Characterization of the infrared/X-ray subsecond variability for the black hole transient GX 339-4

Vincentelli, F.M.; Casella, P.; Maccarone, T.J.; Uttley, P.; Gandhi, P.; Belloni, T.; De Marco, B.; Russell, D.M.; Stella, L.; O'Brien, K.

Abstract

We present a detailed analysis of the X-ray/IR fast variability of the Black-Hole Transient GX 339-4 during its low/hard state in 2008 August. Thanks to simultaneous high time resolution observations made with the VLT and RXTE, we performed the first characterization of the subsecond variability in the near-infrared band – and of its correlation with the X-rays – for a low-mass X-ray binary, using both time- and frequency-domain techniques. We found a power-law correlation between the X-ray and infrared fluxes when measured on time-scales of 16 s, with a marginally variable slope, steeper than the one found on time-scales of days at similar flux levels. We suggest the variable slope – if confirmed – could be due to the infrared flux being a non-constant combination of both optically thin and optically thick synchrotron emission from the jet, as a result of a variable self-absorption break. From cross spectral analysis, we found an approximately constant infrared time lag of ≈0.1 s, and a very high coherence of ∼90 per cent on time-scales of tens of seconds, slowly decreasing towards higher frequencies. Finally, we report on the first detection of a linear rms–flux relation in the emission from a low-mass X-ray binary jet, on time-scales where little correlation is found between the X-rays and the jet emission itself. This suggests that either the inflow variations and jet IR emission are coupled by a non-linear or time-variable transform, or that the IR rms–flux relation is not transferred from the inflow to the jet, but is an intrinsic property of emission processes in the jet.

Citation

Vincentelli, F., Casella, P., Maccarone, T., Uttley, P., Gandhi, P., Belloni, T., De Marco, B., Russell, D., Stella, L., & O'Brien, K. (2018). Characterization of the infrared/X-ray subsecond variability for the black hole transient GX 339-4. Monthly Notices of the Royal Astronomical Society, 477(4), 4524-4533. https://doi.org/10.1093/mnras/sty710

• Journal Article Type: Article
• Acceptance Date: Mar 14, 2018
• Online Publication Date: Mar 16, 2018
• Publication Date: Jul 11, 2018
• Deposit Date: Jun 7, 2018
• Publicly Available Date: Jun 8, 2018
• Journal: Monthly Notices of the Royal Astronomical Society
• Print ISSN: 0035-8711
• Electronic ISSN: 1365-2966
• Publisher: Royal Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 477
• Issue: 4
• Pages: 4524-4533
• DOI: https://doi.org/10.1093/mnras/sty710
• Public URL: https://durham-repository.worktribe.com/output/1329381