The timing stability of three Black Widow pulsars

© Ann-Sofie Bak Nielsen, Gemma Janssen, Golam Shaifullah, Cees Bassa

Black widow pulsars are binary systems where the high energy emission from the millisecond pulsar is ablating the surface of their low-mass binary companion. The resulting matter, lost in the form of a wind, is usually observed to block or 'eclipse' the radio signal of the pulsar when the companion passes closest to the line-of-sight with the pulsar. Due to the ablation, the binary companions are bloated, which leads to tidally induced changes in the orbital period of the binary.

A European and global effort to use high precision pulsar timing of an ensemble of radio millisecond pulsars is ongoing, aimed at detecting gravitational waves from supermassive binary black holes. The sensitivity to detecting these waves depends crucially on the number of pulsars that can be timed to high precision. Including more pulsars will improve the detection sensitivity.

In a new publication, we used pulsar timing observations of the European Pulsar Timing Array, which includes data from the Effelsberg, Lovell, Nancay and Westerbork Synthesis Radio Telescope, to investigate the timing stability of three black widow pulsars. By using 7 to 8 years of pulsar timing observations (see lefthand panels), we found that none showed radio eclipses, which, if present, would lead to increased timing residuals near orbital phase 0.25 (see righthand panels). We also find that only one of the pulsar, J0023+0923, shows significant orbital variations, indicating tidal locking. As these variations are, so far, well described by higher order derivatives of the orbital period, the pulsar timing of all three pulsars is considered precise enough to be included in the pulsar timing programme of the European Pulsar Timing Array.