Accretion in a binary system is a very efficient way to make X-rays.
It's even more efficient than fusion! The first X-ray sources discovered
were accretion-powered binaries because they were the brightest.
Some of the accretion-powered sources have X-ray luminosities of
1038 erg/s. In comparison, the Sun's X-ray luminosity
is only about 1027 erg/s.