The Galactic bulge millisecond pulsars shining in X rays: A gamma-ray perspective

TL;DR

This study assesses the potential of current X-ray telescopes to detect millisecond pulsars in the Galactic bulge, which could explain the gamma-ray excess observed by Fermi-LAT, by creating a synthetic MSP population and comparing it with Chandra data.

Contribution

It introduces a novel method to evaluate X-ray telescope sensitivity to bulge MSPs using a synthetic population and observational data comparison.

Findings

A significant number of Chandra sources may be bulge MSPs.

Current X-ray observations can potentially identify bulge MSPs.

Dedicated multi-wavelength searches are promising for future detection.

Abstract

If the mysterious Fermi-LAT GeV gamma-ray excess is due to an unresolved population of millisecond pulsars (MSP) in the Galactic bulge, one expects this very same population to shine in X rays. For the first time, we address the question of what is the sensitivity of current X-ray telescopes to an MSP population in the Galactic bulge. To this end, we create a synthetic population of Galactic MSPs, building on an empirical connection between gamma- and X-ray MSP emission based on observed source properties. We compare our model with compact sources in the latest Chandra source catalog, applying selections based on spectral observables and optical astrometry with Gaia. We find a significant number of Chandra sources in the region of interest to be consistent with being bulge MSPs that are as yet unidentified. This motivates dedicated multi-wavelength searches for bulge MSPs: Some promising directions are briefly discussed.