Parkes observations for project P1005 semester 2021APRS_10

We propose to conduct observations of PSR J1812-15, a 1-s pulsar in a 20.3-hr circular orbit around a light companion which also exhibits variable emission (turning `on’ and `off’). Binary pulsars are valuable objects of scientific study, allowing for a wide range of applications, including tests of gravity, probes of the neutron star equation of state and fossil records of stellar evolution. Long spin-period pulsars in binary systems are generally much rarer than faster-spinning recycled pulsars, and represent an under-explored region of pulsar binary evolution.\r\n\r\nWe propose a two-pronged campaign designed to address individual aspects of PSR J1812-15’s behaviour. Firstly, although we have developed a binary solution as a consequence of previous P1005 observations, we are still unable to develop a phase-connected timing solution, a key step in understanding this pulsar and its binary formation process. We therefore propose a 6-month monitoring campaign intended to provide the additional constraint required to determine a unique solution. Secondly, we have identified a correlation between the pulsar’s detectability and its orbital phase, suggesting that an eclipse or other complex interaction between the pulsar and its binary companion is at least partially responsible for its variable emission. We propose to monitor a series of consecutive orbits so as to fully cover the pulsar’s orbital phase, exploiting the wide bandwidth of the UWL receiver to distinguish between variability due to the binary companion or other sources (e.g. intrinsic pulse nulling).