Light curve analysis of a transitional millisecond pulsar PSR J1023+0038 with Kepler K2 mission

Abstract

PSR J1023+0038 has been known as a transitional pulsar-low-mass-X-ray binary (LMXB) system, which provides crucial information in understanding the evolution of pulsars in binary systems. We report analysis of 80-day continuous optical light curve of PSR J1023+0038 with the Kepler observations during K2 mission. The light curve was observed from May to August 2017, where the system appeared to be in its LMXB state. At ∼30 minutes time resolution, the data were fitted with a Gaussian window function, which generated a smoothed light curve with 100, 000 from 3545 raw data input. The time at the maxima and minima of the light curve was measured and compared with the orbit ephemeris predicted from a quadratic polynomial function published by previous work. We found that at MJD ∼57935 there appeared to be a constant delay of ∼1.06 hr added to the orbit, which then gradually recovered to the expected period at MJD ∼57965. Possible causes have been proposed to explain such delay includes a third body involvement or hot spots on the star.