Speaker
Description
Gamma-ray Bursts (GRBs) generate powerful relativistic jets that inject a large amount of energy into their surrounding environment, producing blast waves that accelerate particles to high energies. The GRB afterglow radiation provides a powerful means to investigate the microphysics of relativistic shocks and to probe the medium surrounding the progenitor of the burst. In this study, we present a comprehensive multiwavelength analysis of 31 GRBs observed between 2008 and 2024 from the Neil Gehrels Swift Observatory (X-ray Telescope and Burst Alert Telescope) and the Fermi Large Area Telescope, covering photon energies from 0.3 keV to 300 GeV. Our goal is to characterize the broadband spectral properties of GRB afterglows in soft X-rays, hard X-rays, and high-energy gamma rays. We investigate correlations between spectral shape and energy output across different parts of the spectrum. The observed emission is modeled using a forward shock scenario that includes both synchrotron and synchrotron self-Compton (SSC) radiation losses. The results favor an SSC-dominated radiation model in a wind- like medium, consistent with expectations for long-duration GRBs. Crucially, this work provides new benchmarks for the microphysical parameters governing the emission, particularly indicating a notably low magnetic energy fraction, which refines previous estimates. By modeling broadband data, this study offers one of the most detailed SSC analyses in a wind-like environment to date. Notably, our results naturally account for the comparable energy output observed in both the soft X-ray and TeV bands, consistent with the previously detected TeV-GRBs.
Moreover, the early X-ray afterglows of GRBs, observed with the Swift XRT, have revealed distinct temporal features such as X-ray flares beyond those predicted by the standard forward shock afterglow model. X-ray flares are commonly attributed to prolonged central engine activity, although their physical origin remains debated. In this talk, I will present a systematic multi-wavelength study of X-ray flares in a sample of 56 GRBs observed by the Swift XRT over 17 years, all located within the field of view of the Fermi LAT. The flares are classified into prompt, steep-decay, plateau, and afterglow categories based on their temporal behavior in the X-ray light curves. We found that only six events show significant high-energy emission (>3σ). However, detailed modeling indicates that the GeV high-energy emission is consistent with afterglow processes rather than flare-related processes. We explore correlations between spectral properties and energy output at 1 keV, 10 keV, and 1 GeV. The broadband emission is modeled within a forward-shock scenario including synchrotron self-Compton radiation. This framework allows us to constrain the underlying microphysical parameters governing the emission. Our results provide one of the most comprehensive analyses of X-ray flares to date. We also predict very-high-energy emission associated with flares and discuss detections with current and future very high-energy detectors, such as CTAO.
