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Multiwavelength Afterglow Analysis of GRB 221009A: Unveiling the Evolution of a Cooling Break in a Wind-like Medium

Journal Article · · The Astrophysical Journal
 [1];  [2];  [3];  [3];  [4];  [3];  [3];  [5];  [6];  [7];  [8]
  1. Seoul National University (Korea, Republic of); Korea Astronomy and Space Science Institute (KASI), Daejeon (Korea, Republic of)
  2. Korea Astronomy and Space Science Institute (KASI), Daejeon (Korea, Republic of)
  3. Seoul National University (Korea, Republic of)
  4. Kanazawa University (Japan)
  5. SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States); Stanford University, CA (United States)
  6. NASA Goddard Space Flight Center (GSFC), Greenbelt, MD (United States)
  7. National Central University, Jhongli (Taiwan)
  8. University of Nevada, Las Vegas, NV (United States)
+ Show Author Affiliations

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 GRB afterglow physics are still missing, including jet properties, the 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 2 days after the trigger, we trace the evolution of the multiwavelength 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 = 2.29 ± 0.02. We identify a break energy at keV and an exponential cutoff at GeV in the observed multiwavelength spectrum. The break energy increases in time from $$16.0^{+7.1}_{-4.9}$$ keV at 0.65 days to $$46.8^{+25.0}_{-15.5}$$ keV at 1.68 days, favoring a stellar-wind-like profile of the circumburst medium with k = 2.4 ± 0.1 as in ρ(r) ∝ 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 multiwavelength afterglow emission and its evolution.

Research Organization:
SLAC National Accelerator Laboratory (SLAC), Menlo Park, CA (United States)
Sponsoring Organization:
USDOE Office of Science (SC); National Research Foundation of Korea (NRF); Japan Society for the Promotion of Science (JSPS) KAKENHI
Grant/Contract Number:
AC02-76SF00515
OSTI ID:
2530255
Alternate ID(s):
OSTI ID: 2533568
Journal Information:
The Astrophysical Journal, Journal Name: The Astrophysical Journal Journal Issue: 1 Vol. 978; ISSN 0004-637X
Publisher:
IOP PublishingCopyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
Gamma-ray bursts
Non-thermal radiation sources
Relativistic jets