[vsnet-grb-info 22222] LIGO/Virgo S190425z: Spectroscopic observations of two ZTF candidates with SOAR

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24321
SUBJECT: LIGO/Virgo S190425z: Spectroscopic observations of two ZTF candidates with SOAR
DATE:    19/04/28 06:17:29 GMT
FROM:    Matt Nicholl at Royal Astronomical Soc.  <mrn at roe.ac.uk>

M. Nicholl (Edinburgh), R. Cartier (CTIO), I. Pelisoli (Potsdam), E. Berger, P. Blanchard, T. Eftekhari, S. Gomez, G. Hosseinzadeh, A. Villar, P. Williams (Harvard), P. Cowperthwaite (Carnegie), K. Alexander, D. Coppejans, W. Fong, R. Margutti, G. Terreran (Northwestern), R. Chornock (Ohio), J. Braga (INPE), L. Chomiuk, J. Strader (MSU), C. Clemens, D. Reichart (UNC), M. Drout (Toronto), D. Sand, N. Smith (Arizona), D. Kasen (Berkeley), B. Metzger (Columbia)

We report spectroscopic observations with the 4m SOAR telescope and Goodman spectrograph, of two potential electromagnetic counterparts to the gravitational wave trigger S190425z (GCN 24168): ZTF19aasckkq and ZTF19aasckwd, reported by ZTF/GROWTH (Anand et al, GCN 24311). 

These candidates were deemed to be the most likely counterparts as they are offset from bright galaxies and have low spectroscopic or photometric redshifts. ZTF19aasckkq has been detected in follow-up photometry by Perley et al. (GCN 24314), Malesani et al. (GCN 24319) and Ahumada et al. (GCN 24320).

SOAR classifications:

ZTF19aasckwd is a young Type Ia SN at z~0.15, consistent with the photometric redshift of the nearby galaxy.

ZTF19aasckkq also shows clear SN features in the spectrum. Using the code SNID (Blondin & Tonry, 2007) we find good matches to Type IIb SNe at z~0.05, consistent with the galaxy redshift.