Bispectrum analysis of the unresolved gamma-ray background

In recent years, properties of the unresolved gamma ray background (UGRB) have been constrained by measuring the anisotropy in the form of the angular power spectrum (APS). The energy dependence of the anisotropy has been found to be consistent with a broken power law, suggesting the existence of two distinct source classes above and below  ~2 GeV. In this work, we aim to go beyond the angular power spectrum, and use the bispectrum to further constrain the source classes that contribute to the UGRB. As in the case of the APS, for a skymap consisting of unresolved, randomly distributed point sources, we expect the bispectrum to be independent of multipole and therefore to be fully characterised by a single amplitude. The formalism developed in the context of  the angular power spectrum is extended to the angular bispectrum and the resulting analysis pipeline is applied to Fermi-LAT data in the energy range 0.7 GeV – 1 TeV. We find that the analysis of the bispectrum is complicated due to the presence of photon noise and the relatively small signal strength due to unresolved point sources such as blazars.

Discussion timeslot (ZOOM-Meeting): 16. July 2021 - 18:00

ZOOM-Meeting URL: https://icrc2021.desy.de/pf_access_abstracts

Corresponding Session: https://icrc2021-venue.desy.de/channel/Presenter-Forum-1-Evening-All-Categories/48

Authors: Ebo Peerbooms
Indico-ID: 439
Proceeding URL: https://pos.sissa.it/395/659