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8th of April 2020
Evidence for Auroral Radio Emission from the magnetic star ρ Oph A
by Leto et al.
Leto et al. have described ATCA measurements over the frequency range 2.1–21.2 GHz of the magnetic star ρ Oph A. The detection of two highly polarized pulses at 2.1 GHz indicates that the coherent stellar Auroral Radio Emission is being produced. Combining the radio light curves with high-resolution optical spectra and new magnetic field measurements enabled the stellar radio emission to be modelled. The figure above is a sketch of the scenario proposed by Leto et al. to explain the radio and the X-ray observations of ρ Oph A. In the inner magnetospheric region (the light grey area) the magnetic energy is so strong that the radiatively driven stellar wind cannot freely expand. The stellar wind is channeled by the closed field lines of the magnetic dipole producing shocks close to the magnetic equatorial plane, giving rise to thermal X-ray emission. Far from the star, the magnetic field strength decreases and the trapped plasma can open the magnetic field lines to form current sheets. In these regions, magnetic reconnection events can accelerate the local plasma up to relativistic energy (illustrated by the the light-green areas). The non-thermal electrons (represented by the small solid black arrows) freely propagate within the middle-magnetosphere radiating at the radio regime by the gyro-synchrotron emission mechanism. These particles are directly towards to polar regions of the star, and the energy released by the bombardment of the surface produces an unstable energy distribution in the electrons moving outwards (white solid small arrows), triggering the auroral coherent radio emission from rings located above the polar regions. The Auroral Radio Emission beams directed to the observer are highlighted by the two blue bright spots. More details are given in the paper, published in Monthly Notices of the Royal Astronomical Society.

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