X-ray Detection of Pulsar PSR B1757−24 and its Nebular Tail

We report the first X-ray detection of the radio pulsar PSR B1757−24 using the Chandra X-ray Observatory. We detect point-source emission at the pulsar position plus a faint tail extending nearly 20 east of the pulsar, in the same direction and with comparable morphology to the radio tail. Assuming the point-source X-ray emission is magnetospheric, the observed X-ray tail represents only ∼0.01% of the pulsar’s spindown luminosity. This is significantly lower than the analogous efficiencies of most known X-ray nebulae surrounding rotation-powered pulsars. Assuming a non-thermal spectrum for the tail photons, we show that the tail is unlikely to be emission left behind following the passage of the pulsar, but rather is probably from synchrotronemitting pulsar wind particles having flow velocity ∼7000 km s. We also show that there must be a significant break in the tail synchrotron spectrum between the radio and X-ray bands that is intrinsic to the particle spectrum. No emission is detected from the shell supernova remnant G5.4−1.2. The upper limits on remnant emission are unconstraining. Subject headings: pulsars: general — pulsars: individual (PSR B1757−24) — ISM: individual (G5.4−1.2) — X-rays: general