The Chandra Observations of the Two Pulsars PSR 0628 - 28 and PSR 1813 - 36

PSR 0628-28 is an X-ray emitting radio pulsar which was observed with Advanced CCD Imaging Spectrometer (ACIS) on board Chandra on 2001 November 04 and on 2002 March 25 for 2700 s and 17000 s, respectively. The source countrate was 0.0111±0.0008cps. We detected pulsations consistent with the radio frequency of f = 0.80370338 ± 0.000059 at a pulsed fraction 25.4%±%2 making PSR 062828 to be the longest period X-ray emitting pulsar. The spectral distribution of counts can be described by several model fits. A blackbody fit yields a temperature kT = 4.53 −0.14 × 10K where we assumed NH = 1.07 × 10cm and a powerlaw fit yields a photon index of γ = 2.45±0.15 with the same hydrogen column density. The distance of 2.14 kpc calculated from the dispersion measure gives a blackbody radius of ∼1 km. Confirming the previous ROSAT pointed observation for PSR 1813-36, there was no positive detection from the 30ks Chandra ACIS observation on 2001 October 25. We obtained an upper limit for the countrate of 2.3× 10cps.