  We present striking results from Rossi X-ray Timing Explorer (RXTE)
observations of the 21-hr low mass X-ray binary X1624-490, showing five complex
dips in unprecedented detail. For the first time, dipping is detected up to 15
keV. Prominent flares are also observed in the light curves, limited to
energies above 8 keV. Spectra selected by intensity during dip episodes can be
well fit with a two-component model consisting of a point-like blackbody from
the neutron star and progressive covering of an extended Comptonized region,
presumably an accretion disk corona (ADC), corrected for photons scattered into
and out of the X-ray beam by a interstellar dust halo. We find that the outer
regions of the absorber are highly ionized and that electron scattering is
totally responsible for the X-ray attenuation during shallow dipping. The
timescales of dip ingress and egress indicate that the envelope of material
absorbing the ADC has smaller angular size than the ADC itself, and that the
ADC is likely limited to a height-to-radius ratio of 10%, rather than being
spherical in extent. In addition, we have analyzed 4.5 yrs of RXTE All Sky
Monitor (ASM) coverage to derive the first accurate orbital ephemeris for
X1624-490, with phase zero (the time of dip centers) well-described by the
relation 2450088.63918(69) + N*0.869907(12) (JD).
