Optical and near-infrared spectroscopy of the black hole swift J1753.5-0127
Rahoui, Farid and Tomsick, John A. and Coriat, Mickael and Corbel, Stephane and Fürst, Felix and Gandhi, Poshak and Kalemci, Emrah and Migliari, Simone and Stern, Daniel and Tzioumis, Anastasios K. (2015) Optical and near-infrared spectroscopy of the black hole swift J1753.5-0127. Astrophysical Journal, 810 (2). ISSN 0004-637X (Print) 1538-4357 (Online)
Official URL: http://dx.doi.org/10.1088/0004-637X/810/2/161
We report on a multiwavelength observational campaign of the black hole (BH) X-ray binary Swift J1753.5-0127 that consists of an ESO/X-shooter spectrum supported by contemporaneous Swift/X-ray Telescope+Ultra-Violet/Optical Telescope (UVOT) and Australia Telescope Compact Array data. Interstellar medium absorption lines in the X-shooter spectrum allow us to determine E(B-V)=0.45+/- 0.02 along the line of sight to the source. We also report detection of emission signatures of He ii λ 4686, Hα, and, for the first time, H i λ 10906 and Paβ. The double-peaked morphology of these four lines is typical of the chromosphere of a rotating accretion disk. Nonetheless, the paucity of disk features points toward a low level of irradiation in the system. This is confirmed through spectral energy distribution modeling, and we find that the UVOT+X-shooter continuum mostly stems from the thermal emission of a viscous disk. We speculate that the absence of reprocessing is due to the compactness of an illumination-induced envelope that fails to reflect enough incoming hard X-ray photons back to the outer regions. The disk also marginally contributes to the Compton-dominated X-ray emission and is strongly truncated, with an inner radius about 1000 times larger than the BH's gravitational radius. A near-infrared excess is present, and we associate it with synchrotron radiation from a compact jet. However, the measured X-ray flux is significantly higher than what can be explained by the optically thin synchrotron jet component. We discuss these findings in the framework of the radio-quiet versus X-ray-bright hypothesis, favoring the presence of a residual disk, predicted by evaporation models, that contributes to the X-ray emission without enhancing the radio flux.
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