Related papers: Observations of Mkn 421 with the CELESTE Experimen…
The High Altitude Water Cherenkov (HAWC) observatory monitors the gamma-ray sky at energies between 100 GeV and 100 TeV with a wide field of view of $\sim 2$ steradians. A duty cycle of $\sim 90$% allows HAWC to scan two thirds of the sky…
The Very High Energy (VHE) gamma-ray emission of the BL Lacertae objects Markarian 501 and Markarian 421 has been observed by the CAT Imaging Atmospheric Cherenkov Telescope in 1997 and 1998. The spectrum extraction method is presented, and…
To date, only two extragalactic objects have been firmly established as very high-energy gamma-ray sources in the Northern sky: these are the two blazars Markarian 501 and Markarian 421. This paper reviews the most striking results obtained…
The CAT imaging telesope, which uses the Atmospheric Cherenkov Technique to observe TeV gamma-ray sources, has been operating since September 1996. Located in southern France, it features a fine grained camera consisting of 546 PMT with a…
Markarian 421 (Mrk 421) is one the brightest and closest (z=0.031) blazars known (de Vaucouleurs et al 1991). It is also one of the fastest varying TeV $\gamma$-ray sources, with a flaring activity on time scales as short as tens of…
The radiation mechanism of very high energy $\gamma$-ray emission from blazars and crucial parameters like magnetic field, and size of the emitting region are not well understood yet. To understand the above mentioned properties of blazars,…
We have observed Markarian 421 in January and March 2001 with the CANGAROO-II imaging Cherenkov telescope during an extraordinarily high state at TeV energies. From 14 hours observations at very large zenith angles, $\sim70^\circ$, a signal…
The last 20 years have seen the development of new techniques in Astroparticle Physics providing access to the highest end of the electromagnetic spectrum. It has been shown that some sources emit photons up to energies close to 100 TeV.…
We have converted the former solar electrical plant THEMIS (French Pyrenees) into an atmospheric Cherenkov detector called CELESTE, which records gamma rays above 30 GeV (7E24 Hz). Here we present the first sub-100 GeV detection by a ground…
The ``Gamma Ray Astronomy at ALmeria'' (GRAAL) experiment uses 63 heliostat-mirrors with a total mirror area of ~ 2500 m2 from the CESA-1 field at the ``Plataforma Solar de Almeria'' (PSA) to collect Cherenkov light from air showers. The…
Milagro is a gamma-ray observatory employing a water Cherenkov detector to observe extensive air showers produced by high-energy particles impacting in the Earth's atmosphere. We discuss the first detection of TeV gamma-rays from the…
Very high energy gamma-ray emission from the BL Lac object Markarian 421 has been detected over three observing seasons on 59 nights between April 1992 and June 1994 with the Whipple 10-meter imaging Cherenkov telescope. During its initial…
Ground-based atmospheric Cherenkov telescopes are proven to be effective instruments for observations of very high energy (VHE) gamma-radiation from celestial objects. For effective use of such technique one needs detailed Monte Carlo…
The gamma-ray emission above 250 GeV from the BL Lac object Markarian 421 was observed by the CAT Cherenkov imaging telescope between December, 1996, and June, 2000. In 1998, the source produced a series of small flares, making it the…
We describe the design and performance of the Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) in its complete configuration. STACEE uses the heliostats of a solar energy research facility to collect and focus the Cherenkov…
Using air showers induced by TeV gamma-rays from Mrk 501, the radial distribution of Cherenkov light is investigated. The shower geometry is reconstructed from the stereoscopic shower images obtained with the telescopes of the HEGRA IACT…
The gamma-ray energy region between 20 and 250 GeV is largely unexplored. Ground-based atmospheric Cherenkov detectors offer a possible way to explore this region, but large Cherenkov photon collection areas are needed to achieve low energy…
The High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory surveys the very high energy sky in the 300 GeV to $>100$ TeV energy range. HAWC has detected two blazars above $11\sigma$, Markarian 421 (Mrk 421) and Markarian 501 (Mrk 501).…
The CAT imaging telescope, recently built on the site of the former solar plant Themis (French Pyrenees), observed gamma-rays from the Crab nebula from October 1996 to March 1997. This steady source, often considered as the standard candle…
We study the multi-band variability and correlations of the TeV blazar Mrk 421 on year time scales, which can bring additional insight on the processes responsible for its broadband emission. We observed Mrk 421 in the very high energy…