2026ApJ...997..341G

We present a multiwavelength analysis of 1LHAASO J1740+0948u and its surroundings including the pulsar wind nebula of middle-aged pulsar PSR J1740+1000. Although a dozen X-ray sources are found within the ultrahigh-energy (UHE) emission site, careful analysis shows that they are unlikely to produce the observed UHE emission. The most likely particle accelerator is PSR J1740+1000, which if offset by 13${}^{{\prime} }$ north of the UHE source but appears to be connected to it by an extended feature seen in X-rays. For a plausible pulsar distance of 1.2 kpc, 1LHAASO J1740+0948u must be located about 5 pc away, which requires rapid transport of electrons along the feature to avoid radiative losses. This poses several challenges for standard pulsar theory. First, being produced ≲10 kyr ago, particles must have been accelerated to the energy corresponding to a large fraction of the pulsar's full potential drop across the polar cap. Second, due to the lack of TeV emission extension toward the pulsar, particles must be accumulating in the UHE region. In this context, we discuss two possible scenarios: a tail filled with pulsar wind and confined by the bow shock due to the fast pulsar's motion and an interstellar medium filament filled by the most energetic pulsar wind particles escaping from the apex of the bow shock.