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Spectroscopic observations of ASASSN-17io and ATLAS17hpt (SN 2017faf) by NUTS (NOT Un-biased Transient Survey)

ATel #10554; Andrea Pastorello (INAF-Padova), Stefano Benetti (INAF-Padova), Enrico Cappellaro (INAF-Padova), Giacomo Terreran (INAF-Padova), Lina Tomasella (INAF-Padova), Grigori Fedorets (NOT), on befalf of the NUTS collaboration
on 3 Jul 2017; 13:56 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Andrea Pastorello (andrea.pastorello@oapd.inaf.it)

Subjects: Optical, Supernovae

Referred to by ATel #: 10556

The Nordic Optical Telescope (NOT) Unbiased Transient Survey (NUTS; ATel #8992) reports the spectroscopic classification of ASASSN-17io in the galaxy CGCG 316-010, along with the re classification of ATLAS17hpt (SN 2017faf), which was previously classified as a SLSN-I (ATel #10549). The two supernovae were discovered by the All-Sky Automated Survey for Supernovae (ATEL #8944, #8979) and the ATLAS project (ATel #8680).

The observations were performed with the 2.56 m Nordic Optical Telescope equipped with ALFOSC (range 350-950 nm; resolution 1.4 nm FWHM).

Survey Name    | IAU Name   | Discovery (UT)  | Discovery mag | Observation (UT) | Redshift | Type | Phase        | Notes  
ASASSN-17io    | SN 2017fbh  | 2017-06-26.31  | 17.3          | 2017-07-03.00    | 0.0274   | Ia   | -5d from max | (1)  
ATLAS17hpt     | SN 2017faf  | 2017-06-28.43  | 17.52         | 2017-07-03.03    | 0.0295   | II   | 1 week       | (2)  

(1) The spectrum resembles that of a luminous, 1991T-like SN a few days before the maximum light. Adopting for the host galaxy z = 0.0274 (Yoshino & Kisato, 2015, MNRAS, 446, 3749), we measure an expansion velocity of about 11400 km/s for the ejected material from the position of the minimum of the Si II 635.5 nm line. (2) The spectrum of SN 2017faf resembles that of a young Type II event, showing a blue continuum, with superposed broad and shallow Halpha, Hbeta and He I 587.6 nm. A good match is found with the Type IIb SN 2011fu about 4 days after the explosion. We note that our classification contradicts that reported in ATel #10549. In particular, our spectrum does not show the strong O II lines mentioned in ATel #10549. In addition, we do not confirm the large reddening claimed by Siebert et al. In fact, there is no evidence of narrow Na ID absorption lines at the host galaxy redshift. The redshift estimate is obtained from the narrow lines of the faint host galaxy.

Classifications were performed using the GELATO (Harutyunyan et al. 2008, A&A, 488, 383) and SNID (Blondin and Tonry 2007, ApJ, 666, 1024) tools. Calibrated spectra and additional information can be retrieved in the IAU Transient Name Server.