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Spectroscopic classification of optical transients

ATel #8497; D. Milisavljevic, J. Parrent, D. Patnaude, A. Kamble (Harvard-Smithsonian Center for Astrophysics) and R. Margutti (New York University)
on 2 Jan 2016; 23:26 UT
Credential Certification: D. Milisavljevic (dmilisav@cfa.harvard.edu)

Subjects: Optical, Supernovae

We report on low-dispersion (R=1500) optical spectra (range 422-940 nm) obtained on December 31 UT with the Magellan Baade 6.5m telescope at Las Campanas Observatory of four transients.

1) ASASSN-15ut (ATel #8479, #8495): Spectra obtained on December 31.1 UT show it to be a type-I supernova. Sub-classification is not straightforward, as cross-correlations with two libraries of supernova spectra give conflicting results. The "Supernova Identification" code (SNID; Blondin and Tonry 2007, Ap.J. 666, 1024) shows matches with normal and peculiar type-Ia events over one week after maximum light, whereas as the GELATO online database (Harutyunyan et al. 2008, A.Ap. 488, 383) finds 85 per cent match with type-Ib/c. After correcting for the redshift z = 0.011471 (from NED) of the host galaxy NGC 88, the velocity of the minimum of the feature we associate with Si II 635.5-nm is estimated to be approximately 13500 km/s. The relatively high velocity is consistent with a young object discovered not long after explosion. Continued monitoring of the light curve and spectroscopic evolution of this supernova is encouraged.

2) PSN J02003208-5810410 (TOCP): Spectra obtained on December 31.2 UT show it to be a type-II supernova. Cross-correlation with SNID shows multiple matches with type-IIP events around the time of maximum light. Notable features include a blue continuum, conspicuous Na I D absorption (equivalent width = 2.7 Ang) due to the host galaxy PGC127875 (z = 0.020371, NED), and a shallow blueshifted absorption associated with the broad Halpha P-Cyg profile which is often observed in type-IIL supernovae.

3) PSN J08123984-7953078 (TOCP): Spectra obtained on December 31.3 UT show it to be a young type-Ib supernova in ESO 018-G1 (z = 0.014890, NED). Cross-correlation with SNID shows a reasonable match with the type-Ib events 2008D and 1999ex approximately 10 days after maximum light.

4) MASTER OT J103747.94-270507.2 (ATel #8196): Spectra obtained on December 31.3 UT show it to be a type-Ia supernova in IC 2597 (z = 0.007562, NED). Cross-correlations with SNID and GELATO both yield reasonable matches with evolved type-Ia supernovae over 100 days past maximum light.