COPYRIGHT AND CITATION CONSIDERATIONS FOR THIS THESIS/ DISSERTATION o Attribution — You must give appropriate credit, provide a link to the license, and indicate if changes were made. You may do so in any reasonable manner, but not in any way that suggests the licensor endorses you or your use. o NonCommercial — You may not use the material for commercial purposes. o ShareAlike — If you remix, transform, or build upon the material, you must distribute your contributions under the same license as the original. How to cite this thesis Surname, Initial(s). (2012). Title of the thesis or dissertation (Doctoral Thesis / Master’s Dissertation). Johannesburg: University of Johannesburg. Available from: http://hdl.handle.net/102000/0002 (Accessed: 22 August 2017). Gamma-ray bursts as probes of cosmological parameters at high redshifts Author: Supervisor: Feraol Fana Dirirsa Prof. Soebur Razzaque A Thesis submitted to Department of Physics Faculty of Sciences for the degree of Doctor of Philosophy Centre for Astro-Particle Physics (CAPP) University of Johannesburg Johannesburg South Africa 2018 CERTIFICATE This is to certify that the thesis entitled "Gamma-ray bursts as probes of cosmological parameters at high redshifts" submitted by Feraol Fana Dirirsa for the award of the degree of Doctor of Philosophy of University of Johannesburg is his original work. This has not been published or submitted to any other University forany other Degrees or Diploma. Prof Soebur Razzaque Dr. Emanuela Carleschi Thesis Supervisor and Director (CAPP) Head of Department (Physics) Centre for Astro-Particle Physics, and Department of Physics University of Johannesburg PO Box 524 - Auckland Park 2006 Johannesburg South Africa DECLARATION I, Feraol Fana Dirirsa, declare that the work reported in this thesis entitled “Gamma-ray bursts as probes of cosmological parameters at high redshifts”, is entirely original. This thesis was composed independently by me, based on the research carried out under the supervision of Prof. Soebur Razzaque in the Department of Physics at the University of Johannesburg. I further declare that the work enclosed in this thesis is my own contribution and where other’s ideas or words have been included, I have adequately cited and referenced the original sources. Signed: Date: 16 November 2018 iii ABSTRACT Gamma-ray bursts are powerful astronomical transient events emitting large energy in γ-rays within a short period of time. Their emission dominates in the keV–MeV range. High luminosity 54 1 with values up to 10 erg s¡ and huge isotropic energy release in the prompt emission phase can make gamma-ray bursts (GRBs) detectable up to a high redshift, z 9.4. If emission from » GRBs can be standardized, like Supernovae (SNe) Type Ia and which have been observed only up to a redshift of z 2, they have the potential to be used as cosmological probes and help Ç us to understand the nature of dark-energy when the universe was much younger than today. With GRBs as standard candles, we can extend our understanding of the universe’s mysterious expansion over cosmic time. The main aim of this thesis is to explore radiation characteristics from GRBs and utilize them to use GRBs as cosmological standard candles, similar to SNe Type Ia. The standardization of GRBs rests on phenomenological correlations between the spectral properties and energetics, of which one strongly relies on the cosmological model. The fascinating correlation between isotropically radiated energy with the intrinsic peak energy of the ºFº spectrum in the cosmological source frame can be traced back to the Amati relation. In 2004, Yonetoku proposed another correlation between the isotropic peak luminosity and intrinsic peak energy (so-called Yonetoku relation). Besides, over the past sixteen years, many scholars have anticipated studying other correlations of GRB observables. The studied correlations were not tight enough to be used independently to construct the extended GRB Hubble diagram and constrain the cosmological parameters using the parameters obtained from the observational data of SNe Type Ia or cosmic microwave background. In spite of that, using the phenomenological correlations of the combined sample of GRBs detected by different telescopes and also by combining with the SNe Type Ia data, we can construct the extended GRB Hubble diagram that can be used to constrain cosmological parameters at high redshift. In this thesis work, we use high-quality samples of long GRBs to study the Yonetoku relation. These samples were collected from the Fermi Gamma-ray Burst Monitor (GBM) and Swift-Burst Alert Telescope (BAT) until the end of December 2017, whose spectroscopic or photometric redshifts were measured. These GRBs also have well-defined spectra to use for correlation study. In both samples, we have found a strong partial correlation between the peak luminosity and intrinsic peak energy. Using the slope and normalization obtained from the Yonetoku