# The Man Behind the Curtain: X-rays Drive the UV through NIR Variability in the 2013 AGN Outburst in NGC 2617

## TL;DR

This study monitors a dramatic outburst in NGC 2617, revealing that X-ray variations drive subsequent UV to NIR variability, providing insights into AGN physics and black hole accretion processes.

## Contribution

It demonstrates that X-ray emission variations cause the UV to NIR variability in a changing-look AGN, supported by multi-wavelength monitoring and lag analysis.

## Key findings

- X-ray flux increased by over an order of magnitude during outburst.
- UV and NIR emissions lag behind X-rays by days, consistent with a thin disk model.
- The black hole mass is estimated at approximately 4 x 10^7 solar masses.

## Abstract

After the All-Sky Automated Survey for SuperNovae (ASAS-SN) discovered a significant brightening of the inner region of NGC 2617, we began a ~70 day photometric and spectroscopic monitoring campaign from the X-ray through near-infrared (NIR) wavelengths. We report that NGC 2617 went through a dramatic outburst, during which its X-ray flux increased by over an order of magnitude followed by an increase of its optical/ultraviolet (UV) continuum flux by almost an order of magnitude. NGC 2617, classified as a Seyfert 1.8 galaxy in 2003, is now a Seyfert 1 due to the appearance of broad optical emission lines and a continuum blue bump. Such "changing look Active Galactic Nuclei (AGN)" are rare and provide us with important insights about AGN physics. Based on the Hbeta line width and the radius-luminosity relation, we estimate the mass of central black hole to be (4 +/- 1) x 10^7 M_sun. When we cross-correlate the light curves, we find that the disk emission lags the X-rays, with the lag becoming longer as we move from the UV (2-3 days) to the NIR (6-9 days). Also, the NIR is more heavily temporally smoothed than the UV. This can largely be explained by a simple model of a thermally emitting thin disk around a black hole of the estimated mass that is illuminated by the observed, variable X-ray fluxes.