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Spectroscopic Classification of Gaia17blw and Gaia17bro as Likely Superluminous Type II Supernovae

ATel #10616; J. Strader, L. Chomiuk, E. Tremou, L. Shishkovsky (Michigan St), J. L. Prieto (Diego Portales; MAS), K. Z. Stanek (OSU), Subo Dong (KIAA-PKU)
on 2 Aug 2017; 20:20 UT
Credential Certification: Jay Strader (strader@pa.msu.edu)

Subjects: Optical, Supernovae, Transient

We obtained spectroscopy of the transients Gaia17blw (SN2017eni) and Gaia17bro (SN2017fck) on 2017 Aug 1.4 (UT) with the Goodman spectrograph on the SOAR telescope.

Gaia17blw was announced as a Gaia transient on 2017 June 6 with G=17.7 as a candidate SN in the galaxy 6dFGS gJ030511.0-453304. Emission lines from the host galaxy give z=0.08165. The transient itself is blue. Classification with SNID (Blondin and Tonry 2007, ApJ, 666, 1024) does not give an excellent match to any template, but the most similar spectra are of Type IIn (subtype Ia/Ic-CSM) a few weeks past peak. Photometry from the ASAS-SN survey finds a peak at V=16.9 on 2017 Jun 6.44, implying an absolute magnitude of M_V = -21.0.

Gaia17bro was announced as a Gaia transient on 2017 July 3 with G=16.5 as a "hostless" blue transient. Emission lines from the host galaxy give z=0.09442. The transient is blue, and SNID classification suggests a Type IIn (subtype Ia/Ic-CSM) about two weeks past peak. The most recent epoch of photometry from the ASAS-SN survey (2017 Jul 30.4) is V=16.5, implying an absolute magnitude of M_V = -21.8, though the transient may still be rising.

Given their absolute magnitudes, the likely classification of both transients is as Type II superluminous supernovae. Both spectra are available on TNS.