Optical and X-ray Correlations During the 2015 Outburst of the Black Hole V404 Cyg. (arXiv:1905.00949v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Hynes_R/0/1/0/all/0/1">R. I. Hynes</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robinson_E/0/1/0/all/0/1">E. L. Robinson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Terndrup_D/0/1/0/all/0/1">D. M. Terndrup</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gandhi_P/0/1/0/all/0/1">P. Gandhi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Froning_C/0/1/0/all/0/1">C. S. Froning</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Starrfield_R/0/1/0/all/0/1">R. M. Wagner S. Starrfield</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dhillon_V/0/1/0/all/0/1">V. S. Dhillon</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Marsh_T/0/1/0/all/0/1">T. R. Marsh</a>
We present a serendipitous multiwavelength campaign of optical photometry
simultaneous with Integral X-ray monitoring of the 2015 outburst of the black
hole V404 Cyg. Large amplitude optical variability is generally correlated with
X-rays, with lags of order a minute or less compatible with binary light travel
timescales or jet ejections. Rapid optical flaring on time-scales of seconds or
less is incompatible with binary light-travel timescales and has instead been
associated with synchrotron emission from a jet. Both this rapid jet response
and the lagged and smeared one can be present simultaneously. The optical
brightness is not uniquely determined by the X-ray brightness, but the
X-ray/optical relationship is bounded by a lower-envelope such that at any
given optical brightness there is a maximum X-ray brightness seen.} This
lower-envelope traces out a Fopt proportional to Fx^0.54 relation which can be
approximately extrapolated back to quiescence. Rapid optical variability is
only seen near this envelope, and these periods correspond to the hardest hard
X-ray colours. This correlation between hard X-ray colour and optical
variability (and anti-correlation with optical brightness) is a novel finding
of this campaign, and apparently a facet of the outburst behaviour in V404 Cyg.
It is likely that these correlations are driven by changes in the central
accretion rate and geometry.
We present a serendipitous multiwavelength campaign of optical photometry
simultaneous with Integral X-ray monitoring of the 2015 outburst of the black
hole V404 Cyg. Large amplitude optical variability is generally correlated with
X-rays, with lags of order a minute or less compatible with binary light travel
timescales or jet ejections. Rapid optical flaring on time-scales of seconds or
less is incompatible with binary light-travel timescales and has instead been
associated with synchrotron emission from a jet. Both this rapid jet response
and the lagged and smeared one can be present simultaneously. The optical
brightness is not uniquely determined by the X-ray brightness, but the
X-ray/optical relationship is bounded by a lower-envelope such that at any
given optical brightness there is a maximum X-ray brightness seen.} This
lower-envelope traces out a Fopt proportional to Fx^0.54 relation which can be
approximately extrapolated back to quiescence. Rapid optical variability is
only seen near this envelope, and these periods correspond to the hardest hard
X-ray colours. This correlation between hard X-ray colour and optical
variability (and anti-correlation with optical brightness) is a novel finding
of this campaign, and apparently a facet of the outburst behaviour in V404 Cyg.
It is likely that these correlations are driven by changes in the central
accretion rate and geometry.
http://arxiv.org/icons/sfx.gif
