Stellar Xray Sources
The terms Xray and gamma ray refer to electromagnetic radiation of extremely high frequency and short wavelength. The difference between these two terms is mainly a statement about their origin: high energy radiation from atomic processes is called Xray radiation and radiation from nuclear processes is called gamma radiatioin. When we observe such energetic radiation from a star, we may not know the nature of the source, so the designation can be ambiguous.
The star beta Ceti emits about 2000 times as much radiation in the Xray region of the electromagnetic spectrum as does our Sun, but has only about three solar masses.
The emission of Xrays can be associated with an accretion disk around a black hole, the presumed nature of the Xrays from Cygnus X-1. The Xray source in Cygnus X-3 is more energetic and more mysterious.