The Gamma-Ray Luminosity Function of Millisecond Pulsars and Implications for the GeV Excess

TL;DR

This paper reevaluates the gamma-ray luminosity function of millisecond pulsars to assess their potential role in explaining the Galactic Center GeV excess, suggesting many should already be detected by Fermi.

Contribution

It provides a new analysis of MSP luminosity function without relying on uncertain distances, impacting the MSPs' contribution to the gamma-ray excess.

Findings

Fermi should have detected many MSPs if they account for the GeV excess.

MSPs near the Galactic Center could be systematically less luminous.

The revised luminosity function challenges previous assumptions about MSP populations.

Abstract

It has been proposed that a large population of unresolved millisecond pulsars (MSPs) could potentially account for the excess of GeV-scale gamma-rays observed from the region surrounding the Galactic Center. The viability of this scenario depends critically on the gamma-ray luminosity function of this source population, which determines how many MSPs Fermi should have already detected as resolved point sources. In this paper, we revisit the gamma-ray luminosity function of MSPs, without relying on uncertain distance measurements. Our determination, based on a comparison of models with the observed characteristics of the MSP population, suggests that Fermi should have already detected a significant number of sources associated with such a hypothesized Inner Galaxy population. We cannot rule out a scenario in which the MSPs residing near the Galactic Center are systematically less luminous than those present in the Galactic Plane or within globular clusters.