H.E.S.S. High Energy Stereoscopic System Jon Cerny Bancroft-Rosalie School August 2002

Collaboration Consortium of European and African institutions.Consortium of European and African institutions. Led by Max Planck Institute- GermanyLed by Max Planck Institute- Germany –France –United Kingdom –Ireland –Czech Republic –Armenia –Namibia –South Africa

Goals of the Experiment Study non-thermal phenomena in the universe using very high energy gamma rays above 100 GeV. Only gamma rays travel through straight lines in our galaxy.

Location Namibia, South Africa, near the Gamsberg plateau.

Reason For Selection Optical quality of atmosphere above site As high above sea level as possible No extreme weather conditions. Site in southern hemisphere

EQUIPMENT -Telescope  The Cherenkov technique  An incident high-energy gamma ray interacts high up in the atmosphere and generates an air shower of secondary particles. The number of shower particles reaches a maximum at about 10 km height, and the shower dies out deeper in the atmosphere. Since the shower particles move faster than the local speed of light, they emit Cherenkov light, a faint blue light.

The Cherenkov light is beamed around the direction of the incident primary particle and illuminates on the ground an area of about 250 m diameter, sometimes called a Cherenkov light pool. For a primary photon at TeV energy, only about 100 photons per m 2 are seen on the ground. They arrive within a few nanoseconds.

Gamma, 300 GeV (400 x 400 m 2 ) What a 100 m 2 area would see  A telescope located somewhere within the light pool will "see" the air shower, provided that its mirror area is large enough to collect enough photons.  The image obtained with the telescope shows the track of the air shower, which points back to the celestial object where there incident gamma ray originated. The intensity of the image is related to the energy of the gamma ray.

 With a single telescope providing a single view of a shower, it is difficult to reconstruct the exact geometry of the air shower in space. To achieve this, multiple telescopes are used which view the shower from different points and allow a stereoscopic reconstruction of the shower geometry.  This provides good angular resolution (0.1°) of the direction of motion of the original gamma ray photon.

EQUIPMENT Mount and Dish The mount can point the telescope at any point in the sky.

EQUIPMENT Mirror 382 round mirror facets Each 60 cm. Diameter Focal length= 15 m.

EQUIPMENT -Cameras Captures and records the images.

EQUIPMENT -Data Acquisition Drawers containing 16 PMT’s each slide into the camera. Data sent through Internet to processing farm.

Phase I involves the installation of 4 telescopes at the corners of a 100 m x 100 m square

Phase two will add 8-12 more telescopes to cover an area of 0.1 km 2

Experiment Status In construction stage. The first telescope was completed and recorded its first air shower images in June. The full system of four telescopes will be operational in 2004.

June: First air shower images recorded

SUMMARY Uses telescopes to observe air showers. Located in Namibia, South Africa. Study of high energy gamma rays. Began recording in June Research led by Max Planck Institute in Germany in collaboration with 7 other countries.