London | Scientists have discovered the most energetic pulsed emission radiation ever detected from a neutron star known as the Crab pulsar located 6,500 light years away from Earth.
The Crab pulsar is the corpse left over when the star that created the Crab nebula exploded as the supernova 1054. It has 1.5 the mass of the Sun concentrated in about 10 kilometres diameter object, rotates 30 times per second, and is surrounded by a region of intense magnetic field ten thousand 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 Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) and Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatories discovered unexpected very energetic photons.
We performed deep observation of the Crab pulsar with MAGIC to understand this phenomenon, expecting to measure the maximum energy of the pulsating photons, said Principal Investigator Emma de Ona Wilhelmi, from the Institute of Space Sciences (IEEC-CSIC, Barcelona).
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, said Roberta Zanin from ICCUB-IEEC, Barcelona.
The photons arrive in two 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.
However, 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 synchronisation 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 one can say that the electrons responsible from the TeV radiation keep somehow 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, said Daniel Galindo Fernandez, from ICCUB-IEEC, Barcelona.
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