Discovery of X-ray emission from the young radio pulsar PSR J1357-6429

We present the first X-ray detection of the very young pulsar PSR J1357-6429 (characteristic age of 7.3 kyr) using data from the XMM-Newton and Chandra satellites. We find that the spectrum is well described by a power-law plus blackbody model, with photon index Γ=1.4 and blackbody temperature k_BT=160 eV. For the estimated distance of 2.5 kpc, this corresponds to a 2-10 keV luminosity of ~1.2 × 10³² erg s^-1, thus the fraction of the spin-down energy channeled by PSR J1357-6429 into X-ray emission is one of the lowest observed. The Chandra data confirm the positional coincidence with the radio pulsar and allow to set an upper limit of 3 × 10³¹ erg s^-1 on the 2-10 keV luminosity of a compact pulsar wind nebula. We do not detect any pulsed emission from the source and determine an upper limit of 30% for the modulation amplitude of the X-ray emission at the radio frequency of the pulsar.