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Introduction

MAGIC is a system of two imaging atmospheric Cherenkov telescopes (or IACTs). MAGIC-I started routine operation after commissioning in 2004. Construction of MAGIC-II was completed in early 2009, and the two telescopes have been in operation ever since, with a break in 2012 for an upgrade that achieved full homogeneity. The project is funded primarily by the funding agencies BMFB (Germany), MPG (Germany), INFN (Italy), MICINN(Spain), and the ETH Zurich (Switzerland).

MAGIC site
The two MAGIC Telescopes and the Control Building at the Observatory of the Roque de Los Muchachos, La Palma, Canary Islands (Spain). In front the FACT experiment

The picture above shows the two MAGIC Telescopes which are, with their 236 m2 reflective surface each, among the largest operating IACTs. In front the FACT experiment a new small IACT using one of the former HEGRA telescopes. The precursor experiment HEGRA used several telescopes of the same type, but of smaller size; the one renewed for the FACT experiment is shown in the photograph below.


Former HEGRA Telescope now FACT experiment since 2011

The Roque de los Muchachos site is situated on the Canary island of La Palma, a volcanic island off the African coast at 28oN and 17oW. The site has excellent conditions for optical observations, and is run by the IAC. It is also under consideration for an ultra-large optical telescope.

The MAGIC site is at an altitude around 2200 above sea level.


Another view of the Magic Telescopes in 2009 with the TNG (left) and GTC (right) in the foreground

Up to the rim at 2500m, multiple high-quality optical telescopes are installed, as seen in the photograph above. It shows in the foreground the MAGIC telescopes and the MAGIC control building, featuring a red roof and a dome for a LIDAR. Above MAGIC, two optical telescopes are visible, the Telescopio Nazionale Galileo (left), and the Gran Telescopio Canarias (GTC), with its 10.4m diameter segmented mirror the largest worldwide, and in operation since 2011.

Imaging atmospheric Cherenkov telescopes

The cosmos and its evolution are studied using all radiation, charged cosmic rays, neutrinos, and, in particular, electromagnetic waves. The electromagnetic spectrum extends from radio waves (at wavelengths of several tens of meters, or energies of 10-9 eV) to ultra-high enery gamma quanta (wavelengths of picometers or energies of 100 TeV). Observations at visible wavelengths (.5 to 1 micrometer) have a history of centuries, gamma astronomy by satellites (keV to few GeV) and ground-based telescopes (above 300 GeV) are end-of-20th century newcomers. IACTs are ground-based telescopes for the detection of very high energy (VHE) electromagnetic particles, in particular gamma rays. Having no electric charge, VHE gammas are not affected by magnetic fields, and can, therefore, act as messengers of distant cosmic events, allowing straight extrapolation to the source. Although high-energy gamma quanta get absorbed in the atmosphere, they can be observed indirectly. The absorption process proceeds by creation of a cascade or shower of high-energy secondary particles. The Cherenkov method uses the fact that the charged secondary particles emit radiation at a characteristic angle, the Cherenkov radiation. Cherenkov photons have energies in the visible and UV range, and pass through the atmosphere; thus they can be observed on the surface of the earth by sufficiently sensitive instruments. You will find more about IACTs in a dedicated page.

Air shower
Credits: Cherenkov Telescope Array in Argentina

The physics case for IACTs

Most generally, the observation of gamma rays (electromagnetic radiation of high energy) is one aspect of astroparticle physics. Astroparticle physics is a new field developing as an intersection of Particle Physics, Nuclear Physics, Astrophysics, Gravitation and Cosmology. One of its cornerstones is Cosmic Ray Physics, which has its origins many decades in the past; then scientists observed in balloons and in mountain top laboratories the many charged particles impinging upon the earth. Today, the field has substantially widened, and includes all particles. Particularly in recent years, activities (and funding) have accelerated, with fundamental discoveries being made at an astonishing frequency. Using the understanding of particle interactions at very high energies, as derived from experiments in accelerator laboratories, the picture of how the universe developed since its earliest beginnings, some ten billion years ago, is changing fast. Theoretical models fuel multiple experiments, using different particles coming to earth from space.

Very high energy gamma astronomy using ground-based telescopes is a recent addition to the panoply of astroparticle physics instruments and the number of established sources is continuously increasing.

The most interesting subjects of observation at these energies, are
  • Active galactic nuclei:

    Observation results indicate that most part, if not all galaxies (including our own milky way) have an active nucleus, in which a supermassive black hole is accreting matter. Some of them (Mrk 421, Mrk 501) have been observed to be active in the VHE gamma region, with occasional outbreaks and even with quasi-periodic fluctuations. The preferred theory explains the VHE gammas as products of high acceleration fields (shock waves) in the jet that bundles charged particles along two directions at 180 degrees to each other. The VHE gamma rays observed should be produced within the jets, close to the black hole.

