Spectral and spatial analysis of the dark matter subhalo candidates among Fermi Large Area Telescope unidentified sources

Abstract

Fermi-LAT unidentified sources (unIDs) have proven to be compelling targets for performing indirect dark matter (DM) searches. In a previous work, we found that among the 1235 unIDs in Fermi-LAT's catalogs (3FGL, 2FHL and 3FHL) only 44 of those are DM subhalos candidates. We now implement a spectral analysis to test whether these remaining sources are compatible or not with DM origin. This analysis is executed using almost 10 years of Pass 8 Fermi-LAT data. None of the unIDs are found to significantly prefer DMinduced emission compared to other, more conventional, astrophysical sources. In order to discriminate between pulsar and DM sources, we developed a new method which is based on the source's spectral curvature, peak energy, and its detection significance. We also look for spatial extension, which may be a hint for a DM origin according to our N-body simulation studies of the subhalo population. In addition, we used Gaia DR2 data to search for a potential stellar counterpart to our best DM subhalo candidates and, although no firm associations could be found, one of them coincides with the Sagittarius stream. Finally, previous constraints on the DM annihilation cross section are updated with the new number of remaining DM subhalo candidates among unIDs. Our limits now rule out canonical thermal WIMPs up to masses of 10 GeV for bb and 20 GeV for τ + τ − annihilation channels, in this way being as sensitive and complementary to those obtained from other targets and probes.

Constraints to Dark Matter Annihilation from High-Latitude HAWC Unidentified Sources

“…upper limits for the bb (τ + τ − ) annihilation channel. For comparison, we also show as a blue, dot-dashed line the DM constraints obtained from Fermi-LAT unIDs using the same methodology [47]. Limits from the observation of the Galactic center region by H.E.S.S., i.e., the best DM constraints achieved from IACT observations at present, are included in both panels as well as a green, dashed line [65].…”

“…• Spatial extension -Spatial extension has been hailed as a "smoking gun" for DM annihilation [24][25][26]47]. Indeed, low-mass yet sufficiently close DM subhalos may be expected to appear as extended unID sources.…”

Sensitivity of the Cherenkov Telescope Array to dark subhalos

“…We now elucidate the number and the flux of expected dark subhalos for each specific sky region of the three scenarios described in Section 2. To perform this task, we choose the procedure to populate N-body simulations with low-mass dark clumps as described by [5,6], which are based http://cta.irap.omp.eu/ctools/ Publicly available at https://www.cta-observatory.org/science/cta-performance/…”

“…Yet, despite their unknown location, they can be excellent candidates for gamma-ray DM searches given their typical number densities, masses and distances [4]. Indeed, several groups have searched for dark subhalos in gamma-ray data and catalogs, and were able to set competitive constraints in the absence of them [5,6]. For this work we identify three different scenarios in which a subhalo may appear in the CTA FoV: EGAL scenario: the CTA planned Extragalactic Survey.…”

Shedding light on low-mass subhalo survival with numerical simulations

“…Subhalos hosting dwarf satellite galaxies are known to be excellent targets for gamma-ray DM searches. Less massive subhalos can also be excellent candidates since some of them may be close enough to yield large DM annihilation fluxes [5,6]. Also, the DM-annihilation flux is proportional to the DM density squared.…”