Radio detections of the brightening black hole candidate Swift J1753.5-0127 made with the Arcminute Microkelvin Imager Large Array

ATel #10110; J. Bright, T. Staley, R. Fender, S. Motta, (Uni. Oxford), T. Cantwell (Uni. Manchester)
on 22 Feb 2017; 15:14 UT
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Credential Certification: Sara Elisa Motta (sara.motta@physics.ox.ac.uk)

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We report the first new radio detections of the re-brightening black hole X-ray binary candidate Swift J1753.5-0127, obtained on 15 February and 19 February 2017 with the Arcminute Microkelvin Imager Large Array (AMI-LA) interferometer.

The unusual low mass X-ray binary source Swift J1753.5-0127 faded to optical, X-ray and radio quiescence in 2016 (ATels #9708, #9739, #9765, #9735) after an outburst phase lasted ~11 years. Recent monitoring with the Faulkes Telescope North (ATel #10075) revealed a 4 magnitude brightening in the V-band (MJD 57797.6) with the source appearing to remain at this new value in follow-up observations (ATel #10097). The new V-band magnitude is comparable to the pre-fading value. Swift XRT ToO observations of the source (ATels #10081, #10097) also show an increase in activity, with an XRT count rate of 0.83 c/s (~300 times the previous XRT upper limit, ATel #9735).

We observed this source with the AMI-LA interferometer on 15 February 2017 (MJD 57799.2) and 19 February 2017 (MJD 57803.3) with 4-hour exposure times. We detect a point source at the location of Swift J1753.5-0127 and report flux density measurements of 300 ± 80 μJy on 15 February 2017 and 320 ± 50 μJy on 19 February 2017, both at a central frequency of 15.5 GHz. Swift J1753.5-0127 was extensively monitored by the AMI-LA between January 2013 and July 2015 (Rushton et. al., MNRAS, 2016) who reported a time averaged hard-state flux of 300 μJy followed by a soft-state transition below the array detection limit of 150 μJy per beam. Additionally, the Karl G. Jansky Very Large Array provided an upper limit of 7.5 μJy per beam at 9.0 and 10.65 GHz on 7 November 2016 (MJD 57699.9, ATel #9765). When combined with our recent detections, this indicates an increase in radio flux density of at least a factor ~40 over the last 3.5 months.

We plan on continued monitoring of the source with the AMI-LA and would like to thank the Mullard Radio Astronomy Observatory for scheduling these observations.