ROSAT Observations of the Flare Star CC Eri

Abstract

The flare/spotted spectroscopic binary star CC Eri was observed with the Position Sensitive Proportional Counter (PSPC) on the X-ray satellite ROSAT on 1990 July 9-11 and 1992 January 26-27. During the observations, the source was variable on time scales from a few minutes to several hours, with the X-ray (0.2-2 keV) luminosity in the range $\sim 2.5-6.8\times 10^{29} erg s^{-1}$. An X-ray flare-like event, which has a one hour characteristic rise time and a two hour decay time, was observed from CC Eri on 1990 July 10 16:14-21:34 (UT). The X-ray spectrum of the source can be described by current thermal plasma codes with two temperature components or with a continuous temperature distribution. The spectral results show that plasma at $Te\sim 10^{7}$ K exists in the corona of CC Eri. The variations in the observed source flux and spectra can be reproduced by a flare, adopting a magnetic reconnection model. Comparisons with an unheated model, late in the flare, suggest that the area and volume of the flare are substantially larger than in a solar two ribbon flare, while the electron pressure is similar. The emission measure and temperature of the non-flaring emission, interpreted as the average corona, lead to an electron pressure similar to that in a well-developed solar active region. Rotational modulation of a spot related active region requires an unphysically large X-ray flux in a concentrated area.