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 burst^1-3 is 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 ~10³¹ erg s^-1 and supports the hypothesis that either γ bursts are produced by accretion instabilities^5,6 or, if due to published models for a thermonuclear flash⁷, they recur with intervals ≳50 yr. Such long recurrence times may be inconsistent with limits inferred from both the γ burst observations⁸ and optical data⁴.