HEAO A-1 observations of X-ray emission from BL Lacertae objects.

X-ray observations of the BL Lac objects Mkn 501 and I Zw 1727+502 are reported which were made with the HEAO A-1 experiment in the energy range from 0.5 to 25 keV. It is noted that Mkn 501 is a BL Lac object in an elliptical galaxy and that I Zw 1727+502 is a Zwicky compact galaxy with a redshift of 0.0554. The measured intensities are shown to be 2 Uhuru flux units (UFU) for Mkn 501 and 0.5 UFU for I Zw 1727+502. Light curves are constructed for both sources, and some evidence of variability is discerned in the case of Mkn 501.