Evidence for a Disk-Jet Interaction in the Microquasar GRS 1915+105

We report simultaneous X-ray and infrared (IR) observations of the Galactic microquasar GRS1915+105 using XTE and the Palomar 200-inch telescope on August 13-15, 1997 UTC. During the last two nights, the microquasar GRS 1915+105 exhibited quasi-regular X-ray/infrared (IR) flares with a spacing of $\sim 30$ minutes. While the physical mechanism triggering the flares is currently unknown, the one-to-one correspondence and consistent time offset between the X-ray and IR flares establish a close link between the two. At late times in the flares the X-ray and IR bands appear to ``decouple'', with the X-ray band showing large-amplitude fast oscillations while the IR shows a much smoother, more symmetrical decline. In at least three cases, the IR flare has returned to near its minimum while the X-rays continue in the elevated oscillatory state, ruling out thermal reprocessing of the X-ray flux as the source of IR flare. Furthermore, observations of similar IR and radio flares by Fender et al. (1997) imply that the source of the IR flux in such flares is synchrotron emission. The common rise and subsequent decoupling of the X-ray and IR flux and probable synchrotron origin of the IR emission is consistent with a scenario wherein the IR flux originates in a relativistic plasma which has been ejected from the inner accretion disk. In that case, these simultaneous X-ray/IR flares from a black-hole/relativistic-jet system are the first clear observational evidence linking of the time-dependent interaction of the jet and the inner disk in decades of quasar and microquasar studies.