Manuel Meyer, Martin Raue, Daniel Mazin, Dieter Horns
Very high energy (VHE, energy $E \gtrsim 100$\,GeV) \gamma-rays from
cosmological sources are attenuated due to the interaction with photons of the
extragalactic background light (EBL) in the ultraviolet to infrared wavelength
band. The EBL, thus, leaves an imprint on the observed energy spectra of these
objects. In the last four years, the number of extragalactic VHE sources
discovered with imaging atmospheric Cherenkov telescopes (IACTs), such as
MAGIC, H.E.S.S., and VERITAS, has doubled. Furthermore, the measurements of the
\emph{Fermi} satellite brought new insights into the intrinsic spectra of the
sources at GeV energies. In this paper, upper limits on the EBL intensity are
derived by considering the most extensive VHE source sample ever used in this
context. This is accomplished by constructing a large number of generic EBL
shapes and combining spectral informations from \emph{Fermi} and IACTs together
with minimal assumptions about the source physics at high and very high
\gamma-ray energies. The evolution of the EBL with redshift is accounted for
and the possibility of the formation of an electromagnetic cascade and the
implications on the upper limits are explored. The EBL density at $z=0$ is
constrained over a broad wavelength range between 0.4 and 100\,\mu m. At
optical wavelengths, the EBL density is constrained below
24\,nW\,m$^{-2}$\,sr$^{-1}$ and below 5\,nW\,m$^{-2}$\,sr$^{-1}$ between 8\,\mu
m and 31\,\mu m.
View original:
http://arxiv.org/abs/1202.2867
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