Psr B1929+10 Revisited in X-rays

We performed timing and spectral analysis for PSR B1929+10, one of the oldest (about 10 years) of the ordinary pulsars detected in X-rays, using archival ROSAT, ASCA and RXTE data. Pulsed emission was detected at a more than five sigma level for combined ROSAT PSPC and unpublished HRI data. Our pulse profile is in agreement with that obtained by Yancopoulos et al. (1994; ROSAT PSPC) but now with better statistics. An investigation of the behaviour of the pulsed signal as a function of energy , based on PSPC data, provides indications that the pulsed fraction is changing with energy. The most important new result from this work is derived from the spectral analysis. We found that the combined ROSAT PSPC and ASCA GIS spectrum can satisfactorily be described by a power-law as well as by a double black-body model but not by a single black-body model, as was presented earlier by Yancopoulos et al. (1994; ROSAT) and Wang et al. (1997; ASCA). Fitting the combined ROSAT/ASCA 0.1 10 keV spectrum by a power-law model we obtain a photon index of 2.54 ± 0.12 and a neutral Hydrogen column density (NH) towards the source of 9.8 −1.0 · 10 20 cm. For a double black-body fit our results are: T1 = 2.0 +0.05 −0.05 · 10 6 K, T2 = 6.9 +0.23 −0.35 · 10 6 K, and NH= 4.43 +2.08 −1.12 · 10 20 cm. In both cases the derived NH value is higher than that adopted in earlier works, but our result is consistent with the larger distance estimate of 331 ± 10 pc from new parallax measurements performed by Brisken et al. (2002) and with the Hydrogen distribution measured in the direction of the pulsar (Frisch & York, 1983). No significant pulsed signal is found in the RXTE data.