Abstract
A NEW type of time variability of cosmic X-ray sources (‘bursters’) was discovered from Astronomical Netherlands Satellite (ANS) observations on the source 3U1820–30, associated with the globular cluster NGC6624 (refs 1, 2). These X-ray bursts are characterised by a rapid rise in flux ( ∼ 0.5 s) to a relative intensity comparable to the Crab Nebula, followed by an exponential decay at a time scale of ∼ 10 s. Certain characteristic features of the bursts, in particular the shape and spectral hardening, are consistent with a model where the X-ray emitting region is situated in a cloud of hot gas near a massive black hole ( ∼ 1,000M ⊙) (ref. 3). On March 14, 15 and 16, 1976 the ANS spacecraft was pointed in the direction of the remarkable new X-ray burster MXB1730–335 discovered by SAS-3 (ref. 4) in the constellation Scorpius at 5° from the galactic centre in the galactic plane. The source is characterised by rapidly repetitive X-ray bursts of varying intensity. The energy in a given burst is approximately linearly proportional to the time interval to the next burst5. We report here an improved position of this source and give the energy spectrum from data obtained in four observations for which quick-look data are available. An upper limit for the steady source level in between the bursts is obtained.
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HEISE, J., BRINKMAN, A., DEN BOGGENDE, A. et al. ANS observations on the X-ray burster MXB1730—335. Nature 261, 562–564 (1976). https://doi.org/10.1038/261562a0
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DOI: https://doi.org/10.1038/261562a0
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