agreement with the analysis given herein. A strong Amati relation was found for the time-integrated data, whereas the time-resolved Amati relation data was scattered above the Amati best fit. The Yonetoku relation was found to show a few scattered data shifted towards lower luminosity, Liso,g, in the time-integrated spectra, whilst showing a good correlation for the time-resolved spectra. Fermi (GBM+LLE) joint-fit analysis provides high-quality data through which to search for such a cutoff, Ec, from the LLE high energy bands (30 MeV - 130 MeV), and hence estimate Lorentz factor G for three GRBs in the sample.

History

Supervisor(s)

O’Brien, Paul; Willingale, Richard

Date of award

17/05/2019

Author affiliation

Department of Physics and Astronomy

Awarding institution

University of Leicester

Qualification level

Doctoral

Qualification name

PhD

Language

en

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