Galactic Binaries Can Explain the Fermi Galactic Center Excess and 511 keV Emission

TL;DR

This paper proposes that millisecond pulsars and their progenitors, low-mass X-ray binaries, can simultaneously explain the Fermi-LAT Galactic Center gamma-ray excess and the 511 keV positron-annihilation emission, supported by population synthesis models.

Contribution

It introduces a novel scenario linking millisecond pulsars and low-mass X-ray binaries to both observed phenomena, supported by quantitative analysis.

Findings

Neutron star low-mass X-ray binaries can produce the majority of positrons.

Binary millisecond pulsars can account for the gamma-ray excess and positron emission.

The proposed scenario aligns with observed morphological similarities.

Abstract

The Fermi-LAT Galactic Center excess and the 511 keV positron-annihilation signal from the inner Galaxy bare a striking morphological similarity. We propose that both can be explained through a scenario in which millisecond pulsars produce the Galactic Center excess and their progenitors, low-mass X-ray binaries, the 511 keV signal. As a proof-of-principle we study a specific population synthesis scenario from the literature involving so-called ultracompact X-ray binaries. Moreover, for the first time, we quantitatively show that neutron star, rather than black hole, low-mass X-ray binaries can be responsible for the majority of the positrons. In this particular scenario binary millisecond pulsars can be both the source of the Fermi-LAT $\gamma$-ray excess and the bulge positrons. Future avenues to test this scenario are discussed.