First X-Ray Observations of the Young Pulsar J1357-6429

The first short Chandra and XMM-Newton observations of the young and energetic pulsar J1357-6429 provided indications of a tail-like pulsar wind nebula associated with this object as well as pulsations of its X-ray flux with a pulsed fraction p_f>~50% and a thermal component dominating at energies E<~2 keV. The putative nebula is very compact in size and might be interpreted as evidence for a pulsar jet. The thermal radiation is most plausibly emitted from the entire neutron star surface of a 10 km radius and a 1.0+/-0.1 MK temperature, covered with a hydrogen atmosphere. At higher energies, the pulsar's emission is of a nonthermal origin, with a power-law spectrum of a photon index Γ=1.1+/-0.2. This makes the properties of PSR J1357-6429 very similar to those of the young pulsars J1119-6127 and Vela with detected thermal radiation.