I will highlight the key scientific goals of ground-based gamma ray astronomy relevant to three energy domains - (i) below 100 GeV (down to several GeV), (ii) 100 GeV - 10 TeV, and (iii) above 10 TeV (up to and beyond 100 TeV). I will discuss also the expected performance and potential of future arrays of Imaging Atmospheric Cherenkov telescopes in the context of several hot topics with emphasis on the Physics and Astrophysics of Relativistic flows (in Pulsars, Microquasars and AGN), Origin of Galactic and Extragalactic Cosmic Rays, and Observational Cosmology.

The light of the night sky (LONS) is a strong background for Atmospheric Air Cherenkov Telescopes (ACTs). The gamma ray pulses being very short, an ultra- fast read-out of an ACT can minimize the influence of the LONS. This allows one to lower the so-called tail cuts of the shower image and the analysis energy threshold. It could also help to suppress other unwanted backgrounds. Fast 'flash' analog-to-digital converters (FADCs) with GSamples/s are available commercially; they are, however, very expensive and power consuming. Here we present a novel technique of Fiber-Optic Multiplexing which uses a single 2 GSamples/s FADC to digitize 16 read-out channels consecutively. The analog signals are delayed by using optical fibers. The multiplexed (MUX) FADC read-out reduces the cost by about 85\% compared to using one ultra-fast FADC per read-out channel. The ultra-fast read-out system will be described and the prototype test results will be reported. The new system will be implemented for the read-out of the 17~m diameter MAGIC telescope camera.

The High Energy Stereoscopic System (H.E.S.S) is an array of four imaging atmospheric-Cherenkov telescopes located in the Khomas Highlands of Namibia (23$^{\circ}$ 16' 18'' S, 16$^{\circ}$ 30' 1'' E, 1835 m above sea level). H.E.S.S. is the currently the most sensitive detector of VHE photons, with the ability to detect a 1\% Crab flux source in $\sim$25 hours of observation. H.E.S.S. has published the detection of numerous sources of astrophysical gamma-ray emission. The technique used by H.E.S.S. in these publications for rejecting the much more numerous cosmic-ray background and determining the spectrum of the detected sources will be presented.

Four years of AMANDA data have been searched for neutrino signals from steady or flaring point sources. No statistically significant excess of events - neither in the steady point source search nor in the various flare searches - has been detected. However, we observed one suggestive coincidence of neutrino events with gamma flares observed from the AGN 1ES1959+650. The statistical significance of the coincidence cannot be evaluated, because it corresponds to an a-posteriori hypothesis. Nevertheless, the observation provides a strong motivation for improved search stragegies with Amanda as well with its successor IceCube, and for more extensive and multidisciplinary investigations of the phenomenology of this and other gamma sources.

To keep the total weight of the 17m reflector-dish of the MAGIC telescope as low as possible, the structure is not very rigid. Since high reflectivity and good focusing is very important to reach low energy threshold, it is therefore important to realign the individual mirror panels for different telescope orientations. In MAGIC, this is achieved by equipping each of the 247 individual segments with stepping motors, controlled by dedicated electronics. We will explain the implementation and operation of the 'Active Mirror Control' of MAGIC and present some experience gained during the commissioning phase. Additionally, we will present the improvements going to be implemented in the MAGIC-II telescope.

The observation results of point source Cygnus X-3 by mirror Cherenkov telescope SHALON are presented. The galactic source Cygnus X-3, known more than 10 years as a source with variable intensity $le10^{-11}- 5\bullet10^{-12}cm^{- 2}s^{-1}$, was regularly observed since a 1995 with average gamma-quantum flux $F(E_O>0,8 TeV)=(6.8\pm0.7)\bullet10^{-13}cm^{-2}s^{-1}$. The results of observational data processing are integral spectra, temporary analysis of the events, coming from source and background events, obtained simultaneously with observation of source, and source image. The energy spectrum of Cygnus X-3 at 0.8 - 65 TeV $F(>E_0)\sim E_k^ã$ , where $k_ã=-1.21\pm0.05$ is obtained for the first time with flux on the order the less than upper limits published before. The spectrum of events passing through distinguishing criteria with background $k_{on}=-1.33\pm0.05$ and spectrum of background events observed simultaneously with source $koff=-1.74\pm0.05$ are shown in comparison. The flux in 2003 year is $(1.79\pm0.33)\bullet10^{-12}cm^{-2}s^{-1}$. The indexes of integral spectra are $k_\gamma=-1.28\pm0.06$, $k_{on}=-1.65\pm0.11$, $k_{off} =- 1.74\pm0.11$, accordingly. Earlier, in 1997, increase of flux was also observed $(1.2\pm0.5)\bullet10^{-12}cm^{-2}s^{-1}$. Thus, among ten observable gamma- quantum objects, there is galactic source Cygnus X-3, with periodic change of intensity.

Microquasars present emission over the whole spectrum, from radio wavelengths to gamma-rays. The microquasar spectral energy distribution is very complex, being a signature of the different physical processes that generate the radiation emitted by these objects. Nevertheless, if a relativistic population of protons is there, the expected hadronic content of the jets could interact further away with high density regions of the ISM producing a non negligible amount of broad-band emission. In this talk, I will show that, within the EGRET error boxes, a two components source, the microquasar itself and the region of interaction between the jets and the ISM, could be unveiled by the new instruments at high-energy and very high-energy gamma-rays.

