A. Saggion

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.

Energy Calibration of Cherenkov Telescopes using GLAST Data

We discuss the possibility of using the observations by GLAST of steady gamma sources, as the Crab Nebula and some selected AGNs, to calibrate the Imaging Air Cherenkov Telescopes (IACT) and improve their energy resolution, in particular. We show that at around 100 GeV, exploiting the features in the spectrum of the Crab Nebula, the absolute energy calibration uncertainty of Cherenkov telescopes can be reduced to < 10%.

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.

A method to measure the γ-ray content in VHE cosmic ray showers

Abstract An experimental technique is presented to determine the effectiveness of methods to tag photon initiated air showers and reject hadron initiated ones. The technique is based on the rate reduction in the Moon direction. With a photon energy threshold below or equal to 1 TeV, with an angular resolution of a few mrad and being insensitive to visible light, the proposed CLUE detector allows a wide and original physics program. In particular the direct measurement of the fraction of primary photons in the continuum of the cosmic ray flux is feasible with adequate statistics in a few months of data taking.

THE MAGIC EXPERIMENT AND ITS FIRST RESULTS

With its diameter of 17m, the MAGIC telescope is the largest Cherenkov detector for gamma ray astrophysics. It is sensitive to photons above an energy of 30 GeV. MAGIC started operations in October 2003 and is currently taking data. This report summarizes its main characteristics, its first results and its potential for physics.

NEURAL NETWORKS FOR GAMMA-HADRON SEPARATION IN MAGIC

Neural networks have proved to be versatile and robust for particle separation in many experiments related to particle astrophysics. We apply these techniques to separate gamma rays from hadrons for the MAGIC Cerenkov Telescope. Two types of neural network architectures have been used for the classi cation task: one is the MultiLayer Perceptron (MLP) based on supervised learning, and the other is the Self-Organising Tree Algorithm (SOTA), which is based on unsupervised learning. We propose a new architecture by combining these two neural networks types to yield better and faster classi cation results for our classi cation problem.

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.

A THIRD LEVEL TRIGGER PROGRAMMABLE ON FPGA FOR THE GAMMA/HADRON SEPARATION IN A CHERENKOV TELESCOPE USING PSEUDO-ZERNIKE MOMENTS AND THE SVM CLASSIFIER

We studied the application of the Pseudo-Zernike features as image parameters (instead of the Hillas parameters) for the discrimination between the images produced by atmospheric electromagnetic showers caused by gamma-rays and the ones produced by atmospheric electromagnetic showers caused by hadrons in the MAGIC Experiment. We used a Support Vector Machine as classification algorithm with the computed Pseudo-Zernike features as classification parameters. We implemented on a FPGA board a kernel function of the SVM and the Pseudo-Zernike features to build a third level trigger for the gamma-hadron separation task of the MAGIC Experiment.