An Etymological Dictionary of Astronomy and Astrophysics

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.

See also: → X-ray; → transient.