An upper limit to the low-energy X-ray flux from Beta Persei

A region of the sky including the binary system Algol (Beta Persei) was observed with a one-dimensional grazing-incidence X-ray telescope sensitive in the energy range from 0.5 to 4.0 keV. No statistically significant flux was detected above that attributable to the diffuse and cosmic-ray induced backgrounds. This result allows an upper limit of 2 by 10 to the -11th power ergs/sq cm/sec/keV at 1.6 keV to be placed on the X-ray emission from this source at the epoch of observations. It is concluded that the absence of detectable low-energy X-rays is consistent with a thermal radio source, provided that no flares occurred at the time of observation.