Michael Panter

Stereoscopic imaging of air showers with the first two HEGRA Cherenkov telescopes

Abstract With systems of atmospheric Cherenkov telescopes, providing stereo images of air showers, the shower parameters, such as the direction, core location, and height of shower maximum can be determined event by event. Techniques for the reconstruction of air showers are introduced, and are demonstrated using data from the first two HEGRA Cherenkov telescopes. Applied to observations of the Crab nebula, a clear signal is observed; the angular distribution of the excess events is consistent with Monte Carlo simulations of the expected resolution.

The Cosmic Ray Tracking (CRT) detector system

Abstract The Cosmic Ray Tracking (CRT) project represents a study on the use of tracking detectors of the time projection chamber type to detect secondary cosmic ray particles in extensive air showers. In reconstructing the arrival direction of the primary cosmic ray particles, the CRT detectors take advantage of the angular correlation of secondary particles with the cosmic rays leading to these air showers. In this paper, the detector hardware including the custom-designed electronics system is described in detail. A CRT detector module provides an active area of 2.5 m 2 and allows to measure track directions with a precision of 0.4°. It consists of two circular drift chambers of 1.8 m diameter with six sense wires each, and a 10cm thick iron plate between the two chambers. Each detector has a local electronics box with a readout, trigger, and monitoring system. The detectors can distinguish penetrating muons from other types of charged secondaries. A large detector array could be used to search for γ -ray point sources at energies above several TeV and for studies of the cosmic-ray composition. Ten detectors are in operation at the site of the HEGRA air shower array.

Operation and performance of the Cosmic Ray Tracking (CRT) detector system

Abstract The cosmic ray tracking (CRT) detectors consist of two drift chambers of the TPC type and an iron plate as a muon filter between the two chambers. CRT detectors are designed to detect and identify secondary cosmic ray particles in extensive air showers. Each detector has a local electronics box with a readout, trigger, and monitoring system. The local computers at the detector stations are used for hit and track finding in parallel to the detector readout. Detector stations are permanently calibrated online, using the cosmic ray data. The online software, including data processing and calibration procedures, are presented in this paper. Ten detectors are in operation at the site of the HEGRA air shower array. The detector performance has been evaluated using data from these detectors and the HEGRA array as well as by Monte Carlo simulations. The spatial resolution has been found to be about 1 mm both in drift and in wire direction. The corresponding angular resolution is about 0.4° in each projection for a single track. Muons are usually identified if scattered by less than 2.5° in the iron plate, corresponding to energies above about 1 GeV. In HEGRA-triggered showers an overall muon identification efficiency of 87% is achieved, with a fraction of only 0.07% of the electrons being misidentified as muons.

Spectral measurements of TeV γ-ray emission from Mkn501 and Mkn421 using the HEGRA stereoscopic system of IACTs

Since October’96 the HEGRA collaboration is operating the first stereoscopic system world wide. It consists of five imaging atmospheric Cherenkov telescopes (IACTs) installed at La Palma, Canary Islands. The performance of the system shows its unique capabilities for the study of TeV γ-ray sources with an energy threshold of 500 GeV, an angular resolution of 0.1°, and an energy resolution of better than 20%. The stereoscopic system is able to detect within an hour a γ-ray flux of νFν10−11u200aergs/cm2u200asec at 1 TeV with a signal-to-noise ratio of 5σ. The recently developed technique of spectrum evaluation from the stereoscopic data was used in the observations of two BL Lac objects—Mkn501 and Mkn421. The Mkn501 flared with up to ten times the Crab flux in 1997 with an average flux of about three Crabs. Recording of several Cherenkov light images from an individual air shower and the unprecedented statistics of about 38,000 TeV γ-rays allowed us to test each step of the spectrum evaluation procedure in great de...

A Cherenkov camera with integrated electronics based on the “Smart Pixel” concept

An option for the cameras of the HESS telescopes, the concept of a modular camera based on “Smart Pixels” was developed. A Smart Pixel contains the photomultiplier, the high voltage supply for the photomultiplier, a dual-gain sample-and-hold circuit with a 14 bit dynamic range, a time-to-voltage converter, a trigger discriminator, trigger logic to detect a coincidence of X=1…7 neighboring pixels, and an analog ratemeter. The Smart Pixels plug into a common backplane which provides power, communicates trigger signals between neighboring pixels, and holds a digital control bus as well as an analog bus for multiplexed readout of pixel signals. The performance of the Smart Pixels has been studied using a 19-pixel test camera.