The Search for Spatial Extension in High-latitude Sources Detected by the Fermi Large Area Telescope

Abstract

We present a search for spatial extension in high-latitude (>  | | b 5) sources in recent Fermi point source catalogs. The result is the Fermi High-Latitude Extended Sources Catalog, which provides source extensions (or upper limits thereof) and likelihood profiles for a suite of tested source morphologies. We find 24extended sources, 19 of which were not previously characterized as extended. These include sources that are potentially associated with supernova remnants and star-forming regions. We also found extended γ-ray emission in the vicinity of the CenA radio lobes and-at GeV energies for the first time-spatially coincident with the radio emission of the SNR CTA 1, as well as from the Crab Nebula. We also searched for halos around active galactic nuclei, which are predicted from electromagnetic cascades induced by the e + e − pairs that are deflected in intergalactic magnetic fields. These pairs are produced when γ-rays interact with background radiation fields. We do not find evidence for extension in individual sources or in stacked source samples. This enables us to place limits on the flux of the extended source components, which are then used to constrain the intergalactic magnetic field to be stronger than 3×10 −16 G for a coherence length λ10 kpc, even when conservative assumptions on the source duty cycle are made. This improves previous limits by several orders of magnitude.

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

“…Still, using mock data, [64] obtained a conservative limit on the stellar mass of M * < 10 4 M for d < 20 kpc, which provided a constraint on the potential stellar counterpart. However, their targeted sources are either not found in the follow-up studies [51] or are located at lower Galactic latitudes. Hence, it is interesting to apply this new window of searching dwarf galaxies to our DM candidate sources that are carefully selected from the improved spectral analysis.…”

Progress in unveiling extreme particle acceleration in persistent astrophysical jets

“…Spectral observations in the GeV-TeV range constrain the strength of the IGMF to be larger than a few femto-Gauss, while searches for angular broadening have con-strained intervals of even higher magnetic field [71][72][73]. The predicted cascade component at GeV energies is particularly large for extreme blazars, due to their hard intrinsic spectra, and to the relative stability of their flux, which reduces uncertainties introduced by arrivaltime delays.…”

γ-ray and ν Searches for Dark-Matter Subhalos in the Milky Way with a Baryonic Potential

“…We remark that focusing on the brightest halo alone for setting limits is a simplistic assumption in some circumstances. For example, there are numerous yet unidentified sources detected by the Fermi-LAT which could include a (i.e., the brightest) DM subhalo [16][17][18][19][20][21]85,86], so constraints set should be correspondingly weaker in this scenario.…”