| Name: Arijit Sar |
| Affiliation: Presidency University, Kolkata |
| Conference ID: ASI2026_199 |
| Title: Variable Corona Height as the Origin of UV–X-ray Lag Variability in NGC 7469 |
| Abstract Type: Poster |
| Abstract Category: High Energy Phenomena, Fundamental Physics and Astronomy |
| Author(s) and Co-Author(s) with Affiliation: Arijit Sar(Presidency University, Kolkata), Ritaban Chatterjee(Presidency University, Kolkata) |
| Abstract: Past observations have shown that in most active galactic nuclei (AGNs), variability in the X-ray emission from the corona leads that of the UV/optical emission from the accretion disk, consistent with X-ray reprocessing by the disk. However, some Seyfert galaxies exhibit the opposite behavior, with X-ray variations lagging those in the UV. One such source is NGC~7469, for which multiwavelength monitoring over the past three decades has revealed changes in the direction of the UV/X-ray time lag. In particular, simultaneous {\it IUE} and {\it RXTE} observations in 1995 showed X-ray variations lagging the UV by $\sim$3.5 days, whereas more recent campaigns indicate UV emission lagging the X-rays. We present a numerical accretion disk–corona model to simulate UV and X-ray light curves and investigate the origin of these differing lag behaviors. Our model demonstrates that the X-ray lag observed in 1995 can be explained by inward-propagating accretion rate fluctuations combined with a compact corona in a lamppost geometry located close to the central black hole. Conversely, we find that a corona located at a larger height above the disk produces UV emission lagging the X-rays through enhanced X-ray reprocessing. These results suggest that changes in coronal geometry can account for the observed variability and lag reversals in NGC~7469. |
