# PSR J1306--40: An X-ray Luminous Redback with an Evolved Companion

## TL;DR

This paper presents detailed optical and X-ray observations of PSR J1306--40, a redback millisecond pulsar binary with an evolved companion, revealing its fundamental properties, high X-ray luminosity, and potential evolutionary significance.

## Contribution

The study provides new optical photometry and spectroscopy data, constrains the system's component masses and inclination, and suggests PSR J1306--40 as a progenitor of typical pulsar-white dwarf binaries.

## Key findings

- Minimum neutron star mass of 1.75 solar masses
- High, nearly edge-on inclination angle
- X-ray luminosity brighter than most known redbacks

## Abstract

PSR J1306--40 is a millisecond pulsar binary with a non-degenerate companion in an unusually long $\sim$1.097 day orbit. We present new optical photometry and spectroscopy of this system, and model these data to constrain fundamental properties of the binary such as the component masses and distance. The optical data imply a minimum neutron star mass of $1.75\pm0.09\,M_{\odot}$ (1-sigma) and a high, nearly edge-on inclination. The light curves suggest a large hot spot on the companion, suggestive of a portion of the pulsar wind being channeled to the stellar surface by the magnetic field of the secondary, mediated via an intrabinary shock. The H$\alpha$ line profiles switch rapidly from emission to absorption near companion inferior conjunction, consistent with an eclipse of the compact emission region at these phases. At our optically-inferred distance of $4.7\pm0.5$ kpc, the X-ray luminosity is $\sim$10$^{33}$ erg s$^{\textrm{-1}}$, brighter than nearly all known redbacks in the pulsar state. The long period, subgiant-like secondary, and luminous X-ray emission suggest this system may be part of the expanding class of millisecond pulsar binaries that are progenitors to typical field pulsar--white dwarf binaries.