Constraining the Cosmic Background Light with four BL Lac TeV spectra

Abstract

The intrinsic BL Lac spectra above few hundreds GeV can be very different from the observed ones due to the absorption effects by the diffuse Extragalactic Background Light (EBL), at present poorly known. With the recent results, there are now 4 sources with good spectral information: Mkn 421 (z=0.031), Mkn 501 (z=0.034), 1ES 1426+428 (z=0.129) and 1ES 1959+650 (z=0.047). Making simple assumptions on the shape of the intrinsic spectra (according to the present blazar knowledge), we have considered the effects of different EBL spectral energy distributions (SED) for the first time on all 4 objects together, deriving constraints for the EBL fluxes. These resulted significantly lower than many direct estimates.

4 pages, 8 figures; to appear in the proceedings of the 2nd Veritas Symposium: "TeV Astrophysics of extragalactic sources". April 2003, Chicago