Extended multifrequency observations of radio emission from the RS CVn binary HR 1099

Abstract

Eight 10-h sets of four-frequency data from the Australia Telescope Compact Array (ATCA) plus a similar quantity of Very Large Array (VLA) observations have been used to investigate the variations of flux density and polarization of HR 1099 in time and in frequency. The data are discussed from the viewpoint of radio emission processes. Their relation to variations in other spectral regions will be dealt with in a subsequent paper. At the higher frequencies (5-8 GHz) the emissions are found to be X-mode gyrosynchrotron emission, as previously thought. At lower frequencies (1-3 GHz) narrow-band bursts of oppositely polarized emission are detected. These bursts are probably O-mode plasma emission. Gyrosynchrotron model fits to the radio data imply that in the non-flaring state the emission comes from a region of radius 5 × 10 m. It requires a highly organized magnetic field of strength ranging from 1 to 13 mT (10-130 G) to explain the radio data from 1.4 to 15 GHz. At times of strong flares the emitting region extends to 10 m. The magnetic field is tangled in the outer parts.