Characterizing the Radio-X-ray Connection in GRS 1915+105

Abstract

We analyzed radio and X-ray observations of GRS 1915+105, between 1995 May and 2006 June, focusing on the times characterized by radio flares and cycles of hard dips—soft spikes in the X-ray light curve. Assuming these flares to be discrete ejections, we applied a plasmon model to the radio data, with good agreement with the light curves. We fitted a total of 687 radio flares with a standard model of a plasmon. We found that the distribution of width is t ₀ = 1160 s with an rms deviation of 360 s, while that of the amplitude is S _max = 59 mJy with an rms deviation of 28 mJy. The distribution of width is thus rather peaked, while that of the amplitude is not. Regarding radio and X-ray links, this study confirms previous observations on smaller data sets, namely that X-ray cycles of hard dips—soft spikes are always followed by radio flares. A strong correlation is found between the length of X-ray "dips" in the X-ray light curves and the amplitude and fluence of the subsequent radio oscillations. A model of an exponential rise of the form L _{15 GHz}(Δt) = L _max(1 - exp(-(Δt - Δt _min)/τ) is in good agreement with the observations, with the maximum fluence L _max on the order of 70 Jy s, and the characteristic time τ on the order of 200-500 s. We discuss possible physical interpretations of this correlation, regarding the nature of the ejected material and the physical process responsible for the ejection.