PSR J2322$-$2650 -- A low-luminosity millisecond pulsar with a planetary-mass companion

TL;DR

This paper reports the discovery and detailed analysis of PSR J2322-2650, a low-luminosity millisecond pulsar with a planetary-mass companion, highlighting its unique properties and potential significance for understanding MSP evolution.

Contribution

The study provides the first detailed characterization of a low-luminosity MSP with a planetary-mass companion, including precise astrometric, spin, and optical measurements.

Findings

PSR J2322-2650 has the lowest radio luminosity ever measured for an MSP.

The system's companion likely fills its Roche lobe, consistent with optical observations.

The pulsar's intrinsic period derivative indicates a very low magnetic field strength.

Abstract

We present the discovery of a binary millisecond pulsar (MSP), PSR J2322$-$2650, found in the Southern section of the High Time Resolution Universe survey. This system contains a 3.5-ms pulsar with a $\sim10^{-3}$ M$_{\odot}$ companion in a 7.75-hour circular orbit. Follow-up observations at the Parkes and Lovell telescopes have led to precise measurements of the astrometric and spin parameters, including the period derivative, timing parallax, and proper motion. PSR J2322$-$2650 has a parallax of $4.4\pm1.2$ mas, and is thus at an inferred distance of $230^{+90}_{-50}$ pc, making this system a candidate for optical studies. We have detected a source of $R\approx26.4$ mag at the radio position in a single $R$-band observation with the Keck Telescope, and this is consistent with the blackbody temperature we would expect from the companion if it fills its Roche lobe. The intrinsic period derivative of PSR J2322$-$2650 is among the lowest known, $4.4(4)\times10^{-22}$ s s$^{-1}$, implying a low surface magnetic field strength, $4.0(4)\times10^7$ G. Its mean radio flux density of 160 $\mu$Jy combined with the distance implies that its radio luminosity is the lowest ever measured, $0.008(5)$ mJy kpc$^2$. The inferred population of these systems in the Galaxy may be very significant, suggesting that this is a common MSP evolutionary path.