skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background

Abstract

We present a determination of the distributions of gamma-ray flux - the so called LogN-LogS relation - and photon spectral index for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above {+-} 20{sup o} Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation among the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law of slopes -2.37 {+-} 0.13 and -1.70 {+-} 0.26, and the intrinsic photon index distribution can be represented by a Gaussian with mean 2.41 {+-} 0.13 and 1{sigma}more » width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of blazars to the diffuse cosmic gamma-ray background radiation to be 28% {+-} 19%.« less

Authors:
; ;
Publication Date:
Research Org.:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1017212
Report Number(s):
SLAC-PUB-14484
arXiv:1106.3111; TRN: US1103182
DOE Contract Number:  
AC02-76SF00515
Resource Type:
Journal Article
Journal Name:
Submitted to Astrophysical Journal
Additional Journal Information:
Journal Name: Submitted to Astrophysical Journal
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; BACKGROUND RADIATION; COSMIC PHOTONS; DETECTION; DISTRIBUTION; PHOTONS; TELESCOPES; Astrophysics,ASTRO

Citation Formats

Singal, J, /KIPAC, Menlo Park /SLAC /Stanford U., Petrosian, V, /KIPAC, Menlo Park /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept., Ajello, M, and /KIPAC, Menlo Park /SLAC /Stanford U. Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background. United States: N. p., 2011. Web.
Singal, J, /KIPAC, Menlo Park /SLAC /Stanford U., Petrosian, V, /KIPAC, Menlo Park /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept., Ajello, M, & /KIPAC, Menlo Park /SLAC /Stanford U. Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background. United States.
Singal, J, /KIPAC, Menlo Park /SLAC /Stanford U., Petrosian, V, /KIPAC, Menlo Park /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept., Ajello, M, and /KIPAC, Menlo Park /SLAC /Stanford U. 2011. "Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background". United States. https://www.osti.gov/servlets/purl/1017212.
@article{osti_1017212,
title = {Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background},
author = {Singal, J and /KIPAC, Menlo Park /SLAC /Stanford U. and Petrosian, V and /KIPAC, Menlo Park /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept. and Ajello, M and /KIPAC, Menlo Park /SLAC /Stanford U.},
abstractNote = {We present a determination of the distributions of gamma-ray flux - the so called LogN-LogS relation - and photon spectral index for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above {+-} 20{sup o} Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation among the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law of slopes -2.37 {+-} 0.13 and -1.70 {+-} 0.26, and the intrinsic photon index distribution can be represented by a Gaussian with mean 2.41 {+-} 0.13 and 1{sigma} width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of blazars to the diffuse cosmic gamma-ray background radiation to be 28% {+-} 19%.},
doi = {},
url = {https://www.osti.gov/biblio/1017212}, journal = {Submitted to Astrophysical Journal},
number = ,
volume = ,
place = {United States},
year = {Fri Dec 09 00:00:00 EST 2011},
month = {Fri Dec 09 00:00:00 EST 2011}
}