MeerKAT to Mass Constraints: Optical Modelling of PSR J1910-5320

PSR J1910-5320 is a new millisecond pulsar discovered during the TRAPUM large survey project's survey of unidentified gamma-ray sources. The precise localisation obtained from the initial MeerKAT detection was found to be coincident with a new candidate redback binary system, independently discovered through its optical variability in the Catalina Sky Survey (CSS) catalogue, and confirmed via optical spectroscopy. Folding the CSS optical photometry with an initial MeerKAT timing ephemeris confirmed the association, revealing a typical spider pulsar light curve, with an optically bright companion being strongly irradiated by the newly-discovered millisecond pulsar. Spider binaries like PSR J1910-5320 are often seen to contain massive neutron stars, and so new spider mass measurements can provide important constraints on the neutron-star equation-of-state. These mass measurements are obtained by solving the binary mass function using estimates of three key parameters. The first, the orbital inclination angle, can be estimated from modelling of optical light curves, for which we obtained new multi-colour observations with ULTRACAM on ESO's New Technology Telescope. The second key, the companion's velocity, is found through optical spectroscopy. The MeerKAT timing solution provides the final puzzle piece - the pulsar's radial velocity, which constrains the binary mass ratio. I will describe new modifications to the Icarus binary light curve synthesis code that allow us to provide a general optical model for spider binaries, drawing from photometry and spectroscopy simultaneously and self-consistently, and explain how this process leads to a moderate neutron star mass estimate for PSR J1910-5320, and to refined assumptions about the irradiation and atmosphere in redback companion stars.