The Neutron Star in the Supernova Remnant PKS 1209-52

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We re-analyzed soft X-ray data collected with the ROSAT and ASCA observatories on a candidate neutron star (NS) near the center of the supernova remnant PKS 1209-52. We fitted the observed spectra with NS atmosphere models. The hydrogen atmosphere fits yield more realistic parameters of the NS and the intervening hydrogen column than the traditional blackbody fit. In particular, for a NS of mass 1.4 M and radius 10 km, we obtained the NS surface temperature Teff=(1.4-1.9)*10⁶ K and distance d=1.6-3.3 kpc versus T=(4.2-4.6)*10⁶ K and (implausible) d=11-13 kpc for the blackbody fit, at a 90% confidence level. Our fits suggest that the surface magnetic field is either very weak, B < 10¹⁰ G, or it exceeds 2*10¹² G. The hydrogen column density inferred from the atmosphere fits, nₕ=(0.7-2.2)*10²¹ cm⁻², agrees fairly well with independent estimates obtained from UV observations of nearby stars, radio data, and X-ray spectrum of the shell of the supernova remnant, whereas the blackbody and power-law fits give considerably lower and greater values, nₕ=(0.2-0.4)*10²¹ and (5.2-7.0)*10²¹ cm⁻², respectively. The inferred NS surface temperature is consistent with standard NS cooling models.