X-ray burst sources

X-ray burst sources

(X-ray bursters) Sources of intense flashes of cosmic X-rays, discovered in 1975. The bursts, seen primarily in the 1–30 keV energy band, are characterized by a rapid onset, often less than one second, followed by an exponential decay with a time constant of a few seconds to a minute. They are located in our Galaxy, mostly within 40° of the galactic center. Two types have been distinguished: type I repeat on timescales of hours or days; type II emit bursts every few minutes or less for a period of several days. It is widely believed that X-ray bursts arise in X-ray binary systems and are due to thermonuclear flashes when material accreted on to the surface of a neutron star exceeds a critical temperature and pressure (type I) and to spasmodic mass accretion on to a neutron star (type II).