Long-term monitoring of bright blazars with a dedicated Cherenkov telescope

Abstract

Blazar observations in VHE Gamma-rays show intensity variations on time scales of minutes to years, most frequently with variability times of about one day. They could be caused by the interaction of relativistic jets with the surroundings, but also carry the signature of internal processes of the central engine, possibly binary systems of supermassive black holes. Ultimately, long-term monitoring with 24-hour coverage is needed in addition to the shorter high sensitivity exposures provided by telescopes such as MAGIC, VERITAS and H.E.S.S., in order to study the physical origin of such flaring activity. This can be achieved with a global network of small robotic Cherenkov telescopes. As a first step, we plan to set up a fully dedicated small Cherenkov telescope and carry out joint observations with the Whipple 10m monitor telescope. The new low cost, but high performance telescope will be the upgrade of one of the former HEGRA telescopes, still located at the Observatorio del Roque de los Muchachos on the Canarian Island of La Palma (Spain). The most important novelties will be its robotic operation and novel camera, greatly improving its sensitivity and lowering the energy threshold.

FACT—The first Cherenkov telescope using a G-APD camera for TeV gamma-ray astronomy

“…CTA. FACT itself might be the first telescope to be included in a world-wide network of Cherenkov telescopes [32,33] for monitoring bright blazars in the northern hemisphere [34].…”

“…The telescope will receive a complete technological upgrade, including refurbished mirrors, the drive system, and the data acquisition system (as also previously reported [16,17,18]) and will be equipped with a new camera, based entirely on G-APDs.…”

A site evaluation campaign for a ground based atmospheric Cherenkov telescope in Romania

“…Under these circumstances and due to the importance of the observational data, a global network of several small Cherenkov telescopes was proposed to be operated in a coordinated way for long-term monitoring observations of the brightest blazars-the DWARF (Dedicated Worldwide AGN Research Facility) Network [11]. This network will have to be distributed around the globe for 24/7 monitoring, preferably with temporal overlap and redundancy to account for weather and duty cycle constraints, as well as for muon background reduction.…”

Calibration and performance of the photon sensor response of FACT — the first G-APD Cherenkov telescope

“…For long-term and especially continous monitoring the observation time of those instruments is too expensive which suggests the construction of an inexpensive instrument with an adapted sensitivity, c.f. [2]. In addition, the application of silicon based photo sensors promised the increase of available observation time due to their robustness against light exposure as string moon light.…”