GRO J1655-40

K. Horne, E. T. Harlaftis, and R. Baptista, University of St. Andrews; C. Hellier and A. Allan, Keele University; H. Johnston, Anglo-Australian Observatory; J. Patterson and J. Kemp, Columbia University; C. Haswell, University of Sussex and Columbia University; and W. Chen, Goddard Space Flight Center, report on the optical/ultraviolet brightening of GRO J1655-40 during the recent x-ray outburst (IAUC 6393): "Cerro Tololo photometry on May 10.41 UT gave Johnson magnitudes U = 17.0, B = 16.8, V = 15.4, R = 14.4, I = 13.4, which fit a power-law spectrum with slope 1/3, reddened by E(B-V) = 1.5 mag. Anglo-Australian Telescope spectra obtained on May 10.48, 11.57, and 12.57 confirm the red continuum slope, with emission from He II at 468.6 nm and CIII/NIII at 464.0 nm (FWHM = 2 nm, EW = 0.2 nm), and broad absorption filled in by multi-component emission at H-beta and H-alpha. Simultaneous HST/XTE data on May 13.9-14.3 show 5- to 10-percent variations on timescales of 2 s-10 min. Deep 220-nm absorption in the HST spectrum suggests E(B-V) = 1.3 mag. HST/XTE observations were planned for May 20.59-20.80, 27.8-28.1, June 8.53, and two additional times in June."