Pulsed gamma-rays above 25 GeV*) from a pulsar (Crab) have been detected for the first time by the MAGIC (Major Atmospheric Gamma-ray Imaging Cherenkov) telescope, thanks to its sophisticated upgrade in the trigger electronics lowering the observational threshold. The results have been published on October 16, 2008 in ScienceExpress, and appeared the Science Magazine on November 21, 2008 (Science 322, pg.1221-1224). The Crab pulsar is a fast rotating (about 30 times per second), highly magnetized neutron star, that powers the famous Crab Nebula, located at around 6,000 light-years from the Earth in the constellation Taurus. It is the remnant of a supernova explosion that occurred in 1054 C.E.. At its core is a neutron star of a few solar masses, which is about 20 km in diameter. Its magnetic field is more than 1,000 billion times stronger than that of the Earth. The mechanism of the pulsed electromagnetic emission is an open fundamental question. All Crab pulsar emission models predict that the energy spectrum of the pulsed emission drops off sharply somewhere between a few GeV and a few tens of GeV. The MAGIC measurements reveal that the drop-off in the emitted radiation occurs at relatively high energies, which indicates that the emission must occur far out in the pulsar's magnetosphere. All models in which the emitting region is located close to the pulsar surface (e.g., the so-called polar cap model) are ruled out. A strong attenuation of the emission at high energies can result as a consequence of the strong opacity encountered by high-energy photons when they interact with ambient low-energy photons or high-intensity magnetic fields. The present results provide key constraints to all Crab pulsar models. Background Information on the MAGIC Telescope MAGIC is a gamma-ray telescope with a mirror of 17m in diameter, the largest stand-alone gamma telescope worldwide and the largest reflector of all kinds of telescopes. It was built and is operated by a large international collaboration, including about 150 researchers from Germany, Italy, Spain, Switzerland, Poland, Finland, Bulgaria, Armenia and the United States. It is located at the Roque de los Muchachos Observatory, in the Canary Island of La Palma. MAGIC detects short bluish Cherenkov light flashes, that are produced when gamma-rays “bombard” the earth’s atmosphere and initiate avalanches of secondary particles that are moving in the air with a speed higher than that of light. A second MAGIC telescope is under completion near the first, and will start operations soon. (*) 1 GeV defines an energy which is about a billion times higher than that of a visible photon. It approximately corresponds to the energy needed to create a Hydrogen atom through the mechanism of conversion of energy into mass described by the famous Einstein's relation E=mc2. Original Publication MAGIC Collaboration, "Observation of Pulsed γ-Rays Above 25 GeV From the Crab Pulsar with MAGIC", published in Science Vol. 322, pg.1221-1224 Read also Science Perspectives: Gamma Rays and Neutron Stars by Giovanni F. Bignami News Coverage Unizet magazine, University of Dortmund Press release: Press release (English) Press release (Deutsch/German) Press release (Spanish) Press release (Italian) Press release (Suomeksi/Finnish) Press release (Bulgarian) Additional material for the press and journalists

MAGIC Collaboration, "Observation of Pulsed γ-Rays Above 25 GeV From the Crab Pulsar with MAGIC", published in Science Magazine on November 21, 2008 (Science 322, pg.1221-1224). The two MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescopes atop Roque de los Muchachos on the Canary Island of La Palma. With their two 17-m diameter reflectors, the telescopes detect gamma rays through short light flashes that are produced when gamma rays cross the atmosphere (Cherenkov light). The MAGIC (Major Atmospheric Gamma Imaging Cherenkov) telescope has detected pulsed emission of very high energy gamma rays from the Crab pulsar. The composite picture shows the Crab Nebula in optical and X-rays. The so-called light-curve below shows the regular pulsation with a period of 0.033 seconds as seen by MAGIC. Picture courtesy NASA/CXC/ASU/J. Hester et al., HST/ASU/J. Hester et al. Lightcurve © MAGIC Collaboration.