The CELESTE atmospheric Cherenkov detector ran until June 2004 at the Thémis solar facility. Data from the blazar Mrk 501 was recorded in 2000 and 2001 and a 2.5 sigma excess was obtained (1). Improvements of the detector simulation and data analysis confirm the previous result, with smaller uncertainties. We present the evidence for a weak signal from Mrk 501 in 2000 and calculate a flux. (1) R. Le Gallou, "Mesure du flux du blazar Mrk 421 au-dessus de 60 GeV avec l'expérience CELESTE", Ph.D. thesis, 2001.

Motivated by the scientific objective of improving sensitivity for transient sources as cosmological distances, we describe a number of different design concepts for future arrays of large-aperture Atmospheric Cherenkov telescopes. In particular, we discuss tradeoffs in different optical and detector designs, and give approximate scaling laws for the expected detector performance. We present, in detail, ray-tracing simulations of a wide-field modified Ritchie-Chretien Cassegrain design and discuss a novel digital photon-counting approach (dubbed STAR) for synthesizing a large detector aperture out of a number of smaller dishes. We complement the discussion of telescope designs with a report on recent progress in the field of detector development that might provide energy thresholds of tens of GeV with 10m class telescopes. To this end we present work at Washington University on the development of solid state photocathode devices consisting of atomically tailored AlGaN/InGaN structures grown on sapphire by molecular beam epitaxy. We have achieved 40% QE at 250 nm for a transmission mode cathode (comparable to the best results previously obtained for GaN) and have demonstrated improved long-wavelength response out to 400 nm by alloying devices with InGaN.

We present a novel mirror design for use on ground-based Cherenkov telescopes. These mirrors are made from an aluminium honeycomb construction with a highly reflective surface which is particularly suited to the Cherenkov spectrum. These mirrors are manufactured in Durham, UK and have many advantages over currently available alternatives.

I will review the current expectations for very high gamma-ray emission from AGN, blazars, and microquasars. I will discuss the optimal observing strategies for constraining the emission models for these objects.

The detection of unpulsed emission from a number of pulsar wind nebulae (or plerions) in the TeV range have been predicted. A number of plerions have been detected in the TeV range, which allows us to test fundamental pulsar physics models, as well as MHD aspects, which give rise to the extended nature as observed. Even the detection of variable TeV emission from the dynamic plerion in the binary system of PSR B1259-63 allow us to probe conditions on small scale sizes and the properties of the main sequence star companion. The pair production threshold in the magnetospheres of canonical pulsars shift the cutoff energy below the threshold energy of current ground-based Atmospheric Cerenkov telescopes. Next generation telescopes with a factor ten lower threshold energy should however see a significant fraction of radio pulsars, which will allow us to probe the shape of the spectral cutoffs, complementary to AGILE and GLAST. The limited range in the (P,Pdot) parameter space, accesible for current telescopes, will be reported at this meeting.

With the next generation of Atmospheric Cerenkov Telescopes (ACT) well on their way, effort has being shifted now towards a further improvement of the capabilities of these instruments. These next generation experiments have improved up to an order of magnitude their sensitivity over their first generation counterparts, and effort has been concentrated in extending the energy coverage down to about 50 GeV. However, it is not clear whether the same approach is optimal for energies above 1 TeV, and with clear evidence of high energy emission above this energy from several astrophysical sources, we believe that this energy range could be further exploited. Many of our physics goals, such as, limits on quantum gravity, origin of gamma-ray emission in SNRs or spectral variability and features of the high energy emission from AGNs, would benefit from an increase of sensitivity in this direction. Here, we investigate a possible way of increasing the collection area of ACTs above 1 TeV by using a wide-field-of-view (~10 deg) camera. Both, the scientific motivation and the results of Monte Carlo studies of the performance of such a detector, will be discussed.

The next generation of Cherenkov telescopes with its new elaborate techniques and larger size will provide huge amounts of interesting data. To provide a stable analysis of all this data an automatic dataprocessing is essential. For MAGIC such a concept has already been realised. An automatic, failsafe preprocessing of all data is ensured. The status of the analysis can be queried at any time from a database. The flexibility of the concept makes it easy to add new steps at any point of the analysis chain.

To be decided.

The calibration system of the MAGIC telescope is presented, consisting in three methods for the absolute light calibration: The application of the F-Factor method, three obscured photo-multipliers and a calibrated PIN-Diode. Results of the performance of the calibration system, based on data taken during the last year are presented.

The absolute overall light collection efficiency of the MAGIC telescope can be calibrated using isolated muons hitting the reflector. The geometry and the energy of the muons are reconstructed from the measured ring images and compared with Monte Carlo predictions. The amount of Cherenkov light produced by muons can be modeled with small systematic uncertainties. Muon images are recorded during normal observation. A continuous calibration can therefore be performed with no need for dedicated calibration runs. In addition the width of the muon ring images can be used to monitor the spot size of the reflector during normal data taking.

The HESS-2 front-end electronics, with its 20 GeV energy threshold, will require a much higher acquisition rate capability and a larger dynamic range than was relevant for HESS-1. These constraints led to the development of a new ASIC, called SAM for Swift Analog Memory, to replace the ARS used for HESS-1. The SAM chip features 2 channels for the low/high gain outputs of a PMT, each channel having a depth of 256 analog memory cells. The sampling frequency is adjustable from 0.7GS/s up to 2GS/s and the read-out time for one event is decreased from 275 microsecs down to 2.3 microsecs. The input bandwidth and dynamic range are increased up to 300 MHz and 12 bits respectively. We expect that ADC's will be ultimately implemented on the chip. The first prototypes of the SAM chips have been produced and are under testing.

