Rosat observations of FK comae berenices

We obtained ROSAT PSPC observations of FK Com over a period of 24.4 h, or 0.42 rotation. During the observations the x-ray flux increased by a factor of at least 5 before declining toward its previous level. A single temperature Raymond-Smith model is adequate to model the low signal-to-noise ratio spectrum from each observation interval. Initially the spectrum was that of a 8.5×10⁶ K plasma, with L_X=0.66×10³¹ erg s^-1. When the x-ray flux was greatest, the model plasma temperature rose to 2.5×10⁷ K, and L_X=3.46×10³¹ erg s^-1. During the post-maximum decline in luminosity the plasma temperature was ∼12×10⁶ K. We conclude that the increase of x-ray flux recorded by ROSAT was due to an x-ray flare with a 1.5 h decline time scale.