The neutron star (red sphere) with its strong magnetic field (white lines) spins around itself nearly 30 times per second injecting energetic electrons in the space region around it. The green and blue shaded regions depict different particle acceleration zones from where the detected photons could originate. The green zone lies in the vicinity of the pulsar’s magnetosphere, whereas the blue zone could be as far as 100,000 km away from the pulsar. Credit: Patricia Carcelén Marco
Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) observatory has found the most energetic pulsed emission radiation ever detected from the neutron star in the center of the supernova of 1054 A.D. ie Crab pulsar. It is the corpse left over when the star that created the Crab nebula exploded as a supernova. It is 1.5 the mass of the Sun concentrated in about 10 km diameter object, rotates 30X / s, and is surrounded by a region of intense magnetic field 10 000 billion times stronger than that of the Sun. This field is strong enough to dominate the motion of charges and forces them to rotate at the same rate as the stellar surface. This region is called the magnetosphere. The rotation of the magnetic field also generates intense electric fields that literally tear electrons from the surface. As these accelerated electrons stream outward, they produce beams of radiation that we receive every time the beam crosses our line of sight, like a lighthouse.
In 2011, the MAGIC and VERITAS observatories discovered unexpected very energetic photons. Emma de Oña Wilhelmi from IEEC-CSIC, Barcelona says: “We performed deep observation of the Crab pulsar with MAGIC to understand this phenomenon, expecting to measure the maximum energy of the pulsating photons.” Roberta Zanin: “The new observations extend this tail to much higher, above TeV energies, that is, several times more energetic than the previous measurement, violating all the theory models believed to be at work in neutron stars.”
The photons arrive in 2 precise beams which should be created far from the neutron star surface: on the far end of the magnetosphere or outside it, in the ultra-relativistic wind of particles around the pulsar, to be able to accelerate electrons to such energies and to escape the large absorption in the magnetised atmosphere. But surprisingly, the TeV beams arrive at the same time as the radio and X-ray beams, which are very likely produced within the magnetosphere. This tight synchronization of the beams at different energies implies that the bright radiation observed in the multi-wavelength spectrum is produced altogether in a rather small region. Alternatively the electrons keep memory of the low-energy beams. Where and how this TeV emission is created remains still unknown and difficult to reconcile with the standard theories.
The Crab pulsar is located at a distance of about 6500 light years at the center of a magnetized nebula visible in the Taurus constellation. The Crab is the most powerful pulsar in our galaxy and it is one of only a few pulsars detected across all wavelengths, from radio up to gamma rays. In its rotating magnetic field , electrons and positrons are accelerated up to relativistic energies and emit radiation that arrives to our telescopes in the form of pulses every 33 millisecond, each time the neutron star rotates and meets our telescopic sight. Before the MAGIC measurement this radiation was believed to stop abruptly when the photons reach a energy few billion times larger than visible light.
MAGIC is a ground-based gamma-ray instrument located on the Canary island of La Palma, Spain. The system of two 17m diameter Cherenkov telescopes is currently one of the three major imaging atmospheric Cherenkov instruments in the world. It is designed to detect gamma rays tens of billions to tens of trillions times more energetic than visible light. MAGIC has been built with the joint efforts of a largely European collaboration that includes about 160 researchers from Germany, Spain, Italy, Switzerland, Poland, Finland, Bulgaria, Croatia, India and Japan.
https://magic.mpp.mpg.de/dl/0/1452700732/ffe5e01a5b0cbdceb67a1d4600ffc6678988ae40/uploads/media/PR_MAGIC_Crab_01.pdf
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