Title

Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-energy Emission from Prompt to Afterglow

Authors

M. Ajello, Clemson University
M. Arimoto, Kanazawa University
M. Axelsson, Stockholms universitet
L. Baldini, Università di Pisa
G. Barbiellini, Istituto Nazionale di Fisica Nucleare, Sezione di Trieste
D. Bastieri, Istituto Nazionale Di Fisica Nucleare, Sezione di Padova
R. Bellazzini, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
A. Berretta, Università degli Studi di Perugia
E. Bissaldi, Politecnico di Bari
R. D. Blandford, SLAC National Accelerator Laboratory
R. Bonino, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
E. Bottacini, SLAC National Accelerator Laboratory
J. Bregeon, Laboratoire Univers et Particules de Montpellier
P. Bruel, Laboratoire Leprince-Ringuet
R. Buehler, Deutsches Elektronen-Synchrotron (DESY)
E. Burns, NASA Goddard Space Flight Center
S. Buson, Julius-Maximilians-Universität Würzburg
R. A. Cameron, SLAC National Accelerator Laboratory
R. Caputo, NASA Goddard Space Flight Center
P. A. Caraveo, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan
E. Cavazzuti, Agenzia Spaziale Italiana
S. Chen, Istituto Nazionale Di Fisica Nucleare, Sezione di Padova
G. Chiaro, INAF Istituto di Astrofisica Spaziale e Fisica Cosmica, Milan
S. Ciprini, Istituto Nazionale di Fisica Nucleare - INFN
J. Cohen-Tanugi, Laboratoire Univers et Particules de Montpellier
D. Costantin, Università degli Studi di Padova
S. Cutini, Istituto Nazionale di Fisica Nucleare, Sezione di Perugia
F. D'Ammando, Istituto Di Radioastronomia, Bologna
M. Deklotz, Stellar Solutions Inc.
P. De La Torre Luque, Politecnico di Bari
F. De Palma, Istituto Nazionale di Fisica Nucleare, Sezione di Torino
A. Desai, Clemson University
N. Di Lalla, Università di Pisa

Document Type

Article

Publication Date

2-10-2020

Abstract

We report on the observations of gamma-ray burst (GRB) 190114C by the Fermi Gamma-ray Space Telescope and the Neil Gehrels Swift Observatory. The prompt gamma-ray emission was detected by the Fermi GRB Monitor (GBM), the Fermi Large Area Telescope (LAT), and the Swift Burst Alert Telescope (BAT) and the long-lived afterglow emission was subsequently observed by the GBM, LAT, Swift X-ray Telescope (XRT), and Swift UV Optical Telescope. The early-time observations reveal multiple emission components that evolve independently, with a delayed power-law component that exhibits significant spectral attenuation above 40 MeV in the first few seconds of the burst. This power-law component transitions to a harder spectrum that is consistent with the afterglow emission observed by the XRT at later times. This afterglow component is clearly identifiable in the GBM and BAT light curves as a slowly fading emission component on which the rest of the prompt emission is superimposed. As a result, we are able to observe the transition from internal-shock- to external-shock-dominated emission. We find that the temporal and spectral evolution of the broadband afterglow emission can be well modeled as synchrotron emission from a forward shock propagating into a wind-like circumstellar environment. We estimate the initial bulk Lorentz factor using the observed high-energy spectral cutoff. Considering the onset of the afterglow component, we constrain the deceleration radius at which this forward shock begins to radiate in order to estimate the maximum synchrotron energy as a function of time. We find that even in the LAT energy range, there exist high-energy photons that are in tension with the theoretical maximum energy that can be achieved through synchrotron emission from a shock. These violations of the maximum synchrotron energy are further compounded by the detection of very high-energy (VHE) emission above 300 GeV by MAGIC concurrent with our observations. We conclude that the observations of VHE photons from GRB 190114C necessitates either an additional emission mechanism at very high energies that is hidden in the synchrotron component in the LAT energy range, an acceleration mechanism that imparts energy to the particles at a rate that is faster than the electron synchrotron energy-loss rate, or revisions of the fundamental assumptions used in estimating the maximum photon energy attainable through the synchrotron process.

Publication Source (Journal or Book title)

Astrophysical Journal

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