X-ray Timing Analysis of PSR B1951+32 with ASCA and RXTE Data

Hsiang-Kuang Chang；Tz-Feng Guo

Chinese Journal of Physics

38卷3期（2000 / 06 / 01）

429 - 436

英文

PSR B1951+32, like other EGRET-detected high-energy pulsars, shows a power-law spectrum in the EGRET energy band. However, characteristics of this pulsar in soft and hard X-ray bands still remain uncertain. In this paper we report results of a timing analysis of PSR B1951+32 based on ASCA data taken in 1993 and RXTE data taken in 1996 ranging from 0.5 keV to 250 keV. We apply contemporaneous radio ephemerides and various statistical tests to search for evidence of pulsation. Although these analyses all fail to find pulsation in the time series, useful upper limits are derived. The estimated upper limits are consistent with the trend of spectral turn-over from high-energy gamma-ray emissions towards lower-energy bands. We give detailed discussions which argue that such turn-over strongly suggests the outer magnetosphere as the emission site for pulsed gamma-rays. On the other hand, they are not consistent with the reported power-law spectra from the point source observed by ROSAT in the 0.1-2.4 keV band with an assumed constant pulsed fraction. The pulsed soft X-ray emission detected by ROSAT must follow a much softer spectrum than that of the overall point source. This in turn suggests a relatively strong unpulsed power-law component beyond about 1 keV, whose actual spectral behavior calls for future observations.