Persistent X-ray emission from a γ-ray burst source

A quiescent X-ray source detected with the Einstein X-ray Observatory in a location consistent with that of an intense γ-ray burst1–3is shown here to be also consistent with the location of the 1928 optical transient4, the likely optical counterpart of the γ-ray burst source GBS0117 – 29. The probable maximum X-ray luminosity is only ∼1031erg s−1and supports the hypothesis that either γ bursts are produced by accretion instabilities5,6or, if due to published models for a thermonuclear flash7, they recur with intervals \[gsims]50 yr. Such long recurrence times may be inconsistent with limits inferred from both the γ burst observations8and optical data4.