Kavli Affiliate: Li Xin Li
| First 5 Authors: Zhen Cao, F. Aharonian, Q. An, Axikegu, Y. X. Bai
| Summary:
The highest energy photons from gamma-ray bursts (GRBs) have important
implications for the physics of particle acceleration and constraints on the
extragalactic background light (EBL). Here we report for the first time the
detection of photons beyond 10 TeV from the unprecedentedly brightest GRB
221009A by the Large High Altitude Air-shower Observatory (LHAASO). The
LHAASO-KM2A detector registered more than 140 photons with energies above 3 TeV
from GRB 221009A during 230$-$900s after the trigger. The intrinsic energy
spectrum of gamma-rays can be described by a power-law after correcting for EBL
absorption, with the highest energy photon of 13 TeV. Such a hard spectrum
challenges the synchrotron self-Compton (SSC) scenario of relativistic
electrons for the afterglow emission above several TeV, because the
Klein-Nishina effect and the internal $gammagamma$ absorption within the GRB
generally lead to a spectral softening towards high energies. Observations of
photons up to 13 TeV from a source with a measured redshift of z=0.151 requires
more transparency in intergalactic space than previously expected, in order to
avoid an unusual pile-up at the end of the spectrum. Alternatively, one may
invoke new physics such as Lorentz Invariance Violation (LIV) or assume an
axion origin of very high energy (VHE) signals.
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