PSR J1738+0333: The First Millisecond Pulsar + Pulsating White Dwarf Binary

TL;DR

This paper reports the discovery of the first millisecond pulsar with a pulsating white dwarf companion, providing a new benchmark for studying low-mass white dwarfs and neutron star evolution.

Contribution

It presents the first detection of pulsations in a white dwarf companion to a millisecond pulsar, offering a new system for detailed astrophysical analysis.

Findings

Significant optical variability detected in PSR J1738+0333

No variability detected in PSR J1909-3744 to <0.1% amplitude

PSR J1738+0333 serves as a benchmark for low-mass, pulsating white dwarfs

Abstract

We report the discovery of the first millisecond pulsar with a pulsating white dwarf companion. Following the recent discoveries of pulsations in extremely low-mass (ELM, <0.3 Msol) white dwarfs (WDs), we targeted ELM WD companions to two millisecond pulsars with high-speed Gemini photometry. We find significant optical variability in PSR J1738+0333 with periods between roughly 1790-3060 s, consistent in timescale with theoretical and empirical observations of pulsations in 0.17 Msol He-core ELM WDs. We additionally put stringent limits on a lack of variability in PSR J1909-3744, showing this ELM WD is not variable to <0.1 per cent amplitude. Thanks to the accurate distance and radius estimates from radio timing measurements, PSR J1738+0333 becomes a benchmark for low-mass, pulsating WDs. Future, more extensive time-series photometry of this system offers an unprecedented opportunity to constrain the physical parameters (including the cooling age) and interior structure of this ELM WD, and in turn, the mass and spin-down age of its pulsar companion.