The comparison of HI, CO, dust, and gamma-ray maps in the solar neighbourhood has led to the discovery of large amounts of dark gas, located at the interface between the HI and CO phases, but not properly traced in the HI and CO emission maps. The local measurements imply a total dark-gas mass in the Milky Way at least comparable to that detected in CO. The mass and structure of the local dark clouds imply severe revisions of the interstellar emission model to high latitudes, therefore on the EGRET source detectability across the sky. Preliminary revisions of the EGRET source catalogue will be discussed.

A number of rotation-powered millisecond pulsars are powerful sources of high-energy emission, detected so far at X-ray wavelengths. We present predictions for the spectral characteristics of these sources at gamma-ray energies, using a model for acceleration and pair cascades on open magnetic field lines above the polar caps. Although these pulsars have low surface magnetic fields, their short periods allow them to have large magnetospheric potential drops, but the majority do not produce sufficient pairs to completely screen the accelerating electric field. In these sources, the primary and secondary electrons continue to accelerate to high altitude and their Lorentz factors are limited by curvature and synchrotron radiation reaction. The resulting radiation above 1 GeV comes from curvature radiation by primary electrons with radiation-reaction-limited Lorentz factors. The spectra are very hard power-laws with exponential cutoffs between 1 and 50 GeV, and the spectral power peaks near the cutoff energy. Millisecond pulsars are thus ideal targets for air-Cherenkov detectors that are able to reach energy thresholds below 50 GeV.

The 17 m diameter MAGIC-I Cherenkov Telescope has been in operation with the low trigger threshold of about 30 GeV for cosmic gamma rays. In order to access even a lower energy in the MAGIC-II project with a second 17 m telescope, the Hybrid Photon Detector (HPD) has been developed over several years in the collaboration with Hamamatsu Photonics. The new prototype of HPD has a GaAsP photocathode of 18 mm diameter. The QE reaches about 50 % at the peak wavelength of around 500 nm. Using a wavelength shifter coating allows enhancing the UV-sensitivity. Application of these HPDs can be seen as an equivalent increase of the reflector diameter of MAGIC from 17 m to 24 m. Our simulation result indicate that the GaAsP photocathode is expected to have a sufficiently long lifetime to survive adverse starlight and night sky background light for long term operation. In this presentaion, we'll report on the performance of this type of HPDs for MAGIC-II.

Technical developments in ground based gamma-ray astronomy aim towards two main goals: lowering the energy threshold of Cherenkov telescope systems down to about 5 GeV and increasing the field of view of the experiments to cover larger fractions of the sky. In both cases cameras are needed which can deal with event rates of ~10 kHz with negligible dead-time and which provide good background suppression already at the trigger level. In order to be able to build cameras with several thousand pixels,the cost per channel must be minimized. The design of the Smart Pixel Camera, which is under development at the MPIK, fullfills these requirements. It incorporates a next neighbor trigger, highly multiplexed signal digitization and buffered readout of the data. We present the concept of the camera, and show first tests of a prototype.

I present an outline of several background modelling techniques used currently for HESS but also appropriate for future telescope arrays. The importance of accurate background modelling for spectral and morphological analyses is discussed. The choice of background model impacts on the observational strategy of an instrument and the sensitivity ultimately achieved.

For the future evolution of Cherenkov instruments, it is important to know the fundamental limits of such instruments. In simulations, the performance limits were studied assuming that direction and impact point of a major fraction of all photons reaching the ground are measured, and the variation of characteristics with the fraction of photons detected was studied. (Short contribution, ~ 10 min)

In 1974, the Narrabri intensity interferometer was used to measure 32 stellar diameters as small as 0.4 milli-arc-seconds (mas). The interferometer consisted of a pair of 7m telescopes similar to those used nowadays as Atmospheric Cherenkov imaging Telescopes (ACT). We explore the possibility of implementing a modern intensity interferometer on an ACT array. Developments in fast digital signal processing technology now make such a system easy to implement, as well as improving the sensitivity. Allowing measurements at short wavelength (<400nm) with long baselines (~100m) that are very challenging for Michelson interferometry, they could be used to measure stellar diameters and possibly reveal stellar surface features as small as 0.2 mas with present arrays, and smaller if large ACT arrays were constructed in the future. Such a project could operate during bright moon periods, providing valuable scientific output for very little expense and no impact on the gamma-ray observing schedule.

The current generation of Cherenkov telescopes have typically mirror collection areas of 100-200 sqm and operate at 2000 m above sea level. In this contribution, a system of 5 comparably small (35 sqm mirror area) Cherenkov telescopes at an high altitude site (4300 m a.s.l.) is studied with detailed Monte Carlo simulations. The performance in terms of energy threshold (150 GeV) and sensitivity is improved by the high altitude site. A system of telescopes of this size is inexpensive and competitive with current telescopes for point like sources. Furthermore, it could serve as a prototype for future large Cherenkov telescopes at high altitude sites.

