Coordinated Ginga, IUE, and VLA Observations of Stellar Activity in sigma 2 Coronae Borealis

Abstract

Observations of the active cool star binary system Sigma(2) Corona Borealis with the Large Area Counters on the Ginga X-ray satellite over 2.5 d, or about two orbital periods, are reported. Throughout the observations, Sigma(2) CrB exhibited X-ray variability on time scales ranging from tens of minutes to hours. The X-ray light curve shows evidence of flaring during the course of the observations. The summed X-ray pulse height spectrum from flaring events compared with similar spectra from quiescent periods indicates an increase in coronal temperature. Periodogram analysis of the entire X-ray light curve shows a possible periodicity at about 0.40-0.44 d, with no strong signal at the orbital period or 1/2 of the orbital period. Coordinated multiwavelength observations of IUE and the VLA indicate both UV and microwave flaring during one X-ray outburst. The quiescent microwave spectrum is not consistent with a thermal gyrosynchrotron process; nonthermal gyrosynchrotron radiation is argued to be the most likely emission process.