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

Abstract

Circinus X-1 is a bright and highly variable X-ray binary which displays strong and rapid evolution in all wavebands. Radio flaring, associated with the production of a relativistic jet, occurs periodically on a ~17-day timescale. A longer-term envelope modulates the peak radio fluxes in flares, ranging from peaks in excess of a Jansky in the 1970s to an historic low of milliJanskys during the years 1994 to 2007. Here we report first observations of this source with the MeerKAT test array, KAT-7, part of the pathfinder development for the African dish component of the Square Kilometre Array (SKA), demonstrating successful scientific operation for variable and transient sources with the test array. The KAT-7 observations at 1.9 GHz during the period 13 December 2011 to 16 January 2012 reveal in temporal detail the return to the Jansky-level events observed in the 1970s. We compare these data to contemporaneous single-dish measurements at 4.8 and 8.5 GHz with the HartRAO 26-m telescope and X-ray monitoring from MAXI. We discuss whether the overall modulation and recent dramatic brightening is likely to be due to an increase in the power of the jet due to changes in accretion rate or changing Doppler boosting associated with a varying angle to the line of sight.

7 pages, 5 figures, accepted for publication in MNRAS 14 May 2013

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Cited by in corpus (9)

• Evidence for simultaneous jets and disk winds in luminous low-mass X-ray binaries
• Theory of Disk Accretion onto Magnetic Stars
• The evolving polarised jet of black hole candidate Swift J1745-26
• The twisted jets of Circinus X-1
• Early Science with the Karoo Array Telescope: a Mini-Halo Candidate in Galaxy Cluster Abell 3667
• The nature of the companion star in Circinus X-1
• Sudden End of X-Ray Outbursts around Periastron of Circinus X-1 Observed with MAXI
• Discovery of a suspected giant radio galaxy with the KAT-7 array
• Connecting the m-dots: accretion rates and thermonuclear burst recurrence times on neutron stars and white dwarfs