We discuss a possible next generation Cherenkov telescope experiment consisting of between 2 and 4 telescopes each with an effective mirror area of ~300m^2 diameter and ~1500 m^2. We propose to build each of these large telescopes from a large number of small ~2.5 m diameter telescopes, a so-called Small Telescope ARray (STAR). Each small telescope is equipped with a full camera, and the signals from the small telescopes are combined before the trigger of a large telescope is derived and before the signals are digitized. In this contribution, we discuss general advantages and disadvantages of the STAR approach and present first results of Monte Carlo simulations.

Recent IACT measurements have indicated new classes of point source emission of GeV/TeV gamma rays at the 10 millicrab level and below; but progress on measurement of extended gamma sources (extent > several degrees) has been substantially slower. For highly extended sources, such as the galactic plane, or molecular clouds, high angular resultion may be less important than total number of hours of observation, thereby giving discovery advantage to wide fov instruments such as Tibet, Milagro/HAWC. In this talk I will discuss the tradeoffs between using IACT and wide fov techniques for large fov imaging and the discovery potential for each technique as a function of source dimension. Consideration of background esimation will be presented. I will describe some alternate classes of next generation IACT detectors that would be specifically designed to provide wide fov survey coverage for extended gamma ray sources and compare these approaches with wide fov, non-IACT techniques.

The construction of H.E.S.S., which is a superior system of four 12 m imaging atmospheric Cherenkov telescopes, has been completed recently in Namib desert. This ground-based gamma-ray detector of a new generation has an energy threshold around 100 GeV and sensitivity of about 1% Crab flux. Similar stereoscopic arrays are currently under construction at Kitt Peak, Arizona, and at Woomera, Australia. Two telescopes of somewhat larger size of 17 m diameter are being built by the MAGIC collaboration at Canary Island of La Palma. First such telescope has been taken data since fall 2003. Development of further instrumentation is primarily motivated by the various physics goals perceived by the astrophysics community nowadays. Ultimately, a design of a major ground-based Cherenkov facility for future dedicated gamma-ray observations has to conform to many requirements provided to tweak the observations to the expected gamma-ray fluxes from the objects of entirely different nature. A stereo array of 30 m imaging atmospheric Cherenkov telescope is such a detector, which may allow to achieve an energy threshold as low as 10-20 GeV given a unique sensitivity of about $10^{-13}\,\,\rm erg\, cm^{-2}\, s^{-1}$, with a dynamic energy range expanding up to a few TeV. Basic results on performance and sensitivity for a single stand-alone 30 m Cherenkov telescope, as well as for a system of two and five of such telescopes, derived from the Monte Carlo simulations, will be summarized.

As Grid technology is fast evolving, the new field of e-science offers new perspectives for reseachers in many application domains.Grids at production level are used in high energy physics and in astronomy already. The general ideas of e-science and grid technology will be presented and benefits for ground based VHE gamma ray astronomy will be discussed. The architecture of a distributed Grid based Monte Carlo production system for the MAGIC telescope will be shown. A report about the first experience with the prototype system will be presented. An outlook towards a virtual observatory for ground based gamma ray telescopes will be given.

A new large area(21m diameter) imaging gamma ray telescope is being set up at the high altitude (4200m asl) location at Hanle in the ladakh region of North India. The imaging camera of the telescope will have a resolution of 0.1 deg and a full field of view of 4deg. Preliminary simulation studies show that the high altitude location of the telescope will help substantially in lowering its threshold energy to beloe 20GeV for vertically incident gamma rays. Although a single large telescope has some drawbacks in terms of less sensitivity and poor angular and energy resolution in comparision to a sterioscopic system, the main aim of setting up this telescope is to cover the unexplored energy window in the 20-200 GeV energy band. The overall design concept and implementation details of the telescope will be presented in the paper

The potential detection of gamma ray bursts with wide field of view air Cherenkov telescopes could be achieved with two different shower detection techniques outlined in this paper. The first one relies on the sensitivity of the imaging Cherenkov technique to individual gamma rays and is limited to primary energies above at least 5 - 10s of GeV. The second technique is based on the detection of the accumulative Cherenkov light from a short burst of gamma rays. In this case, the energy threshold is 200 MeV. We discuss the sensitivity of next generation imaging Cherenkov telescopes employing wide field of view cameras for both detection techniques. In particular we discuss the science potential for moderate to large size telescopes.

A number of atmospheric monitoring devices are being used at the H.E.S.S. site in Namibia. Our setup includes an automated weather station, paraxially aligned infrared radiometers, a ceilometer -- a LIDAR with built-in atmospheric data reduction code -- and since January 2005 a multi-wavelength transmissometer. While radiometers are sensitive to water vapour and droplets crossing the telescope field of view, the ceilometer is used in conjunction with the transmissometer to estimate the extinction of the Cherenkov light above the site. Results from these instruments will be presented here.

Systems Development & Solutions (S.D.S.) is a long-established designer and manufacturer of High Voltage Power Supplies for laboratory applications and instrument manufacture. In France, the company is the only one to reach our level of miniaturization, while guaranteeing high regulation and low residual ondulation. S.D.S. is dedicated to the provision of customised solutions for specific needs from the one-of-a-kind made-to-measure unit for the research or development laboratory to the cost-effective fulfilment of production orders for equipment manufacturers or in physics facilities requiring high voltage supplies. Its range of products covers a large voltage scale from 600V to 50kV with a maximum power of 500W. In addition to its power conversion modules, S.D.S. manufactures devices for electro-optical commutation, radiation probe including their own high voltage power supply and the command & control boards able to drive such devices. Those boards can be used through serial ports or field buses.

