Chandra, Extreme Ultraviolet Explorer, and very large array observations of the active binary system σ2 coronae borealis

We present the results of a coordinated observing campaign on the short-period RS CVn binary sigma(2) Coronae Borealis (F6V+G0V; P-orb=1.14 days) with the Very Large Array, the Extreme Ultraviolet Explorer, and the Chandra X-Ray Observatory High-Energy Transmission Grating Spectrometer. The radio emission is consistent with previously determined quiescent gyrosynchrotron properties. Multiple flares were seen with Extreme Ultraviolet Explorer, five occurring within two consecutive orbital periods. The first of these flares was observed with Chandra. The Chandra observations of sigma(2) CrB showed no systematic variations of line fluxes, widths, or Doppler shifts with orbital phase, nor any response in line width or offset due to the are. This is consistent with both stars being equally active coronal emitters. We have developed a self-consistent method of spectral analysis to derive information from the line and continuum emissions concerning the distribution of plasma with temperature and elemental abundances. A bimodal temperature distribution is appropriate for both quiescent and are intervals, with a stable peak at 6-8 MK and another variable enhancement at higher temperatures, with evidence for significant contribution from temperatures up to 50 MK during the are, compared to 30 MK during quiescence. The iron abundance is subsolar during quiescence but is enriched by about a factor of 2 during a large are seen with Chandra. The noble gas elements neon and argon show elevated abundances with respect to iron, but there is no clear evidence for any first ionization potential based abundance pattern during quiescence or the are. We have determined coronal electron densities from the helium-like ions O VII Ne IX Mg XI andSi XIII which imply densities >10(10) cm(-3). There is a small enhancement in the electron densities derived for the are, but it is not statistically significant. We call attention to electron temperature constraints provided by the ratios of 1s(21) S-0-1snp P-1(1) transitions of the helium-like ions O VII Ne IX Mg XI and Si XIII The derived coronal electron pressures change by 1-2 orders of magnitude over a 25% change in temperature, implying nonisobaric coronal conditions. We find no evidence for significant departures from the effectively thin coronal assumption. The electron densities inferred from the soft X-ray spectra are inconsistent with cospatial gyrosynchrotron emission; further observations are necessary to discriminate the relative locations of the radio and soft X-ray-emitting plasma.