# Low Mass X-Ray Binaries in the Inner Galaxy: Implications for Millisecond Pulsars and the GeV Excess

## TL;DR

This study estimates the contribution of millisecond pulsars to the gamma-ray excess in the Inner Galaxy by analyzing low-mass X-ray binaries, concluding MSPs account for at most 23% of the excess, challenging their role as the primary source.

## Contribution

It provides a robust, data-driven estimate of MSPs' contribution to the gamma-ray excess using extensive LMXB and globular cluster data, refining previous smaller-sample analyses.

## Key findings

- MSPs likely contribute only 4-23% of the gamma-ray excess.
- Only 42 LMXBs observed near the Galactic Center, far fewer than the ~1000 predicted if MSPs caused the entire excess.
- The results challenge the hypothesis that MSPs are the main source of the gamma-ray excess.

## Abstract

If millisecond pulsars (MSPs) are responsible for the excess gamma-ray emission observed from the region surrounding the Galactic Center, the same region should also contain a large population of low-mass X-ray binaries (LMXBs). In this study, we compile and utilize a sizable catalog of LMXBs observed in the the Milky Way's globular cluster system and in the Inner Galaxy, as well as the gamma-ray emission observed from globular clusters, to estimate the flux of gamma rays predicted from MSPs in the Inner Galaxy. From this comparison, we conclude that only up to $\sim$4-23% of the observed gamma-ray excess is likely to originate from MSPs. This result is consistent with, and more robust than, previous estimates which utilized smaller samples of both globular clusters and LMXBs. If MSPs had been responsible for the entirety of the observed excess, INTEGRAL should have detected $\sim$$10^3$ LMXBs from within a $10^{\circ}$ radius around the Galactic Center, whereas only 42 LMXBs (and 46 additional LMXB candidates) have been observed.