2019MNRAS.489.5547Z

We present optical time-resolved multiband photometry of the black widow binary millisecond pulsar J2052+1219 using direct-imaging observations with the 2.1-m telescope of the Observatorio Astronomico Nacional San Pedro Martir (OAN-SPM), Mexico. The observations reveal a variable optical source whose position and periodicity, P = 2.752 h, coincide with the pulsar coordinates and the orbital period obtained from radio timing. This has allowed us to identify it with its binary companion. We reproduce the light curves of the source, modelling the companion's heating by the pulsar and accounting for the system parameters obtained from the radio data. As a result, we estimate the distance to the system independently as 3.94(16) kpc, which agrees with the dispersion measure distance. The size of the companion star is 0.12-0.15 R_☉, close to filling its Roche lobe. It has a surface temperature difference of about 3000 K between the side facing the pulsar and the back side. We summarize characteristics of all black widow systems studied in the optical and we compare them with the parameters of PSR J2052+1219 derived from our observations.