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Spectrum of the Isotropic Diffuse Gamma-Ray Emission Derived from First-Year Fermi Large Area Telescope Data
Stockholm University, Faculty of Science, Department of Neurochemistry.
Stockholm University, Faculty of Science, Department of Physics. (Cosmology, Particle Astrophysics and String Theory)
Stockholm University, Faculty of Science, Department of Physics. (Cosmology, Particle Astrophysics and String Theory)
2010 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 104, no 101101Article in journal (Refereed) Published
Abstract [en]

We report on the first Fermi Large Area Telescope (LAT) measurements of the so-called ‘‘extra- galactic’’ diffuse gamma-ray emission (EGB). This component of the diffuse Υ-ray emission is generally considered to have an isotropic or nearly isotropic distribution on the sky with diverse contributions discussed in the literature. The derivation of the EGB is based on detailed modeling of the bright foreground diffuse Galactic gamma-ray emission, the detected LAT sources, and the solar gamma-ray emission. We find the spectrum of the EGB is consistent with a power law with a differential spectral index of 2.41 \pm 0.05 and intensity I(>100 MeV)=(1.03\pm 0.17) e-5 cm**2 s **-1 sr**-1 , where the error is systematics dominated. Our EGB spectrum is featureless, less intense, and softer than that derived from EGRET data.

Place, publisher, year, edition, pages
2010. Vol. 104, no 101101
National Category
Natural Sciences
Identifiers
URN: urn:nbn:se:su:diva-38906DOI: 10.1103/PhysRevLett.104.101101ISI: 000275543500007OAI: oai:DiVA.org:su-38906DiVA: diva2:317449
Note
Totalt 183 författare.Available from: 2010-05-03 Created: 2010-05-03 Last updated: 2017-12-12Bibliographically 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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