Characterizing the radio--X-ray connection in GRS 1915+105

TL;DR

This study analyzes radio and X-ray data of GRS 1915+105 over 11 years, confirming that X-ray dips are followed by radio flares, and finds a strong correlation between dip duration and radio flare properties, supporting a plasmon ejection model.

Contribution

It provides a detailed statistical analysis of radio flares and their relation to X-ray dips, applying a plasmon model to a large dataset, and establishes a quantitative correlation between X-ray dip length and radio flare fluence.

Findings

Radio flares are well-modeled by a plasmon with a typical width of 1160 seconds.

X-ray dip durations correlate strongly with radio flare amplitude and fluence.

The exponential rise model fits the radio flare fluence data well.

Abstract

We analyzed radio and X-ray observations of GRS 1915+105, between May 1995 and June 2006, focusing on the times characterized by radio flares and cycles of hard dips-soft spikes in the X-ray lightcurve. Assuming these flares to be discrete ejections, we applied a plasmon model to the radio data, with good agreement with the lightcurves. 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 not. Regarding radio and X-ray links, this study confirms previous observations on smaller datasets, 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 lightcurves, and the amplitude and fluence of the subsequent radio oscillations. A model of an exponential rise of the form L_{15 GHz}(Delta t) = L_{max} (1-exp(-(Delta t - Delta t_{min})/tau) is in good agreement with the observations, with the maximum fluence L_{max} of the order 70 Jy.s, and the characteristic time tau of the order 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.