  We report the discovery in archival Rossi X-ray Timing Explorer (RXTE) data
of a 40 Hz quasiperiodic oscillation (QPO) in the hard X-ray flux from the
galactic microquasar GRS 1915+105. The QPO is detected only in the hard X-ray
band above 13 keV and was discovered in observations in which the previously
known 67 Hz QPO is present. The 40 Hz QPO has a typical rms amplitude of 2 % in
the 13 - 27 keV band, and a width of about 8.5 Hz (FWHM). We show that the 67
and 40 Hz QPOs are detected in the same observations in July and November,
1997. However, the QPO is not detected in observations from April, May and
June, 1996 in which the 67 Hz QPO was first discovered. The frequency of the 67
Hz QPO is significantly higher in the 1997 observations by about 5 % compared
with the 1996 data. The identification of the 40 Hz QPO makes GRS 1915+105 the
second black hole binary to show a pair of simultaneous high frequency QPO (the
other being GRO J1655-40). The similarities between the properties of the 67 Hz
QPO in GRS 1915+105 and the recently discovered 450 Hz QPO in GRO J1655-40
suggest that the pairs of frequencies in these systems may be produced by the
same physical mechanism, with the frequency differences between the two being
likely due to different black hole masses in the two systems. We discuss the
implications of our result for the mass and spin of GRS 1915+105 as well as for
models of X-ray variability in black holes and neutron stars.
