Bibcode
Durant, M.; Shahbaz, T.; Gandhi, Poshak; Cornelisse, R.; Muñoz-Darias, T.; Casares, J.; Dhillon, Vik; Marsh, Tom; Spruit, Hendrik; O'Brien, Kieran; Steeghs, Danny; Hynes, Rob
Bibliographical reference
Monthly Notices of the Royal Astronomical Society, Volume 410, Issue 4, pp. 2329-2338.
Advertised on:
2
2011
Citations
32
Refereed citations
25
Description
Using simultaneous observations in X-rays and optical, we have performed
a homogeneous analysis of the cross-correlation behaviours of four X-ray
binaries: SWIFT J1753.5-0127, GX 339-4, Sco X-1 and Cyg X-2. With
high-time-resolution observations using ULTRACAM and RXTE, we
concentrate on the short time-scale, δt < 20 s, variability in
these sources. Here we present our data base of observations, with three
simultaneous energy bands in both the optical and the X-ray, and
multiple epochs of observation for each source, all with ˜second
or better time resolution. For the first time, we include a dynamical
cross-correlation analysis, i.e. an investigation of how the
cross-correlation function changes within an observation. We describe a
number of trends which emerge. We include the full data set of results,
and pick a few striking relationships from among them for further
discussion.
We find, that the surprising form of X-ray/optical cross-correlation
functions, a positive correlation signal preceded by an anticorrelation
signal, is seen in all the sources at least some of the time. Such
behaviour suggests a mechanism other than reprocessing as being the
dominant driver of the short-term variability in the optical emission.
This behaviour appears more pronounced when the X-ray spectrum is hard.
Furthermore, we find that the cross-correlation relationships themselves
are not stable in time, but vary significantly in strength and form.
This all hints at dynamic interactions between the emitting components
which could be modelled through non-linear or differential
relationships.
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