Peta-electron volt gamma-ray emission from the Crab Nebula

Kavli Affiliate: Li Xin Li

| First 5 Authors: The LHAASO Collaboration, Zhen Cao, F. Aharonian, Q. An, Axikegu

| Summary:

The Crab pulsar and the surrounding nebula powered by the pulsar’s rotational
energy through the formation and termination of a relativistic
electron-positron wind is a bright source of gamma-rays carrying crucial
information about this complex conglomerate. We report the detection of
$gamma$-rays with a spectrum showing gradual steepening over three energy
decades, from $5times 10^{-4}$ to $1.1$ petaelectronvolt (PeV). The
ultra-high-energy photons exhibit the presence of a PeV electron accelerator (a
pevatron) with an acceleration rate exceeding 15% of the absolute theoretical
limit. Assuming that unpulsed $gamma$-rays are produced at the termination of
the pulsar’s wind, we constrain the pevatron’s size, between $0.025$ and $0.1$
pc, and the magnetic field $approx 110 mu$G. The production rate of PeV
electrons, $2.5 times 10^{36}$ erg $rm s^{-1}$, constitutes 0.5% of the
pulsar’s spin-down luminosity, although we do not exclude a non-negligible
contribution of PeV protons to the production of the highest energy
$gamma$-rays.

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