Parkes observations for project P1021 semester 2020OCTS_05

We propose to continue our observations of PSR J1653-45, a 951-ms pulsar in a long, 1.5-yr orbit, and experiences apparent eclipses whose duration and nature have yet to be fully understood. 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. Based upon previous Parkes proposals, our understanding of this pulsar has significantly increased. We have detected the pulsar in previously unexplored regions of its orbit, and have constrained the duration of the eclipse, such that a targeted campaign in the 2021APRS semester (during which the next eclipse is expected) will provide the breakthrough needed to solve and understand this pulsar. For the 2020OCTS semester, we propose a lower-cadence monitoring campaign, intended to allow these future observations to be successfully-phase connected with the existing dataset, maximising their scientific utility. We also propose to conduct a small set of high-cadence observations of PSR J1653-45 intended to characterise its emission and explore any short-term variability which may be inhibiting our ability to determine a timing solution. Through this, we hope to gain a greater understanding of this pulsar’s properties and how it fits into this under-explored class of unrecycled pulsar binaries.