ASAS-SN Discovery of a Strong AGN Outburst and Dramatic Seyfert Type Change in NGC 2617
ATel #5010; B. J. Shappee (Ohio Sate), J. L. Prieto (Princeton), J. Nugent (University of Oklahoma), C. S. Kochanek, K. Z. Stanek, J. Jencson, A. Talabere, J. F. Beacom (Ohio State), D. Szczygiel, G. Pojmanski (Warsaw University Observatory), M. Dubberley, M. Elphick, S. Foale, E. Hawkins, D. Mullens, W. Rosing, R. Ross, Z. Walker (Las Cumbres Observatory)
on 26 Apr 2013; 04:37 UT
Credential Certification: Benjamin Shappee (shappee@astronomy.ohio-state.edu)
During the ongoing All Sky Automated Survey for SuperNovae (ASAS-SN or "Assassin"), using data from the double 14-cm "Brutus" telescope in Haleakala, Hawaii, we have discovered a candidate outburst in a known Seyfert galaxy NGC 2617. NGC 2617 is a face-on Sc galaxy at a distance of about 62 Mpc (distance modulus 34.0; NED). ASAS-SN transient source detection was triggered by an image taken at 2013 UT Apr. 10.27 by a ~10% relative flux increase from the inner region (host galaxy + AGN; Brutus CCD camera has 7.5" pixels) of NGC 2617, equivalent to detecting a new point source source of V ~ 16.7 mag superimposed on the image of the galaxy. The ASAS-SN lightcurve of the two fields covering NGC 2617 can be found here.
Follow-up imaging obtained by J. Nugent on Apr. 24.14 with the OSMOS + R4K CCD on the 2.4-m telescope at MDM Observatory showed that the central region of NGC 2617 continued to brighten to g = 15.15 +/- 0.05 (calibrated using archival SDSS data of the region), an increase of 1.3 +\- 0.1 mag (brightening by a factor of 3.3) compared to the archival SDSS g-band image. This corresponds to an absolute g-band magnitude of M_g=-19, after correcting for a small amount of foreground reddening (NED). A comparison between our ASAS-SN image (top-left), the SDSS image (top-right), our follow-up MDM image (bottom-left) and a difference image showing the brightening of the central region between the SDSS image and MDM image (bottom-right) can be found here. The increase in flux is associated with the center of the galaxy to within ~0.03", corresponding to a projected physical distance of less than ~9 pc at NGC 2617 (NED).
In order to investigate the nature of this significant brightening, we requested DD time with the Apache Point Observatory 3.5m-telescope. We obtained an optical spectrum (range 350-960 nm) using DIS on UT Apr 25.1. A comparison between the current APO spectrum and a 6dF galaxy survey spectrum taking in 2003 can be found
here. NGC 2617 underwent a dramatic spectral evolution and appears to have changed from a Type 2 Seyfert to a Type 1 Seyfert in the intervening decade, possibly associated with the current strong outburst. Continued follow-up is both planned and encouraged.
We thank the APO director, S. Hawley, for granting us Director's Discretionary Time for this observation, and the observatory crew.
