X-RAY-IDENTIFICATION OF THE SOFT GAMMA-RAY REPEATER 1806-20

THE nature of gamma-ray bursters-astrophysical sources that emit abrup t bursts of gamma-rays-presents a long-standing question in high-energ y astronomy. Soft gamma-ray repeaters (SGRs) are distinguished from cl assical gamma-ray bursters by the short duration, softer gamma-ray spe ctrum and recurrent activity of their outbursts(1-6). Millisecond-scal e structure in these bursts suggests that SGRs are compact, and many m odels invoke neutron stars as the emitting objects(1,5). This idea is supported by the association of two SGRs, SGR0526-66 (ref. 6) and SGR1 806-20 (ref. 7), with supernova remnants, SNR N49 and the radio nebula G10.0-0.3 respectively. Very recently, Kulkarni et al.(8,9) have sugg ested that a compact radio source in G10.0-0.3 corresponds to a young pulsar at the centre of this nebula, and can be identified with SGR180 6-20. Here we report the detection of a burst from SGR1806-20 with the X-ray satellite ASCA(10), which allows us to identify the burster wit h a new X-ray source which we designate AX1805.7-2025. The burst is co incident in time with that detected by the BATSE(11,12) instrument on board the Compton Gamma Ray Observatory. This result provides strong e vidence that SGRs are indeed neutron stars.