Evidence for a compact jet dominating the broadband spectrum of the black hole accretor XTE J1550-564

Understand

[abridged] The black hole X-ray binary XTE J1550-564 was monitored extensively at X-ray, optical and infrared wavelengths throughout its outburst in 2000.

• We show that it is possible to separate the optical/near-infrared (OIR) jet emission from the OIR disc emission.
• Focussing on the jet component, we find that as the source fades in the X-ray hard state, the OIR jet emission has a spectral index consistent with optically thin synchrotron emission (alpha ~ -0.6 to -0.7, where F_nu \propto nu^alpha).
• This jet emission is tightly and linearly correlated with the X-ray flux; L_OIR,jet \propto L_X^(0.98 +- 0.08) suggesting a common origin.