... emitters

So far, all but one detected extragalactic VHE $\gamma$-ray emitters belong to the class of TeV blazars.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

... criteria

A similar technique (scaling of a certain shape until the de-abs rbed spectrum reaches an exclusion criterion) was previously used by Guy et al. (2000) to derive limits on the EBL from the Mkn 501 spectrum measured by the CAT experiment during a flare in 1997.

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.

... EBL limit

In addition to the fixed shape, several other possible EBL components, like a bump in the UV, were examined (Aharonian et al. 2006a).

.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.
.