X-ray emission from the radio-quiet neutron star in puppis A

We show that X-rays detected with the ROSAT and ASCA observatories from the radio-quiet neutron star candidate RX J0822-4300 in the Puppis A supernova remnant can be interpreted as radiation from a hydrogen or helium neutron star atmosphere. Fitting the observed X-ray spectra with the atmosphere models gives more realistic values for the effective temperatures and emitting areas than the commonly used blackbody model. The temperature obtained T-eff(infinity) = (1.6-1.9) x 10(6) K, is consistent with the standard neutron star cooling models. The corresponding distance and hydrogen column density are in good agreement with those obtained from independent estimates. Timing analysis of the combined results of the ROSAT PSPC and HRI observations separated by 4.6 yr enabled us to co-align phases of pulse profiles and find more accurate ephemeris parameters of this putative 75 ms isolated X-ray pulsar.