The black hole candidate XTE J1752−223 towards and in quiescence: optical and simultaneous X‐ray–radio observations

Abstract

We present optical, X‐ray and radio observations of the black hole transient (BHT) XTE J1752−223 towards and in quiescence. Optical photometry shows that the quiescent magnitude of XTE J1752−223 is fainter than 24.4 mag in the i ′ band. A comparison with measurements of the source during its 2009–2010 outburst shows that the outburst amplitude is more than 8 mag in the i ′ band. Known X‐ray properties of the source combined with the faintness of the quiescence optical counterpart and the large outburst optical amplitude point towards a short orbital‐period system ( P orb ≲ 6.8 h) with an M type (or later) mass donor, at a distance of 3.5 ≲ d ≲ 8 kpc. Simultaneous X‐ray and radio data were collected with Chandra and the Expanded Very Large Array (EVLA), allowing constraints to be placed on the quiescent X‐ray and radio flux of XTE J1752−223. Furthermore, using data covering the final stage of the outburst decay, we investigated the low‐luminosity end of the X‐ray–radio correlation for this source and compared it with other BHTs. We found that XTE J1752−223 adds to the number of outliers with respect to the ‘standard’ X‐ray–radio luminosity relation. Furthermore, XTE J1752−223 is the second source, after the BHT H1743−322, that shows a transition from the region of the outliers towards the ‘standard’ correlation at low luminosity. Finally, we report on a faint, variable X‐ray source we discovered with Chandra at an angular distance of ∼2.9 arcsec to XTE J1752−223 and at a position angle consistent with that of the radio jets previously observed from the BHT. We discuss the possibility that we detected X‐ray emission associated with a jet from XTE J1752−223.