Spectroscopic study of Ultra-long GRB 220627A

The ultra-relativistic, highly collimated jets generated by Gamma-Ray Bursts (GRBs) provide crucial insights into particle emission. These jets also reveal the physical mechanisms driving the rapid release of high-energy gamma-ray photons. We discuss time-resolved spectroscopy and flux variability for the ultra-long GRB 220627A. The analysis spans a duration exceeding 1200 seconds using Fermi telescope data. Two prompt emission episodes observed by Fermi-GBM, separated by more than 500 s, were analyzed. Due to its unique characteristics, GRB 220627A serves as an excellent source for studying particle emission processes, small-scale variability, and the properties of its central engine. To investigate gravitational lensing, the time bins of the first episode were correlated with those of the second episode. A coherent relationship was observed between flux and photon spectral distribution. This relationship was modeled using an exponentially cut-off power law model for both episodes. The MeV-to-GeV photon ratio detected by LAT is inconsistent between the two episodes. High-energy gamma-ray photons were only detected by LAT for up to 700 seconds, which further rules out gravitational lensing but suggests that the progenitor underwent a burst into an ultra-long GRB with two episodes. Our findings from spectral analysis reveal characteristics most consistent with those of an ultra-long GRB. Parameters such as isotropic energy, spectral signatures, and burst duration align with the established limits for a blue supergiant progenitor, as described in the literature.