Description
PSR J1023+0038 is a transitional millisecond pulsar (tMSP), the only one where coherent pulsations
were discovered in both the Optical and X-ray energy bands to date. We present a detailed
timing analysis of new Aqueye+ optical data taken from 2021 through 2023, obtaining an updated
timing solution for the pulsar. We perform a new measurement of the phase lag between optical
and X-ray pulsations and investigate the recent evolution of the binary system, monitoring the
variation of the time of passage at the ascending node. We measured a phase lag between the optical
and X-ray pulses of 112.3 ± 30.7 μs, confirming a common origin. After 2017, the evolution of
the passage at the ascending node follows a well-defined parabolic increasing trend, suggesting a
corresponding increment in the orbital period and orbital separation of the system. This evolution
is consistent with a scenario in which the binary system is evolving through non-conservative
Roche lobe overflow and the donor is interacting with the pulsar wind, losing mass at a rate much
higher than the inferred accretion rate. Finally, we offer a glimpse of the results from observations
of PSR J1023+0038 obtained with Iqueye
recently installed at Gemini South, which achieved unprecedented photon statistics and time resolution.