Unidentified sources in the Fermi-LAT second source catalog: the case for DM subhalos

TL;DR

This study investigates unassociated gamma-ray sources from the Fermi-LAT catalog to identify potential dark matter subhalos, analyzing multi-wavelength data and gamma-ray spectra, and concludes most are likely astrophysical objects rather than dark matter.

Contribution

The paper provides a detailed multi-wavelength analysis of 13 gamma-ray source candidates, assessing their nature and discussing future dark matter search strategies.

Findings

All sources are compatible with point-source scenarios.

Infrared color data suggest most are high-frequency peaked BL Lac objects.

No source shows definitive signs of dark matter origin.

Abstract

The Large Area Telescope (LAT) aboard the Fermi satellite allows us to study the high-energy gamma-ray sky with unprecedented sensitivity. However, the origin of 31% of the detected gamma-ray sources remains unknown. This population of unassociated gamma-ray sources may contain new object classes, among them sources of photons from self-annihilating or decaying non-baryonic dark matter. Fermi-LAT might be capable to detect up to a few of these dark matter subhalos as faint and moderately extended gamma-ray sources with a temporally steady high-energy emission. After applying corresponding selection cuts to the second year Fermi catalog 2FGL, we investigate 13 candidate objects in more detail including their multi-wavelength properties in the radio, infrared, optical, UV, and X-ray bands. For the gamma-ray band, we analyze both the 24-month and 42-month Fermi-LAT data sets. We probe the gamma-ray spectra for indications of a spectral cutoff, which singles out four sources of particular interest. We find all sources to be compatible with a point-source scenario. Multi-wavelength associations and, in particular, their infrared color-color data indicate no source to be compatible with a dark matter origin, and we find the majority of the candidates to probably originate from faint, high-frequency peaked BL Lac type objects. We discuss possibilities to further investigate source candidates and future prospects to search for dark matter subhalos.