The Colloquium takes place every Wednesday at 11:15 AM - Warsaw Copernicus Astronomical Centre online by means of Zoom platform. The Colloquium is given in English and chaired by dr Stanisław Bajtlik (bajtlik@camk.edu.pl). People from outside of the Copernicus Center are very welcome to participate. For technical detailes please contact Dr. Stanislaw Bajtlik.
Biswaraj Palit (CAMK PAN, Warsaw)
The changing-look (CL) behavior in active galactic nuclei (AGNs) is characterized by dramatic fluctuations in the overall brightness of sources, leading to restructuring of circum-nuclear environments such as the inner accretion geometry, broad line region (BLR), and outflows. They offer a rare opportunity to witness accretion state transitions in real time, akin to those seen in stellar-mass X-ray binaries (XRBs). In this talk, I will present a decade long multiwavelength study of the Seyfert galaxy, which captures a complete spectral state transition--from a faint, hard X-ray phase to a bright, UV- and soft X-ray-dominated state within just $\sim$10 years. Using diagnostics like the X-ray loudness parameter ($\alpha_{\rm OX}$) and the hardness-intensity diagram (HID), we identify a critical Eddington ratio ($\lambda_{\rm Edd} \sim 0.02$) marking the onset of inner accretion flow restructuring. These findings provide strong evidence that CLAGNs trace accretion physics analogous to XRBs, scaled up in mass but compressed in time.
Journal Club takes place on Mondays at 11:15 AM in the Seminar Room. The presentation is given in English and is chaired by Journal Club Coordinators. Anyone interested in giving a Journal Club talk is encouraged to contact the email: journalclub(@camk.edu.pl).
Ricardo Salinas (NCAC, Warsaw)
Based on the collection of papers.
