CSP Spectroscopic Classification of AT 2016adj in NGC 5128 (Centaurus A)

ATel #8657; M. Stritzinger (Aarhus U), E. Y. Hsiao (FSU), N. Morrell, M. M. Phillips, C. Contreras, S. Castellón (Las Campanas Observatory, LCO) and A. Clocchiatti (PUC), on behalf of the Carnegie Supernova Project
on 9 Feb 2016; 16:27 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Eric Hsiao (hsiao@physics.fsu.edu)

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We report spectroscopic classification of AT 2016adj (cf. ATEL #8651) based on a visual-wavelength spectrum obtained on Feb. 9.2 UT with the 2.5-m du Pont Telescope (+ WFCCD) at LCO. The spectrum exhibits prevalent Na-I D absorption at the redshift of NGC 5128 characterized by an equivalent width of 0.44-nm. An additional feature coincident with the 578.0-nm diffuse interstellar band is measured to have an equivalent width of 0.06-nm, suggesting an A(V) value between 2 to 4 mag (Phillips et al. 2013, ApJ, 779, 38). Given the significant reddening the blue portion of the spectrum has very low signal-to-noise, however discernible features are present in the red portion of the spectrum that we attribute to H-alpha, the Ca-II near-infrared triplet, and Mg-II 922.7-nm. After manually de-reddening the spectrum assuming E(B-V)=1.0 and Rv=3.1 and then using the spectral identification tool superfit (Howell et al, 2005, ApJ, 634, 119), we find the spectrum of AT 2016adj to best resemble the Type-Ib supernova 1999dn around a week past maximum. This is in contrast to the Type II supernova classification previously reported (cf. ATEL #8655). Furthermore, close inspection of the spectrum reveals shallow absorption features at the expected wavelengths of He-I 667.8-nm and He-I 706.5-nm. Further observations are warranted to secure this classification.

In addition, optical photometry was also computed from multiple images taken on Feb. 9.2 UT under photometric conditions with the 1-m Swope Telescope (+ e2v CCD camera) located at LCO. Computed photometry is as follows:
filter u 18.943 +/- 0.040
filter B 17.395 +/- 0.041
filter g 16.565 +/- 0.038
filter V 15.701 +/- 0.031
filter r 14.613 +/- 0.021
filter i 13.304 +/- 0.017