AGILE and Konus-Wind Observations of GRB 190114C: The Remarkable Prompt and Early Afterglow Phases
A. Ursi, M. Tavani, D. Frederiks, M. Romani, F. Verrecchia, M. Marisaldi, R. Aptekar, L. A. Antonelli, A. Argan, A. Bulgarelli, G. Barbiellini, P. A. Caraveo, M. Cardillo, C. Casentini, P. W. Cattaneo, A. Chen, E. Costa, I. Donnarumma, Y. Evangelista, M. Feroci, A. Ferrari, F. Fuschino, M. Galli, A. Giuliani, C. Labanti, F. Lazzarotto, F. Longo, F. Lucarelli, A. Morselli, F. Paoletti, N. Parmiggiani, G. Piano, M. Pilia, C. Pittori, D. Svinkin, A. Trois, A. Tsvetkova, S. Vercellone, V. Vittorini
Abstract
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 νF ν 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 νF ν 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 T 0 + 15 s. We identify a new, so-far-unnoticed flux temporal break near T 0 + 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.