Speaker
Description
Gamma-ray bursts (GRBs) are among the most energetic phenomena in the Universe. Their emission typically consists of a brief prompt phase observed in the sub-MeV energy range, followed by a delayed and longer-lasting afterglow detected across the electromagnetic spectrum. In a few cases, GRB afterglows have also been observed at TeV energies, from minutes to several hours after the trigger time, particularly in long GRBs. In this work, we use data from the High Altitude Water Cherenkov (HAWC) Observatory to search for delayed and extended TeV gamma-ray emission during the afterglow phase of a sample of long GRBs detected by the Fermi-GBM and Swift-BAT instruments between December 2014 and December 2023. We selected bursts located within the HAWC field of view at the trigger time, with positional uncertainties smaller than 1° and high keV fluences. For each GRB, we searched for TeV gamma-ray emission over a time interval extending up to ten times the reported prompt-emission duration. No statistically significant emission was found. Consequently, we derived flux upper limits for each burst, assuming a simple power-law spectrum with spectral indices consistent with synchrotron self-Compton (SSC) emission from forward external shock models. This work was supported by UNAM-PAPIIT IG100726 y SECIHTI LNC-2023-117.