I want to give two talks : 1. 3D-Reconstruction of gamma-ray showers with a stereoscopic system : Gamma-ray showers are characterised by two simple properties : rotational symmetry with respect to the axis and relatively small lateral spread. These properties are used in the framework of a simple 3D-model to provide an efficient discrimination from hadronic showers. The performance of the method will be presented. 2. A new method of background subtraction adapted to the study of extended sources : A method is presented which allows to produce separate skymaps for gamma-ray origins and for those of hadronic events without making any assumption on the morphology of the source. It is based on the different distributions of the lateral spreads of gamma-rays and hadrons as reconstructed by the preceding 3D-model. The method is applied to HESS data on the Supernova Remnant RXJ1713.7-3946.

After the inauguration, and a first phase of commissioning and tuning, Magic has started to operate in a standard way since fall 2004. The basic performances of the telescope have been studied with known sources, and data from several other sources are under analysis. Magic is at present the largest Telescope in the world with the lowest energy threshold. Several technological innovation have been used in the construction of the instrument and now are functional for the first time in a Cherenkov Telescope. The currently achieved performance of the telescope will be reported. Preliminary results on a few observed sources will be presented.

CACTUS is a ground-based ACT at the Solar 2 facility located near Barstow, California. It uses an array of 160 large solar tracking mirrors (heliostats) and a camera with 80 photomultiplier tubes to collect atmospheric Cherenkov radiation produced by intermediate energy air showers. CACTUS has incorporated novel techniques of time projection imaging and triggering to improve upon the first generation sampling arrays of its kind. We will present results from our February and March campaigns on the Crab and Mk421 where we observed excesses at high data rates, indicating a low energy threshold. We will also present preliminary results on a search for high energy emissions from the Geminga pulsar. Analysis methods and a preliminary extraction of the Crab energy spectrum will also be presented.

One of the more notable features of the Large Area Telescope (LAT) on GLAST is its extremely large field of view, which covers more than 20% of the sky at any instant. In survey mode the LAT will be rocked about the orbital plane to provide coverage of the entire gamma-ray sky above 20 MeV every three hours. This will be the default observing mode for the first year of operations and is likely to be the dominant observing mode throughout the rest of the mission. Thus the LAT will provide long, evenly sampled, gamma-ray lightcurves over a broad energy range (20 MeV to >300 GeV) for a large number of sources. In this talk we describe the nature and quality of the data that will be provided by the LAT and use simulations to illustrate some of the scientific questions that can be addressed with LAT observations.

Triggers from the so-called single muon events are an unwanted background for atmospheric air Cherenkov telescopes, degrading their sensitivity. That background is becoming intense when lowering the threshold of telescopes below a few hundred GeV energy domain. From general considerations one can anticipate that the arrival time profile of photons from muons shall have a narrow structure. In fact, our simulations show that light pulses from muons have very narrow time signature that is well below the time resolutions of most currently operating telescopes. In this report we elaborate on the triggers from muons and show that a telescope with ultra-fast time response can open a new dimension in tagging and rejecting muon events.

The MAGIC Telescope, now taking data with an energy threshold well below 100 GeV, will soon be able to take full advantage of its fast slewing capability. Exploiting the link with the GCN network, the MAGIC Telescope could be one of the first ground-based experiments able to see the prompt emission of Gamma Ray Bursts in the few tens of GeV region.

The CANGAROO-III atmospheric Cherenkov telescope array has been in operation since 2004 March in Woomera, South Australia, in international collaboration of Japanese and Australian institutions. The array consists of four 10m telescopes set at corners of a diamond shape of about 100m side. Southern celestial objects, mainly Galactic objects such as supernova remnants, have been observed in stereo mode to detect gamma-rays above a few hundred GeV. The outline of the experiment and recent results are presented.

We explore the possible direct and indirect links of the TeV signal from the Galactic Center to the supermassive black hole (SMBH). We show that at least three gamma-ray production scenarios that take place close to the event horizon of the SMBH can explain the reported TeV fluxes. An alternative (or additional) channel of TeV radiation is related to the run-away protons accelerated in Sgr~A*. Quasi-continuous injection of relativistic protons into the surrounding dense gas environment initiates detectable high energy gamma-ray emission. The absolute flux and the energy spectrum of this radiation component strongly depend on the history of particle injection and the character of diffusion of protons during the last $10^5$ years. For a reasonable combination of a few model parameters, one can explain the detected gamma-ray flux solely by this diffuse component.

Pulsed emission from a number of gamma-ray pulsars is expected to be detectable with next generation ground-based gamma-ray telescopes such as MAGIC within a few hours of observation. The sensitivity is however not sufficient to enable a detection within a few seconds as reached by radio surveys. In some cases we may be fortunate to do a period search given a few hours's data, but if the signal is marginal, the correct period parameters must be known to allow a folding of the gamma-ray arrival times. The residual phases are then subjected to a test for uniformity from which the significance of a signal can be assessed. If contemporary radio parameters are not available, we have to extrapolate archival radio parameters to the observation time in question. Such an extrapolation must then be accurate enough to avoid significant pulse smearing. We apply this periodicity searching to the millisecond pulsar PSR B1957+20.

