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Circinus X-1 is a bright and highly variable X-ray binary which displaysstrong and rapid evolution in all wavebands. Radio flaring, associated with theproduction of a relativistic jet, occurs periodically on a ~17-day timescale. Alonger-term envelope modulates the peak radio fluxes in flares, ranging frompeaks in excess of a Jansky in the 1970s to an historic low of milliJanskysduring the years 1994 to 2007. Here we report first observations of this sourcewith the MeerKAT test array, KAT-7, part of the pathfinder development for theAfrican dish component of the Square Kilometre Array (SKA), demonstratingsuccessful scientific operation for variable and transient sources with thetest array. The KAT-7 observations at 1.9 GHz during the period 13 December2011 to 16 January 2012 reveal in temporal detail the return to theJansky-level events observed in the 1970s. We compare these data tocontemporaneous single-dish measurements at 4.8 and 8.5 GHz with the HartRAO26-m telescope and X-ray monitoring from MAXI. We discuss whether the overallmodulation and recent dramatic brightening is likely to be due to an increasein the power of the jet due to changes in accretion rate or changing Dopplerboosting associated with a varying angle to the line of sight.

A return to strong radio flaring by Circinus X-1 observed with the Karoo Array Telescope test array KAT-7