|X-ray transient sources
An X-ray source that enhances its emission well above its usual level for a period typically longer than a week. Recurrences can be periodic or aperiodic, but there is no obvious correlation between recurrence time and the luminosity amplitude of the outburst. X-ray transients seem to be divided into two classes: those associated with high-mass X-ray binary (HMXB) stars and those associated with low-mass X-ray binary (LMXB) stars. The HMXBs contain a neutron star or black hole paired with a massive star. Often, the stellar companion is a Be star, Be star, which sometimes sheds material from its equatorial region. In these systems, the transient event is characterized by having more higher energy X-rays in the spectrum. The LMXBs contain a neutron star or black hole orbiting around a cooler, low-mass star. These transient events often generate more lower-energy X-rays.