Kavli Affiliate: Nicola Omodei
| First 5 Authors: Donggeun Tak, Z. Lucas Uhm, Gregory S. H. Paek, Myungshin Im, Makoto Arimoto
| Summary:
Gamma-ray bursts (GRBs) are the most energetic explosions in the universe,
and their afterglow emission provides an opportunity to probe the physics of
relativistic shock waves in an extreme environment. Several key pieces for
completing the picture of the GRB afterglow physics are still missing,
including jet properties, emission mechanism, and particle acceleration. Here
we present a study of the afterglow emission of GRB 221009A, the most energetic
GRB ever observed. Using optical, X-ray, and gamma-ray data up to approximately
two days after the trigger, we trace the evolution of the multi-wavelength
spectrum and the physical parameters behind the emission process. The broadband
spectrum is consistent with the synchrotron emission emitted by relativistic
electrons with its index of $p = 2.29pm 0.02$. We identify a break energy at
keV and an exponential cutoff at GeV in the observed multi-wavelength spectrum.
The break energy increases in time from $16.0_{-4.9}^{+7.1}$ keV at 0.65 days
to $46.8_{-15.5}^{+25.0}$ keV at 1.68 days, favoring a stellar wind-like
profile of the circumburst medium with $k=2.4pm0.1$ as in $rho (r) propto
r^{-k}$. The high-energy attenuation at around 0.4 to 4 GeV is attributed to
the maximum of the particle acceleration in the relativistic shock wave. This
study confirms that the synchrotron process can explain the multi-wavelength
afterglow emission and its evolution.
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