Evidence for Intergalactic Absorption in the TeV Gamma-Ray Spectrum of Mkn 501

Abstract

The recent HEGRA observations of the blazar Mkn 501 show strong curvature in the very high energy gamma-ray spectrum. Applying the gamma-ray opacity derived from an empirically based model of the intergalactic infrared background radiation field (IIRF), to these observations, we find that the intrinsic spectrum of this source is consistent with a power-law: dN/dE~ E^-alpha with alpha=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 Mkn 501 does not vary with luminosity, combined with the correlated, spectrally variable emission in X-rays, as observed by the BeppoSAX and RXTE instruments, also independently implies that the intrinsic spectrum must be close to alpha=2. Thus, the observed curvature in the spectrum is most easily understood as resulting from intergalactic absorption.

7 pages, 1 figure, accepted in ApJ Letters 1999 April 2

References in corpus (7)

• A theoretical unifying scheme for gamma-ray bright blazars
• The COBE Diffuse Infrared Background Experiment Search for the Cosmic Infrared Background: IV. Cosmological Implications
• Discovery of >350 GeV Gamma Rays from the BL Lacertae Object 1ES 2344+514
• VHE Gamma Rays from PKS 2155-304
• Detection of Gamma Rays of Up to 50 TeV From the Crab Nebula
• Performance of the Stereoscopic System of the HEGRA Imaging Air Cherenkov Telescopes: Monte Carlo Simulations & Observations
• Modeling the variability of the BL Lacertae object PKS 2155-304

Cited by in corpus (22)

• The Cosmic Infrared Background: Measurements and Implications
• Implications of Cosmological Gamma-Ray Absorption II. Modification of gamma-ray spectra
• New Tests of Lorentz Invariance Following from Observations of the Highest Energy Cosmic Gamma Rays
• Gamma-Ray Background from Structure Formation in the Intergalactic Medium
• Time Dependent Modeling of the Markarian 501 X-ray and TeV Gamma-Ray Data Taken During March and April, 1997
• Detection of a Far IR Excess with DIRBE at 60 and 100 Microns
• Modelling the TeV gamma-ray spectra of two low redshift AGNs: Mkn 501 and Mkn 421
• An Empirically Based Model for Predicting Infrared Luminosity Functions, Deep Infrared Galaxy Counts and the Diffuse Infrared Background
• Extragalactic Gamma-ray Absorption and the Intrinsic Spectrum of Mkn 501 During the 1997 Flare
• GeV Emission from TeV Blazars and Intergalactic Magnetic Fields
• The TeV Energy Spectrum of Mkn 501 Measured with the Stereoscopic Telescope System of HEGRA during 1998 and 1999
• Electron Acceleration and Time Variability of High Energy Emission from Blazars
• On the origin of highest energy gamma-rays from Mkn 501
• Reanalysis of the high energy cutoff of the 1997 Mkn 501 TeV energy spectrum
• New constraints on the cosmic mid-infrared background using TeV gamma-ray astronomy
• Search for Point Sources of High Energy Neutrinos with AMANDA
• Strong GeV Emission Accompanying TeV Blazar H1426+428
• Constraining the cosmic abundance of stellar remnants with multi-TeV gamma-rays
• Automatic quenching of high energy gamma-ray sources by synchrotron photons
• Rejection of the hypothesis that Markarian 501 TeV photons are pure Bose-Einstein condensates
• An original constraint on the Hubble constant: h>0.74
• Improved limits on photon velocity oscillations