PS1-13cbe: the rapid transition of a Seyfert 2 to a Seyfert 1

• Published in: Monthly notices of the Royal Astronomical Society 2019-08, Vol.487 (3), p.4057-4070
• Main Authors: Katebi, Reza, Chornock, Ryan, Berger, Edo, Jones, David O, Lunnan, Ragnhild, Margutti, Raffaella, Rest, Armin, Scolnic, Daniel M, Burgett, William S, Kaiser, Nick, Kudritzki, Rolf-Peter, Magnier, Eugene A, Wainscoat, Richard J, Waters, Christopher
• Format: Article
• Language: English
• Subjects: accretion; accretion discs; Astrophysics; black hole physics; galaxies: active; galaxies: nuclei; Physics
• ISSN: 0035-8711; 1365-2966; 1365-2966
• DOI: 10.1093/mnras/stz1552

ABSTRACT We present a nuclear transient event, PS1-13cbe, that was first discovered in the Pan-STARRS1 survey in 2013. The outburst occurred in the nucleus of the galaxy SDSS J222153.87+003054.2 at z = 0.123 55, which was classified as a Seyfert 2 in a pre-outburst archival Sloan Digital Sky Survey (SDSS) spectrum. PS1-13cbe showed the appearance of strong broad H α and H β emission lines and a non-stellar continuum in a Magellan spectrum taken 57 d after the peak of the outburst that resembled the characteristics of a Seyfert 1. These broad lines were not present in the SDSS spectrum taken a decade earlier and faded away within 2 yr, as observed in several late-time MDM spectra. We argue that the dramatic appearance and disappearance of the broad lines and a factor of ∼8 increase in the optical continuum are most likely caused by variability in the pre-existing accretion disc than a tidal disruption event, supernova, or variable obscuration. The time-scale for the turn-on of the optical emission of ∼70 d observed in this transient is among the shortest observed in a ‘changing-look’ active galactic nucleus.