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Unresolved Gamma-Ray Sky through its Angular Power Spectrum
Deutsches Elekt Synchrotron DESY, D-15738 Zeuthen, Germany..
Clemson Univ, Dept Phys & Astron, Kinard Lab Phys, Clemson, SC 29634 USA..
Univ Pisa, I-56127 Pisa, Italy.;Ist Nazl Fis Nucl, Sez Pisa, I-56127 Pisa, Italy..
CEA Saclay, Serv Astrophys, Univ Paris Diderot, Lab AIM,CEA IRFU,CNRS, F-91191 Gif Sur Yvette, France..
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2018 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 121, no 24, article id 241101Article in journal (Refereed) Published
Abstract [en]

The gamma-ray sky has been observed with unprecedented accuracy in the last decade by the Fermi-large area telescope (LAT), allowing us to resolve and understand the high-energy Universe. The nature of the remaining unresolved emission [unresolved gamma-ray background (UGRB)] below the LAT source detection threshold can be uncovered by characterizing the amplitude and angular scale of the UGRB fluctuation field. This Letter presents a measurement of the UGRB autocorrelation angular power spectrum based on eight years of Fermi-LAT Pass 8 data products. The analysis is designed to be robust against contamination from resolved sources and noise systematics. The sensitivity to subthreshold sources is greatly enhanced with respect to previous measurements. We find evidence (with similar to 3.7 sigma significance) that the scenario in which two classes of sources contribute to the UGRB signal is favored over a single class. A double power law with exponential cutoff can explain the anisotropy energy spectrum well, with photon indices of the two populations being 2.55 +/- 0.23 and 1.86 +/- 0.15.

Place, publisher, year, edition, pages
American Physical Society, 2018. Vol. 121, no 24, article id 241101
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Physical Sciences
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URN: urn:nbn:se:kth:diva-240722DOI: 10.1103/PhysRevLett.121.241101ISI: 000452960100001PubMedID: 30608723Scopus ID: 2-s2.0-85059494376OAI: oai:DiVA.org:kth-240722DiVA, id: diva2:1279476
Note

QC 20190116

Available from: 2019-01-16 Created: 2019-01-16 Last updated: 2020-03-09Bibliographically approved

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