Parkes observations for project P1021 semester 2021OCTS_02

We propose to continue our observations of PSR J1653-45 and PSR J1812-15, a pair of long spin-period binary pulsars which both show degrees of orbitally-dependent variability. Binary pulsars are valuable objects of scientific study, allowing for multiple 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. This is particularly true of PSR J1812-15, for which only one other pulsar (B1718-19) seems remotely comparable. Based upon previous Parkes proposals, our understanding of these pulsars and their place with binary evolution has significantly increased, such that we anticipate their publication in early 2022. We therefore propose a low-cadence campaign intended to finalise the timing of both pulsars. For PSR J1812-15, this data will be useful in addressing on-going problems with phase connection, which may be caused by an undiagnosed glitch or other un-modeled timing effect. For PSR J1653-45, this data will be useful in both capitalising on the breakthroughs of the 2021APRS campaign (detection of the pulsar during its eclipse phase) and in setting up a future eclipse campaign should it be deemed of sufficient scientific merit. These observations are the final step needed to ensure the publication of these pulsars in the immediate term.