Multi-wavelength observations of the TeV Blazars Mkn~421, 1ES1959+650,   and H1426+428 with the HEGRA Cherenkov telescopes and the RXTE X-ray   satellite
  Recent results obtained with the HEGRA system of imaging Cherenkov telescopes on the TeV emission of the Blazars Mkn~421 ($z=0.030$), 1ES1959+650 ($z=0.047$), and H1426+428 ($z=0.129$) are reported. For Mkn~421, a close connection of the average flux level and spectral shape has been observed during the periods of increased activity in the years 2000 and 2001. Simultaneously taken data with the RXTE X-ray satellite reveal a complex light curve at X-ray and TeV energies. After a deep exposure of 94 hrs, the object 1ES1959+650 was detected at the significance level of 5.4$\sigma$ with a soft energy spectrum following a power-law with a photon-index of $3.3 \pm 0.7$. During recent observations in May 2002, the source has shown increased activity with indications for a flattening of the energy spectrum.   The high energy peaked Blazar H1426+428 has recently been identified as a source of TeV photons. Since the source is fairly distant (z=0.129), absorption of TeV photons due to pair-production on the optical and near infrared extragalactic light becomes important and should leave a signature in the observed TeV energy spectrum. Notably, the TeV energy spectrum determined with the HEGRA system of Cherenkov telescopes agrees with the expectation of a strongly absorbed source spectrum. 
D. Horns (1), and the HEGRA collaboration ((1) Max-Planck-Institute f.   Kernphysik, Heidelberg)