Related papers: HEGRA search for TeV emission from BL Lac objects
The HEGRA system of 4 Imaging Atmospheric Cherenkov Telescopes (IACTs) has been used since March 1997 for a comprehensive study of the gamma-ray emission from the BL Lac object Mkn 501 in the energy range above 500 GeV. Taking advantage of…
Observational and theoretical results indicate that low-redshift BL Lacertae objects are the most likely extragalactic sources to be detectable at TeV energies. In this paper we present the results of observations of 4 BL Lacertae objects…
The HEGRA system of imaging air Cherenkov telescopes has been used to observe the BL Lac object H1426+428 ($z=0.129$) for 217.5 hours in 2002. In this data set alone, the source is detected at a confidence level of $5.3~\sigma$, confirming…
During 1997, the BL Lac Object Mkn 501 was the brightest known object in the TeV gamma-ray sky. The emission was characterized by dramatic variations in intensity with a mean flux exceeding by a factor of three the steady gamma-ray flux of…
The HEGRA-IACT-system with a FoV of ~1.5 deg radius has been used for surveying one quater of the Galactic disc in respect to point sources, moderately extended sources and for diffuse emission in the energy range above 1 TeV. In total 140…
We present results from observations of 29 BL Lacertae objects, taken with the Whipple Observatory 10 m Gamma-Ray Telescope between 1995 and 2000. The observed objects are mostly at low redshift (z < 0.2) but observations of objects of z up…
Since its commissioning in fall 1996, the stereoscopic system of Imaging Atmospheric Cherenkov Telescope (IACTs) of HEGRA with an energy threshold of 500 GeV, an angular resolution of 0.1 degree and an energy resolution of 20% per…
A sample of 54 selected Active Galactic Nuclei (AGN) has been observed with the HEGRA stereoscopic system of Cherenkov Telescopes between 1996 and 2002 in the TeV energy regime. The observations were motivated by the positive results…
The HEGRA collaboration has achieved outstanding results during the operation of the six imaging atmospheric Cherenkov telescopes from 1996 to 2002. The experimental work pioneered the field of TeV gamma-ray astronomy with observations…
During 1997, the BL Lac object Mkn 501 went into an extraordinary state of high X-ray and TeV gamma-ray activity, lasting more than 6 months. In this paper we report on the TeV emission characteristics of the source in the subsequent years…
Two active galactic nuclei have been detected at TeV energies using the atmospheric Cherenkov imaging technique. The Whipple Observatory gamma-ray telescope has been used to observe all the BL Lacertae objects in the northern hemisphere out…
A very high energy (VHE) gamma-ray signal has been detected at the 5.4 sigma level from H1426+428, an x-ray selected BL Lacertae object at a redshift of 0.129. The object was monitored from 1995 - 1998 with the Whipple 10m imaging…
The REX (Radio-Emitting X-ray sources) is a catalogue produced by cross-matching X-ray data from the ROSAT-PSPC archive of pointed observations and radio data from the NRAO VLA Sky Survey, aimed at the selection of blazars. From the REX…
Using the HEGRA system of imaging atmospheric Cherenkov telescopes, a region of the Galactic plane (-10 deg < b < 5 deg, 38 deg < l < 43 deg) was surveyed for TeV gamma-ray emission, both from point sources and of diffuse nature. The region…
The BL Lac object Mkn 501 has shown very high emission in TeV gamma-rays from March to October, 1997. During this period the source was continuously monitored with the HEGRA stereoscopic system of 4 imaging air Cherenkov telescopes for a…
In this paper, we present results of TeV $\gamma$--ray observations of the high synchrotron peaked BL Lac object 1ES 1218+304 (z=0.182) with the $TACTIC$ (TeV Atmospheric Cherenkov Telescope with Imaging Camera). The observations are…
We focus our analysis on 55 BL Lac objects with a hard Fermi gamma-ray spectrum, and for which a redshift or a lower limit to it has been determined by a previous study of ours. We extrapolate the spectral fits given by the 4FGL catalogue…
High-frequency-peaked BL Lacs (HBLs) dominate the extragalactic TeV sky, with more than 50 objects detected by the current generation of TeV observatories. Still, the properties of TeV-emitting HBLs as a population are poorly understood due…
All but three (M87, BL Lac and 3C 279) extragalactic sources detected so far at very high energy (VHE) gamma-rays belong to the class of high-frequency peaked BL Lac (HBL) objects. This suggested to us a systematic scan of candidate sources…
Extreme high-frequency peaked BL Lac objects (EHBLs) are blazars which exhibit extremely energetic synchrotron emission. They also feature non-thermal gamma-ray emission whose peak lies in the very high-energy (VHE, E > 100 GeV) range, and…