Kavli Affiliate: Wei Gao
| First 5 Authors: Zhen Cao, Zhen Cao, , ,
| Summary:
Ultra-high-energy (UHE), exceeding 100 TeV (10^12 electronvolts),
gamma-rays manifests extreme particle acceleration in astrophysical sources.
Recent observations by gamma-ray telescopes, particularly by the Large High
Altitude Air Shower Observatory (LHAASO), have revealed a few tens of UHE
sources, indicating numerous Galactic sources capable of accelerating particles
to PeV (10^15 electronvolts) energies. However, discerning the dominant
acceleration mechanisms (leptonic versus hadronic), the relative contributions
of specific source classes, and the role of particle transport in shaping their
observed emission are central goals of modern UHE astrophysics. Here we report
the discovery of a giant UHE gamma-ray emitter at -17.5deg off the
Galactic plane – a region where UHE gamma-ray sources are rarely found. The
emitter exhibits a distinctive asymmetric shape, resembling a giant "Peanut"
spanning 0.45deg times 4.6deg, indicative of anisotropic particle
distribution over a large area. A highly aged millisecond pulsar (MSP)
J0218+4232 is the sole candidate accelerator positionally coincident with the
Peanut region. Its association with UHE gamma-rays extending to 0.7 PeV, if
confirmed, would provide the first evidence of a millisecond pulsar powering
PeV particles. Such a finding challenges prevailing models, which posit that
millisecond pulsars cannot sustain acceleration to PeV energies. The detection
reveals fundamental gaps in understanding particle acceleration, cosmic-ray
transport, and interstellar magnetic field effects, potentially revealing new
PeV accelerator (PeVatron) classes.
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