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Spectroscopic observation of SN 2017eaw by NUTS (NOT Un-biased Transient Survey)

ATel #10377; L. Tomasella, S. Benetti, E. Cappellaro, N. Elias-Rosa, A. Pastorello, G. Terreran, Y. Cai, S. Yang, P. Ochner (INAF OAPd), P. B. Serrano (NOT) on behalf of the NUTS collaboration
on 15 May 2017; 09:39 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Lina Tomasella (lina.tomasella@oapd.inaf.it)

Subjects: Optical, Supernovae, Transient

Referred to by ATel #: 10378, 10380, 10381, 10401, 10407, 10427

The Nordic Optical Telescope (NOT) Unbiased Transient Survey (NUTS; ATel #8992) reports the spectroscopic classification of SN 2017eaw in host galaxy NGC 6946. The candidate was discovered by Patrick Wiggins at 12.8 mag on 2017-05-14 05:42:43 and confirmed by Subo Dong and K.Z.Stanek in Atel#10372.

The observation was performed with the 2.56 m Nordic Optical Telescope equipped with ALFOSC (range 350-950 nm; resolution 1.6 nm FWHM).

Survey Name    | IAU Name   | Discovery (UT)        | Discovery mag | Observation (UT)   | Redshift | Type | Phase   | Notes  
AT2017eaw      | SN2017eaw  | 2017-05-14 05:42:43   | 12.8          | 2017-05-15 03:08:34| 0.000133 | II   | young   | (1)  

(1) We agree with the classification of Atel#10374 and Atel#10376 as a young Type-II SN. The best match is obtained with the first spectrum of SN 1999gi (Leonard eta al. 2002, AJ 124, 2490) a few days (3.8 d) after explosion. A narrow absorption line of Na~I~D is also detected (EW~0.14 nm). From this, we infer a reddening of E(B-V)~0.22 mag (from the Turatto et al. 2003 relation, published in ESO ASTROPHYSICS SYMPOSIA “From Twilight to Highlight: The Physics of Supernovae"). The ALFOSC spectrum shows a blue continuum (T_BB~16000 K with the above reddening) with superposed a broad (FWHM~11400 km/s) H-alpha with a shallow, narrow P-Cygni absorption. From this absorption, we infer a velocity of 14300 km/s for the SN ejecta. Several features are visible in the blue part of the spectrum, with the most prominent centred at about 401.5 nm and 454.0 nm. We identify them as blends of H-delta/He II lines and C III/N III/He II lines, respectively (following Polshaw et al. 2016, A&A 588, 1). H-beta and H-gamma are not clearly visible in this early spectrum.

Classification was 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.