Constraints to Energy Spectra of Blazars based on Recent EBL Limits from Galaxy Counts

摘要

We combine the recent estimate of the contribution of galaxies to the 3.6micron intensity of the extragalactic background light (EBL) with optical andnear-infrared (IR) galaxy counts to set new limits on intrinsic spectra of someof the most distant TeV blazars 1ES 0229+200, 1ES 1218+30.4, and 1ES 1101-232,located at redshifts 0.1396, 0.182, and 0.186, respectively. The new lowerlimit on the 3.6 micron EBL intensity is significantly higher than the previousone set by the cumulative emission from resolved Spitzer galaxies. Correctingfor attenuation by the revised EBL, we show that the differential spectralindex of the intrinsic spectrum of the three blazars is 1.28 +- 0.20 or harder.These results present blazar emission models with the challenge of producingextremely hard intrinsic spectra in the sub-TeV to multi-TeV regime. Theseresults also question the reliability of recently derived upper limits on thenear-IR EBL intensity that are solely based on the assumption that intrinsicblazar spectra should not be harder than 1.5.