Study of Markarian 421 in the γ-ray energy range 30-100 Tev

P. L. Ghia, M. Aglietta, B. Allessandro, P. Antonioli, F. Arneodo, L. Bergamasco, M. Bertaina, C. Castagnoli, A. Castellina, A. Chiavassa, G. Cini Castagnoli, B. D'Ettorre Piazzoli, G. Di Sciascio, W. Fulgione, P. Galeotti, P. L. Ghia, M. Iacovacci, G. Mannocchi, C. Morello, G. NavarraO. Saavedra, G. C. Trinchero, P. Vallania, S. Vernetto, C. Vigorito

Research output: Contribution to journalArticlepeer-review


The active galactic nucleus Markarian 421 (Mrk 421) is studied through the EAS-TOP extensive air shower array in the γ-ray energy ranges 20-50 TeV and 80-120 TeV. No evidence of d.c. emission is found in both datasets: the 90% flux limits are Φ(>25 TeV) < 1.3 · 10-13 cm-2 s-1 and Φ(>90 TeV) < 2.5 · 10-4 cm-2 s-1. A straight power law extrapolation up to E0 ≈ 1015 eV of the spectrum obtained from the observations by the EGRET and Whipple experiments - above 100 MeV and 0.5 TeV respectively - is excluded with a confidence level >99.99%, as expected from the absorption of VHE γ-rays by the 2.7K cosmic microwave background radiation. An indication (at ≈ 90% c.l.) of a steepening of the spectrum, with respect to such extrapolation, at γ-ray energies lower than expected from the 2.7K cutoff is derived. This could be due either to a break in the source spectrum or to the absorption of VHE γ-rays by intergalactic infrared photons of wavelength ≈ 100 μm.

Original languageEnglish (US)
Pages (from-to)506-508
Number of pages3
JournalNuclear Physics B - Proceedings Supplements
Issue number1-3
StatePublished - Jan 1999

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Nuclear and High Energy Physics


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