TeV AND MULTI-WAVELENGTH OBSERVATIONS OF Mrk 421 IN 2006-2008

Abstract

We report on TeV gamma-ray observations of the blazar Mrk 421 (redshift of\n0.031) with the VERITAS observatory and the Whipple 10m Cherenkov telescope.\nThe excellent sensitivity of VERITAS allowed us to sample the TeV gamma-ray\nfluxes and energy spectra with unprecedented accuracy where Mrk 421 was\ndetected in each of the pointings. A total of 47.3 hrs of VERITAS and 96 hrs of\nWhipple 10m data were acquired between January 2006 and June 2008. We present\nthe results of a study of the TeV gamma-ray energy spectra as a function of\ntime, and for different flux levels. On May 2nd and 3rd, 2008, bright TeV\ngamma-ray flares were detected with fluxes reaching the level of 10 Crab. The\nTeV gamma-ray data were complemented with radio, optical, and X-ray\nobservations, with flux variability found in all bands except for the radio\nwaveband. The combination of the RXTE and Swift X-ray data reveal spectral\nhardening with increasing flux levels, often correlated with an increase of the\nsource activity in TeV gamma-rays. Contemporaneous spectral energy\ndistributions were generated for 18 nights, each of which are reasonably\ndescribed by a one-zone SSC model.\n