Spectroscopic Analysis of an Ultra-Long Gamma-Ray Burst: Insights into Emission Mechanisms and Progenitor Characteristics

Ultra-luminous Gamma-Ray Bursts (GRBs) are among the most energetic events in the universe, providing a wealth of data that encapsulates information about spectral evolution, particle emission, and underlying physical processes. These bursts release most of their energy within seconds to minutes, contingent upon their progenitor. In this presentation, I will explore the spectroscopic studies of a unique GRB characterized by two distinct episodes separated by over 500 seconds. This peculiar temporal structure raises critical questions regarding the nature of the burst, specifically whether it is a gravitational lensing event or an ultra-long GRB. Our investigation focuses on the emission mechanisms and jet regions, correlating time bins from both episodes to assess potential gravitational lensing effects. We observed a coherent relationship between flux and photon spectral distribution, which we modelled using an exponentially cut-off power law model for both episodes. However, the hardness ratio exhibited inconsistencies, and high-energy gamma-ray photons detected by the Fermi Large Area Telescope (LAT) were only present for up to 700 seconds, effectively ruling out gravitational lensing as a viable explanation. The results of our spectral analysis strongly indicate that this GRB is an ultra-long event characterized by two episodes rather than a lensed GRB, aligning with observations from other GRBs. Our findings reveal isotropic energy, jet velocity, and burst duration parameters consistent with the theoretical framework for rapidly rotating newborn magnetar progenitors. This research enhances our understanding of ultra-long GRBs and contributes to the broader discourse on the mechanisms driving these extraordinary cosmic phenomena.