@article {22738,
	title = {Evidence for Intergalactic Absorption in the TEV Gamma-Ray Spectrum of Markarian 501},
	volume = {518},
	year = {1999},
	month = {1999/06/1},
	pages = {L13 - L15},
	abstract = {The recent High-Energy Gamma-Ray Array (HEGRA) observations of the blazar Mrk 501 show strong curvature in the very high energy γ-ray spectrum. Applying the γ-ray opacity derived from an empirically based model of the intergalactic infrared background radiation field to these observations, we find that the intrinsic spectrum of this source is consistent with a power law: dN<SUB>γ</SUB>/dE~E<SUP>-α</SUP>, with α=2.00+/-0.03 over the range 500 GeV-20 TeV. Within current synchrotron self-Compton scenarios, the fact that the TeV spectral energy distribution of Mrk 501 does not vary with luminosity, combined with the correlated, spectrally variable emission in X-rays as observed by the BeppoSAX and Rossi X-Ray Timing Explorer instruments, also independently implies that the intrinsic spectrum must be close to α=2. Thus, the observed curvature in the spectrum is most easily understood as resulting from intergalactic absorption.},
	keywords = {Astrophysics, galaxies: active, Galaxies: BL Lacertae Objects: Individual: Name: Markarian 501, gamma rays: theory},
	isbn = {0004-637X},
	url = {https://ui.adsabs.harvard.edu/abs/1999ApJ...518L..13K},
	author = {Konopelko, Alexander K. and Kirk, John G. and Stecker, Floyd W. and Mastichiadis, Apostolos}
}
