Sub-second optical and X-ray timing correlations in V404 Cygni
Abstract
The 2015 outburst of V404 Cygni was the most prolific X-ray binary outburst of the century so far, and the binaries community came together in coordinating several global monitoring campaigns. We will review some of the main lessons learnt from multiwavelength fast (sub-second) timing efforts. In particular, we will show strong evidence pointing to a jet origin for the most rapid detected optical variability on timescales of just ∼ 30 ms. The source of such optical variations has hitherto been controversial, with a magnetically-active corona, an advective flow, a jet or a combination of components having been suggested. Using data from ULTRACAM and NuSTAR, we find an optical delay with respect to X-rays of ∼ 0.1s, with this delayed cross-correlation signal strengthening together with a brightening AMI radio jet. A red optical spectral slope and high brightness flare temperatures further point to the inner jet being the most plausible emission source. Our result sets a characteristic elevation of ∼ 10^3 Schwarzschild radii for the jet base optical emission zone above the black hole. This size scale appears to be common to other sources and is thus constraining for jet MHD and internal shock models.
- Publication:
-
The X-ray Universe 2017
- Pub Date:
- October 2017
- Bibcode:
- 2017xru..conf...85G