Up to now all major high energy astrophysics experiment use conventional bialkali photomultiplier (PMTs) as photon detectors with all the disadvantages. Since a few years mainly Russian groups are developing a novel sensor to detect photons in the visible spectrum. These so-called silicon photomultipliers operate at low bias (<100 V), show large gain (10**5-10**6), are completely insensitive to magnetic fields, are extremely fast (order subnsec pulses for single photoelectrons) and are very compact. They are not damaged by prolonged exposure to ambient light. At this development stage their photon detection efficiencies (PDE) approaches that of bialkali PMTs. Two deficiencies are the high noise rate and the recovery time of cells (order 0.1-1 microsec). Current developments aim for a peak PDE around 40%, an extended UV sensitivity, significant noise reduction and reduced recovery time, thus promizing another significant improvement in light detection for IACTs. We are developing SiPMs for the experiments MAGIC and EUSO. In one project we advance existing SiPM prototypes in collaboration with MEPhI and PULSAR in Moscow. In another study we develop in collaboration with the semiconductor laboratory (HLL) attached to MPI für Physik a backilluminated version of a SiPM. The working principle and features of the SiPM and the status of the projects will be presented.

Not yet available

The best detector in Atmospheric Cerenkov experiments still remains the PM tube, thanks to its characteristics of sensitivity and speed. But its disadvantages are its low quantum efficiency and its cost. We are currently exploring the field of solid state silicon detectors, used in the Geiger photon counter mode. We have conducted a series of tests using standard APD, but with an electronic circuitry to rise the polarisation towards the Geiger mode. Thus, we have measured gains around 10 E+4. With our current developments, both in command circuitry and in the geometry of the photodetector itself, we should reach values such as 10 E+6 or more for the gain and 80 percent for the quantum efficiency. As the photodiode is polarized over its own breakdown bias, a single photon passing through it may start an electron avalanche resulting in about 10 E+6 electrons collected. After that, the diode should recover as soon as possible to be available for the next photon. This process is under modelling: electrical diagrams (PSPICE), differential equations (VHDL AMS) and components physics equations (SABER) are needed to reproduce closely the physical processes and to allow optimisation and improvement of the electronics both for triggering and for reading the detectors. Our most promising results will be presented, under both aspects: simulation of expected response and design of the Si detector component itself.

The MAGIC Collaboration is operating the Cherenkov telescope with the largest reflecting surface, in order to lower the energy threshold well below 100 GeV. The MAGIC Telescope has a 17 m diameter parabolic surface F/1, consisting of 964 spherical aluminium mirrors, each 50-cm square in size. In this contribution, we describe the technology used for the production of the mirrors and the methods used to measure the optical quality in terms of: reflectivity, roughness factor, radius of curvature and overall geometry. We present also a new technology, that producing pre-shaped panels, will yield lighter mirrors and requires even less machining times than the current one. The new technology can also be applied to make bigger mirrors with ~1 m of side.

I discuss the proposal of an improvement to the standard Imaging Air Cherenkov Telescope (IACT) observing technique. Generalizing the traditional concept of taking on-source/off-source observations of equal duration (e.g. 30 minutes ON followed by 30 minutes OFF), the Faster Background Determination (FBD) method permits an off-source observation with the same zenith angle distribution as the on-source observation to be obtained within less time. The on-source observation time can be maximized without compromising the quality of the background determination. The method also increases the signal significance for strong sources without introducing additional systematic errors. Even for IACTs with large field of view, the FBD method may be superior to the now common "Wobble Mode" technique when observing extended sources.

CELESTE is a gamma-ray atmospheric Cherenkov telescope with an energy threshold below 100 GeV. We performed the analysis of some OFF-source data from this experiment in a view of detecting galactic diffuse gamma-rays and electrons in this energy range. Since models and extrapolations from fluxes measured at lower energies predict a rather low signal, we developed a new analysis method based on composed discriminant variables. It aims to improve the sensitivity of the instrument, which is limited by the hadronic background coming from the showers induced by cosmic protons and ions. A large set of Monte-Carlo simulations has been used to identify signature of the different particles triggering the detector. We present the results so far obtained from this on-going study and future expected developments.

Broadband observations of targets that are studied with VHE instruments are an inevitable part of any VHE physics program. Potential VHE sources are monitored e.g. in X-rays, and are observed by VHE instruments when the sources become active. Coordinated broadband observations of variable objects such as TeV blazars are regularly performed across all wavebands, to obtain time-resolved broadband spectral energy distributions. Follow-up observations of sources that are newly detected in the VHE band are required to pin down the nature of these objects. We describe the multifrequency program that is carried out by the H.E.S.S. collaboration and encompasses all these aspects, and discuss future broadband opportunities.

We present a study of the sensitivity of the MAGIC telescope for extended field of view observations. The results presented have been obtained for Crab data on and off the telescope axis, for several different positions of the source in the FOV. The source position is reconstructed for every image using the DISP method. The results are compared with the Monte Carlo simulations. This study allows us to assess the capabilities of MAGIC to perform sky scans.

If dark matter is made of neutralinos, annihilation of such Majorana particles in the halos of galaxies should produce high energy cosmic rays in high density regions, like the centres of galaxies. M31 (Andromeda) is the nearest neighbour spiral galaxy, and both its high mass and its low distance make it a source of interest for the indirect search for dark matter through gamma-ray detection. The ground based atmospheric Cherenkov telescope CELESTE has been observing M31 for the last 3 years, in the energy range 50-1000 GeV. These observations provide a limit on the predicted flux above 50 GeV in the frame of supersymmetric Dark Matter, and more generally on any gamma emission from M31.

