EDP Sciences
Free access
Volume 413, Number 3, January III 2004
Page(s) 807 - 815
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20031542

A&A 413, 807-815 (2004)
DOI: 10.1051/0004-6361:20031542

Implications of cosmological gamma-ray absorption

II. Modification of gamma-ray spectra
T. M. Kneiske1, T. Bretz1, K. Mannheim1 and D. H. Hartmann2

1  Universität Würzburg, Am Hubland, 97057 Würzburg, Germany
2  Clemson University, Clemson, SC 29634-0978, USA

(Received 10 April 2003 / Accepted 16 September 2003)

Bearing on the model for the time-dependent metagalactic radiation field developed in the first paper of this series, we compute the gamma-ray attenuation due to pair production in photon-photon scattering. Emphasis is on the effects of varying the star formation rate and the fraction of UV radiation assumed to escape from the star forming regions, the latter being important mainly for high-redshift sources. Conversely, we investigate how the metagalactic radiation field can be measured from the gamma-ray pair creation cutoff as a function of redshift, the Fazio-Stecker relation. For three observed TeV-blazars (Mkn 501, Mkn 421, H1426+428) we study the effects of gamma-ray attenuation on their spectra in detail.

Key words: cosmology: diffuse radiation -- galaxies: BL Lacertae objects: general -- galaxies: BL Lacertae objects: individual: Mkn 421, Mkn 501, H1426+428

Offprint request: T. M. Kneiske, kneiske@astro.uni-wuerzburg.de

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