A Cooling Neutron Star in Supernova Remnant G296.5+10.0

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Abstract
We present a ~20 ks Advanced Satellite for Cosmology and Astrophysics (ASCA) observation of the intriguing X-ray source 1E 1207.4-5209. The source is situated near the center of G296.5+10.0, one of the original barrel-shaped supernova remnants (SNRs). ASCA and ROSAT PSPC data are very well described by a blackbody model of temperature kT = 0.28 keV with a foreground absorbing column of NH = 4 × 1020 cm-2 in the range 0.1-10.0 keV. Previous stringent upper limits for optical and radio emission from the source support a cooling neutron star hypothesis. At its likely distance of 2 kpc, the luminosity LX ~ 1033d22 ergs s-1 implies a radiating surface area A ~ 30d22 km2, which is significantly less than the total area of a canonical neutron star. Despite the large number of detected photons, we see no evidence for rotationally induced X-ray pulsations. Surprisingly, no pulsar-like behavior is found in 1E 1207.4-5209, except that a faint radio nebulosity surrounding it may well be a pulsar-powered plerion. We deduce that the neutron star may have been born spinning very slowly (a birth period P ~ 0.5 s) and is a weak pulsar, which strengthens our belief that the observed radiation is indeed due to surface cooling.

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