A giant peanut-shaped ultra-high-energy γ-ray emitter off the galactic plane.

Ultra-high-energy (UHE) gamma (γ) rays serve as unique probes for investigating new non-thermal astronomical phenomena within the Galaxy and also for studying PeV particle acceleration and propagation. Based on the UHE γ-ray survey conducted by LHAASO, this paper reports the discovery of a new source distinct from all previously identified high energy γ-ray objects. This source exhibits an elongated, peanut-like structure, which can be described as a rectangular strip measuring 4.6° in length and 0.45° in width, featuring two bright knots. It is located at a Galactic latitude of -17.5°, well below the Galactic plane and away from regions rich in UHE sources. The energy spectrum is spatially uniform across the entire region and is well fitted by a power-law model with an index of -1.95 and a cutoff at 250 TeV. The highest detected photon energy reaches 760 TeV. Morphological and spectral analyses indicate the presence of a powerful particle accelerator in this region, capable of accelerating particles beyond 1 PeV. An energetic millisecond pulsar (MSP) J0218 + 4232 is located at the brighter end of this source, with a spatial chance coincidence probability of 3.6 × 10-4, corresponding to 3.4σ. This suggests that the emission from this region very likely originates from particles accelerated within the MSP wind nebulae, potentially providing the first observational evidence supporting the wind nebulae of MSP as sources of UHE γ rays. However, the presence of other hidden accelerators, whether associated with known or entirely new populations of PeVatrons, cannot be ruled out, motivating future multi-wavelength observations.