Title: The detection of variable radio emission from the fast rotating magnetic hot B-star HR7355 and evidence for its X-ray aurorae,
Abstract: In this paper we investigate the multiwavelengths properties of the magnetic
early B-type star HR7355. We present its radio light curves at several
frequencies, taken with the Jansky Very Large Array, and X-ray spectra, taken
with the XMM X-ray telescope. Modeling of the radio light curves for the Stokes
I and V provides a quantitative analysis of the HR7355 magnetosphere. A
comparison between HR7355 and a similar analysis for the Ap star CUVir, allows
us to study how the different physical parameters of the two stars affect the
structure of the respective magnetospheres where the non-thermal electrons
originate. Our model includes a cold thermal plasma component that accumulates
at high magnetic latitudes that influences the radio regime, but does not give
rise to X-ray emission. Instead, the thermal X-ray emission arises from shocks
generated by wind stream collisions close to the magnetic equatorial plane. The
analysis of the X-ray spectrum of HR7355 also suggests the presence of a
non-thermal radiation. Comparison between the spectral index of the power-law
X-ray energy distribution with the non-thermal electron energy distribution
indicates that the non-thermal X-ray component could be the auroral signature
of the non-thermal electrons that impact the stellar surface, the same
non-thermal electrons that are responsible for the observed radio emission. On
the basis of our analysis, we suggest a novel model that simultaneously
explains the X-ray and the radio features of HR7355 and is likely relevant for
magnetospheres of other magnetic early type stars.