future events

Multi-Wavelength Monitoring and Reverberation Mapping of NGC 2617 at Deepest Minimum With a Sharp Upward Turn During 2021–2024

TYPEAstrophysics Seminar
Speaker:Victor, L. Oknyansky
Affiliation:Haifa U
Organizer:Shmuel Bialy
Time:14:30 - 15:30
Location:Lidow 620

We present the results of new photometric and spectroscopic monitoring campaigns of the changing-look AGN NGC2617 carried out from March 2022 until March 2024 and covering the wavelength range from the X-ray to near-IR. The facilities included the telescopes of the SAI MSU, the 2.3-m WIRO telescope, the 1.9-m SAAO telescope, the 0.7-m and 0.8-m telescopes at the Wise observatory, and the $Swift$ (UVOT and XRT telescopes). We found significant variability at all wavelengths and, specifically, in the intensities and profiles of the broad Balmer lines. The reverberation mapping was done for the last three observational seasons in 2021-2024. We measured a time delay of ~ 4 days in the response of the H-beta line to optical continuum variations. We found the X-ray variations to correlate well with the UV and optical (with a small time delay of a few days for longer wavelengths). The K band lagged the B band by 15  days during the last three seasons,  significantly shorter than the delays reported previously by the 2016 and 2017--2019 campaigns. Near-IR variability arises from two emission regions: the outer part of the accretion disc and a more distant dust component. The $HK$-band variability is governed primarily by dust. The Balmer decrement of the broad components is inversely correlated with the X-ray(UV) flux. The object type change from Sy1.8 to Sy1.9 was recorded in October 2023 - January 2024, and then a fast reverse change to Sy1.8-Sy1.5 happened in February 2024.  We interpret these changes as a combination of two factors:  changes in the accretion rate as a dominating reason and the dust recovery (sublimation) processes along the line of sight.