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Anisotropies in the Diffuse Gamma-Ray Background Measured by the Fermi LATThe 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 LAT at Galactic latitudes absolute value of b > 30 deg in four energy bins spanning 1 to 50 GeV. At multipoles l >= 155, corresponding to angular scales approx < 2 deg, angular power above the photon noise level is detected at > 99.99% CL in the 1-2 GeV, 2- 5 GeV, and 5- 10 GeV energy bins, and at > 99% CL 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(sub p) / (I)(exp 2) = 9.05 +/- 0.84 x 10(exp -6) sr, while the energy dependence of C(sub p) is consistent with the anisotropy arising from one or more source populations with power-law photon spectra with spectral index Gamma (sub 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.
Document ID
20120016487
Acquisition Source
Goddard Space Flight Center
Document Type
Preprint (Draft being sent to journal)
Authors
Ferrara, E. C. (Maryland Univ. College Park, MD, United States)
McEnery, J. E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Troja, E. (NASA Goddard Space Flight Center Greenbelt, MD, United States)
Date Acquired
August 26, 2013
Publication Date
February 13, 2012
Subject Category
Astronomy
Report/Patent Number
GSFC.JA.7332.2012
Funding Number(s)
CONTRACT_GRANT: NSF AST-0807649
CONTRACT_GRANT: NAS8-03060
CONTRACT_GRANT: NNX08AL43G
CONTRACT_GRANT: NSF PFI-120089
CONTRACT_GRANT: NSF PHY-0758153
Distribution Limits
Public
Copyright
Public Use Permitted.

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