Challenges in Explaining the Galactic Center Gamma-Ray Excess with Millisecond Pulsars

TL;DR

This paper evaluates whether millisecond pulsars can account for the gamma-ray excess near the Galactic Center, concluding they likely contribute only a small fraction of the observed excess.

Contribution

It provides a new estimate of the millisecond pulsar population's contribution to the gamma-ray excess using X-ray binary data and luminosity functions.

Findings

Millisecond pulsars account for only 1-5% of the gamma-ray excess.

The upper limit on diffuse emission from millisecond pulsars is consistent with local measurements.

Most of the gamma-ray excess cannot be explained by millisecond pulsars.

Abstract

Millisecond pulsars have been discussed as a possible source of the gamma-ray excess observed from the region surrounding the Galactic Center. With this in mind, we use the observed population of bright low-mass X-ray binaries to estimate the number of millisecond pulsars in the Inner Galaxy. This calculation suggests that only ~1-5% of the excess is produced by millisecond pulsars. We also use the luminosity function derived from local measurements of millisecond pulsars, along with the number of point sources resolved by Fermi, to calculate an upper limit for the diffuse emission from such a population. While this limit is compatible with the millisecond pulsar population implied by the number of low-mass X-ray binaries, it strongly excludes the possibility that most of the excess originates from such objects.