The Orbit and Companion of PSR J1622-0315: Variable Asymmetry and a Massive Neutron Star

TL;DR

This study models the binary system of PSR J1622-0315, revealing a massive neutron star, variable light curve asymmetry, and low irradiation, using optical observations and binary modeling over several years.

Contribution

It provides the first detailed modeling of PSR J1622-0315's system, indicating a high neutron star mass and variable asymmetry likely caused by intrabinary shock effects.

Findings

Neutron star mass estimated at 2.3 solar masses.

Detected low-level irradiation and changing asymmetry in light curves.

Better fit with star spot models than symmetric direct heating.

Abstract

The companion to PSR J1622-0315, one of the most compact known redback millisecond pulsars, shows extremely low irradiation despite its short orbital period. We model this system to determine the binary parameters, combining optical observations from NTT in 2017 and NOT in 2022 with the binary modeling code ICARUS. We find a best-fit neutron star mass of $2.3 \pm 0.4\,\text{M}_\odot $, and a companion mass of $0.15 \pm 0.02\,\text{M}_\odot$. We detect for the first time low-level irradiation from asymmetry in the minima as well as a change in the asymmetry of the maxima of its light curves over five years. Using star spot models, we find better fits than those from symmetric direct heating models, with consistent orbital parameters. We discuss an alternative scenario where the changing asymmetry is produced by a variable intrabinary shock. In summary, we find that PSR J1622-0315 combines low irradiation with variable light curve asymmetry, and a relatively high neutron star mass.