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

TL;DR

This study assesses the potential of optical photometry to detect quiescent black hole X-ray binaries and other compact stellar objects, demonstrating that photometric methods can effectively identify these faint sources and distinguish among different populations.

Contribution

It introduces a photometric approach using existing filters to detect quiescent black hole binaries and differentiate them from other compact objects, expanding observational capabilities.

Findings

Photometric detection of black hole binaries is feasible with current filters.

The method can recover Halpha emission line widths with high accuracy.

The survey can also identify other compact star populations.

Abstract

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 Halpha 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 FWHM of the Halpha emission line to better than 10% for targets with a wide range of line EWs and down to magnitude r~22. We further explore the potential of our photometric system to disentangle other populations of compact stars and Halpha 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 ultra-compact binaries.