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Change in radio behaviour of Cygnus X-1

ATel #10446; Guy Pooley (Cavendish Laboratory, Cambridge)
on 31 May 2017; 11:29 UT
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Credential Certification: Guy Pooley (ggp1@cam.ac.uk)

Subjects: Radio, X-ray, Black Hole

Referred to by ATel #: 10459

Negoro et al report in ATel#10322 unusual soft X-ray behaviour in the X-ray binary (and probable black hole) Cygnus X-1. I report changes in the 15-GHz radio flux over a similar interval. The radio source is monitored at a near-daily rate using the AMI Large Array (Cambridge, UK). A plot of the data from 2017 Jan 01 to 2017 May 30 is available at http://www.mrao.cam.ac.uk/~guy/cx1/2017-jan-may.ps Data points on this plot are typically integrations of 10 min. The gap between MJD 57850 and 57870 (Apr 07 to Apr 27) results from operational constraints (weather, observing programs with higher priority), unfortunately coinciding with the change in the behaviour of the soft X-ray and radio emission. Before MJD57850, the mean flux density was 13.3 mJy and the rms scatter 3.2 mJy; corresponding values after MJD57870 were mean 18.8, rms 7.7 mJy. We plan to continue the radio monitoring; I thank the AMI team for organising the observing program.