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Title: Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics

Abstract

Here, the Fermi Large Area Telescope (LAT) Collaboration has recently released the Third Catalog of Hard Fermi-LAT Sources (3FHL), which contains 1556 sources detected above 10 GeV with seven years of Pass 8 data. Building upon the 3FHL results, we investigate the flux distribution of sources at high Galactic latitudes ($$|b| \gt 20^\circ $$), which are mostly blazars. We use two complementary techniques: (1) a source-detection efficiency correction method and (2) an analysis of pixel photon count statistics with the one-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the γ-ray sky, we calculate the efficiency of the LAT to detect point sources. This enables us to find the intrinsic source-count distribution at photon fluxes down to 7.5 × 10 –12 ph cm –2 s –1. With this method, we detect a flux break at (3.5 ± 0.4) × 10 –11 ph cm –2 s –1 with a significance of at least 5.4σ. The power-law indexes of the source-count distribution above and below the break are 2.09 ± 0.04 and 1.07 ± 0.27, respectively. This result is confirmed with the 1pPDF method, which has a sensitivity reach of ~10 –11 ph cm –2 s –1. Integrating the derived source-count distribution above the sensitivity of our analysis, we find that (42 ± 8)% of the extragalactic γ-ray background originates from blazars.

Authors:
 [1];  [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [1]; ORCiD logo
  1. Stanford Univ., Stanford, CA (United States)
  2. Univ. of Torino, Torino (Italy); Istituto Nazionale di Fisica Nucleare, Torino (Italy)
  3. Istituto Nazionale di Fisica Nucleare, Torino (Italy)
  4. Clemson Univ., Clemson, SC (United States)
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1436087
Grant/Contract Number:  
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 856; Journal Issue: 2; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; gamma rays: diffuse background; gamma rays: galaxies

Citation Formats

Di Mauro, M., Manconi, S., Zechlin, H. -S., Ajello, M., Charles, E., and Donato, F. Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics. United States: N. p., 2018. Web. doi:10.3847/1538-4357/aab3e5.
Di Mauro, M., Manconi, S., Zechlin, H. -S., Ajello, M., Charles, E., & Donato, F. Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics. United States. doi:10.3847/1538-4357/aab3e5.
Di Mauro, M., Manconi, S., Zechlin, H. -S., Ajello, M., Charles, E., and Donato, F. Thu . "Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics". United States. doi:10.3847/1538-4357/aab3e5.
@article{osti_1436087,
title = {Deriving the Contribution of Blazars to the Fermi-LAT Extragalactic γ-ray Background at E > 10 GeV with Efficiency Corrections and Photon Statistics},
author = {Di Mauro, M. and Manconi, S. and Zechlin, H. -S. and Ajello, M. and Charles, E. and Donato, F.},
abstractNote = {Here, the Fermi Large Area Telescope (LAT) Collaboration has recently released the Third Catalog of Hard Fermi-LAT Sources (3FHL), which contains 1556 sources detected above 10 GeV with seven years of Pass 8 data. Building upon the 3FHL results, we investigate the flux distribution of sources at high Galactic latitudes ($|b| \gt 20^\circ $), which are mostly blazars. We use two complementary techniques: (1) a source-detection efficiency correction method and (2) an analysis of pixel photon count statistics with the one-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the γ-ray sky, we calculate the efficiency of the LAT to detect point sources. This enables us to find the intrinsic source-count distribution at photon fluxes down to 7.5 × 10–12 ph cm–2 s–1. With this method, we detect a flux break at (3.5 ± 0.4) × 10–11 ph cm–2 s–1 with a significance of at least 5.4σ. The power-law indexes of the source-count distribution above and below the break are 2.09 ± 0.04 and 1.07 ± 0.27, respectively. This result is confirmed with the 1pPDF method, which has a sensitivity reach of ~10–11 ph cm–2 s–1. Integrating the derived source-count distribution above the sensitivity of our analysis, we find that (42 ± 8)% of the extragalactic γ-ray background originates from blazars.},
doi = {10.3847/1538-4357/aab3e5},
journal = {The Astrophysical Journal (Online)},
number = 2,
volume = 856,
place = {United States},
year = {Thu Mar 29 00:00:00 EDT 2018},
month = {Thu Mar 29 00:00:00 EDT 2018}
}

Journal Article:
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