Optical and Near Infrared Monitoring of the Black-Hole X-ray Binary GX
  339-4 During 2002-2010
  We present the optical/infra-red lightcurve (O/IR) of the black hole X-ray
binary GX 339-4 collected at the SMARTS 1.3m telescope from 2002 to 2010.
During this time the source has undergone numerous state transitions including
hard-to-soft state transitions when we see large changes in the near-IR flux
accompanied by modest changes in optical flux, and three rebrightening events
in 2003, 2005 and 2007 after GX 339-4 transitioned from the soft state to the
hard. All but one outburst show similar behavior in the X-ray
hardness-intensity diagram. We show that the O/IR colors follow two distinct
tracks that reflect either the hard or soft X-ray state of the source. Thus,
either of these two X-ray states can be inferred from O/IR observations alone.
From these correlations we have constructed spectral energy distributions of
the soft and hard states. During the hard state, the near-IR data have the same
spectral slope as simultaneous radio data when GX 339-4 was in a bright optical
state, implying that the near-IR is dominated by a non-thermal source, most
likely originating from jets. Non-thermal emission dominates the near-IR bands
during the hard state at all but the faintest optical states, and the fraction
of non-thermal emission increases with increasing optical brightness. The
spectral slope of the optical bands indicate that a heated thermal source is
present during both the soft and hard X-ray states, even when GX 339-4 is at
its faintest optical state. We have conducted a timing analysis of the light
curve for the hard and soft states and find no evidence of a characteristic
timescale within the range of 4-230 days.
