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SALT spectroscopic classification of DLT17ch (= SN 2017gax) as a type-Ib/c supernova before maximum light

ATel #10640; S. W. Jha, Y. Camacho, K. Dettman (Rutgers), D. Sand, S. Wyatt (UA), L. Tartaglia (UA, UC Davis), S. Valenti (UC Davis), B. Miszalski (SALT/SAAO)
on 15 Aug 2017; 06:34 UT
Distributed as an Instant Email Notice Supernovae
Credential Certification: Saurabh Jha (saurabh@physics.rutgers.edu)

Subjects: Optical, Supernovae

Referred to by ATel #: 10956

We obtained SALT (+RSS) spectroscopy of DLT17ch (= SN 2017gax; ATel #10638) on 2017 Aug 15.1 UT, covering the wavelength range 350-940 nm. The spectrum shows a blue continuum with well-developed, broad absorption features. Narrow interstellar emission lines are consistent with the redshift of the host galaxy NGC 1672 (z = 0.0044; Koribalski et al. 2004, AJ, 128, 16, via NED). Cross-correlation of the supernova spectrum with a template library using SNID (Blondin & Tonry 2007, ApJ, 666, 1024) shows a wide range of reasonable matches, even including 1999aa-like SN Ia, but the more plausible analogues, based on age and expansion velocity, are SN Ib and Ic.

The most compelling match is with the type-Ib SN 2004gq at -9 days from maximum light, though the putative helium lines are weaker and at higher velocity in DLT17ch. It is possible that DLT17ch was caught at an even earlier epoch and that the helium lines will strengthen, leading to a type-Ib classification, but for now we classify DLT17ch as a type-Ib/c supernova.

Our spectrum is posted on the Transient Name Server SN 2017gax page.