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TeV gamma-ray observations are reported of 1H1426+428 (1H1426), an X-ray selected BL Lacertae object at a redshift of 0.129. The X-ray spectrum appears to peak near 100 keV; if this is the peak of the synchrotron emission, then this AGN is a prime candidate for TeV gamma-ray emission assuming a Compton-synchrotron model. During the 1999, 2000 and 2001 observing seasons, the source has been intensively studied with the Whipple 10m imaging atmospheric Čerenkov telescope; these observations, together with the indications from earlier observations confirm this hypothesis. The average signal was at the 4.2σ level during the 2000 observing season, while the average signal recorded during 2001 was at the 4.9σ level. [ABSTRACT FROM AUTHOR]

A ToO observation of the TeV-emitting blazar Mrk 421 with INTEGRAL was triggered in June 2006 by an increase of the RXTE count rate to more than 30 mCrab. The source was then observed with all INTEGRAL instruments with the exception of the spectrometer SPI for a total exposure of 829 ks. During this time several outbursts were observed by IBIS and JEM-X. Multiwavelength observations were immediately triggered and the source was observed at radio, optical and X-ray wavelengths up to TeV energies. The data obtained during these observations are analysed with respect to spectral evolution and correlated variability. Preliminary results of the analysis are presented in this poster. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]