It has been Magic (Major Atmospheric Gamma Imaging Cherenkov telescope) to observe, for the first time simultaneously with a X rays satellite, a gamma rays flash in full activity. The results have been illustrated at the “International Cosmic Ray Conference” in Pune (India).
Magic is the biggest Cherenkov light telescope in the world for the gamma astronomy - which is dedicated to the study of cosmic gamma rays - and it’s the result of an international collaboration to which the researchers of the National Institute for Nuclear Physics (Infn) have provided a fundamental contribution.
“ The gamma rays flashes consist of an emission of high energy photons coming from a cosmic source, which nature is up to now uncertain although researches and hypothesis have pursued for over thirty years. It is presumed that these mysterious and fascinating sources, probably the objects with the highest energy in the Universe, are originated from the collapse of a high mass star evolving in a black hole. During this process, in a few seconds, photons with energy up to 10 billion times the energy of the photons composing the visible light, would be emitted as cosmic rays” explains the national spokesman of Magic, Alessandro De Angelis, Infn researcher and professor of experimental physics at Udine University.
Magic is part of a satellites’ grid for the observation of high variability events, mainly managed by Nasa. The framework includes also the satellite for the detection in the X rays range, Swift, which first revealed the recently observed gamma flash, after named GRB050713A. Magic has a light and precise mechanics and it is able to make a complete rotation in 22 seconds. It was expressly due to this characteristic, besides the perfect functioning in real time of the grid of satellites and instruments on hearth, that Magic could start the observation of the flash just 40 seconds after the burst, for the first time with about 30 second of overlap with the X rays observation operated by a satellite like Swift. “ The first analysis of Magic data has been realized by the Infn group of the University of Siena and it has revealed gamma signals of weak intensity during the primary burst, and a weak signal, congruent with instrumental effects, matching with a secondary burst measured by Swift. The maximum flux at high energies during the primary burst has been very low: from 2 to 3 order of magnitude lower than the one expected from the extrapolation of Swift data. This result could be justified if the gamma source was settled at great distances and the flux was lowered due to the interaction with the background radiation left over from the Big Bang. This allows us now to introduce important constraints on the theoretical models developed to explain these enigmatic sources”, says Alessandro De Angelis.
GENERAL INFORMATION ABOUT THE TELESCOPE MAGIC
Magic is not an optical astronomical telescope, but it is rather more similar to a huge particle detector. Actually, gamma rays are made up of very high-energy photons, thus they cannot be observed by the traditional optical systems you use with the visible light. Then, you cannot easy “capture” gamma rays bursts: their observation needs the most over-refined technology used in sub-nuclear physics.
When gamma rays cross the atmosphere, change their state, thus to observe them it is necessary to collocate detectors on satellites, outside the atmosphere itself.
Magic is able to pick up the fleeting gamma rays by detecting the so-called Cherenkov light. The Cherenkov light is emitted by charged particles generated by the interaction between gamma rays and the atmosphere.
In particular, the Cherenkov light is a flash produced when a charged particle cross a medium at a higher speed than light. Of course, nothing goes faster then light in the vacuum, but in a medium, like atmosphere is, light goes more slowly then in the vacuum and sometimes even more slowly than high energy particles, as electron and positrons created by gamma rays.
The Magic reflecting surface is an Italian technology result. It focuses the weak Cherenkov light flash generated by gamma ray crossing the atmosphere. The flash is 2-3 nanoseconds long (a nanosecond is the billionth part of a second) and its photo must be enlarged and cleaned by means of advanced computer technologies.
Inaugurated in October 2003, Magic got is final configuration in September 2004: it has a diameter of 17 m and a reflecting surface of 240 sqm. This reflecting surface, the hugest among those of all the working telescopes, has a kind of active optic, which means it can dynamically change its configuration.
Magic is collocated at an altitude of 2300 m, on the edge of Tabiriente volcano’s crater in the La Palma Island, one of the Canaries archipelago.
Magic is the result of an international collaboration between Italy, Germany and Spain. Optical and data acquisition systems are made by Infn, in particular by scientists of Padova, Siena/Pisa and Udine/Trieste sections, under the direction respectively of Mosè Mariotti, Riccardo Paoletti and Barbara De Lotto.
Thanks to its observations, Magic will get precious information about cosmic rays origin, how the most ancient objects in the Universe were formed, how gravitational energy works closed to black halls and also about dark matter and the space-time geometry of the Universe. A second telescope is under construction close to the first in order to increase sensitiveness for an even deeper observation of the Universe.