Classification certificate for object 2017gfo
TNS Classification Report No. 1215

Date Received (UTC): 2017-09-16 15:59:59
Sender: Prof. Stephen Smartt
Group: ePESSTO

J. Lyman (Univ. of Warwick), D. Homan (Univ. of Edinburgh), K. Maguire (QUB), M. T. Botticella (INAF-Capodimonte), M. Fraser (UCD), C. Inserra (Southampton), E. Kankare, S. J. Smartt, K. W. Smith (QUB), M. Sullivan (Southampton), S. Valenti (UC Davis), O. Yaron, I. Manulis (Weizmann), D. Young (QUB), T.-W. Chen (MPE), S. Campana (INAF-Brera), S. Benetti, L. Tomasella (INAF-Padova), G. Leloudas (DARK, Copenhagen), Z. Cano (IAA, Granada) report/s a classification of object: AT 2017gfo

Type: Kilonova
Redshift: 0.00984

Remarks: Classified in Ligo-Virgo GCN 21582 DATE: 17/08/19 01:46:26 GMT : The continuum is featureless, similar to the report of the first Magellan spectrum in Drout et al. (GCN 21547). But it peaks at 5500 and falls off rapidly in the blue. This is consistent with the Swift colours reported and the fading U-band and UV flux. The red part (beyond 5000Angs) can be fit with a black-body temperature of around 6000K or a power law. But neither are consistent with the turn over in the blue. There are no strong features in the blue that indicate line absorption or could be identified with known transitions. There are no Balmer lines, no Ca II H&K, or Si II absorption seen in supernova-like transients. We can certainly conclude this is not a young supernova of any type in this host, nor is it consistent with being a background supernova of any standard type. The UV dimming and maintaining of the red and NIR flux appears broadly consistent with many flavours of kilonova models.

The following Classification spectrum was provided:

Obsdate: 2017-08-18 23:20:00
Instrument: EFOSC2-NTT
Telescope: The ESO New Technology Telescope

Remarks: The observations were performed on the ESO New Technology Telescope at La Silla with the EFOSC2 instrument in spectroscopic mode starting from 2018-08-18 at 23:20 UT, using the Gr11 and Gr16 which provide coverage 3345-9995 at a resolution between 260-396 (v = 1150 - 756 km/s) for a 1.5" slit, which was used in roughly 1.5-2.0" seeing. This spectrum is fully reduced and corrected to r-band photometry.

Details of the object and its spectra can be viewed here: https://wis-tns.weizmann.ac.il/object/2017gfo