Spectroscopy of SN 2016hnk (= ATLAS16dpc) with SOAR and SALT: A Peculiar Type-Ia Supernova Similar to PTF09dav

ATel #9705; Y.-C. Pan, A. S. Duarte, R. J. Foley (UCSC), S. W. Jha (Rutgers), A. Rest (STScI), D. Scolnic (Chicago/KICP), A. Kniazev (SALT/SAAO)
on 3 Nov 2016; 04:24 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Saurabh Jha (saurabh@physics.rutgers.edu)

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We obtained spectroscopic observations of SN 2016hnk (= ATLAS16dpc) with the Goodman spectrograph on the Southern Astrophysical Research (SOAR) telescope on UT 2016 Oct 30.3 and with the Robert Stobie Spectrograph (RSS) on the Southern African Large Telescope (SALT) on UT 2016 Oct 31.0.

The spectra are red, and show numerous features including strong Si II (rest 6355 A) and a deep, wide "trough" between 4100 and 4500 A that is typically attributed to Ti II. We thus concur with Cannizzaro et al. (2016, ATel #9703) and Dimitriadis et al. (2016, ATel #9704) in classifying SN 2016hnk as a peculiar type-Ia supernova. Using SNID (Blondin & Tonry, 2007, ApJ, 666, 1024), we find plausible matches to 91bg-like SN Ia (like SN 1999da near maximum light), as well as SN 2006bt (Foley et al., 2010, ApJ, 708, 1748). SN 2016hnk is also somewhat similar to PTF10ops (Maguire et al., 2011, MNRAS, 418, 747), though none of these classifications are decisively compelling, given the host redshift (z = 0.016; SDSS DR13), likely SN phase, color, and absolute magnitude.

The most convincing analogue to SN 2016hnk we have found is PTF09dav (Sullivan et al., 2011, ApJ, 732, 118), which had similar features, color, and absolute magnitude near maximum light. In particular, we see the unusual absorption features at 5350 and 5540 A (host rest frame) also seen in PTF09dav +5 days past maximum light and a feature at 7120 A (host rest frame) that has a match in PTF09dav at +11 days. Sullivan et al. (2011) ascribe these lines to Sc II (rest 5527, 5658 A; though note the wavelength ratio is not a perfect match in SN 2016hnk) and Ti II (blend of rest 7327, 7355 A?), respectively.

We also note that unlike PTF09dav, which was located far in the outskirts of its host (41 kpc projected distance), SN 2016hnk is projected on its host galaxy disk close to a spiral arm (4 kpc projected distance to the host nucleus).

We encourage continued follow-up observations of this interesting supernova.

Our spectra are posted on the Transient Name Server SN 2016hnk page, and a figure showing these with comparison spectra is also available.

SN 2016hnk spectra with comparisons