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The May 1989 outburst of the Soft X-ray Transient GS 2023+338 (V404 Cyg)

P. Zycki·C. Done·D. Smith
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Abstract

We re-analyze archival Ginga data of the soft X-ray transient source GS 2023+338 covering the beginning of its May 1989 outburst. The source showed a number of rather unusual features: very high and apparently saturated luminosity, dramatic flux and spectral variability (often on ~1 sec time scale), generally very hard spectrum, with no obvious soft thermal component characteristic for soft/high state. We describe the spectrum obtained at the maximum of flux and we demonstrate that it is very different from spectra of other soft X-ray transients at similar luminosity. We confirm previous suggestions that the dramatic variability was due to heavy and strongly variable photo-electric absorption. We also demonstrate that for a short time the source's spectrum did look like a typical soft/high state spectrum but that this coincided with very heavy absorption.

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P. Zycki, C. Done, D. Smith. 1999-04-22. The May 1989 outburst of the Soft X-ray Transient GS 2023+338 (V404 Cyg). https://doi.org/10.1046/j.1365-8711.1999.02885.x

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