C. Bigongiari

SIMULTANEOUS MULTIWAVELENGTH OBSERVATIONS OF THE BLAZAR 1ES 1959+650 AT A LOW TeV FLUX

We present the resultsfroma multiwavelength campaignonthe TeVblazar1ES 1959+650, performed in2006May. Data from the optical, UV, soft- and hard-X-ray, and very high energy (VHE) gamma-ray (E > 100 GeV) bands were obtained with the Suzaku and Swift satellites, the MAGIC telescope, and other ground-based facilities. The source spectral energy distribution (SED), derived from Suzaku and MAGIC observations at the end of 2006 May, shows the usual double hump shape, with the synchrotron peak at a higher flux level than the Compton peak. With respect to historicalvalues,duringourcampaignthe sourceexhibiteda relatively highstateinX-raysand optical, while inthe VHEbanditwasatoneof thelowestlevelsofarrecorded.Wealsomonitoredthesourceforfluxspectralvariability onatimewindowof 10daysintheoptical-UVandX-raybandsand7daysintheVHEband.Thesourcevariesmorein the X-ray than in the optical band, with the 2Y10 keV X-ray flux varying by a factor of � 2. The synchrotron peak is locatedintheX-raybandandmovestohigherenergiesasthesourcegetsbrighter,withtheX-rayfluxesaboveitvarying more rapidly than the X-ray fluxes at lower energies. The variability behavior observed in the X-ray band cannot be

A two-level pattern trigger for the MAGIC telescope

Strong scientific motivation are pushing the second generation of ground base Cherenkov telescopes to lower as much as possible their energy threshold. MAGIC will be the biggest single telescope, in terms of collection area (250 m 2 ), foreseen for the second-half of 2001. The large collection area, the newphotodetector and the electronic design will allow the telescope to lower the energy threshold below 30 GeV. For this telescope a two-level pattern trigger is designed to work in severe high pixel rate. The MAGIC trigger architecture and its implementation is presented. # 2001 Elsevier Science B.V. All rights reserved. PACS: 95.55.Ka

The CLUE experiment operating with 4 telescopes in La Palma

Abstract The CLUE experiment has started operation with four of the nine telescopes that are foreseen for its beginning. These telescopes are at present at Roque de Los Muchachos in the Canary Islands, in the same site as the HEGRA experiment. In winter 1997 we started taking data with the telescopes pointing directly at the moon. A description of the telescopes and the performance of the detector are given.

Status report on CLUE

Abstract The CLUE experiment uses a new cosmic ray detector array planned to operate for the next decade. It utilises a MWPC chambers sensitive to UV, to image Cherenkov radiation produced in cosmic ray showers. This approach is unique in that the instrument is insensitive to skylight backgrounds, has a threshold similar to that of visible Cherenkov experiments but a longer duty cycle. These features make possible a class of interesting cosmic ray physics experiments. The CLUE experiment has started operation with two of the ten telescopes that are foreseen for its beginning. These telescopes are at present at Roque de Los Muchachos in the Canary Islands, in the same site as the HEGRA experiment. A description of the telescopes is given and some data on the tests performed are presented.

Shower reconstruction in the CLUE experiment

Abstract The CLUE experiment studies primary cosmic rays (E≥2 TeV ) by detecting UV (190–230 nm) Cherenkov light produced by atmospheric showers. Since atmospheric absorption in the UV range is higher than in the visible range, CLUE cannot apply algorithms normally used in IACT 1 experiments to determine primary cosmic-ray direction. In this paper, we present a new method developed by CLUE. The algorithm performances were evaluated using simulated showers. Preliminary results of the source analysis using this new method are shown.

THE CLUE TRIGGER: A VME BASED TWO LEVEL TRIGGER FOR VHE EXPERIMENTS

Abstract We describe a trigger architecture developed for shower selection in the CLUE Cherenkov telescopes. The selection is made first in each telescope of the array looking at the low resolution images produced by fast electronics, than requiring temporal coincidence between units. Big effort has been put to simplify the programming of trigger configurations to help the user to switch easily between different observational and calibration requests.

A novel background reduction strategy for high level triggers and processing in gamma‐ray Cherenkov detectors

Gamma ray astronomy is now at the leading edge for studies related both to fundamental physics and astrophysics. The sensitivity of gamma detectors is limited by the huge amount of background, constituted by hadronic cosmic rays (typically two to three orders of magnitude more than the signal) and by the accidental background in the detectors. By using the information on the temporal evolution of the Cherenkov light, the background can be reduced. We will present here the results obtained within the MAGIC experiment using a new technique for the reduction of the background. Particle showers produced by gamma rays show a different temporal distribution with respect to showers produced by hadrons; the background due to accidental counts shows no dependence on time. Such novel strategy can increase the sensitivity of present instruments.

The global trigger system of the magic telescope array

The Magic experiment is located in the La Palma island, Canary (Spain) and has started collecting data in 2004. The upgrade project of the experiment consists in the construction of a second telescope similar to the first one using new technologies such as high efficiency photon detectors, last generation VCSELs for optical signal transmission and signal sampling at GHz frequencies. With the operation of the first telescope the collaboration has succeeded in lowering the energy threshold the very low value of 30 GeV never reached before by other Cherenkov telescopes. The construction of the second telescope will allow the experiment to perform stereo observations of the atmospheric showers and help in resolving structured objects. For the simultaneous observation it is possible to drastically reduce the muonic background by applying a narrow time coincidence between the trigger signals from the two telescopes. During normal operation each telescope operates with several trigger sources and it is therefore mandatory to discriminate the trigger source when applying the coincidence logic. The design of the global trigger system is described in detail and performances of the system are presented.