Spectroscopic classification of 2017jmk as a type II supernova and Early follow-up observations

ATel #11152; Subhash Bose, Subo Dong (KIAA-PKU), A. Pastorello, Y. Cai (INAF-OAPd), E. A. Barsukova (SAO, RAS), V. P. Goranskij (SAI, Moscow U), K. Z. Stanek, J. Shield (OSU), R. Post (Post Obs.), Yang Huang (PKU; Yunnan U), Yangwei Zhang (YNAO), M. Fraser (UCD), M. Stritzinger (Aarhus U), P. Brown (Mitchell Institute/Texas A&M), Ping Chen (KIAA-PKU)
on 10 Jan 2018; 11:27 UT
Credential Certification: Subo Dong (dongsubo@pku.edu.cn)

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We report optical spectroscopic observations of the supernova (SN) candidate 2017jmk located in the NGC 7541. Two optical spectra were obtained on UT 2018-01-05.1 and UT 2018-01-06.6 with the MDM 2.4m telescope (+ OSMOS; spectral range 398-686 nm) at KPNO and the 2.4m telescope (LJT + YFOSC) located in Lijiang, China, respectively.

The OSMOS spectrum exhibits a broad and weak P-Cygni H_alpha profile. The estimated H_alpha expansion velocity is ~4700 km/s, which is relatively low for a normal type II SN at a relatively young age (as indicated from the SN imaging data obtained from the recent, pre-discovery HST observations; see #Atel 11119). The peak of H_alpha is slightly blueshifted (by ~1000 km/s) from the rest velocity, which is commonly seen in relatively young SNe II. We also identify host H, N, and S emission lines along with narrow Na I D lines at z = 0.0095, which is consistent with the redshift of the host galaxy NGC 7541 at z = 0.0090 via NED. The Na I D lines are partially resolved, and the corresponding D1 and D2 lines have equivalent widths of approximately 0.12 nm and 0.10 nm, indicative of significant host-galaxy dust extinction.

We perform multi-band imaging follow-ups from the SAO 1-m Zeiss reflector with the CCD photometer based on EEV CCD42-40 chip, the 24-in telescope at Post Observatory as well as Swift UVOT. The Zeiss-100 photometry measurements are summarized below:

 
Date     MJD          B     Berr   V     Verr  R     Rerr  I     Ierr  S notes 
20180102 58120.657    19.13 0.14   18.08 0.05  17.46 0.04  17.08 0.04  1 CCD 
20180103 58121.760     NaN   NaN   18.06 0.06  17.43 0.04   NaN  NaN   1 CCD 
20180107 58125.660    18.99 0.03   18.03 0.03  17.44 0.05  16.73 0.04  1 CCD 

The position of SN 2017jmk was serendipitous observed by the Hubble Space Telescope on multiple occasions during the three months prior to discovery, as part of program 15145 (PI: Riess). As mentioned in ATel #11119, examination of the pre-explosion images reveal no obvious coincident progenitor candidate. In light of the reddening and distance to SN 2017jmk, it may be challenging to obtain good constraints on the pre-explosion luminosity of the progenitor.

We thank the Swift Acting PI Brad Cenko, the Observation Duty Scientists and the science planners.