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Remarkable flaring activity in Cygnus X-1 at 15 GHz

ATel #10648; Guy Pooley MRAO, Cambridge, UK
on 17 Aug 2017; 11:45 UT
Credential Certification: Guy Pooley (ggp1@cam.ac.uk)

Subjects: Radio, Black Hole

The radio emission at 15 GHz from Cygnus X-1 is monitored regularly by the the AMI Large Array at MRAO, Cambridge. The radio flux density is typically near 20 mJy, but is subject to wide variations, including very rare events lasting for some minutes and which are usually termed 'flares'. These events became more frequent in early August, until the sequence observed on 2017 Aug 11 which included about 6 'flares' in a 3-hour observation. These flares are typically 5 to 10 min in duration and 10 to 25 mJy in amplitude. The plot is unlike any other from this source in many years of observing. A pdf plot is to be found at http://www.mrao.cam.ac.uk/~guy/cx1/cx1-170811.pdf Details of the observation: Start time 2017 Aug 11 21h13m UT Duration 3.0h Integration time: 10s per point Gaps in the upper plot correspond to a visit to the phase calibrator source. The lower plot is to be ignored. There is a superficial resemblance to the behaviour of the XRB GRS1915+105, although at first sight Cyg X-1 does not show the same regularity in the timing of the flares.