Anti-correlated hard and soft X-ray intensity variations of the black-hole candidates Cyg X-1 and A0620-00

EXTENDED spectral measurements are now available at more than one time epoch for the powerful Monoceros transient, A0620-00, discovered by Elvis et al.¹, and the binary source Cyg X-l. We here point out a basic similarity in the unusual spectral time variations of these sources. Both are black-hole candidates, Cyg X-l by virtue of its orbital dynamics and A0620-00 as suggested by arguments based on the Eddington limit¹ and distance estimates of the optical counterpart. Thus the X-ray emission mechanism could be common.