Radio, X-ray, and extreme-ultraviolet coronal variability of the short-period RS canum venaticorum binary sigma(2) coronae borealis

We present the results of a coordinated observing campaign on the short-per iod (1.14 days) RS CVn binary sigma (2) Coronae Borealis with the VLA, ASCA , and RXTE. We also discuss earlier observations of the same system obtaine d by the Extreme Ultraviolet ExpEorer (EUVE). Dramatic coronal variability is present in all of these observations across the electromagnetic spectrum . sigma (2) CrB undergoes frequent large flares that occur close together i n time. Radio flares are unambiguously correlated with X-ray flares; the X- ray flares peak as much as 1.4 hr before the corresponding radio maxima. Re sponse to flares is more rapid in higher energy X-ray bandpasses, signaling an increase in temperature during the course of the flare. Flares are seen more frequently in the harder RXTE bandpass than in simultaneously taken A SCA observations. There is greater contrast between flaring and nonflaring conditions in the RXTE light curve. Complex Raring is seen in the radio at 3 and 6 cm, consistent with optically thin nonthermal gyrosynchrotron emiss ion for most of the duration of the observation. Bursts of left-circularly polarized emission at 20 cm lasting less than or equal to 5 minutes appear to be due to a coherent emission process. EUVE spectra reveal coronal mater ial at n(e) less than or equal to 10(12) cm(-3), With no discernible densit y differences between flaring and quiescent time intervals. Quiescent ASCA spectra show lower than solar photospheric abundances with iron depleted by a factor of 4 from the solar photospheric value. The abundances increase d uring a large flare observed with ASCA, with iron enhanced to the solar pho tospheric value during the rise phase of the hare. Two-temperature fits to extracted spectra show a low-temperature quiescent value of 8 MK and a high -temperature component that varies from 22 MK during quiescence to 50 MK at the peak of the flare. Emission measure distributions measured from the AS CA observations are consistent with the temperatures derived from the discr ete two-temperature fits and indicate the presence of very hot (> 100 MK) p lasma during the rise phase of the ASCA Bare. Many of the flares observed w ith EUVE, ASCA, and RXTE show a double exponential decay phase, further hig hlighting the importance of this phenomenon in diagnosing flaring condition s. We also find that the observed second decay timescale cannot be explaine d by some of the currently used flare parameterizations.