Unusual Pulsed X-Ray Emission from the Young, High Magnetic Field Pulsar PSR J1119-6127

We present XMM-Newton observations of the radio pulsar PSR J1119-6127, which has an inferred age of 1700 yr and surface dipole magnetic field strength of 4.1×10¹³ G. We report the first detection of pulsed X-ray emission from PSR J1119-6127. In the 0.5-2.0 keV range, the pulse profile shows a narrow peak with a very high pulsed fraction of 74%+/-14%. In the 2.0-10.0 keV range, the upper limit for the pulsed fraction is 28% (99% confidence). The pulsed emission is well described by a thermal blackbody model with a temperature of T^∞=2.4^+0.3_-0.2×10⁶ K and emitting radius of 3.4^+1.8_-0.3 km (at a distance of 8.4 kpc). Atmospheric models result in problematic estimates for the distance/emitting area. PSR J1119-6127 is now the radio pulsar with smallest characteristic age from which thermal X-ray emission has been detected. The combined temporal and spectral characteristics of this emission are unlike those of other radio pulsars detected at X-ray energies and challenge current models of thermal emission from neutron stars.