Ultra-high-energy γ-ray emission associated with the tail of a bow-shock pulsar wind nebula

In this study, we present a comprehensive analysis of an unidentified point-like ultra-high-energy (UHE) γ-ray source, designated as 1LHAASO J1740+0948u, situated in the vicinity of the middle-aged pulsar PSR J1740+1000. The detection significance reached 17.1 σ (9.4 σ) above 25 TeV (100 TeV). The source energy spectrum extended up to 300 TeV, which was well fitted by a log-parabola function with <i>N</i> ₀ = (1.93 ± 0.23) × 10^-16 TeV^-1 cm^-2 s^-1, α = 2.14 ± 0.27, and β = 1.20 ± 0.41 at <i>E</i> ₀ = 30 TeV. The associated pulsar, PSR J1740+1000, resides at a high galactic latitude (Gb) and powers a bow-shock pulsar wind nebula (BSPWN) with an extended X-ray tail. The best-fit position of the γ-ray source appeared to be shifted by 0.2° with respect to the pulsar position. As (1) the currently identified pulsar halos do not demonstrate such offsets and (2) the centroid of the γ ray emission is approximately located at the extension of the X-ray tail, we speculate that the UHE γ-ray emission may originate from re-accelerated electron/positron pairs that are advected away in the bow-shock tail.