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ePESSTO spectroscopic classification of optical transients

ATel #10747; M. Fraser (University College Dublin), K. Rybicki, M. Gromadzki (Warsaw Observatory), E. Callis (University College Dublin), J, Anderson (ESO), A. De Cia (ESO), I. Manulis, O. Yaron (Weizmann), C. Inserra (Southampton), E. Kankare (QUB), K. Maguire (QUB), S. J. Smartt (QUB), K. W. Smith (QUB), M. Sullivan (Southampton), S. Valenti (UC Davis), O. Yaron (Weizmann), D. Young (QUB), Tonry, B. Stalder, L. Denneau., A. Heinze, H. Weiland (IfA, Univ. of Hawaii), A. Rest (STScI)
on 14 Sep 2017; 20:35 UT
Distributed as an Instant Email Notice Transients
Credential Certification: Morgan Fraser (morgan.fraser@ucd.ie)

Subjects: Optical, Cataclysmic Variable, Supernovae, Transient

ePESSTO, the extended Public ESO Spectroscopic Survey for Transient Objects (see Smartt et al. 2015, A&A, 579, 40 http://www.pessto.org ), reports the following supernova classifications. Targets were supplied by the ATLAS survey, see Tonry et al. (2011, PASP, 123, 58) and Tonry et al. (ATel #8680). All observations were performed on the ESO New Technology Telescope at La Silla on 2017 Sept. 13, using EFOSC2 and Grism 13 (3985-9315A, 18A resolution). Classifications were done with SNID (Blondin & Tonry, 2007, ApJ, 666, 1024) and GELATO (Harutyunyan et al., 2008, A&A, 488, 383). Classification spectra and additional details can be obtained from http://www.pessto.org (via WISeREP) and the IAU Transient Name Server.

Survey Name  | IAU Name  | RA (J2000)  | Dec (J2000) | Disc. Date | Source    | Disc Mag  | z     | Type | Phase | Notes 
ATLAS17kol   | AT2017gsa | 01 02 06.79 | +01 16 32.7 | 20170912   | ATLAS     | 16.7      | 0     | CV   | -     | (1)     
ATLAS17jrp   | AT2017gge | 16 20 34.86 | +24 07 25.6 | 20170710   | ATLAS     | 19.8      | 0.066 | ?    | +3w   | (2) 

(1) Blue continuum with Hbeta and higher Balmer lines in absorption.
(2) Narrow Halpha and Hbeta, with broad wings, on a blue continuum. There are also some possible broad features in the blue. Our spectrum is markedly different from the pre-discovery SDSS spectrum. The transient appears to be located in the nucleus of a galaxy, and had a smooth rise to a peak magnitude of ~-19.8. The transient is now approximately three weeks after maximum, and the blue continuum at this phase is inconsistent with a SN. It is possible that AT2017gge is a tidal disruption event, while we note that the smoothly evolving lightcurve is atypical for AGN variability.