A feasibility study on the photometric detection of quiescent black hole X-ray binaries

We investigate the feasibility of detecting quiescent black hole X-ray binaries using optical photometric techniques. To test this, we employ a combination of r-band and H α filters currently available at the Roque de los Muchachos Observatory. Photometric observations of four dynamical black holes (GRO J0422+320, A 0620-00, XTE J1118+480, and XTE J1859+226) at SNR ≳ 35-50, supplemented with near simultaneous spectroscopic data, demonstrate that it is possible to recover the full width at half-maximum of the H α emission line to better than 10 per cent for targets with a wide range of line equivalent widths and down to magnitude r ∼ 22. We further explore the potential of our photometric system to disentangle other populations of compact stars and H α emitters. In particular, we show that HAWKs, a survey designed to unveil quiescent black holes, will also provide a detailed census of other Galactic populations, most notably short period (eclipsing) cataclysmic variables, neutron star X-ray binaries, and ultracompact binaries.