An XMM-Newton Observation of the High Magnetic Field Radio Pulsar PSR B0154+61

We present the results obtained from a 31 ks XMM-Newton observation of the high magnetic field radio pulsar PSR B0154+61. This relatively nearby pulsar has an inferred dipole surface magnetic field strength of 2.1×10¹³ G, among the highest in the population. This makes the pulsar a possible transition object between the classical radio pulsars and magnetars, whose enhanced X-ray emission is believed to be powered by their large magnetic fields. However, our analysis shows that no X-ray emission is detected from the position of PSR B0154+61 with XMM-Newton. The upper flux limit derived from the observation implies a blackbody temperature of T^∞_bb<~73 eV and unabsorbed 0.3-10.0 keV X-ray luminosity of <~1.4×10³² ergs s^-1 (assuming a distance of 2.2 kpc and column density of N_H<~3×10²¹ cm^-2). This luminosity is much lower than those exhibited by all known magnetars. When corrections for the presence of a light-element atmosphere on the neutron star are made, our estimates favor the temperature predictions of rapid cooling models over those of standard cooling models. However, the uncertainties in distance, column density, and atmospheric composition prevent a definite conclusion regarding initial cooling.