A jet model for the fast IR variability of the black hole X-ray binary GX 339-4

Abstract

Using the simultaneous Infra-Red (IR) and X-ray light curves obtained by Kalamkar et al. (2016), we perform a Fourier analysis of the IR/X-ray timing correlations of the black hole X-ray binary (BHB) GX 339-4. The resulting IR vs X-ray Fourier coherence and lag spectra are similar to those obtained in previous studies of GX 339-4 using optical light curves. In particular, above 1 Hz, the lag spectrum features an approximately constant IR lag of about 100 ms. We model simultaneously the radio to IR Spectral Energy Distribution (SED), the IR Power Spectral Density (PSD), and the coherence and lag spectra using the jet internal shock model ISHEM assuming that the fluctuations of the jet Lorentz factor are driven by the accretion flow. It turns out that most of the spectral and timing features, including the 100 ms lag, are remarkably well reproduced by this model. The 100 ms time-scale is then associated with the travel time from the accretion flow to the IR emitting zone. Our exploration of the parameter space favours a jet which is at most mildly relativistic (Γ < 3), and a linear and positive relation between the jet Lorentz factor and X-ray light curve i.e. Γ(t) −1 ∝ L X (t). The presence of a strong Low Frequency Quasi Periodic Oscillation (LFQPO) in the IR light curve could be caused by jet precession driven by Lense-Thirring precession of the jet-emitting accretion flow. Our simulations confirm that this mechanism can produce an IR LFQPO similar to that observed in GX 339-4.

X-ray dips and a complex UV/X-ray cross-correlation function in the black hole candidate MAXI J1820+070

“…Its optical/X-ray CCF has a similar peak, but complemented by the precognition dip (Gandhi et al 2010). The single-peak CCF has been successfully modelled using the jet internal shocks scenario (e.g., Malzac et al 2018), and the short delay in this model corresponds to the propagation time between the central engine and the region of maximal IR radiation within the jet. The observed CCF in MAXI J1820+070 peaks at time lags which are at least an order of magnitude higher than those detected in GX 339-4, and is more consistent with those of Swift J1753.5-0127, thus supporting the irradiated disc scenario.…”

Physical Constraints from Near-infrared Fast Photometry of the Black Hole Transient GX 339–4

“…Lags: The IR 0.1 second lag observed at high frequencies is easily explained in terms of travel time of the fluctuations from the inflow to the jet (Malzac 2014;Malzac et al 2018). Malzac et al (2018) have shown that also the negative lags observed at low frequencies can be accounted for by the model, due to a differential response of the shocks together with Doppler boosting modulation. Also in this case, dedicated simulations are in order to quantify this scenario for this dataset.…”

“…In this scenario, the whole IR variable emission is interpreted in terms of synchrotron emission from a jet, in which shells with different velocity collide and dissipate their differential energy (Jamil et al 2010;Malzac 2014;Malzac et al 2018). The shell Lorentz factor PSD is assumed to be identical to the X-ray PSD, which is assumed to be a proxy for the accretion rate.…”

“…In some cases, an inflow could reproduce neatly the data (Veledina et al 2017), while in other cases a jet origin has been securely identified, at least for the fastest (subsecond) variability component (Gandhi et al 2008) and especially at infrared wavelengths (Casella et al 2010), often showing a ∼ 0.1-second delay with respect to the X-ray variability. In at least some cases, an internalshock jet model could reproduce successfully both the short timescale variability and the average broad-band spectral energy distribution (Malzac 2014;Malzac et al 2018). Further datasets have yielded further constraints on the geometry of relativistic jets , and on the physical processes taking place at their base (Vincentelli et al 2018).…”

Optical and X-ray correlations during the 2015 outburst of the black hole V404 Cyg

“…Synthesizing these results, a possible scenario is then that the disc is recessed between large flares, with a quasi-steady compact jet. Transient instabilities in the jet could give rise to rapid optical flaring (Malzac et al 2018). During major flares, the disc moves inward with the flare then ending with disruption of this transient disc and ejection of a plasmon, leading to a delayed optical flare (Mirabel et al 1998).…”