2009 Fermi Symposium, Washington, D.C., Nov. 2-5 3 to the distributions of the observed quantities of the EGRET blazars (gamma-ray flux and redshift). See Ref. [26] for a detail. We take q and the faint-end slope index of XLF γ 1 in addition to q as free param- eters . These are hereafter called as U03( q ), H05( q ), U03( q , γ 1 ) and H05( q , γ 1 ) fits, respectively. Figure 2 shows the distributions of redshift and gamma-ray luminosity predicted by the best-fit models, in com- parison with the EGRET data. ground, this model gives the most natural explanation for the observed MeV background spectrum that is a simple power-law smoothly connected to CXB. We performed the Kolmogorov-Smirnov (KS) test to see the goodness of fits for the best-fit results of each of the four fits, and the chance probabilities of getting the observed KS deviation. Since the best KS test value is obtained for the U03( q, γ 1 ) GLF model, we use this GLF model as the baseline below. Theoretically, there is no particular reason to ex- pect a cut-off of the nonthermal emission around 10 MeV, and it is well possible that this emission ex- tends beyond 10 MeV with the same power index. Then, this component could make some contribution to GeV EGRB. The EGRB spectra from the non- blazar AGNs are calculated based on the model of ITU08. The model parameters of ITU08 have been determined to explain the EGRB in the MeV band. There is some discrepancy between the MeV EGRB data of SMM [43] and COMPTEL [44], and the rea- son for this is not clear. Here we use two model pa- rameter sets of (Γ , γ tr ) = (3 . 5 , 4 . 4) and (3 . 8 , 4 . 4) in ITU08, where Γ is the power-law index of nonthermal electron energy distribution and γ tr is the transition electron Lorentz factor above which the nonthermal component becomes dominant. These two parameter sets are chosen so that they fit to the COMPTEL and SMM data, respectively. We calculate the EGRB spectrum by integrating our blazar SED sequence model using the blazar GLF derived in § III. Since EGRET has already resolved bright gamma-ray sources, we should not include those sources in the EGRB calculation. Therefore, the maximum gamma-ray luminosity in the integra- tion should be L$_{γ}$ ( F EGRET , z ), which is the luminosity of the blazar having a flux F$_{γ}$ = F EGRET at a given z , where F EGRET = 7 × 10 $_{−}$8 photons cm $_{−}$2 s $_{−}$1 is the EGRET sensitivity above 100 MeV. A. On the Origin of the EGRB: Comparison with the Fermi EGRB Spectrum IV. THE EGRB SPECTRUM Fig. 3 compares our model predictions with the ob- served EGRB data, including the very recent Fermi results [5] [54]. Since the flux thresholds of EGRET and Fermi are different, we must be careful when directly comparing with the Fermi data. However, when the sensitivity threshold of Fermi is set to be the same as that of EGRET, the EGRB flux changes by only ∼ 10 % [47]. Therefore, our predicted EGRB spectrum can be considered to be in excellent agree- ment with the Fermi data. This agreement strongly suggests that blazars are the principal sources of the EGRB above 1 GeV, and the contribution from other sources like dark matter annihilation is minor. This also implies that use of the blazar sequence is a valid assumption. High energy photons ( > ∼ 20 GeV) from high redshift are absorbed by the interaction with the cosmic in- frared background (CIB) radiation [37–40]. We adopt the model of Ref. [38] for the CIB optical depth. We also take into account the cascading emission to calcu- late EGRB spectrum, considering only the first gener- ation of created pairs [17]. We found that the amount of energy flux absorbed and reprocessed in intergalac- tic medium is only a small fraction of the total EGRB energy flux , and hence the model dependence of CIB or the treatment of the cascading component does not have serious effects on our conclusions in this work [26]. In addition to blazars, we take into account non- blazar AGNs as the source of EGRB. Ref. [28] (here- after ITU08) has shown that non-blazar AGNs are a promising source of EGRB at ∼ 1–10 MeV. In this scenario, a nonthermal power-law component extends from hard X-ray to ∼ 10 MeV band in AGN spec- tra, because of nonthermal electrons that is assumed to exist in hot coronae around AGN accretion disks. The existence of such nonthermal electrons is theo- retically reasonable, because magnetic reconnection is the promising candidate for the heating source of the hot coronae [46] where hard X-ray photons are emit- ted. Magnetic reconnections should produce nonther- mal particles, as is well known in e.g., solar flares or the earth magnetosphere. Although several sources have been proposed as the origin of the MeV back- The EGRB prediction using the ITU08 non-blazar background model with Γ = 3 . 5 also agrees nicely with the observed data from X-rays to 100 GeV. In this case, the predicted EGRB flux above 100 MeV can account for 80% of the observed flux, consider- ably higher than in previous studies [6, 12, 13]. It should be noted that the contribution to the EGRB flux above 100 MeV from blazars alone is ∼ 45 %, while the remaining ∼ 35 % comes from non-blazar AGNs. Based on these results and considerations, we con- clude that most, and probably all, of the EGRB flux can be explained by blazars together with non-blazar AGNs, whose luminosity functions are consistent with the EGRET blazar data and X-ray AGN surveys. eConf C091122