Ponente
Descripción
Prompt emission of GRB is believed to be produced from electrons accelerated up to non thermal energies in the internal shocks. This results in a spectrum which typically peaks in the keV-MeV energy band. In the last 15 years of LAT operation, many GRBs showed HE gamma-ray emission temporally coincident with prompt emission phase, but with different spectral properties. This GeV emission has been interpreted in several previous works as mostly dominated by the afterglow. I will present new results based on a systematic study of GRBs with an early GeV emission detected jointly with Fermi/GBM and Fermi/LAT during the prompt emission phase. This study uses a physical model based on synchrotron emission to explain the prompt emission. The systematic temporal and broad-band keV-GeV spectral analysis reveals that in many cases the GeV radiation is part of the main spectral component of the prompt emission. However, in some other cases, these GeV photons are related to a second spectral component, which might peak at VHE gamma rays. I will discuss the physical origin of the GeV photons and the possible implications of a second spectral component in light of the upcoming CTAO. In this context, I will also touch upon the identification of a second spectral component in GRB 221009A and its impact on on our understanding of prompt/ early VHE emission through extensive modeling of the broadband spectra thanks to the well samples spectra jointly detected with Fermi/GBM, KONUS, Fermi/LAT, AGILE and LHAASO.
