ASCA observations of the young rotation-powered pulsars PSR B1046-58 and PSR B1610-50

We present X-ray observations of two young energetic radio pulsars, PSRs B1 046 - 58 and B1610 - 50, and their surroundings, using archival data from t he Advanced Satellite for Cosmology ann Astrophysics (ASCA). The energetic pulsar PSR B1610--50 is detected in X-rays with a significance of 4.5 a. Th e unabsorbed flux, estimated assuming a power-law spectrum and a neutral hy drogen column density N-H of 5 x 10(21) Cm-2, is (2.5 +/- 0.3) x 10(-13) er gs cm(-2) s(-1) in the 2-10 keV band. Pulsed emission is not detected; the pulsed fraction is less than 31% at the 90% confidence level for a 50% duty cycle. We argue that the emission is best explained as originating from a pulsar-powered synchrotron nebula. The X-ray counterpart of the pulsar is t he only hard source within the 95% error region of the previously unidentif ied gamma-ray source 3EG J1048--5840. This evidence supports the results of Kaspi et al., who suggest, in a companion paper, that PSR B1046--58 is the counterpart to 3EG J1048--5840. X-ray emission from PSR B1610--50 is not d etected. Using assumptions similar to those above, the derived 3 sigma uppe r limit for the unabsorbed 2-10 keV X-ray flux is 1.5 x 10(-13) ergs cm(-2) s(-1). We use the flux limit to estimate the pulsar's velocity to be less than similar to 170 km s(-1), casting doubt on a previously reported associ ation between PSR B1610--50 and supernova remnant Kes 32. Kes 32 is detecte d, as is evident from the correlation between X-ray and radio emission. The ASCA images of PSR B1610--50 are dominated by mirror-scattered emission fr om the X-ray-bright supernova remnant RCW 103, located 33' away. We find no evidence for extended emission around either pulsar, in contrast to previo us reports of large nebulae surrounding both pulsars.