Radio-loud AGN contribution to the Extragalactic Gamma-Ray Background

📝 Abstract

Origin of extragalactic gamma-ray background (EGRB) is still a matter of debate. EGRB can either have truly diffuse or unresolved discrete point sources origin. Majority of the Fermi and EGRET detected identified sources are blazar. So, they are expected to be a significant contributors to the EGRB. In order to estimate their contribution to the EGRB one needs to construct their luminosity functions. Here, we examine and construct the evolution and luminosity function of blazars using first LAT AGN catalog. We consider both pure luminosity and pure density evolution models for flat spectrum radio quasars (FSRQs). We also describe the methodology to estimate the contribution from misaligned blazars to the EGRB.

💡 Analysis

Origin of extragalactic gamma-ray background (EGRB) is still a matter of debate. EGRB can either have truly diffuse or unresolved discrete point sources origin. Majority of the Fermi and EGRET detected identified sources are blazar. So, they are expected to be a significant contributors to the EGRB. In order to estimate their contribution to the EGRB one needs to construct their luminosity functions. Here, we examine and construct the evolution and luminosity function of blazars using first LAT AGN catalog. We consider both pure luminosity and pure density evolution models for flat spectrum radio quasars (FSRQs). We also describe the methodology to estimate the contribution from misaligned blazars to the EGRB.

📄 Content

arXiv:1112.1033v1 [astro-ph.HE] 5 Dec 2011 2011 Fermi Symposium, Roma., May. 9-12 1 Radio-loud AGN contribution to the Extragalactic Gamma-Ray Background Debbijoy Bhattacharya Inter-University Centre for Astronomy& Astrophysics, Pune-411007, India M. Errando, R. Mukherjee Barnard College, Columbia University, New York, NY 10027, USA M. B¨ottcher Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA P. Sreekumar Space Astronomy Group, ISRO Satellite Centre, Bangalore, India R. Misra Inter-University Centre for Astronomy& Astrophysics, Pune, India P. Coppi Department of Astronomy, Yale University, P.O. Box 208101, New Haven, CT 06520, USA Origin of extragalactic γ-ray background (EGRB) is still a matter of debate. EGRB can either have truly diffuse or unresolved discrete point sources origin. Majority of the Fermi and EGRET detected identified sources are blazar. So, they are expected to be a significant contributors to the EGRB. In order to estimate their contribution to the EGRB one needs to construct their luminosity functions. Here, we examine and construct the evolution and luminosity function of blazars using first LAT AGN catalog. We consider both pure luminosity and pure density evolution models for flat spectrum radio quasars (FSRQs). We also describe the methodology to estimate the contribution from misaligned blazars to the EGRB.

1. Introduction Observational γ-ray astronomy got a massive boost after the launch of the Fermi Gamma-ray Space Tele- scope (Fermi) on 11th June, 2008. The Large Area Telescope (LAT) onboard Fermi provides an increase in sensitivity by more than an order of magnitude over EGRET and AGILE. The origin of extragalactic γ-ray background (EGRB) is one of the fundamental unsolved prob- lem in astrophysics. EGRB can arise from some dif- fuse processes like black hole evaporation, large scale structure formation, matter-antimatter annihilation, etc (e.g., [1, 2, 3]). Alternatively, due to the limited instrument sensitivity, unresolved γ-ray sources could contribute significantly to the observed EGRB. Recently, the EGRB has been rederived from Fermi Large Area Telescope (LAT) data [4]. EGRB is consis- tent with a featureless power law of index (2.41±0.05). The integrated flux above 100 MeV is (1.03 ± 0.17) × 10−5 photon cm−2 s−1 sr−1. Fermi already detected ∼1500 sources in 11 months of observation (First Fermi catalog; [5]) and is ex- pected to detect many more. In contrast to the less than 100 active galactic nuclei (AGNs) in the EGRET catalog, the first Fermi-LAT AGN catalog [6] con- sist of ∼600 blazars. Fermi also detected 11 non- blazar AGN [7], three normal (M 31, LMC and Milky Way) and two starburst galaxies (M 82 and NGC 253). Thus, Fermi provides an excellent opportunity to un- derstand the origin of EGRB. Since the dominant class of identified EGRET and Fermi sources are blazars, they are expected to con- tribute to the EGRB. The contribution from blazars to the EGRB is estimated using two different ap- proaches: (a) Considering a relationship between the blazar γ- ray luminosity with their luminosity at some other wavelength, their γ-ray luminosity function is as- sumed to be the scaled luminosity function at that wavelength (e.g., [8, 9, 10, 11, 12, 13, 14, 15, 16]). (b) Constructing the γ-ray luminosity function di- rectly from observed γ-ray blazars (e.g., [17, 18, 19, 20]). In an earlier work [17, 18] following a similar ap- proach of Chiang & Mukherjee [19] but with almost twice the number of sources, we constructed the γ-ray luminosity functions of flat spectrum radio quasars (FSRQs) and BL Lacs from EGRET-detected sources only. We found strong positive evolution for FSRQs, while BL Lacs did not show any significant evolu- tion. The maximum contribution from blazars to EGRB was found to be ∼20%. However, due to the limited number of sources in the EGRET catalog, the luminosity function and hence, the contribution from blazars was not well constrained. M¨ucke & Pohl [21] estimated the contribution from FSRQs and BL Lacs to the EGRB in the context of AGN unification paradigm, and found that unresolved blazars (both “aligned” and “misaligned”) contribute 20% −40% to the EGRB. In a similar approach, Dermer [22] estimated that FSRQs and BL Lacs contribute ∼ 10%−15% and 2%−3% at 1 GeV respectively. From the first three months of Fermi observation, Abdo et al. [23] found that FSRQs exhibit strong evolu- tion while BL Lacs show no evolution. Using the 1st eConf C110509 2 2011 Fermi Symposium, Roma., May. 9-12 Fermi catalog, Abdo et al. [24] found from the source count distribution that the point source contribution is ∼16% of the EGRB. Here, we construct the luminosity function of FS- RQs and BL Lacs following the methodology de- scribed in Bhattacharya, Sreekumar & Mukherjee [17]. Utilizing the Fermi observed sources we con- struct a complete source list, apply the V/Vmax method to search for the presence of evolution, find parameters by modified V/Vmax method, a

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