Welllll...So far as I know, there are no reports of anyone having detected 'Alpha Orionis' as an X-ray source. The Einstein X-ray Observatory launched in the late 1970's did find that virtually all stars emit X-rays, EXCEPT for stars like Betelgeuse and Antares which are red, M-type, supergiants...normally considered to be precursors to supernovae. In fact, Einstein could not find any emission from Betelgeuse brighter than about 1/10000 the X-ray brightness of solar coronal holes seen on our very own Sun. The explanation is that most stars have active chromospheres and are surrounded by very hot coronae with temperatures above 100,000 degrees. These make excellent X-ray sources. Supergiants like Betelgeuse do not have much, if any, X-ray emission because they are simply too cool to have hot coronae. There may, however, exist the possibility of brief, short-lived transient events caused by the equivalent of solar flares, where magnetic fields get tangled up and 'reconnect', liberating a lot of energy in small regions of the star.
The ROSAT, X-ray satellite is currently examining the sky for more X-ray sources and mapping the ones we already know about. I have not heard news about their detecting any X-ray emission from Betelgeuse either.
As for supernova precursor events, there is most certainly going to be a lot of surface activity as a star prepares to blow its top, but we have never monitored a star just before it becomes a supernova to see if it has a precursor X-ray flash or something like that.