Probing the pulsar explanation of the Galactic-Center GeV excess using continuous gravitational-wave searches

TL;DR

This study investigates whether unresolved millisecond pulsars could explain the Galactic Center GeV gamma-ray excess by analyzing gravitational-wave search data, providing new constraints on pulsar populations and their properties.

Contribution

It introduces the first analysis linking gravitational-wave search results to the pulsar explanation of the gamma-ray excess, constraining pulsar population models.

Findings

Large parameter space for pulsar luminosity functions is excluded.

Null gravitational-wave detections limit the number of unresolved pulsars.

Results bridge gamma-ray astrophysics, gravitational-wave astronomy, and dark matter physics.

Abstract

Over ten years ago, Fermi observed an excess of GeV gamma rays from the Galactic Center whose origin is still under debate. One explanation for this excess involves annihilating dark matter; another requires an unresolved population of millisecond pulsars concentrated at the Galactic Center. In this work, we use the results from LIGO/Virgo's most recent all-sky search for quasi-monochromatic, persistent gravitational-wave signals from isolated neutron stars, which is estimated to be about 20-50\% of the population, to determine whether unresolved millisecond pulsars could actually explain this excess. First, we choose a luminosity function that determines the number of millisecond pulsars required to explain the observed excess. Then, we consider two models for deformations on millisecond pulsars to determine their ellipticity distributions, which are directly related to their gravitational-wave radiation. Lastly, based on null results from the O3 Frequency-Hough all-sky search for continuous gravitational waves, we find that a large set of the parameter space in the pulsar luminosity function can be excluded. We also evaluate how these exclusion regions may change with respect to various model choices. Our results are the first of their kind and represent a bridge between gamma-ray astrophysics, gravitational-wave astronomy, and dark-matter physics.