Low X-ray Efficiency of a Young High-B Pulsar PSR J1208‑6238 Observed with Chandra

High magnetic field (high-B) pulsars are key sources to bridge magnetars and conventional rotation powered pulsars, and thus to understand the origin of magnetar activities. We have estimated a tight upper limit on the X-ray flux of one of the youngest high-B pulsars PSR J1208‑6238 for the first time; a Chandra 10 ks observation shows no significant source. Depending on the emission models, we have the 3σ upper limit on the intrinsic 0.5–7 keV flux to 2.2–10.0×10‑14 erg s^‑1 cm^‑2. Assuming the distance to the pulsar to be 3 kpc, we suggest that the conversion efficiency from the spin-down energy to the X-ray luminosity of this pulsar is almost the smallest among known high-B pulsars, and even smaller for those for a typical rotation-powered one. We also discuss possible associations of a surrounding pulsar wind nebula and a hosting supernova remnant around this high-B pulsar.