2016ApJ...824...87I

The relativistic double neutron star binary PSR J0737-3039 shows clear evidence of orbital phase-dependent wind-companion interaction, both in radio and X-rays. In this paper, we present the results of timing analysis of PSR J0737-3039 performed during 2006 and 2011 XMM-Newton Large Programs that collected ∼20,000 X-ray counts from the system. We detected pulsations from PSR J0737-3039A (PSR A) through the most accurate timing measurement obtained by XMM-Newton so far, the spin period error being of 2 x 10^–13 s. PSR A's pulse profile in X-rays is very stable despite significant relativistic spin precession that occurred within the time span of observations. This yields a constraint on the misalignment between the spin axis and the orbital momentum axis δ_{A}~{6.6}_{-5.4}^{+1.3} deg, consistent with estimates based on radio data. We confirmed pulsed emission from PSR J0737-3039B (PSR B) in X-rays even after its disappearance in radio. The unusual phenomenology of PSR B's X-ray emission includes orbital pulsed flux and profile variations as well as a loss of pulsar phase coherence on timescales of years. We hypothesize that this is due to the interaction of PSR A's wind with PSR B's magnetosphere and the orbital-dependent penetration of the wind plasma onto PSR B closed field lines. Finally, the analysis of the full XMM-Newton data set provided evidence of orbital flux variability (∼7%) for the first time, involving a bow-shock scenario between PSR A's wind and PSR B's magnetosphere.