Keck Spectroscopy of Millisecond Pulsar J2215+5135: a Moderate-M_NS, High-Inclination Binary

TL;DR

This study uses Keck spectroscopy to analyze the millisecond pulsar binary J2215+5135, revealing a lower neutron star mass and potential gamma-ray eclipses, offering new insights into pulsar binary systems.

Contribution

It provides the first spectroscopic measurement of the neutron star mass in J2215+5135 and investigates gamma-ray eclipses to probe the system's environment.

Findings

Neutron star mass estimated at 1.6 solar masses

Detection of heating effects on the companion star

Weak evidence for gamma-ray eclipses

Abstract

We present Keck spectroscopic measurements of the millisecond pulsar binary J2215+5135. These data indicate a neutron-star (NS) mass M_NS=1.6Mo, much less than previously estimated. The pulsar heats the companion face to T_D~9000K; the large heating efficiency may be mediated by the intrabinary shock dominating the X-ray light curve. At the best-fit inclination i=88.8deg, the pulsar should be eclipsed. We find weak evidence for such eclipses in the pulsed gamma-rays; an improved radio ephemeris allows use of up to 5 times more Fermi-LAT gamma-ray photons for a definitive test of this picture. If confirmed, the gamma-ray eclipse provides a novel probe of the dense companion wind and the pulsar magnetosphere.