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Anisotropies in the diffuse gamma-ray background from dark matter with Fermi LAT: a closer look
Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
2011 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 414, no 3, 2040-2054 p.Article in journal (Refereed) Published
Abstract [en]

We perform a detailed study of the sensitivity to the anisotropies related to dark matter (DM) annihilation in the isotropic gamma-ray background (IGRB) as measured by the Fermi Large Area Telescope (Fermi LAT). For the first time, we take into account the effects of the Galactic foregrounds and use a realistic representation of the Fermi LAT. We implement an analysis pipeline which simulates Fermi LAT data sets starting from model maps of the Galactic foregrounds, the Fermi-resolved point sources, the extragalactic diffuse emission and the signal from DM annihilation. The effects of the detector are taken into account by convolving the model maps with the Fermi LAT instrumental response. We then use the angular power spectrum to characterize the anisotropy properties of the simulated data and to study the sensitivity to DM. We consider DM anisotropies of extragalactic origin and of Galactic origin (which can be generated through annihilation in the MilkyWay substructures) as opposed to a background of anisotropies generated by sources of astrophysical origin, blazars for example. We find that with statistics from 5 yr of observation, Fermi is sensitive to a DM contribution at the level of 1-10 per cent of the measured IGRB depending on the DM mass m. and annihilation mode. In terms of the thermally averaged cross-section <sigma(A)v >, this corresponds to similar to 10(-25) cm(3) s(-1), i. e. slightly above the typical expectations for a thermal relic, for low values of the DM mass m(x) less than or similar to 100 GeV. The anisotropy method for DM searches has a sensitivity comparable to the usual methods based only on the energy spectrum and thus constitutes an independent and complementary piece of information in the DM puzzle.

Place, publisher, year, edition, pages
2011. Vol. 414, no 3, 2040-2054 p.
Keyword [en]
methods: statistical, dark matter, large-scale structure of Universe, gamma-rays: diffuse background
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:su:diva-80714DOI: 10.1111/j.1365-2966.2011.18525.xISI: 000292977600018OAI: oai:DiVA.org:su-80714DiVA: diva2:557325
Note

AuthorCount:4;

Available from: 2012-09-27 Created: 2012-09-27 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Cosmological Dark Matter and the Isotropic Gamma-Ray Background: Measurements and Upper Limits
Open this publication in new window or tab >>Cosmological Dark Matter and the Isotropic Gamma-Ray Background: Measurements and Upper Limits
2010 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis addresses the isotropic diffuse gamma-ray background, as measured by the Fermi gamma ray space telescope, and its implications for indirect detection of dark matter. We describe the measurement of the isotropic background, including also an alternative analysis method besides the one published by the Fermi-LAT collaboration. The measured isotropic diffuse background is compatible with a power law differential energy spectrum with a spectral index of  -2.41 ± 0.05 and -2.39 ± 0.08, for the two analysis methods respectively. This is a softer spectrum than previously reported by the EGRET experiment. This rules out any dominant contribution with a significantly different shape, e.g. from dark matter, in the energy range 20 MeV to 102.4 GeV. Instead we present upper limits on a signal originating from annihilating dark matter of extragalactic origin. The uncertainty in the dark matter signal is primarily dependent on the cosmological evolution of the dark matter distribution. We use recent N-body simulations of structure formation, as well as a semi-analytical calculation, to assess this uncertainty. We investigate three main annihilation channels and find that in some, but not in all, of our scenarios we can start to probe, and sometimes rule out, interesting parameter spaces of particle physics models beyond the standard model.We also investigate the possibility to use the angular anisotropies of the annihilation signal to separate it from a background originating from conventional sources, e.g. from active galactic nuclei. By carefully modelling the performance of the Fermi gamma-ray space telescope and galactic foregrounds we find that this method could be as sensitive as using information from the energy spectrum only.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2010. 118 p.
Keyword
dark matter theory, dark matter simulations, dark matter experiments, isotropic gamma-ray background, Fermi gamma-ray space telescope
National Category
Subatomic Physics
Research subject
Theoretical Physics
Identifiers
urn:nbn:se:su:diva-38900 (URN)978-91-7447-082-6 (ISBN)
Public defence
2010-06-03, FD5, AlbaNova universitetscentrum, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: Manuscript.

Available from: 2010-05-11 Created: 2010-05-03 Last updated: 2013-01-22Bibliographically approved

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