On the Origin of the Various Types of Radio Emission in Grs 1915+105

We investigate the association between the radio “plateau” states and the large superluminal flares in GRS 1915+105 and propose a qualitative scenario to explain this association. To investigate the properties of the source during a superluminal flare, we present GMRT observations during a radio flare which turned out to be a pre-plateau flare as shown by the contemporaneous Ryle telescope observations. A major superluminal ejection was observed at the end of this “plateau” state (Dhawan et al. 2003), associated with highly variable X-ray emission showing X-ray soft dips. This episode, thus has all the three types of radio emission: a pre-plateau flare, a “plateau” state and superluminal jets. We analyze all the available RXTE-PCA data during this episode and show that: (1) the pre-flare “plateau” state consists of a three-component X-ray spectra which includes a multicolor disk-blackbody, a Comptonized component and a power-law and (2) the Compton cloud, which is responsible for the Comptonizing component, is ejected away during the X-ray soft dips. We investigate all the available monitoring data on this source and identify several candidate superluminal flare events and analyze the contemporaneous RXTE pointed observations. We detect a strong correlation between the average X-ray flux during the “plateau” state and the total energy emitted in radio during the subsequent radio flare. We find that the sequence of events is similar for all large radio flares with a fast rise and exponential decay morphology. Based on these results, we propose a qualitative scenario in which the separating ejecta during the superluminal flares are observed due to the interaction of the matter blob ejected during the X-ray soft dips, with the steady jet already established during the “plateau” state. This picture can explain all types of radio emission observed from this source in terms of its X-ray emission characteristics. Subject headings: accretion — radio continuum: stars — X-rays: binaries — X-rays: individual: GRS 1915+105