| Abstract : | Gamma-Ray Bursts (GRBs), are the most energetic events in our Universe spewing out intense bursts of photons from keV to TeV energies with a duration of a few milliseconds up to days. Depending on the duration, GRBs are characterized in two types: short GRBs (SGRB) and long GRBs (LGRB) with duration less than 2s and more than 2s, respectively. In the case of LGRBs, the collapse of a massive star first produces a highly variable and luminous gamma-ray emission followed by the external dissipation of the ultra-relativistic jets in the circumburst medium. The latter produces the multi-wavelength after-glow emission. In most cases, the Fermi-LAT GRBs follow a regular decay pattern as expected from the standard afterglow model. However, some of the LAT-GRBs do not follow the standard GRB afterglow and show slower decay. In this work, we select such GRBs from the latest Fermi-LAT catalog and quantify the disagreement between the observed emission and the prediction of the afterglow emission. In addition to that, we also add the X-ray light curves in order to evaluate these cases in multi-wavelength scenarios.
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