Millisecond Pulsars from Accretion Induced Collapse as the Origin of the Galactic Centre Gamma-ray Excess Signal

TL;DR

This paper proposes that millisecond pulsars formed via accretion-induced collapse of white dwarfs in the Galactic bulge can explain the gamma-ray excess observed at the Galactic Center, matching its morphology, spectrum, and intensity.

Contribution

It introduces a binary population synthesis model showing MSPs from AIC can account for the GCE, addressing previous issues with MSP origin theories.

Findings

MSP population from AIC reproduces GCE morphology and spectrum.

Model satisfies constraints from low-mass X-ray binaries.

Synchrotron emission from MSPs may explain the Galactic microwave haze.

Abstract

Gamma-ray data from the Fermi-Large Area Telescope reveal an unexplained, apparently diffuse, signal from the Galactic bulge that peaks near 2 GeV with an approximately spherical intensity profile $\propto r^{-2.4}$ that extends to angular radial scales of at least 10 degrees, possibly to 20 degrees. The origin of this "Galactic Centre Excess" (GCE) has been debated with proposed sources prominently including self-annihilating dark matter and a hitherto undetected population of millisecond pulsars (MSPs). However, the conventional channel for the generation of MSPs has been found to predict too many low mass X-ray binary (LMXB) systems and, because of the expected large natal kicks, may not accommodate the close spatial correspondence between the GCE signal and stars in the bulge. Here we report a binary population synthesis forward model that demonstrates that an MSP population arising from the accretion induced collapse (AIC) of O-Ne white dwarfs in Galactic bulge binaries can naturally reproduce the morphology, spectral shape, and intensity of the GCE signal while also obeying LMXB constraints. Synchrotron emission from MSP-launched cosmic ray electrons and positrons may simultaneously explain the mysterious, microwave "haze" from the inner Galaxy