Ackermann, M. and Pavlidou, V. and Siegal-Gaskins, J. (2012) Anisotropies in the diffuse gamma-ray background measured by the Fermi LAT. Physical Review D, 85 (8). Art. No. 083007. ISSN 0556-2821. http://resolver.caltech.edu/CaltechAUTHORS:20120521-071102690
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The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales. We analyze the angular power spectrum of the diffuse emission measured by the Fermi Large Area Telescope at Galactic latitudes |b|>30° in four energy bins spanning 1–50 GeV. At multipoles ℓ≥155, corresponding to angular scales ≲2°, angular power above the photon noise level is detected at >99.99% confidence level in the 1–2 GeV, 2–5 GeV, and 5–10 GeV energy bins, and at >99% confidence level at 10–50 GeV. Within each energy bin the measured angular power takes approximately the same value at all multipoles ℓ≥155, suggesting that it originates from the contribution of one or more unclustered source populations. The amplitude of the angular power normalized to the mean intensity in each energy bin is consistent with a constant value at all energies, C_P/⟨I⟩^2=9.05±0.84×10^(-6) sr, while the energy dependence of C_P is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index Γ_s=2.40±0.07. We discuss the implications of the measured angular power for gamma-ray source populations that may provide a contribution to the diffuse gamma-ray background.
|Additional Information:||© 2012 American Physical Society. Received 2 November 2011; published 23 April 2012; publisher error corrected 2 May 2012. The Fermi LAT Collaboration acknowledges generous ongoing support from a number of agencies and institutes that have supported both the development and the operation of the LAT as well as scientific data analysis. These include the National Aeronautics and Space Administration and the Department of Energy in the United States, the Commissariat à l’Energie Atomique and the Centre National de la Recherche Scientifique / Institut National de Physique Nucléaire et de Physique des Particules in France, the Agenzia Spaziale Italiana and the Istituto Nazionale di Fisica Nucleare in Italy, the Ministry of Education, Culture, Sports, Science and Technology (MEXT), High Energy Accelerator Research Organization (KEK) and Japan Aerospace Exploration Agency (JAXA) in Japan, and the K. A. Wallenberg Foundation, the Swedish Research Council and the Swedish National Space Board in Sweden. Additional support for science analysis during the operations phase is gratefully acknowledged from the Istituto Nazionale di Astrofisica in Italy and the Centre National d’E´ tudes Spatiales in France. Some of the results in this paper have been derived using the HEALPIX package. E. Komatsu is supported in part by NSF Grants No. AST- 0807649 and No. PHY-0758153, and NASA Grant No. NNX08AL43G. J. Siegal-Gaskins thanks the Galileo Galilei Institute for Theoretical Physics for hospitality, and acknowledges support from NASA through Einstein Postdoctoral Fellowship Grant No. PF1-120089 awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under Contract No. NAS8-03060. J. Conrad acknowledges support from a grant from the K. A. Wallenberg Foundation, and M. Lemoine-Goumard is supported by Contract No. ERC-StG-259391 from the European Community.|
|Classification Code:||PACS: 98.70.Vc, 95.85.Pw, 98.70.Rz|
|Official Citation:||Anisotropies in the diffuse gamma-ray background measured by the Fermi LAT M. Ackermann et al. (Fermi LAT Collaboration) Published 23 April 2012 (28 pages) 083007|
|Usage Policy:||No commercial reproduction, distribution, display or performance rights in this work are provided.|
|Deposited By:||Ruth Sustaita|
|Deposited On:||21 May 2012 15:05|
|Last Modified:||26 Dec 2012 15:14|
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