AMI detection of a flare from BHC XTE1908+094 at 2cm
ATel #5551; A. P. Rushton, R. Fender, G. Anderson, T. Staley (Uni. of Oxford & Southampton), C. Rumsey, D. Titterington (MRAO, Cambridge)
on 6 Nov 2013; 10:52 UT
Credential Certification: Anthony Rushton (anthony.rushton@astro.ox.ac.uk)
Subjects: Radio, Request for Observations, Binary, Black Hole, Transient, Variables
Referred to by ATel #: 5575
The black hole candidate XTE J1908+094 recently entered a hard X-ray state starting around 2013-10-26 (Krimm et al. ATel #5523, Atel #5529). This hard state event has been associated with a flat radio spectrum, between 5-15 GHz (via VLA and AMI), emitting a flux of around ~1 mJy (Miller-Jones et al. Atel #5530, Rushton et al. Atel #5532).
A noticeable drop in the hard Swift/BAT X-ray lightcurve started to occur around 2013-11-02 (MJD 56598). Negoro et al. (Atel #5549) also reported a clear hard-to-soft spectral evolution using MAXI-GSC. A rapid increase in 2-4 keV X-rays was observed in the MAXI band on 2013-11-05 with a significant drop in the hardness ratio, suggesting the source has entered a soft state.
We report a rapid increase in the 2 cm radio flux, detected by the AMI telescope (in Cambridge, UK), which occurred during the apparent hard-to-soft state transition. On 2013-11-04T14:22-18:19 UT the flux was 930+/-70 microJy/beam, this increased to 7310+/-73 microJy/beam on 2013-11-05T14:27-20:24 UT (observations were taken at a central frequency of 16.13 GHz, with a bandwidth covering 4.5 GHz). Optically thin radio-emitting ejecta are known to be associated with hard-to-soft state transitions (e.g. review Fender & Belloni, 2012, Science, 337, 540); therefore it is highly probable this BHC ejected plasma between 5th and 6th November 2013 UT. We encourage continued multi-wavelength observations of this event, particular at high angular resolution. The AMI telescope will continue to monitor this source at 2cm.
