The 1997 hard state outburst of the X-ray transient GS 1354-64/BW Cir


Brocksopp, Catherine; Fender, Robert P.; Groot, Paul J.; Jonker, Peter G.; Tingay, Steven J.; van der Klis, Michael


We present observations of the 1997 outburst of the X-ray transient GS 1354−64 (BW Cir) at X-ray, optical and, for the first time, radio wavelengths; our results include upper limits to the linear and circular polarization for the radio data. The X-ray outburst was unusual in that the source remained in the low/hard X-ray state throughout; the X-ray peak was also preceded by at least one optical outburst, suggesting that it was an 'outside-in' outburst – similar to those observed in dwarf novae systems, although possibly taking place on a viscous time-scale in this case. It therefore indicates that the optical emission was not dominated by the reprocessing of X-rays, but that instead we see the instability directly. While the radio source was too faint to detect any extended structure, spectral analysis of the radio data and a comparison with other similar systems suggest that mass ejections, probably in the form of a jet, took place and that the emitted synchrotron spectrum may have extended as far as infrared wavelengths. Finally, we compare this 1997 outburst of GS 1354−64 with possible previous outbursts and also with other hard-state objects, both transient and persistent. It appears that a set of characteristics – such as a weak, flat-spectrum radio jet, a mHz QPO increasing in frequency, a surprisingly high optical/X-ray luminosity ratio, and the observed optical peak preceding the X-ray peak – may be common to all hard-state X-ray transients.

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Journal article


Monthly Notices of the Royal Astronomical Society, Vol. 323, no. 1 (2001), pp. 517-528






Copyright © 2001 RAS.