X-ray identification of the soft γ-ray repeater 1806 – 20

Abstract

THE nature of γ-ray bursters—astrophysical sources that emit abrupt bursts of γ-rays—presents a long-standing question in high-energy astronomy. Soft γ-ray repeaters (SGRs) are distinguished from classical γ-ray bursters by the short duration, softer γ-ray spectrum and recurrent activity of their outbursts^1–6. Millisecond-scale structure in these bursts suggests that SGRs are compact, and many models invoke neutron stars as the emitting objects^1,5. This idea is supported by the association of two SGRs, SGR0526 – 66 (ref. 6) and SGR1806 – 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 suggested 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 SGR1806 – 20. Here we report the detection of a burst from SGR1806 – 20 with the X-ray satellite ASCA¹⁰, which allows us to identify the burster with a new X-ray source which we designate AX1805.7 – 2025. The burst is coincident in time with that detected by the BATSE^11,12 instrument on board the Compton Gamma Ray Observatory. This result provides strong evidence that SGRs are indeed neutron stars.