Intrinsic spectra of H.E.S.S. blazars : what would we see without EBL absorption

Authors:Carlo Romoli, David Sanchez, Matthias Lorentz, Pierre Brun on behalf of the H.E.S.S. collaboration

The vast majority of extragalactic sources detected in the very high
energy (E> 200 GeV) are active galactic nuclei (AGN) located at
cosmological distances. During their travel towards earth, the emitted
gamma-rays suffer for absorption by the extragalatic background light
(EBL). The density of the EBL is not very well constraint by direct or
indirect measurement which leads to uncertainties on the intrisic
spectrum of the sources. high-quality AGN’s spectra obtained with the
High Energy Stereoscopic System (H.E.S.S.) have been used to perform a
model-independent measurement of the EBL spectral energy distribution.
While the precision of this measurement remains limited, it reflects
the sensitivity of H.E.S.S. alone to the EBL and offers the possibility
to access the intrinsic spectra of AGNs in a consistent manner, taking
into account the derived uncertainties on the EBL spectral energy
distribution.


In this constribution, we study the intrinsic spectra as measured by
H.E.S.S. and by the Fermi Large Area Telescope (LAT) of several blazars
of the H.E.S.S. sky. This is then the opportunity to have an new
insight in the emission processes at play in the jets of AGN. The data
presented consist of monitoring data of quiecent state of blazars and
also flares of bright objects, such as PKS 2155-304, Mrk 421, recorded
by H.E.S.S.