Detection of the BL Lacertae Object H1426+428 at TeV Gamma‐Ray Energies

A very high energy (VHE) gamma-ray signal has been detected at the 5.4 sigmalevel from H1426+428, an x-ray selected BL Lacertae object at a redshift of0.129. The object was monitored from 1995 - 1998 with the Whipple 10m imagingatmospheric Cherenkov telescope as part of a general blazar survey; the resultsof these observations, although not statistically significant, wereconsistently positive. X-ray observations of H1426+428 during 1999 with theBeppoSAX instrument revealed that the peak of its synchrotron spectrum occursat > 100 keV, leading to the prediction of observable TeV emission from thisobject. H1426+428 was monitored extensively at the Whipple Observatory duringthe 1999, 2000, and 2001 observing seasons. The strongest TeV signals weredetected in 2000 and 2001. During 2001, an integral flux of 2.04 +/- 0.35x10e-11 cm-2 s-1 above 280 GeV was recorded from H1426+428. The detection ofH1426+428 supports the idea that, as also seen in Markarian 501 and1ES2344+514, BL Lacertae objects with extremely high synchrotron peakfrequencies produce gamma rays in the TeV range.Comment: 35 pages, 7 figures, accepted by ApJ Two upper limits in Table 3 (upper limits for 1995 and 1997) are different from the ApJ versio