Hynes, R.I.; Haswell, C.A.; Cui, W.; Shrader, C.R.; O'Brien, K.; Chaty, S.; Skillman, D.R.; Patterson, J. and Horne, K.
|DOI (Digital Object Identifier) Link:||http://doi.org/10.1046/j.1365-8711.2003.06938.x|
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The transient black-hole binary XTE J1118+480 exhibited dramatic rapid variability at all wavelengths which were suitably observed during its 2000 April–July outburst. We examine time-resolved X-ray, ultraviolet, optical and infrared data spanning the plateau phase of the outburst. We find that both X-ray and infrared bands show large amplitude variability. The ultraviolet and optical variability is more subdued, but clearly correlated with that seen in the X-rays. The ultraviolet, at least, appears to be dominated by the continuum, although the lines are also variable. Using the X-ray variations as a reference point, we find that the ultraviolet (UV) variability at long wavelengths occurs later than that at short wavelengths. Uncertainty in the Hubble Space Telescope timing prohibits a determination of the absolute lag with respect to the X-rays, however. The transfer function is clearly not a delta-function, exhibiting significant repeatable structure. For the main signal we can rule out an origin in reprocessing on the companion star – the lack of variation in the lags is not consistent with this, given a relatively high orbital inclination. Weak reprocessing from the disc and/or companion star may be present, but is not required, and another component must dominate the variability. This could be variable synchrotron emission correlated with X-ray variability, consistent with our earlier interpretation of the infrared (IR) flux as due to synchrotron emission rather than thermal disc emission. In fact, the broad-band energy distribution of the variability from IR to X-rays is consistent with expectations of optically thin synchrotron emission. We also follow the evolution of the low-frequency quasi-periodic oscillation in X-rays, UV, and optical. Its properties at all wavelengths are similar, indicating a common origin.
|Item Type:||Journal Article|
|Keywords:||accretion; accretion discs; binaries: close; stars; XTE J1118+480; ultraviolet; X-rays|
|Academic Unit/Department:||Science > Physical Sciences
|Interdisciplinary Research Centre:||Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)|
|Depositing User:||Users 6041 not found.|
|Date Deposited:||12 Jul 2006|
|Last Modified:||14 Jan 2016 16:09|
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