Binary phase correlated X-ray intensity variations and flaring in theRS CVn binary HR 1099.

A study of X-ray variability of the RS CVn binary HR 1099 has been carried out. Evidence is found for the variation of the X-ray intensity with the 2.837 day period of the binary. The phase of the X-ray maximum coincides with that of the minimum of the optical wave and the X-ray minimum occurs close to the optical wave maximum. An intense X-ray flare, having rise time of ≥16 min, decay time of 76 min, and total 2 - 10 keV X-ray energy release of ≈5×10³⁴erg, was detected on 1980 February 17. The X-ray spectrum near the flare peak was hard and is best described by a thermal spectrum with kT = 11.3 (+2.6,-1.8) keV compared to a quiescent state value of 2.0±0.4 keV. A second but less intense flare having decay time of >33 min was detected on 1979 January 31. The binary phase correlated variations are explained in terms of the star spot model.