We present optical monitoring of the black hole candidate XTE J1752–223 during its 2009–2010 outburst and decay to quiescence .
The optical light curve can be described by an exponential decay followed by a plateau , then a more rapid fade towards quiescence .
The plateau appears to be due to an extra component of optical emission that brightens and then fades over \sim 40 days .
We show evidence for the origin of this optical ‘ flare ’ to be the synchrotron jet during the decaying hard state , and we identify and isolate both disc and jet components in the spectral energy distributions .
The optical flare has the same morphology and amplitude as a contemporaneous X-ray rebrightening .
This suggests a common origin , but no firm conclusions can be made favouring or disfavouring the jet producing the X-ray flare .
The quiescent optical magnitudes are B \geq 20.6 , V \geq 21.1 , R \geq 19.5 , i ^ { \prime } \geq 19.2 .
From the optical outburst amplitude we estimate a likely orbital period of < 22 h. We also present near-infrared ( NIR ) photometry and polarimetry and rare mid-infrared imaging ( 8 – 12 \mu m ) when the source is nearing quiescence .
The fading jet component , and possibly the companion star may contribute to the NIR flux .
We derive deep mid-IR flux upper limits and NIR linear polarization upper limits .
With the inclusion of radio data , we measure an almost flat jet spectral index between radio and optical ; F _ { \nu } \propto \nu ^ { \sim + 0.05 } .
The data favour the jet break to optically thin emission to reside in the infrared , but may shift to frequencies as high as the optical or UV during the peak of the flare .