# The curtain remains open: NGC 2617 continues in a high state

## TL;DR

NGC 2617 remains a type-1 Seyfert galaxy with ongoing variability across optical, UV, and X-ray bands, showing spectral and brightness changes over several years linked to accretion and dust sublimation processes.

## Contribution

This study provides detailed multi-wavelength monitoring of NGC 2617, revealing its persistent high activity state and offering insights into the mechanisms behind its changing spectral type.

## Key findings

- NGC 2617's type change occurred between 2010 and 2012.
- X-ray and UV-optical variations are correlated, with X-ray possibly leading by 2-3 days.
- Infrared lags suggest different emission regions in the accretion disk and dust.

## Abstract

Optical and near-infrared photometry, optical spectroscopy, and soft X-ray and UV monitoring of the changing look active galactic nucleus NGC 2617 show that it continues to have the appearance of a type-1 Seyfert galaxy. An optical light curve for 2010-2016 indicates that the change of type probably occurred between 2010 October and 2012 February and was not related to the brightening in 2013. In 2016 NGC 2617 brightened again to a level of activity close to that in 2013 April. We find variations in all passbands and in both the intensities and profiles of the broad Balmer lines. A new displaced emission peak has appeared in H$\beta$. X-ray variations are well correlated with UV-optical variability and possibly lead by $\sim$ 2-3 d. The $K$ band lags the $J$ band by about 21.5 $\pm$ 2.5 d. and lags the combined $B+J$ filters by $\sim$ 25 d. $J$ lags $B$ by about 3 d. This could be because $J$-band variability arises from the outer part of the accretion disc, while $K$-band variability comes from thermal re-emission by dust. We propose that spectral-type changes are a result of increasing central luminosity causing sublimation of the innermost dust in the hollow biconical outflow. We briefly discuss various other possible reasons that might explain the dramatic changes in NGC 2617.