An Estimation of the Lower Bound on the Extragalactic TeV γ-ray Background

Fermi satellite released fairly accurate measurement of extragalactic gamma-ray background (EGB) from 100 MeV to 820 GeV, which dramatically improves our understanding of the high energy gamma-ray background. But for TeV band, space detectors are useless, and we must rely on ground based gamma-ray telescopes such as imaging atmospheric Cherenkov telescopes (IACTs). Until now, the extragalactic TeV gamma-ray background has not been well investigated. In this paper, we calculate the lower bound of extragalactic TeV gamma-ray background radiation by using the energy spectrum of low state of 61 TeV sources, including 53 blazars, 6 radio galaxies, and 2 star-burst galaxies, respectively. Our results show that blazars are the main contributor of the extragalactic TeV gamma-ray background, especially for Mrk 501 and Mrk 421, whose contribution at 0.5-4.5 TeV is about 58%. And the contribution above 4.5 TeV are mainly from the sources H 1426+428, 1ES 1959+650, and 1ES 0229+200, their energy spectrum distribution has been extended to more than 10 TeV. Finally, we calculate the contribution of blazars, radio galaxies, and star-burst galaxies, respectively. Similar calculation is used to subclass of blazars and sources with different redshifts.