Discovery of Hidden Extragalactic Pulsars in the Parkes Archival Data

Abstract: Just over 1% of the known radio pulsar population resides in the Large and Small Magellanic Clouds (MCs), the satellite galaxies that are 50-62 kpc distant from the Milky Way. These pulsars are important for constraining the peak of the pulsar luminosity function, and may give insights into neutron star populations formed from stars of different metallicities than the Milky Way. Using search techniques that have proven highly effective at discovering a large number of pulsars in archival data by folding candidates near the noise floor at high harmonic folds, we reprocessed the original Parkes Multibeam MC surveys and discovered six pulsars. Five of these pulsars are located in the Large Magellanic Cloud (LMC), including one with a spin period of 3.8s, making it the slowest pulsar known in the MCs. The remaining pulsar was detected toward the Small Magellanic Cloud (SMC), and is associated with the Milky Way foreground. Four of the newly discovered pulsars exhibit scintillation, with one showing clear nulling and others showing possible nulling behavior. These discoveries bring the total number of radio pulsars known in the LMC to 49. A luminosity function and duty cycle analysis of all current MC pulsars shows that they are consistent with Galactic canonical pulsars. Population synthesis simulations suggest that deeper surveys would reveal many more pulsars in the MCs, including up to handful of millisecond pulsars, based on the adopted upper limits for their parent populations. Finally, this reprocessing demonstrates the continued importance of reanalyzing archival data, both to improve the completeness of pulsar surveys and detect scientifically valuable objects.