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Title: Resolving the Extragalactic γ -Ray Background above 50 GeV with the Fermi Large Area Telescope

The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument. Most of the 2FHL sources at high Galactic latitude are blazars. In this paper, using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, dN/dS, of extragalactic γ-ray sources at E > 50 GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL (~8 x 10 -12 ph cm -2s -1). We employ a one-point photon fluctuation analysis to constrain the behavior of dN/dS below the source detection threshold. Overall, the source count distribution is constrained over three decades in flux and found compatible with a broken power law with a break flux, S b, in the range [8 x 10 -12, 1.5 x 10 -11] ph cm -2s -1 and power-law indices below and above the break of α 2 ϵ [1.60, 1.75] and α 1 = 2.49 ± 0.12, respectively. Integration of dN/dS shows that point sources account for at least 86$$+16\atop{-14}$$ % of the total extragalactic γ-ray background. The simple form of the derived source count distribution is consistent with a single population (i.e., blazars) dominating the source counts to the minimum flux explored by this analysis. Finally, we estimate the density of sources detectable in blind surveys that will be performed in the coming years by the Cherenkov Telescope Array.
Authors:
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Publication Date:
Grant/Contract Number:
AC02-76SF00515
Type:
Accepted Manuscript
Journal Name:
Physical Review Letters
Additional Journal Information:
Journal Volume: 116; Journal Issue: 15; Journal ID: ISSN 0031-9007
Publisher:
American Physical Society (APS)
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE; National Aeronautic and Space Administration (NASA); National Inst. for Nuclear Physics (INFN) (Italy)
Contributing Orgs:
The Fermi-LAT Collaboration
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1355687
Alternate Identifier(s):
OSTI ID: 1247444

Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bregeon, J., Britto, R. J., Bruel, P., Buehler, R., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Charles, E., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Cominsky, L. R., Costanza, F., Cutini, S., D’Ammando, F., de Angelis, A., de Palma, F., Desiante, R., Digel, S. W., Di Mauro, M., Di Venere, L., Domínguez, A., Drell, P. S., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Godfrey, G., Green, D., Grenier, I. A., Guiriec, S., Hays, E., Horan, D., Iafrate, G., Jogler, T., Jóhannesson, G., Kuss, M., La Mura, G., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Madejski, G. M., Magill, J., Maldera, S., Manfreda, A., Mayer, M., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Negro, M., Nuss, E., Ohsugi, T., Okada, C., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Petrosian, V., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Reposeur, T., Romani, R. W., Sánchez-Conde, M., Schmid, J., Schulz, A., Sgrò, C., Simone, D., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Thayer, J. B., Tibaldo, L., Torres, D. F., Troja, E., Vianello, G., Yassine, M., and Zimmer, S.. Resolving the Extragalactic γ-Ray Background above 50 GeV with the Fermi Large Area Telescope. United States: N. p., Web. doi:10.1103/PhysRevLett.116.151105.
Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bregeon, J., Britto, R. J., Bruel, P., Buehler, R., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Charles, E., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Cominsky, L. R., Costanza, F., Cutini, S., D’Ammando, F., de Angelis, A., de Palma, F., Desiante, R., Digel, S. W., Di Mauro, M., Di Venere, L., Domínguez, A., Drell, P. S., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Godfrey, G., Green, D., Grenier, I. A., Guiriec, S., Hays, E., Horan, D., Iafrate, G., Jogler, T., Jóhannesson, G., Kuss, M., La Mura, G., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Madejski, G. M., Magill, J., Maldera, S., Manfreda, A., Mayer, M., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Negro, M., Nuss, E., Ohsugi, T., Okada, C., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Petrosian, V., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Reposeur, T., Romani, R. W., Sánchez-Conde, M., Schmid, J., Schulz, A., Sgrò, C., Simone, D., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Thayer, J. B., Tibaldo, L., Torres, D. F., Troja, E., Vianello, G., Yassine, M., & Zimmer, S.. Resolving the Extragalactic γ-Ray Background above 50 GeV with the Fermi Large Area Telescope. United States. doi:10.1103/PhysRevLett.116.151105.
Ackermann, M., Ajello, M., Albert, A., Atwood, W. B., Baldini, L., Ballet, J., Barbiellini, G., Bastieri, D., Bechtol, K., Bellazzini, R., Bissaldi, E., Blandford, R. D., Bloom, E. D., Bonino, R., Bregeon, J., Britto, R. J., Bruel, P., Buehler, R., Caliandro, G. A., Cameron, R. A., Caragiulo, M., Caraveo, P. A., Cavazzuti, E., Cecchi, C., Charles, E., Chekhtman, A., Chiang, J., Chiaro, G., Ciprini, S., Cohen-Tanugi, J., Cominsky, L. R., Costanza, F., Cutini, S., D’Ammando, F., de Angelis, A., de Palma, F., Desiante, R., Digel, S. W., Di Mauro, M., Di Venere, L., Domínguez, A., Drell, P. S., Favuzzi, C., Fegan, S. J., Ferrara, E. C., Franckowiak, A., Fukazawa, Y., Funk, S., Fusco, P., Gargano, F., Gasparrini, D., Giglietto, N., Giommi, P., Giordano, F., Giroletti, M., Godfrey, G., Green, D., Grenier, I. A., Guiriec, S., Hays, E., Horan, D., Iafrate, G., Jogler, T., Jóhannesson, G., Kuss, M., La Mura, G., Larsson, S., Latronico, L., Li, J., Li, L., Longo, F., Loparco, F., Lott, B., Lovellette, M. N., Lubrano, P., Madejski, G. M., Magill, J., Maldera, S., Manfreda, A., Mayer, M., Mazziotta, M. N., Michelson, P. F., Mitthumsiri, W., Mizuno, T., Moiseev, A. A., Monzani, M. E., Morselli, A., Moskalenko, I. V., Murgia, S., Negro, M., Nuss, E., Ohsugi, T., Okada, C., Omodei, N., Orlando, E., Ormes, J. F., Paneque, D., Perkins, J. S., Pesce-Rollins, M., Petrosian, V., Piron, F., Pivato, G., Porter, T. A., Rainò, S., Rando, R., Razzano, M., Razzaque, S., Reimer, A., Reimer, O., Reposeur, T., Romani, R. W., Sánchez-Conde, M., Schmid, J., Schulz, A., Sgrò, C., Simone, D., Siskind, E. J., Spada, F., Spandre, G., Spinelli, P., Suson, D. J., Takahashi, H., Thayer, J. B., Tibaldo, L., Torres, D. F., Troja, E., Vianello, G., Yassine, M., and Zimmer, S.. 2016. "Resolving the Extragalactic γ-Ray Background above 50 GeV with the Fermi Large Area Telescope". United States. doi:10.1103/PhysRevLett.116.151105. https://www.osti.gov/servlets/purl/1355687.