correlation, we estimated the cosmological parameters of the Hubble constant (H0) and dark-energy density v (­¤), first, for the samples of GRBs alone and then together with the latest union SNe Ia data. The obtained values of H0 and ­¤ for the best-fit spectral model of the present GBM and BAT 0.533 1 samples of GRBs combining with the latest SNe Type Ia data provide H0 69.908Å km s¡ Æ 0.517 1 0.027 ¡ Mpc¡ and ­¤ 0.715 0.030 in 1σ confidence intervals. The obtained result in 1σ confidence level Æ ¡ is consistent with the currently acceptable ranges of H0 and ­¤ but the errors on parameters are rather large that arise due to the large extrinsic systematics scattering associated to the simulated sample. The Hubble diagram was also plotted using these best-fit values, obtained from both the GRB and SNe data. The obtained result has shown a substantial refinement in the robustness of the Yonetoku relation. We have also studied the Amati relation by performing spectral analysis of 26 GRBs with measured redshift that have been detected by the Fermi-Large Area Telescope (LAT) during its nine years of operations from July 2008 to September 2017, thus extending the computation of isotropically radiated energy in the 100 MeV range. We found that multiple components are required to fit the spectra of a number of GRBs. The Amati relation is satisfied by the 25 long GRBs, with fitting parameters similar to previous studies that used data from different satellite instruments, while the only short GRB 090510 detected by LAT with known redshift is an outlier. However, there is large scatter in fit parameters, dominated by unknown extrinsic systematics, that may be due to the hidden parameters related to the physical origin of the Amati relation. We have also performed fits to the Amati relation using the Fermi data together with another sample of 94 GRBs (W2016) to explore the redshift dependence. Using the Amati relation we extend the Hubble diagram and constrain the Hubble constant and dark-energy density in the flat ¤CDM cosmological model. These exercises are done with the sample of GRBs alone and with the latest SNe Type Ia data. For the combined GRB samples (Fermi and W2016) with the Type Ia 0.54 1 1 data, we obtained good fit to the cosmological parameters of H0 69.95Å0.45 km s¡ Mpc¡ and Æ ¡ ­ 0.72 0.03. We have also fitted cosmological parameters using GRBs with z 1.414 and ¤ Æ § È 0.48 1 1 SNe U2.1 sample obtaining H0 70.03Å0.54 km s¡ Mpc¡ and ­¤ 0.72 0.03. The obtained Æ ¡ Æ § results are consistent with the presently suitable ranges of those cosmological parameters. We have also studied the sensitivity of the Amati relation to the initial choice of the cosmological parameters. The results from our research indicate that phenomenological correlations such as Amati and Yonetoku relations for long GRBs can potentially be useful to standardize GRBs for cosmological studies. Key words: Gamma-ray bursts, prompt emission–phenomenological correlations: extended Hubble diagram, cosmological parameters–Hubble constant, dark-energy density vi ACKNOWLEDGEMENTS I am grateful to my thesis supervisor, Prof. Soebur Razzaque for his kind support and his strong encouragement, which were crucial to my progress on this fascinating Astrophysics research area. I would also like to thank the NASA Fermi collaboration, especially the LAT group, for building a magnificent instrument and developing Fermi science tools which reshaped our understanding of energetic Gamma-ray bursts. I appreciate the support from Dr. Richard Britto, who has enabled me to understand the Fermi data analysis and introduced me to the relevant software. I would like to thank Dr. Reetanjali Moharana for her valuable discussions in my research and encouragement. Thanks go to excellent members of the University of Johannesburg Centre for Astro-Particle Physics: Dr. Jagdish Joshi, Dr. Salvador Miranda-Palacios, Mr. Mfuphi Ntshatsha and Mr. Lutendo Nyadzani for helpful discussions and friendships in any condition during my study. I would like to take this chance to thank Prof. Frédéric Piron for his mentor-ship at the Université Montpellier, France. I learned a lot about the process of the maximum binned likelihood analysis and the physics of GRBs. I would also like to acknowledge the Erasmus+ MIC for the internship research opportunity and financial support they awarded me. I also acknowledge the National Research Foundation (NRF) of South Africa, Department of Physics, and the University of Johannesburg for their generous financial support. I must also thank several persons who contributed directly or indirectly for my studies during this period. I have to thank all the academics of the Physics Department for all the support I have received from each and every one of them. I owe thanks especially to Dr. Emanuela Carleschi (HOD), Prof. Hartmut Wikler and Prof. Chris Engelbrecht for supporting me with their valuable comments for different applications of postgraduate funding.