News from a Multi-Wavelength Monitoring Campaign on Mrk 421

Abstract

We conducted a daily monitoring campaign on Mrk 421 in 2003 and 2004 with the Whipple 10 m telescope and the large-area instruments aboard RXTE, simultaneously covering TeV and X-ray energies. Supporting observations at optical and radio wavelengths were also frequently carried out. Mrk 421 was observed over a wide range of fluxes (with a dynamic range of ~30 both at TeV and X-ray energies). The source was relatively quiet in 2003 but became unusually active in 2004, with flares reaching peak fluxes of ~80 mCrab in X-rays and >3 Crab at TeV energies! We will describe the multiwavelength campaign and present some preliminary results. We will also discuss the implications of the results on the proposed emission models for TeV blazars.