The CRTS-II Discovery of Superluminous Supernova MLS160616:160420+392813

A.J. Drake, S.G. Djorgovski, A.A. Mahabal, M.J. Graham (Caltech); D. Stern (JPL), M. Catelan (PUC Chile); E. Christensen, S.M. Larson (LPL/UA).

Discovery

MLS160616:160420+392813 was first observed with the MLS 1.5m telescope on 2016 June 16th UT. The data was processed by the new CRTS-II pipeline on July 2nd. The transient was classified as having an unclear nature due to the lack of prior MLS or SDSS data and was selected for spectroscopic follow-up.

Palomar 5m Spectrum


Palomar 5m spectra from 2016 July 3rd UT of MLS160616:160420+392813 compared to the Keck spectrum of known SLSNe PTF09cnd. Left: blue DBSP spectrum showing the distinctive hydrogen-poor SLSNe. Right: The combined full DBSP spectrum with separate the blue and red beams coloured separately.

As noted in Drake et al. 2016 the best spectroscopic match is to the pre-maximum spectra of known SLSN LSQ14bdq. However, due to the relatively low S/N of the public LSQ14bdq spectra, here we present a comparison with the high S/N Keck spectrum of SLSN PTF09cnd.

CSS telescope detection

The supernova was independently detected with the CSS telescope on 2016 July 10th UT and designated ID CSS160710:160420+392813. The source was immediately noted as a potential very luminous supernova due to the high apparent magnitude combined with the very long rise time and lack of a clear optical (SDSS), UV (Galex), near-IR (Wise) or radio (FIRST) detection.

The CSS lightcurve shows that the event occured around June 3rd and took at least a month to reach maximum. Additional observations by Gregor Krannich suggest that the object remained of similar brightness on July 16th.

Comparison of the spectroscopic features suggest the supernova has a redshift of z=0.18. Based on the CSS lightcurve the peak was V~17.4. This suggests that the supernova had Mv=-22.2 at maximum (without correction for extinction), consistent with the SLSNe classification.