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| In recent work done by Sun et al., the color variation of quasars, namely the bluer-when-brighter trend, was found to be timescale-dependent using SDSS g/r band light curves in the Stripe 82. Such timescale dependency, e.g. bluer variation at shorter timescales, supports the thermal fluctuation origin of the UV/optical variation in quasars, and can be well modeled with an inhomogeneous accretion disk model. In this paper, we extend the study to much shorter wavelengths in the rest frame (down to extreme UV), using GALEX's photometric data of quasars collected in two ultraviolet bands (NUV and FUV). We develop Monte Carlo simulations to correct possible biases due the considerably larger photometric uncertainties in GALEX light curves (particularly in FUV, comparing with SDSS g/r band), which otherwise could produce artificial results. We securely confirm the previously discovered timescale dependence of the color variability with independent datasets and at shorter wavelengths. |
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| Keywords:black hole astrophysics; galaxies: active, quasars; accretion, accretion disks; time-domain astrophysics |
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