Created in Lebedev Physical Institute and installed 1991-1992 in ALATOO mountains at 3338m high, the mirror telescope SHALON during 1992-2004 was used for observation of metagalactic sources Mkn421, Mkn501, NGC1275, 3c454.3, 1739+522 and galactic sources Crab Nebula, Cygnus X-3, Tycho's SNR, Geminga, 2129+47XR. The new metagalactic sources of gamma-quanta with energy of more than 0.8TeV are detected. It is the Seyfert galaxy NGC1275 with flux of $(0.78 \pm0.13)\bullet10^{-12}cm^{-2}s^{-1}$, as well active galactic nuclei 3c454.3 and 1739+522 (z=0.859 and z=1.375) with flux of $(0.43\pm0.13)\bullet10^{-12}cm^ {-2}s^{-1}$ and $(0.53\pm0.10)\bullet10^{-12}cm^{-2}s^{-1}$ accordingly. The most far metagalactic source 1739+522 with red shift of z=1.375 is also most powerful. But the spectral distribution of emmiting gamma-quanta differs from average on other known distant metagalactic sources - quasars $F(>E_0)\sim E^k$: Mkn 421 (z=0.031) $k_ã=-1.53\pm0.41$, $k_{on}=-1.46\pm0.06$, $k_{off}=- 1.75\pm0.06$; Mkn 501 (z=0.034) $k_ã=-1.89\pm0.11$, $k_{on}=-1.83\pm0.06$, $k_ {off}=-1.72\pm0.06$; 1739+522 (z=1.375) $k_ã=-1.10\pm0.06$, $k_{on}=-1.38\pm0.07 $, $k_{off}=-1.72\pm0.08$. Thus, the energy spectrum of metagalactic sources quasars Mkn421, Mkn501 at range $10^{12} - 10^{13}$ eV differs from spectra of far quasars 1739+522 and 3c454.3 that don't contradict to united energy spectrum $F(>E_ã) \sim E_ã^{-1.2\pm0.1$.

The cosmological processes, connecting the physics of matter in active galactic nuclei will be observed in the energy spectrum of electromagnetic radiation or, perhaps, in very high energy neutrino flux. The observation has been carried out since 1992 at high mountainous Tien -Shan station with SHALON Cherenkov mirror telescope with $\sim 11.2 m^2$ mirror area and image matrix of 144 PMT with full angle $>8^o$. The telescope characteristics permited to start the search of local neutrino sources with energy $10^{13} - 10^{16}$ eV on EAS generating in mountain-range located at some 7.5 and more kilometers from gamma- telescope (in Russian the abbreviation SHALON means - the Extensive Air Showers from Neutrino). The analysis of results of observation of extensive air showers at height of 3338 m above the sea level by means of gamma-telescope SHALON at the zenith angles $72^o$, $76^o$, $84^o$, $97^o$ are presented and compared with the data of detection of showers according to the direction into the zenith. The analysis of 200 hours of SHALON observation of Cherenlov bursts at angle of $97^o$ results in 4 events from possible source that may be interpreted as Extensive Air Showers from neutrino interaction products. So, at energy range of $10^{13} - 10^{16}$ eV the flux of neutrino from source $10^{- 14} cm^{-2}s^{-1}$ is obtained, that according with the theoretical expected flux.

The HAWC collaboration is currently developing a design for a High Altitude Water Cherenkov air-shower array to be constructed at a high altitude site. The HAWC detector will have sensitivity similar to first Generation ACTs for VHE point source detections (~5-7 sigma/hr for the Crab), but operate continuously with a 2 steradians aperture making it ideally suited for detection of diffuse VHE sources as well as prompt emission from GRBs. In order to better understand the engineering and operational challenges of the HAWC instrument, miniHAWC has been developed as a low cost proof of concept. miniHAWC will utilize the PMT's and DAQ electronics from the Milagro experiment. The equipment will be redeployed at a high altitude site. The increased altitude along with design changes to the pond layout will result in a greatly increased sensitivity and a lower energy threshold compared to Milagro. Initial simulations indicate that a point source sensitivity ~10 times greater than Milagro is expected, sufficient to detect (5 sigma) all transiting sources brighter than ~70 mCrab in a year of operation. If a suitable site is identified, relocation of the Milagro electronics could take place as soon as 2006.

For several years the only experiments sensitive to astrophysical gamma rays with energies beyond the reach of EGRET but below that of the Cherenkov imaging telescopes were the "solar tower" detectors. They use ~2000 m2 mirror areas to sample the Cherenkov wavefront generated by ~100 GeV gamma rays, obtaining Crab sensitivities of more than 5 sigma in one ON-source hour. I will review the history of the solar tower Cherenkov experiments from 1992 to the present and their key design features. I will describe some succesful analysis strategies, then summarize the principal results obtained. I will attempt to analyse the lessons learned.

The MAGIC is the world largest ground based gamma ray telescope, which has been in the scientific operation since summer of 2004. The major motivation of the MAGIC project is to study the high energy phenomena in the universe in the unexplored energy region between 10GeV and 300GeV. MAGIC-II; two 17m telescope system with advanced photon detectors is designed to lower the threshold energy further and simultaneously to achieve higher sensitivity in the stereoscopic / coincidence operational mode. The design and the performance of MAGIC-II will be discussed in detail. The construction of the second telescope will be completed in 2007 in order to enable the simultaneous observations with gamma ray satellite missions GLAST and AGILE with the best sensitivity so far not-achieved by ground based gamma ray telescopes. At the end of the talk, the future vision beyond MAGIC-II will be also discussed.