@article{osti_1355687,
title = {Resolving the Extragalactic γ-Ray Background above 50 GeV with the Fermi Large Area Telescope},
author = {Ackermann, M. and Ajello, M. and Albert, A. and Atwood, W. B. and Baldini, L. and Ballet, J. and Barbiellini, G. and Bastieri, D. and Bechtol, K. and Bellazzini, R. and Bissaldi, E. and Blandford, R. D. and Bloom, E. D. and Bonino, R. and Bregeon, J. and Britto, R. J. and Bruel, P. and Buehler, R. and Caliandro, G. A. and Cameron, R. A. and Caragiulo, M. and Caraveo, P. A. and Cavazzuti, E. and Cecchi, C. and Charles, E. and Chekhtman, A. and Chiang, J. and Chiaro, G. and Ciprini, S. and Cohen-Tanugi, J. and Cominsky, L. R. and Costanza, F. and Cutini, S. and D’Ammando, F. and de Angelis, A. and de Palma, F. and Desiante, R. and Digel, S. W. and Di Mauro, M. and Di Venere, L. and Domínguez, A. and Drell, P. S. and Favuzzi, C. and Fegan, S. J. and Ferrara, E. C. and Franckowiak, A. and Fukazawa, Y. and Funk, S. and Fusco, P. and Gargano, F. and Gasparrini, D. and Giglietto, N. and Giommi, P. and Giordano, F. and Giroletti, M. and Godfrey, G. and Green, D. and Grenier, I. A. and Guiriec, S. and Hays, E. and Horan, D. and Iafrate, G. and Jogler, T. and Jóhannesson, G. and Kuss, M. and La Mura, G. and Larsson, S. and Latronico, L. and Li, J. and Li, L. and Longo, F. and Loparco, F. and Lott, B. and Lovellette, M. N. and Lubrano, P. and Madejski, G. M. and Magill, J. and Maldera, S. and Manfreda, A. and Mayer, M. and Mazziotta, M. N. and Michelson, P. F. and Mitthumsiri, W. and Mizuno, T. and Moiseev, A. A. and Monzani, M. E. and Morselli, A. and Moskalenko, I. V. and Murgia, S. and Negro, M. and Nuss, E. and Ohsugi, T. and Okada, C. and Omodei, N. and Orlando, E. and Ormes, J. F. and Paneque, D. and Perkins, J. S. and Pesce-Rollins, M. and Petrosian, V. and Piron, F. and Pivato, G. and Porter, T. A. and Rainò, S. and Rando, R. and Razzano, M. and Razzaque, S. and Reimer, A. and Reimer, O. and Reposeur, T. and Romani, R. W. and Sánchez-Conde, M. and Schmid, J. and Schulz, A. and Sgrò, C. and Simone, D. and Siskind, E. J. and Spada, F. and Spandre, G. and Spinelli, P. and Suson, D. J. and Takahashi, H. and Thayer, J. B. and Tibaldo, L. and Torres, D. F. and Troja, E. and Vianello, G. and Yassine, M. and Zimmer, S.},
abstractNote = {The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This catalog was obtained using 80 months of data re-processed with Pass 8, the newest event-level analysis, which significantly improves the acceptance and angular resolution of the instrument. Most of the 2FHL sources at high Galactic latitude are blazars. In this paper, using detailed Monte Carlo simulations, we measure, for the first time, the source count distribution, dN/dS, of extragalactic γ-ray sources at E > 50 GeV and find that it is compatible with a Euclidean distribution down to the lowest measured source flux in the 2FHL (~8 x 10-12 ph cm-2s-1). We employ a one-point photon fluctuation analysis to constrain the behavior of dN/dS below the source detection threshold. Overall, the source count distribution is constrained over three decades in flux and found compatible with a broken power law with a break flux, Sb, in the range [8 x 10-12, 1.5 x 10-11] ph cm-2s-1 and power-law indices below and above the break of α2 ϵ [1.60, 1.75] and α1 = 2.49 ± 0.12, respectively. Integration of dN/dS shows that point sources account for at least 86$+16\atop{-14}$ % of the total extragalactic γ-ray background. The simple form of the derived source count distribution is consistent with a single population (i.e., blazars) dominating the source counts to the minimum flux explored by this analysis. Finally, we estimate the density of sources detectable in blind surveys that will be performed in the coming years by the Cherenkov Telescope Array.},
doi = {10.1103/PhysRevLett.116.151105},
journal = {Physical Review Letters},
number = 15,
volume = 116,
place = {United States},
year = {2016},
month = {4}
}