After the All-Sky Automated Survey for SuperNovae ( ASAS-SN ) discovered a significant brightening of the inner region of NGC 2617 , we began a \sim 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 H \beta line width and the radius-luminosity relation , we estimate the mass of central black hole to be ( 4 \pm 1 ) \times 10 ^ { 7 } M _ { \odot } .
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 .