X-ray emission from J1446-4701, J1311-3430 and other black widow pulsars

Abstract

We present the results of detailed X-ray analysis of two black-widow pulsars (BWPs), J1446-4701 and J1311-3430. PSR J1446-4701 is a BWP with orbital parameters near the median values of the sample of known BWPs. Its X-ray emission detected by $XMM-Newton$ is well characterized by a soft power-law (PL) spectrum (photon index $\Gamma \approx 3$), and it shows no significant orbital modulations. In view of a lack of radio eclipses and an optical non-detection, the system most likely has a low orbital inclination. PSR J1311-3430 is an extreme BWP with a very compact orbit and the lowest minimum mass companion. Our $Chandra$ data confirm the hard, $\Gamma \approx 1.3$, emission seen in previous observations. Through phase-restricted spectral analysis, we found a hint ($\sim 2.6 \sigma$) of spectral hardening around pulsar inferior conjunction. We also provide a uniform analysis of the 12 BWPs observed with $Chandra$ and compare their X-ray properties. Pulsars with soft, $\Gamma > 2.5$, emission seem to have lower than average X-ray and $\gamma$-ray luminosities. We do not, however, see any other prominent correlation between the pulsar's X-ray emission characteristics and any of its other properties. The contribution of the intra-binary shock to the total X-ray emission, if any, is not discernible in this sample of pulsars with shallow observations.