Spatial extension of dark subhalos as seen by Fermi-LAT and implications for WIMP constraints

TL;DR

This study assesses Fermi-LAT's ability to detect spatially extended dark matter subhalos, showing that extension detection requires higher flux and can help distinguish true signals from background, impacting dark matter constraints.

Contribution

It provides a realistic simulation-based analysis of Fermi-LAT's sensitivity to extended dark matter subhalos and explores their implications for WIMP detection.

Findings

Detection of extended subhalos requires flux 2-10 times higher than point sources.

Spatial extension can help identify true dark matter signals among unidentified sources.

Dark matter constraints from extended sources are less stringent than from point sources.

Abstract

Spatial extension has been hailed as a "smoking gun" in the gamma-ray search of dark galactic subhalos, which would appear as unidentified sources for gamma-ray telescopes. In this work, we study the sensitivity of the Fermi-LAT to extended subhalos using simulated data based on a realistic sky model. We simulate spatial templates for a set of representative subhalos, whose parameters were derived from our previous work with N-body cosmological simulation data. We find that detecting an extended subhalo and finding an unequivocal signal of angular extension requires, respectively, a flux 2 to 10 times larger than in the case of a point-like source. By studying a large grid of models, where parameters such as the WIMP mass, annihilation channel or subhalo model are varied significantly, we obtain the response of the LAT as a function of the product of annihilation cross section times the J-factor. Indeed, we show that spatial extension can be used as an additional filter to reject subhalos candidates among the pool of unidentified LAT sources, as well as a "smoking gun" for positive identification. For instance, typical angular extensions of a few tenths of degree are expected for the considered scenarios. Finally, we also study the impact of the obtained LAT sensitivity to such extended subhalos on the achievable dark matter constraints, which are a few times less constraining than comparable point-source limits.