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Classifications of Two Optical Transients

ATel #7955; I. Shivvers, H. Yuk, M. L. Graham, A. V. Filippenko (UC Berkeley)
on 26 Aug 2015; 18:14 UT
Credential Certification: Isaac Shivvers (ishivvers@berkeley.edu)

Subjects: Optical, Supernovae, Transient

We report classifications of two recent optical transients based upon spectra (330-1000 nm) obtained on UT August 24, 2015 with the 3-m Shane reflector (+ Kast) at Lick Observatory. Classifications were performed though cross-correlation with a library of supernova spectra using the "SuperNova IDentification" code (SNID; Blondin & Tonry 2007, Ap.J. 666, 1024) including the updated templates of Silverman et al. 2012, MNRAS, 425, 1789 and Liu & Modjaz, 2014, arXiv:1405.1437.

PSN J01101191+3313536, discovered in a 2MASS galaxy, appears to be a post-maximum Type IIb SN with high ejecta velocities. H-alpha and H-beta are visible in absorption at around 12,000 km/s alongside He I lines (v ~ 8,000 km/s) and normal O I and Ca II features. SNID estimates the phase to be around +10 days and the redshift (z) to be ~0.018.

PSN J02331624+1915252, discovered near the center of an anonymous galaxy, is probably a Type IIn supernova, although it might instead be an active galactic nucleus (AGN) in outburst, possibly because of a tidal disruption event (TDE). The spectrum bears a strong resemblance to those of Type IIn SN 2009kn 30-60 days after peak (Kankare et al. 2012, MNRAS, 424, 855) with strong intermediate-width Balmer emission lines (FWHM about 1500 km/s, for H-alpha) and no broad absorption features. A noisy light curve of this object was presented in ATel #7940: the single-passband photometry shows a peak about 50 days before our spectrum was obtained, and the light curve is consistent with either a supernova or an AGN classification with an absolute magnitude of approximately -18.3 (using z = 0.0135, measured from the H-alpha emission feature). Arguments against the AGN or TDE interpretation include the lack of any apparent narrow-line region (e.g., no [O III] 500.7 nm emission), that the object is reported to be offset by 2" from the host-galaxy nucleus, and that the host galaxy seems to have a somewhat diffuse (not AGN-like) nucleus. Overall, we favor the SN IIn classification, but further observations are encouraged.