Eclipses and orbital modulations in binary pulsar PSR J0737-3039

Abstract

Binary radio pulsar system J0737-3039 provides an exceptional opportunity to study innermost structure of pulsar magnetospheres due to very tight orbit, favorable directions of pulsars' rotation and magnetic axes and extremely fortuitous orientation of the orbit. In this system the millisecond pulsar A is eclipsed once per orbit. During eclipse a clear modulation at the 2.77 s period of pulsar B is seen, pointing unambiguously to magnetospheric origin of eclipses. A simple geometric model, based on the idea that the radio pulses are attenuated by synchrotron absorption on the closed magnetic field lines of pulsar B, can successfully reproduces the eclipse light curves down to intricate details. This detailed agreement confirms the dipolar structure of the neutron star's magnetic field. The model gives clear predictions for temporal evolution of eclipse profile due to geodetic precession of pulsar B. In addition, pulsar B shows orbital modulations of intensity, being especially bright at two short orbital phases. We showed that these modulations are due to distortion of pulsar B magnetosphere by pulsar A wind which produces orbital phase-dependent changes of the direction along which radio waves are emitted. Thus, pulsar B is intrinsically bright at all times but its radiation beam misses the Earth at most orbital phases.