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All but three (M87, BL Lac and 3C 279) extragalactic sources detected so farat very high energy (VHE) gamma-rays belong to the class of high-frequencypeaked BL Lac (HBL) objects. This suggested to us a systematic scan ofcandidate sources with the MAGIC telescope, based on the compilation of X-rayblazars by Donato et al. (2001). The observations took place from December 2004to March 2006 and cover sources on the northern sky visible under small zenithdistances zd < 30 degrees at culmination. The sensitivity of the search wasplanned for detecting X-ray bright F(1 keV) > 2 uJy) sources emitting at leastthe same energy flux at 200 GeV as at 1 keV. In order to avoid strong gamma-rayattenuation close to the energy threshold, the redshift of the sources wasconstrained to values z<0.3. Of the fourteen sources observed, 1ES 1218+304 and1ES 2344+514 have been detected in addition to the known bright TeV blazars Mrk421 and Mrk 501. A marginal excess of 3.5 sigma from the position of 1ES1011+496 was observed and has been confirmed as a source of VHE gamma-rays by asecond MAGIC observation triggered by a high optical state (Albert et al.2007). For the remaining sources, we present here the 99% confidence levelupper limits on the integral flux above ~200 GeV. We characterize the sample ofHBLs (including all HBLs detected at VHE so far) by looking for correlationsbetween their multi-frequency spectral indices determined from simultaneousoptical, archival X-ray, and radio luminosities, finding that the VHE emittingHBLs do not seem to constitute a unique subclass. The absorption correctedgamma-ray luminosities at 200 GeV of the HBLs are generally not higher thantheir X-ray luminosities at 1 keV.

Systematic search for VHE gamma-ray emission from X-ray bright high-frequency BL Lac objects