Open AccessThe 1997 hard‐state outburst of the X‐ray transient GS 1354−64/BW Cir
Author(s) -
Brocksopp C.,
Jonker P. G.,
Fender R. P.,
Groot P. J.,
Van Der Klis M.,
Tingay S. J.
Publication year - 2001
Publication title -
monthly notices of the royal astronomical society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.058
H-Index - 383
eISSN - 1365-2966
pISSN - 0035-8711
DOI - 10.1046/j.1365-8711.2001.04193.x
Subject(s) - physics , astrophysics , luminosity , x ray transient , wavelength , astronomy , light curve , polarization (electrochemistry) , instability , synchrotron , galaxy , optics , neutron star , chemistry , mechanics
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.