Further spectral classification of PESSTO blue transients

ATel #4329; C. Inserra, S. J. Smartt, M. Fraser, D. Wright, D. R. Young, K. W. Smith (Queens University Belfast), Flora Cellier-Holzem (LPHNE, Paris), A. Pastorello, S. Valenti, S. Benetti (INAF-Osservatorio Astronomico di Padova), S. Taubenberger (MPA), M. Sullivan (University of Oxford), A. Gal-Yam, O. Yaron (Weizmann Institute for Science), C. Baltay, N. Ellman, E. Hadjiyska, R. McKinnon, D. Rabinowitz (Yale University), U. Feindt, M. Kowalski (Universitat Bonn), P. Nugent (LBL Berkeley)
on 23 Aug 2012; 15:38 UT
Credential Certification: Stephen Smartt (s.smartt@qub.ac.uk)

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PESSTO, the Public ESO Spectroscopic Survey for Transient Objects (see Valenti et al., ATel #4037; http://www.pessto.org ), reports updates to three blue transients with uncertain classifications reported in ATels #4313, #4299. Each of these transients were observed again by PESSTO with higher signal-to-noise (S/N).

LSQ12dlf (ATel #4299) was observed on 2012 August 9 and 18, showing the expected transition to a type Ic SN. If z=0.25 is adopted, then the August 18 spectrum closely matches SN2010gx at +21d after peak (restframe, Pastorello et al. 2011, ApJ, 724, 16). The La Silla-QUEST lightcurve shows a 20 day rise and peaks around 2012 July 30, hence the spectrum on August 18 corresponds to an epoch of approximately +16d after maximum. The higher S/N spectrum still does not reveal any narrow line nebular emission from a host galaxy, nor is the MgII ISM absorption seen at the expected wavelength of 3494-3503Angs (c.f. Quimby et al. 2011 Nat. 474, 487 ; Chomiuk et al. 2011, ApJ 743, 114)

SSS120810:231802-560926 (ATel #4313), found by the CRTS Survey, was observed again in excellent conditions on 2012 August 18, with substantial improvement in signal (S/N~40 per pixel at 6000Angs). Broad features are apparent, which again resemble the ultraluminous type I SNe at z~0.2 (Quimby et al. 2011). A reasonable spectral match is found (assuming z=0.18) with PS1-12fo (Smartt et al. ATel #3918) around peak and SN2010gx (Pastorello et al. 2011) at +4d after peak. The epoch from the CRTS lightcurve is not constrained and the absolute magnitude at detection is around -21.6. Again, no narrow lined emission features are observed and the MgII absorption would not fall in the covered wavelength region at z~0.2.

No host galaxies are detected in the reference images of LSQ or CRTS for either of these transients.

LSQ12dyw (ATel #4299) was observed on 2012 August 8 with EFSOC2 and Gr11+Gr16, and we confirm the narrow emission line is resolved into H-alpha and [NII] 6584Angs at z=0.09. The rise time is at least 22 days with a broad peak (~1.3mag rise). The spectrum is unlike the ultraluminous type I SNe. There are two distinct very broad features which are possibly H-alpha and H-beta, but both have FWHM velocities of ~24000 km/s. As the transient is coincident with an apparently passive z=0.09 galaxy (SDSS J232924.87-072320.5), this could either be a 2008es-like supernova (Gezari et al. 2009, ApJ 690, 1313 ; Miller et al. 2009, ApJ 690, 1313) or a tidal disruption event. It has a peak magnitude of -19.7, somewhat faint for a 2008es-like SN.

Further PESSTO observations of all three are ongoing.