An EXOSAT observation of quiescent and flare coronal X-ray emission from Algol

Abstract

X-ray emission from the Algol system is believed to originate in a corona associated with the K star. The authors have used the EXOSAT Observatory to make a 35 hr continuous observation centered on the occultation of the K star by the B star primary. The spectrum of the quiescent emission in the 1 - 10 keV band gives a temperature of 2.5×10<SUP>7</SUP>K. This spectrum, extrapolated to lower energies, can account for more than 80% of the observed count rate. No obvious X-ray eclipse was seen. An X-ray flare was detected with a rise time of ≡1700 s and an exponential decay of ≡7000 s. The 0.1 - 10 keV peak luminosity was 1.4×10<SUP>31</SUP>ergs s<SUP>-1</SUP>. The peak temperature was 6×10<SUP>7</SUP>K, with an iron K line confirming the thermal character of the emission.