XMM-Newton Observes the Intrabinary Shock of PSR J1959+2048

In a multi-orbit (100 ks) $XMM-Newton$ exposure of the original black widow pulsar, PSR J1959+2048, we measure the strong orbital modulation caused by intrabinary shock (IBS) emission. The IBS light curve peak appears asymmetric, which we attribute to sweep-back effects in the companion wind. We also see evidence for an X-ray eclipse by the companion and its wind. Together with the IBS fit, this supports an edge-on $i\sim {90}^{\circ }$ view of the system and a modest $\sim 1.8M_{\odot }$ mass for the recycled pulsar. Our IBS fit parameters imply a wind flux that, if persistent, would evaporated the companion within a few Gyr.