The recent results from the H.E.S.S. experiment demonstrate that Cherenkov Astronomy is entering a new era. The sensitivity and accuracy of the H.E.S.S. telescopes allows for a precise study of many astrophysical sources above 100GeV. In the second phase of the experiment an extension of the energy range to lower energies and an improvement of the sensitivity of the current H.E.S.S. system above 100GeV is planned. To achieve these goals, we will build a very large Cherenkov telescope (28m diameter) in the center of the current system of four Cherenkov telescopes. Depending on the trigger conditions, the trigger rate of this telescope is expected to reach two to several tens kHz. In order to keep the acquisition rate below a certain level (approx. 3kHz), a second level trigger is planned. The concepts and first estimations (based on simulations) of the efficiency of such a second level trigger will be presented.

We present a low power sampling system for data read out of camera signals based on the Domino chip. The chip has been developed in PSI (Paul Shrerrer Institute) in Switzerland, has 10 input channels with the capability to sample signals from 1.5 GHz up to 4 GHz. The principle of working of the chip is based on a ring array of 1024 capacitors written in sequence by a writing strobe that circle at a speed that is controlled by an external PLL. The chip now is at his second revision, DRSII, and it is forseen a third revision in the next future with more advanced features to reduce intrinsic dead time. The read out system developed in Siena University is based on a 9 VME unit carrier board, called Pulsar, that hosts four domino mezzanine with 8 channels plus trigger each, for a total of 32 input channels plus 4 trigger. The data recorded by the pulsar is sent to a DAQ PC trough a fast serial “S-link” developed at CERN for LHC experiments.

Driven by the science motivations of observing cosmologically distant transient phenomena with sub-minute time resolution, we define the parameters of a ground based observatory utilizing the atmospheric Cherenkov technique. The instrument should operate in the 20-200 GeV energy range, have close to full sky coverage, and yet have a cost comparable to a modern satellite mission so that its construction is viable. The individual elements of the observatory, its concepts and technology, exist to some degree in the commercial and scientific worlds; we explore whether they can be assembled within the requirements of cost and science to be achieved.

The AMS02 detector will be installed at the beginning of 2008 on the International Space Station. Cosmic Ray studies, Antimatter and Dark Matter searches are the main physics topics to be covered by AMS. The Gamma Ray physics domain will be probed by measuring converted e+e- pairs in the Silicon Tracker, as well as single photons in the Electromagnetic Calorimeter. AMS-02 will provide precise gamma measurements in the GeV range, which are particularly relevant for Dark Matter searches. In addition, the good angular resolution and identification capabilities of the detector will allow clean studies of the main galactic and extra-galactic sources, as well as of GRBs.

(1) Institut für Theoretische Physik und Astronomie, Universität Würzburg, Am Hubland, D-97074 Würzburg (2) Max-Planck-Institut für Physik, Föhringer Ring 6, D-80805 München With the aim to reach lower energy thresholds the next generation of Cherenkov telescopes will become larger and heavier. Therefore more powerful drive systems will be needed. The scalable drive system of the MAGIC Telescope is suited to meet this challenge. With its servo motors and their master-slave setup it can easily be extended for larger telescopes and a pointing accuracy at least in the range of the shaft encoder steps is guaranteed. Bendings of the telescope can easily be corrected and fast slewing for Gamma Ray Burst follow-up is possible. 2nd abstract for a POSTER contribution: --------------------------------------- M. Lopez(1) and R. Wagner(2) on behalf of the MAGIC collaboration (1) Universidad Complutense de Madrid, Facultad de Ciencias Fisicas, Avd. Ciudad Universitaria S/N, E-28040 Madrid (2) Max-Planck-Institut für Physik, Föhringer Ring 6, D-80805 München The MAGIC telescope has become operational during the last year. Here we present the first results obtained from the observations of the Crab nebula. Special emphasis will be put on the new analysis methods used to achieve the first gamma signals below 100 GeV with a Cherenkov telescope.

VERITAS (Very Energetic Radiation Imaging Telescope Array System) is an array of four reflectors of 12 m aperture and focal length 12 m. Each reflector is equipped with a camera with 499 pixels; the cameras are characterized by FADCs operating at 500 MHz. The array will be located in Horseshoe Canyon on Kitt Peak (elevation: 1.8km) in southern Arizona. The first telescope has been completed and is in operation at a temporary site near Mount Hopkins. This telescope saw first gamma-ray light on February 1, 2005 with strong detections of the Crab Nebula and Markarian 421. The three remaining telescopes are under construction and will be on-site this summer; it is hoped to have all four telescopes in operation as an array by the end of the summer of 2006. ~

We have started discussions on beyond-CANGAROO projects among the Very High Energy (VHE) gamma-ray community in Japan. Three straightforward directions using the imaging atmospheric Cherenkov technique have been considered: 1) telescopes of a large aperture or at a high altitude to explore the so-called unopened window between 10 and 100 GeV, 2) telescopes of a wide field of view to discover transient sources and obtain better survey ability, and 3) telescopes of a large effective area to obtain better sensitivity or explore the higher energy region around 100 TeV. The considerations are summarized together with physics cases favored by each direction.