    AGN: artistic view
    Artist view of an Active Galactic Nuclei
    Credits: courtesy of NASA, Dana Berry/Skyworks Digital

    The origin of the jets is not yet understood. Models relate the jet directions (seemingly constant over millions of years) to the spin axis (axis of rotation) of the black hole. Understanding more about these objects and the acceleration mechanisms both in the vicinity of the black holes and in intergalactic space is a task in which IACTs have an important role to play. MAGIC, in particular, with its emphasis on optimal light collection is probing more deeply into the earlier part of the developing universe: the lower the energy threshold, the larger the observable redshifts.

  • Supernova remnants:

    In the wake of a certain class of supernova explosions, the so-called SN of types II and Ia, gas clouds expand and a very dense core develops; the core may be a spinning neutron star or a black hole. In the example of the Crab nebula (the picture below is a multiwavelength view), the neutron star is observed as a pulsar, because it rotates at 30 cycles and 'pulses' in the X-ray domain; it is also observed at optical and UV wavelengths and recently also at GeV energies by MAGIC and other IACTs. A rather constant radiation at higher energy, in the TeV range, has also been observed by IATCs. Supernova remnants may be VHE gamma sources of different types. According to the standard model of cosmic ray origin, the shell type supernova remnants (radiating from the expanding cloud) are sites of acceleration of nuclei to very high energies: if so, they are not only the main accelerators of charged cosmic rays, but should also copiously produce gamma rays. SN remnants of the plerion type, instead, are expected to radiate from the core. A systematic high-sensitivity scan of candidates, most of them lying in our own galaxy, has still to be done.

    CRAB nebula pulsar shrugs
    The Crab Nebula Pulsar Shrugs: a composite image of the center of the Crab Nebula, where red represents radio emission, green represents visible emission, and blue represents X-ray emission.
    Credits: J. Hester (ASU), CXC, HST, NRAO, NSF, NASA

  • Gamma Ray Bursts:

    Almost once per day, a powerful transient gamma ray source appears in the gamma ray sky in an unpredictable location and suddenly fades away. Gamma ray bursts last for seconds to minutes only. Generally an afterglow in the X-ray, optical and radio domain is observed at the position of the gamma ray event after much longer delays. The energy observed makes them the beacons of most likely the most energetic events known in the universe. Discovered 40 years ago, these Gamma Ray Bursts have been objects for research and speculation ever since. The most popular theory, the fireball or hypernova model, adopted to explain these mysterious events supposes that they are extremely violent explosions releasing in excess of 1044 J (or 1051 erg), and creating violent shockwaves as the materials flowing out from the explosion at different velocities collide.

    GRB: artistic view
    Artist view of a Gamma Ray Burst
    Credits: ESO/A. Roquette

    GRB021004
    GRB021004 detected by the HETE satellite and observed by the 48-inch Samuel Oschin Telescope and the JPL/NEAT CCD camera just 9 minutes after the explosion and compared with a DSS plate. The optical afterglow is clearly detected in the NEAT image.
    Credits: courtesy of Caltech/Derek Fox

    At present, thousands gamma ray bursts have been detected studied and localized by several dedicated space experiments (e.g. BATSE, SAX-GBM+WFC, HETE, SWIFT, Fermi-GBM, etc.). These objects are homogenously distributed in the sky and are definitively recognised as extragalactic objects exploding in other galaxies at cosmological distances. Many of them have large redshifts and GRBs are also among the farthest objects ever observed in the Universe so far (i.e. we observe them at billions of years in the past). Observations in the very high-energy gamma domain are not available yet but such an emission is expected and it will help in clarifying these mysterious phenomena.

  • Other contributions to cosmology and fundamental physics:

    Observations of VHE gammas, if done systematically, will also allow to constraint the star formation in the early universe, by measuring the extragalactic infrared radiation field. They will further allow searches for the stable lightest super-symmetric particle, expected (if it exists) to annihilate with its own self-conjugate antiparticle into photons in areas of high gravitational field, e.g. in the vicinity of the massive black holes in the center of the galaxies (including our own). Quantum gravity effects might become apparent if subtle time differences can be detected in the arrival of gammas from a given source, at different wavelengths. If they occur in nature, the MAGIC telescopes have the capability to record such phenomena.

Multi-wavelength observations

The combination of results obtained at different wavelengths is a crucial ingredient for understanding the most part of the astrophysical phenomena. The correlation in time and in amplitude for expected signal fluctuations at different wavelengths will give important clues to the mechanisms of production, acceleration, and transport through space. Multiple measurements are equally important in obtaining curves of total flux over a large band of energies (the example showed in figure span over about 20 orders of magnitude!). Comprehension of the production and the transport of the observed radiation is entirely dependent on the collaboration between multiple experiments at different wavelengths.


MAGIC is participating in multi-wavelength campaigns (simultaneous observations) in close collaboration with several X-ray, optical, and radio experiments for studying several different classes of astrophysical sources.