Radio Emission and the Timing Properties of the Hard X‐Ray State of GRS 1915+105

We combine a complete sample of 113 pointed observations taken with the RossiX-ray Timing Explorer between 1996-1999, monitoring observations taken with theRyle telescope and the Green Bank Interferometer, and selected observationswith the Very Large Array to study the radio and X-ray properties of GRS1915+105 when its X-ray emission is hard and steady. We establish that radioemission always accompanies the hard-steady state of GRS 1915+105, but that theradio flux density at 15.2 GHz and the X-ray flux between 2-200 keV are notcorrelated. Therefore we study the X-ray spectral and timing properties of GRS1915+105 using three approaches: first, by describing in detail the propertiesof three characteristic observations, then by displaying the time evolution ofthe timing properties during periods of both faint and bright radio emission,and lastly by plotting the timing properties as a function of the the radioflux density. We find that as the radio emission becomes brighter and moreoptically thick, 1) the frequency of a ubiquitous 0.5-10 Hz QPO decreases, 2)the Fourier phase lags between hard (11.5-60 keV) and soft (2-4.3 keV) in thefrequency range of 0.01-10 Hz change sign from negative to positive, 3) thecoherence between hard and soft photons at low frequencies decreases, and 4)the relative amount of low frequency power in hard photons compared to softphotons decreases. We discuss how these results reflect upon basic models fromthe literature describing the accretion flow around black holes and thepossible connection between Comptonizing electrons and compact radio jets.Comment: 22 pages with 8 figures and 2 tables in emulateapj style. Submitted to Ap