Optical and cm follow-ups of the Changing-Look event in Mkn 590

TL;DR

Facing a Changing-Look AGN in Mkn 590 undergoing a renewed turn-on across X-ray, UV, optical, and cm bands, the study combines three NOT optical spectra and three GMRT 1.4 GHz measurements with Swift-XRT/UVOT monitoring to trace how the BLR responds to rising ionizing flux and how the radio core evolves during an accretion-event. The authors find a clear brightening of broad Balmer-line components in tandem with increased high-energy emission, while the cm-band flux tracks long-term X-ray variability, hinting at a connected accretion–jet system. These results support a scenario where the CL transition is driven by changes in the accretion rate, causing both BLR illumination changes and weak jet activity, and highlight the value of simultaneous multiwavelength coverage. The work sets the stage for detailed radiative-transfer modeling of the warm corona and for high-resolution radio imaging to disentangle disk–corona–jet coupling in Changing-Look AGNs.

Abstract

The Changing-Look active galactic nucleus Mkn 590 is currently in a rejuvenated state, exhibiting a contemporaneous flux rise across X-rays, UV, optical and cm wavelengths. In this study, we present three new optical spectra obtained with the Nordic Optical Telescope, alongside three 1.4 GHz continuum measurements from the Giant Meterwave Radio Telescope, acquired since Nov. 2024. We identified a clear increase in the broad hydrogen Balmer line emission in the most recent observational epochs. Additionally, the core radio flux densities appear to track the overall X-ray variability, suggesting a possible connection between the accretion flow and jet activity. Based on these data, we aim to explore the evolution of the circumnuclear gas in this source and potential links between accretion and ejection activity.

Figures (3)

• Figure 1: Top: Multi-band light curves of Mkn 590 from 2022 to 2025, showing the pre-ignition state followed by the eventual ' turn-on' state since August 2024. The mean-normalized light curves from Swift-XRT and UVW2 are shown in black and red respectively, where the UVW2 lightcurve is offset by an arbitrary amount for clarity. The observational timestamps of optical spectra obtained with DESI, LCO and NOT presented in this paper are denoted by '*'. Similarly, the timestamps for 1.4 GHz GMRT observations taken in 2025 are denoted by $\bigotimes$. Bottom: A light curve of X-ray hardness ratios calculated according to the definition in Sec. \ref{['subsec:swift']} along with a mean uncertainty level on the hardness ratios indicated by shaded region.
• Figure 2: Optical archival spectra taken using DESI, LCO/FLOYDS, and NOT. The spectra are normalized and offset by arbitrary values for clarity. Emission lines are marked with dotted, blue lines. Dashed gray horizontal lines indicate the continuum flux level at 5100 A.
• Figure 3: The three GMRT images at 1.4 GHz taken in early 2025, coinciding with the prolonged X-ray/far-UV flux rise. All images show an unresolved radio core centered at the source coordinates, marked by black contours at 3$\sigma$ and 5$\sigma$ levels and their respective beam sizes (see Sec \ref{['subsec:gmrt']}) are represented by a red ellipse in the lower left corner.