تقرير
What Drives the Variability in AGN? Explaining the UV-Xray Disconnect Through Propagating Fluctuations
| العنوان: | What Drives the Variability in AGN? Explaining the UV-Xray Disconnect Through Propagating Fluctuations |
|---|---|
| المؤلفون: | Hagen, Scott, Done, Chris, Edelson, Rick |
| سنة النشر: | 2024 |
| المجموعة: | Astrophysics |
| مصطلحات موضوعية: | Astrophysics - High Energy Astrophysical Phenomena, Astrophysics - Astrophysics of Galaxies |
| الوصف: | Intensive broadband reverberation mapping campaigns have shown that AGN variability is significantly more complex than expected from disc reverberation of the variable X-ray illumination. The UV/optical variability is highly correlated and lagged, with longer lags at longer wavelengths as predicted, but the observed timescales are longer than expected. Worse, the UV/optical lightcurves are not well correlated with the X-rays which should drive them. Instead, we consider an intrinsically variable accretion disc, where slow mass accretion rate fluctuations are generated in the optical-UV disc, propagating down to modulate intrinsically faster X-ray variability from the central regions. We match our model to Fairall 9, a well studied AGN with $L \sim 0.1L_{\rm{Edd}}$, where the spectrum is dominated by the UV/EUV. Our model produces lightcurves where the X-rays and UV have very different fast variability, yet are well correlated on longer timescales, as observed. It predicts that the intrinsic variability has optical/UV leading the X-rays, but including reverberation of the variable EUV from an inner wind produces a lagged bound-free continuum which matches the observed UV-optical lags. We conclude that optical/UV AGN variability is likely driven by intrinsic fluctuations within the disc, not X-ray reprocessing: the observed longer than expected lags are produced by reverberation of the EUV illuminating a wind not by X-ray illumination of the disc: the increasing lag with increasing wavelength is produced by the increased contribution of the (constant lag) bound-free continuum to the spectrum, rather than indicating intrinsically larger reverberation distances for longer wavelengths. Comment: 15 Pages, 11 Figures, 2 Appendices - Accepted for publication in MNRAS |
| نوع الوثيقة: | Working Paper |
| URL الوصول: | http://arxiv.org/abs/2401.03452 |
| رقم الأكسشن: | edsarx.2401.03452 |
| قاعدة البيانات: | arXiv |
| الوصف غير متاح. |