Multi-TeV Gamma-Ray Flares from Markarian 421 in 2000 and 2001 Observed with the Tibet Air Shower Array

Abstract

Several strong TeV gamma-ray flares were detected from Markarian 421 in the years 2000 and 2001 by the Tibet III air shower array at a level of statistical significance of 5.1 sigma. Markarian 421 was unprecedentedly active at X-ray and TeV gamma-ray energies during this period, and a positive correlation was found between the change of the ASM/RXTE X-ray flux and the Tibet TeV gamma-ray flux. When a power-law energy spectrum for gamma-rays from this source is assumed, the spectral index is calculated to be -3.24+-0.69 at the most active phase in 2001. The spectral index observed by the Tibet air shower array is consistent with those obtained via imaging air Cerenkov telescopes.

arXiv comment22 pages, 10 figures, accepted by ApJ

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