Swift J1753.5-0127 flux is steady

ATel #10097; Guobao Zhang, David M. Russell, Joseph D. Gelfand, Ahlam Al Qasim, Aisha AlMannaei (NYU Abu Dhabi), Fraser Lewis (Faulkes Telescope Project & Astrophysics Research Institute, LJMU)
on 19 Feb 2017; 14:01 UT
Credential Certification: David M. Russell (dave.russell5@gmail.com)

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We report on new X-ray, UV and optical observations of the unusual re-brightening black hole candidate Swift J1753.5-0127. The source has recently increased its brightness in the optical, UV, and X-ray wavebands (ATel #10075, #10081).

We requested Swift ToO observations which commenced on 2017 February 19, 08:04 UT with a 1 ks pointing. The source is continuously detected in X-ray; the 0.3-10 keV X-ray spectrum can be well constrained (chi^2/dof = 1.02) by an absorbed power law with n_H = 0.26(+/- 0.10)E22 /cm^2 and power-law photon index Gamma = 1.78 +/- 0.20. The unabsorbed 0.3-10 keV flux is calculated to be 5.8(+/- 0.5)E-11 ergs/cm^2/s. This is very similar to the last Swift XRT observation on 2017 February 16 (ATel #10081). The spectrum indicates the source is still in the hard X-ray state.

Swift J1753.5-0127 was also clearly detected at UV wavelengths with Swift/UVOT in the uvw1 filter with magnitude uvw1 = 17.17 +/- 0.05 (stat) +/- 0.03 (sys).

We have continued monitoring Swift J1753.5-0127 with the 2-m Faulkes Telescope North, increasing the cadence and extending our coverage to also make use of the Faulkes Telescope South (at Siding Spring, Australia) and the 1-m Las Cumbres Observatory (LCO) telescopes (so far, data have been collected from a 1-m at Siding Spring, and one at Cerro Tololo, Chile). Since our last reported magnitudes of V = 17.27 +- 0.05; i' = 16.95 +- 0.02 on 2017 February 13 (MJD 57797.6; ATel #10075), the source has remained fairly steady. Between February 14 and February 18 (MJD 57798.6 - 57802.8), the magnitudes were consistent within errors, at V = 17.20 +- 0.07; i' = 16.86 +- 0.03, from seven images in each band spanning the last five days. It is interesting to note that these optical magnitudes are similar to last year, when the source spent a prolonged period (2016 February to August; see our light curve linked below) at very similar magnitudes (ATel #9708). This new outburst may be peaking now, and could remain steady for a long time at these flux levels, or start fading again towards quiescence.

Further ToO observations with Swift have been scheduled and multi-wavelength (particularly infrared and radio) observations are encouraged. We would like to thank the Swift team for promptly scheduling these observations. The Faulkes Telescope / LCO 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