Follow-up optical observations of Swift J1753.5-0127 as it fades into quiescence

ATel #9739; Ahlam Al Qasim, Aisha AlMannaei, David M. Russell (NYU Abu Dhabi), Fraser Lewis (Faulkes Telescope Project & Astrophysics Research Institute, LJMU)
on 10 Nov 2016; 11:21 UT
Credential Certification: David M. Russell (dave.russell5@gmail.com)

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Swift J1753.5-0127, the black hole candidate X-ray binary is fading and going into quiescence. We observed an initial optical decay of 0.043 mag/day between 19 September and 1 November (ATel #9708). Follow up X-ray and UV observations with Swift show no detections of the source on 6 and 7 November (ATel #9735). We have continued to monitor the source with the 2-m robotic Faulkes Telescope North (located at Haleakala on Maui) before it becomes Sun-constrained. We also acquired one observation with the Las Cumbres Observatory (LCO) 1-m telescope at the McDonald Observatory in Texas.

In our follow-up observations on 6 November 2016 at 4:48 UTC (MJD 57698.20), the magnitude of the source was observed to be V = 20.65 +- 0.30; i' = 19.96 +- 0.16. This magnitude was fainter by 0.44 +- 0.19 in the i'-band compared to our previous detection of i' = 19.52 +- 0.11 on 1 November. The new V-band detection was only marginal, with S/N = 3.9. This most recent magnitude is close to the DSS limit that we previously mentioned to be V > 21. The magnitudes are consistent with the continued reddening during the decay due to the decreasing temperature of the disc during the fade, but the errors are large on the recent color estimate. On 8 November, two weak i'-band detections were made with the 1-m at 00:57 UT and the 2-m at 04:40 UT. The magnitudes were i' = 19.92 +- 0.35 and i' = 20.14 +- 0.30 respectively with S/N = 3.3 and 3.8. These are again consistent with the continued fading of the source.

These magnitudes can be useful for planning deep imaging or spectroscopy with large telescopes. The Faulkes Telescope observations are part of an on-going monitoring campaign of ~ 40 low-mass X-ray binaries (Lewis et al. 2008). This work makes use of observations from the Las Cumbres Observatory (LCO).

Swift J1753.5-0127 Faulkes Telescope light curve