The contribution to Galactic Centre {\gamma}-ray excess from cluster-born millisecond pulsars. Constraints from direct N-body simulations

TL;DR

This study models millisecond pulsars originating from globular clusters using N-body simulations to explain the Galactic Centre gamma-ray excess, supporting an astrophysical origin over dark matter.

Contribution

It introduces a dynamical framework tracking neutron stars from globular clusters to reproduce the gamma-ray excess, a novel approach compared to previous static models.

Findings

MSPs from surviving clusters contribute significantly to gamma-ray flux.

Disrupted clusters increase the amplitude and central concentration of the gamma-ray signal.

Combined MSP populations can reproduce the observed properties of the GCE.

Abstract

The Galactic Centre {\gamma}-ray excess (GCE), observed by Fermi-LAT around Sgr A*, exceeds expectations from standard cosmic-ray models and is commonly attributed either to dark matter annihilation or to unresolved millisecond pulsars (MSPs). We revisit the MSP scenario within a fully dynamical framework by tracking neutron stars (NSs) formed in globular clusters (GCs) and deposited into the central kiloparsec. Using high-resolution direct N-body simulations of GCs evolving in a time-dependent Milky Way potential, we model both present-day clusters and an early population of disrupted systems. From the simulated NS distributions, we infer the MSP population via an empirically calibrated MSP-to-NS ratio and construct mock {\gamma}-ray flux profiles assuming representative pulsar luminosities. MSPs associated with surviving clusters already produce a substantial {\gamma}-ray contribution, while disrupted clusters enhance both the amplitude and central concentration of the signal. Under reasonable assumptions, the combined MSP population reproduces the observed GCE properties, favouring an astrophysical origin over dark matter interpretations.