X-ray pulsations from the central source in Puppis A

There are several supernova remnants that contain unresolved X-ray sources close to their centers, presumably radio-quiet neutron stars. To prove that these objects are indeed neutron stars, to understand the origin of their X-ray radiation, and to explain why they are radio quiet, one should know their periods and period derivatives. We searched for pulsations of the X-ray flux from the radio-quiet neutron star candidate RX J0822-4300 near the center of the Puppis A supernova remnant observed with the ROSAT PSPC and HRI. A standard timing analysis of the separate PSPC and HRI data sets does not allow one to detect the periodicity unequivocally. However, a thorough analysis of the two observations separated by 4.56 yr enabled us to find a statistically significant period of P ≃ 75.3 ms and its derivative P ≃ 1.49 x 10 ¹³ s s^-1. The corresponding characteristic parameters of the neutron star-age τ = P/(2P) = 8.0 kyr, magnetic field B = 3.4 x 10¹² G, and rotational energy loss E = 1.4 x 10³⁷ ergs s^-1 - are typical for young radio pulsars. Since the X-ray radiation has a thermal-like spectrum, its pulsations may be due to a nonuniform temperature distribution over the neutron star surface caused by anisotropy of the heat conduction in the strongly magnetized crust.