Evidence for Intergalactic Absorption in the TEV Gamma-Ray Spectrum of Markarian 501
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: dNγ/dE~E-α, 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.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- June 1999
- DOI:
- 10.1086/312062
- arXiv:
- arXiv:astro-ph/9904057
- Bibcode:
- 1999ApJ...518L..13K
- Keywords:
-
- GALAXIES: BL LACERTAE OBJECTS: INDIVIDUAL: NAME: MARKARIAN 501;
- GALAXIES: ACTIVE;
- GAMMA RAYS: THEORY;
- Galaxies: BL Lacertae Objects: Individual: Name: Markarian 501;
- Galaxies: Active;
- Gamma Rays: Theory;
- Astrophysics
- E-Print:
- 7 pages, 1 figure, accepted in ApJ Letters 1999 April 2