A coronal loop model for the production of X-ray and radio flares in the RS CVn binary HR 1099

Abstract

The RS CVn binary stellar system HR 1099 is a source of both X-ray and radio flares. We present here a model of the system in which the two types of flare are produced by the same population of mildly-relativistic (γ ≲ 10) electrons, injected into a coronal loop. After reviewing possible radiation mechanisms we conclude that, given the probable conditions in the flaring region, the radio emission is gyrosynchrotron radiation and the X-ray emission is thermal bremsstrahlung. The thermal X-ray source must lie in the stellar chromosphere, but the apparent absence of plasma absorption at radio frequencies indicates that the radio source is located high in the coronal loop. Using the relationships given by Dulk and Marsh (1982) for the radio emission from a power-law electron energy spectrum,N(γ)α (γ - 1)−δ, we conclude that 3 ≲δ ≲ 7, with ≳ 30% of the electron population trapped in the radio source. Some implications of these results for one particular version of the model are discussed.