Sunday, August 4, 2013

1308.0279 (Nestor M. Lasso-Cabrera et al.)

Fast X-Ray/IR cross-correlations and relativistic jet formation in GRS 1915+105    [PDF]

Nestor M. Lasso-Cabrera, Stephen S. Eikenberry
We present cross-correlation analyses of simultaneous X-ray and near-infrared (near-IR) observations of the microquasar GRS 1915+105 during relativistic jet-producing epochs (X-ray class $\alpha$ and $\beta$). While previous studies have linked the large-amplitude IR flares and X-ray behaviors to jet formation in these states, our new analyses are sensitive to much lower-amplitude IR variability, providing more sensitive probes of the jet formation process. The X-ray to IR cross-correlation function (CCF) shows significant correlations which vary in form between the different X-ray states. During low/hard dips in both classes, we find no significant X-ray/IR correlation. During high-variability epochs, we find consistently significant correlations in both $\alpha$ and $\beta$ classes, but with strong differences in the CCF structure. The high-variability $\alpha$ CCF shows strong anti-correlation between X-ray/IR, with the X-ray preceding the IR by $\sim$ 13 $\pm$ 2s. The high-variability $\beta$ state shows time-variable CCF structure, which is statistically significant but without a clearly consistent lag. Our simulated IR light curves, designed to match the observed CCFs, show variably-flickering IR emission during the class $\beta$ high-variability epoch, while the class $\alpha$ can be fit by IR flickering with frequencies in the range 0.1 to 0.3 Hz, strengthening $\sim$10 s after every X-ray subflare. We interpret these features in the context of the X-ray-emitting accretion disk and IR emission from relativistic jet formation in GRS 1915+105, concluding that the CCF analysis places the origin in a synchrotron-emitting relativistic compact jet at a distance from the compact object of $\sim$0.02AU.
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