Discovery of a large X-ray burst from an X-ray nova, Centaurus X-4.

The X-ray satellite Hakucho detected an X-ray burst from the nova-like transient Cen X-4 on May 31, 1979. The time profile and the spectral softening of the burst show the same properties as those of a type I X-ray burst. The peak intensity of approximately 25 times the Crab in the energy range 1.5-12 keV is the strongest X-ray burst observed so far. The burst occurred during a nova-like outburst which is similar to one observed in 1969. The present discovery suggests that a soft transient source such as Cen X-4 comprises a neutron star and a late dwarf and can be an X-ray burster.