Visit ASIAA Homepage Registration Deadline: November 1, 2018 (Taiwan Time)
East-Asia AGN Workshop 2019
January 21(Mon)-23(Wed), 2019
ASIAA Auditorium, 1st Floor AS/NTU Astronomy-Mathematics Building

Poster Presentation

EUCLIA - Exploring the UV/optical continuum lag in active galactic nuclei. I. a model without light echoing

Author(s): Zhen-Yi Cai (USTC), Jun-Xian Wang (USTC), Fei-Fan Zhu (USTC), Mou-Yuan Sun (USTC), Wei-Min Gu (XMU), Xin-Wu Cao (SHAO), Feng Yuan (SHAO)

Presenter: Zhen-Yi Cai (USTC/China)

The tight inter-band correlation and the lag-wavelength relation among UV/optical continua of active galactic nuclei have been firmly established. They are usually understood within the widespread reprocessing scenario, however, the implied inter-band lags are generally too small. Furthermore, it is challenged by new evidences, such as the X-ray reprocessing yields too much high frequency UV/optical variations as well as it fails to reproduce the observed timescale-dependent color variations among Swift lightcurves of NGC 5548.
In a different manner, we demonstrate that an upgraded inhomogeneous accretion disk model, whose local independent temperature fluctuations are subject to a speculated common large-scale temperature fluctuation, can intrinsically generate the tight inter-band correlation and lag across UV/optical, and be in nice agreement with several observational properties of NGC 5548, including the timescale-dependent color variation. The emergent lag is a result of the differential regression capability of local temperature fluctuations when responding to the large-scale fluctuation. An average speed of propagations as large as $\gtrsim 15\%$ of the speed of light may be required by this common fluctuation. Several potential physical mechanisms for such propagations are discussed. Our interesting phenomenological scenario may shed new light on comprehending the UV/optical continuum variations of active galactic nuclei.

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