Classification of super-luminous SN : MLS130517:131841-070443

ATel #5128; S. J. Smartt, M. Nicholl, C. Inserra, D. Wright, T.-W., Chen (Queen's University Belfast) and Andy Lawrence, Alex Mead (University of Edinburgh)
on 13 Jun 2013; 08:57 UT
Credential Certification: Stephen Smartt (s.smartt@qub.ac.uk)

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We report that a spectrogram of MLS130517:131841-070443 (aka CSS130530:131841-070443) was obtained on Jun. 10.96 UT with the 4.2-m William Herschel Telescope (+ ISIS ; range 3270-9990 A; resolution about 1000)

The spectrum has a blue continuum with several broad absorption features. Narrow absorption from the Mg II H&K resonance doublet (2795.5/2802.7 Angs) arising either in the host galaxy interstellar medium or in intervening intergalactic medium is detected at redshift of z=0.1918 +/-0.002. At this redshift of z~0.2, the blue continuum and broad absorption resemble that of SN2010gx (Pastorello et al. 2010,ApJ 724, L16; Quimby et al. 2011, Natur., 474, 487) and PTF09cnd (Quimby et al. 2011, Natur., 474, 487) around peak but an exact redshift of z=0.26 is required to match the restframe broad absorption of the photospheric OII and MgII lines. This discrepancy could either be due to the narrow MgII absorption arising not in the host galaxy, but in lower redshift intervening material or due to MLS130517:131841-070443 showing different ionic species in absorption. The absolute magnitude of the supernova would be approximately in the range -21 to -22 in the restframe B-band, depending on the source redshift. In conclusion this appears to be a super-luminous supernova of type Ic (Gal-Yam 2012, Sci, 337, 927 ; Inserra et al. 2013, ApJ, 770, 128) at, or around, peak magnitude. The discrepancy between the redshift derived from the interstellar medium features and the supernova photospheric absorption requires further work to resolve. No host galaxy is visible in the CSS or MLS deeper reference images and no narrow host galaxy emission lines are observed in the WHT spectrum (e.g. H-alpha, H-beta or [OIII], [OII]).

MLS130517:131841-070443 will become a PESSTO public survey target (www.pessto.org) when the PESSTO survey restarts operations on 26th July, after the Galactic Centre break. Further coverage with VLT+xshooter and LCOGT/LT photometric follow-up are scheduled. Observations at other wavelengths are encouraged.