Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-Energy Emission from Prompt to Afterglow. (arXiv:1909.10605v1 [astro-ph.HE])

Fermi and Swift Observations of GRB 190114C: Tracing the Evolution of High-Energy Emission from Prompt to Afterglow. (arXiv:1909.10605v1 [astro-ph.HE])
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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
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 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 constrain 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 and find that high-energy photons observed by Fermi
LAT 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.

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