We combine a complete sample of 113 pointed observations taken with the Rossi X-ray Timing Explorer between 1996–1999 , monitoring observations taken with the Ryle telescope and the Green Bank Interferometer , and selected observations with the Very Large Array to study the radio and X-ray properties of GRS 1915 + 105 when its X-ray emission is hard and steady .
We establish that radio emission always accompanies the hard-steady state of GRS 1915 + 105 , but that the radio flux density at 15.2 GHz and the X-ray flux between 2–200 keV are not correlated .
Therefore we study the X-ray spectral and timing properties of GRS 1915 + 105 using three approaches : first , by describing in detail the properties of three characteristic observations , then by displaying the time evolution of the timing properties during periods of both faint and bright radio emission , and lastly by plotting the timing properties as a function of the the radio flux density .
We find that as the radio emission becomes brighter and more optically 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 the frequency range of 0.01–10 Hz change sign from negative to positive , 3 ) the coherence between hard and soft photons at low frequencies decreases , and 4 ) the relative amount of low frequency power in hard photons compared to soft photons decreases .
We discuss how these results reflect upon basic models from the literature describing the accretion flow around black holes and the possible connection between Comptonizing electrons and compact radio jets .