GX 339-4 is a moderately strong variable galactic low-mass X-ray binary (LMXB) source[1][2] and black hole candidate that flares from time to time. From spectroscopic measurements, the mass of the black-hole was found to be at least of 5.8 solar masses.[3]
Thomas Henry Markert et al. discovered GX 339-4 in 1973, in data obtained by the MITCosmic Ray Experiment on OSO-7.[4][5] An optical counterpoint to the X-ray source was found by Jonathan E. Grindlay in 1979, and it is optically variable.[6] For that reason it was given a variable star designation, V821 Arae, in 1981.[7]
During the outbursts GX 339-4 shows evolution of quasi-periodic oscillations (QPOs). In the rising phase the QPO frequency monotonically increase as the CENBOL propagates closer to the black hole and in the declining phase the QPO frequency monotonically decreases since the CENBOL recedes away from the black hole after viscosity is decreased. The frequency variation is thus well modeled by the propagating and oscillating shock in the sub-Keplerian flow. The entire spectrum also fits very well using two component advective flow solution.
A strong, variable relativistic jet, emitting from radio to infrared wavelengths was observed by several studies.[9][10][11]