2003ApJ...590.1035S

We present results from four Rossi X-Ray Timing Explorer observations of the bright, low-mass X-ray binary LMC X-2. During these observations, which span 1 yr and include over 160 hr of data, the source exhibits clear evolution through three branches on its hardness-intensity and color-color diagrams, consistent with the flaring, normal, and horizontal branches (FB, NB, HB) of a Z source and remarkably similar to Z tracks derived for GX 17+2, Sco X-1, and GX 349+2. LMC X-2 was observed in the FB, NB, and HB for roughly 30%, 40%, and 30%, respectively, of the total time covered. The source traces out the full extent of the Z in ∼1 day, and the Z track shows evidence for secular shifts on a timescale in excess of a few days. Although the count rate of LMC X-2 is low compared with the other known Z sources due to its greater distance, the power density spectra selected by branch show very low frequency noise characteristics at least consistent with those from other Z sources. We thus confirm the identification of LMC X-2 as a Z source, the first identified outside our Galaxy.