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Title: The origin of the extragalactic gamma-ray background and implications for dark matter annihilation

Abstract

The origin of the extragalactic γ-ray background (EGB) has been debated for some time. The EGB comprises the γ-ray emission from resolved and unresolved extragalactic sources, such as blazars, star-forming galaxies, and radio galaxies, as well as radiation from truly diffuse processes. This Letter focuses on the blazar source class, the most numerous detected population, and presents an updated luminosity function and spectral energy distribution model consistent with the blazar observations performed by the Fermi-Large Area Telescope (LAT). Additionally, we show that blazars account for 50$$_{-11}^{+12}$$% of the EGB photons (>0.1 GeV), and that Fermi-LAT has already resolved ~70% of this contribution. Blazars, and in particular hard-spectrum sources such as BL Lacs, are responsible for most of the EGB emission above 100 GeV. We find that the extragalactic background light, which attenuates blazars' high-energy emission, is responsible for the high-energy cutoff observed in the EGB spectrum. Finally, we show that blazars, star-forming galaxies, and radio galaxies can naturally account for the amplitude and spectral shape of the background in the 0.1–820 GeV range, leaving only modest room for other contributions. In conclusion, this allows us to set competitive constraints on the dark matter annihilation cross section.

Authors:
ORCiD logo; ORCiD logo; ORCiD logo; ; ; ORCiD logo; ; ; ORCiD logo; ; ; ORCiD logo; ; ;
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
Contributing Org.:
Fermi-LAT Collaboration
OSTI Identifier:
1355170
Grant/Contract Number:
AC02-76SF00515
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
The Astrophysical Journal. Letters
Additional Journal Information:
Journal Volume: 800; Journal Issue: 2; Journal ID: ISSN 2041-8213
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; cosmology; observations – dark matter – gamma rays; diffuse background – galaxies; jets galaxies; active –surveys

Citation Formats

Ajello, M., Gasparrini, D., Sánchez-Conde, M., Zaharijas, G., Gustafsson, M., Cohen-Tanugi, J., Dermer, C. D., Inoue, Y., Hartmann, D., Ackermann, M., Bechtol, K., Franckowiak, A., Reimer, A., Romani, R. W., and Strong, A. W.. The origin of the extragalactic gamma-ray background and implications for dark matter annihilation. United States: N. p., 2015. Web. doi:10.1088/2041-8205/800/2/L27.
Ajello, M., Gasparrini, D., Sánchez-Conde, M., Zaharijas, G., Gustafsson, M., Cohen-Tanugi, J., Dermer, C. D., Inoue, Y., Hartmann, D., Ackermann, M., Bechtol, K., Franckowiak, A., Reimer, A., Romani, R. W., & Strong, A. W.. The origin of the extragalactic gamma-ray background and implications for dark matter annihilation. United States. doi:10.1088/2041-8205/800/2/L27.
Ajello, M., Gasparrini, D., Sánchez-Conde, M., Zaharijas, G., Gustafsson, M., Cohen-Tanugi, J., Dermer, C. D., Inoue, Y., Hartmann, D., Ackermann, M., Bechtol, K., Franckowiak, A., Reimer, A., Romani, R. W., and Strong, A. W.. Thu . "The origin of the extragalactic gamma-ray background and implications for dark matter annihilation". United States. doi:10.1088/2041-8205/800/2/L27. https://www.osti.gov/servlets/purl/1355170.
@article{osti_1355170,
title = {The origin of the extragalactic gamma-ray background and implications for dark matter annihilation},
author = {Ajello, M. and Gasparrini, D. and Sánchez-Conde, M. and Zaharijas, G. and Gustafsson, M. and Cohen-Tanugi, J. and Dermer, C. D. and Inoue, Y. and Hartmann, D. and Ackermann, M. and Bechtol, K. and Franckowiak, A. and Reimer, A. and Romani, R. W. and Strong, A. W.},
abstractNote = {The origin of the extragalactic γ-ray background (EGB) has been debated for some time. The EGB comprises the γ-ray emission from resolved and unresolved extragalactic sources, such as blazars, star-forming galaxies, and radio galaxies, as well as radiation from truly diffuse processes. This Letter focuses on the blazar source class, the most numerous detected population, and presents an updated luminosity function and spectral energy distribution model consistent with the blazar observations performed by the Fermi-Large Area Telescope (LAT). Additionally, we show that blazars account for 50$_{-11}^{+12}$% of the EGB photons (>0.1 GeV), and that Fermi-LAT has already resolved ~70% of this contribution. Blazars, and in particular hard-spectrum sources such as BL Lacs, are responsible for most of the EGB emission above 100 GeV. We find that the extragalactic background light, which attenuates blazars' high-energy emission, is responsible for the high-energy cutoff observed in the EGB spectrum. Finally, we show that blazars, star-forming galaxies, and radio galaxies can naturally account for the amplitude and spectral shape of the background in the 0.1–820 GeV range, leaving only modest room for other contributions. In conclusion, this allows us to set competitive constraints on the dark matter annihilation cross section.},
doi = {10.1088/2041-8205/800/2/L27},
journal = {The Astrophysical Journal. Letters},
number = 2,
volume = 800,
place = {United States},
year = {Thu Feb 19 00:00:00 EST 2015},
month = {Thu Feb 19 00:00:00 EST 2015}
}

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