  The X-ray spectrum of the Galactic X-ray binary V4641 Sgr in outburst has
been found to exhibit a remarkably broad emission feature above 4 keV, with
inferred equivalent widths up to 2 keV. Such a feature was first detected
during the X-ray flaring activity associated with the giant outburst that the
source experienced in 1999 September. The extraordinarily large equivalent
width line was then ascribed to reflection/reprocessing of fluorescent Fe
emission within an extended optically thick outflow enshrouding the binary
system as a result of a short-lived, super-Eddington accretion episode. Making
use of new and archival X-ray observations, we show here that a similar feature
persists over four orders of magnitude in luminosity, down to Eddington ratios
as low as log(L_Edd) = -4.5, where the existence of an optically thick envelope
appears at odds with any viable accretion flow model. Possible interpretations
for this highly unusual X-ray spectrum include a blend of Doppler
shifted/boosted Fe lines from unresolved X-ray jets (a la SS433), or, the first
Galactic analog of a blazar spectrum, where the >4 keV emission would
correspond to the onset of the Inverse Compton hump. Either requires a low
inclination angle of the jet with respect to the line of sight, in agreement
with the estimates for the 1999 superluminal jet (i_jet<10 deg). The fast
variability of the feature, combined with the high orbital axis inclination (60
deg< i_orb<71 deg), argue for a rapidly precessing accretion flow around V4641
Sgr, possibly leading to a transient microblazar behavior.
