AGILE and Konus-Wind Observations of GRB 190114C: The Remarkable Prompt and Early Afterglow Phases
Antonelli, L. A.; Costa, E.; Barbiellini, G.; Longo, F.; Morselli, A.; Pilia, M.; Frederiks, D. D.; Svinkin, D. S.; Feroci, M.; Chen, A.; Donnarumma, I.; Evangelista, Y.; Trois, A.; Vercellone, S.; Verrecchia, F.; Vittorini, V.; Tavani, M.; Bulgarelli, A.; Giuliani, A.; Argan, A.; Caraveo, P.; Cattaneo, P. W.; Ferrari, A.; Fuschino, F.; Galli, M.; Labanti, C.; Lazzarotto, F.; Marisaldi, M.; Piano, G.; Pittori, C.; Lucarelli, F.; Ursi, A.; Romani, M.; Parmiggiani, N.; Cardillo, M.; Casentini, C.; Paoletti, F.; Aptekar, R. L.; Tsvetkova, A. E.
Italy, Russia, Norway, South Africa, United States
Abstract
GRB 190114C represents a breakthrough for the physics of gamma-ray bursts (GRBs), being the first GRB with delayed emission above 300 GeV, as reported by MAGIC. We present in this paper the sub-MeV/MeV data of the prompt and early afterglow emissions of GRB 190114C, as detected by AGILE and Konus-Wind, in the 20 keV-100 MeV energy range. The first stages of the burst exhibit multiple emission components, associated with an interesting spectral evolution. The first 2 s of the prompt emission can be described by a single "Band-like" spectral component. The successive 4 s show the presence of an additional high-energy spectral component, which quickly evolves into a "hard-flat" component of the νFν spectrum, extending up to 10-100 MeV and likely produced by inverse Compton radiation, whose onset and evolution are clearly shown in our data. After this phase, the νFν spectrum evolves into a "V shape," showing the persistence and spectral hardening of the additional high-energy component in substantial agreement with Fermi and Swift results. We also analyze the first ∼200 s of the early afterglow that show a reflaring episode near T0 + 15 s. We identify a new, so-far-unnoticed flux temporal break near T0 + 100 s, which is detected in hard X-rays by both Konus-Wind and INTEGRAL/SPI-ACS. We find this break incompatible with the commonly assumed adiabatic evolution of a fireball in a constant-density medium. We interpret this break as a consequence of radiative evolution of the early afterglow from a fireball expanding in a wind-like circumburst medium.