# Precise optical timing of PSR J1023+0038, the first millisecond pulsar detected with Aqueye+ in Asiago

## TL;DR

This paper reports the first optical detection of millisecond pulsations from PSR J1023+0038 using Aqueye+, confirming and refining previous X-ray timing measurements with high precision.

## Contribution

It presents the first optical timing of PSR J1023+0038 with Aqueye+, providing an independent confirmation and a highly precise timing solution for the pulsar.

## Key findings

- Detected highly significant optical pulsations from PSR J1023+0038
- Achieved an optical timing accuracy of ~12 microseconds
- Found a phase shift in the pulsar's orbital parameters compared to X-ray data

## Abstract

We report the first detection of an optical millisecond pulsar with the fast photon counter Aqueye+ in Asiago. This is an independent confirmation of the detection of millisecond pulsations from PSR J1023+0038 obtained with SiFAP at the Telescopio Nazionale Galileo. We observed the transitional millisecond pulsar PSR J1023+0038 with Aqueye+ mounted at the Copernicus telescope in January 2018. Highly significant pulsations were detected. The rotational period is in agreement with the value extrapolated from the X-ray ephemeris, while the time of passage at the ascending node is shifted by $11.55 \pm 0.08$ s from the value predicted using the orbital period from the X-rays. An independent optical timing solution is derived over a baseline of a few days, that has an accuracy of $\sim 0.007$ in pulse phase ($\sim 12$ $\mu$s in time). This level of precision is needed to derive an accurate coherent timing solution for the pulsar and to search for possible phase shifts between the optical and X-ray pulses using future simultaneous X-ray and optical observations.