[vsnet-grb-info 22334] LIGO/Virgo S190426c: INT Observations of ZTF19aassfws

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24433
SUBJECT: LIGO/Virgo S190426c: INT Observations of ZTF19aassfws
DATE:    19/05/09 15:13:58 GMT
FROM:    Mansi M. Kasliwal at Caltech/Carnegie  <mansikasliwal at gmail.com>

Christoffer Fremling (Caltech), Andrew Levan (Radboud),  Mansi Kasliwal
(Caltech) and Nial Tanvir (Leicester)

report on behalf of a larger collaboration

We imaged ZTF19aassfws (Perley et al. GCN 24331, Coughlin et al. GCN 24283)
with the INT on UT 2019-04-08. Difference imaging relative to PanSTARRS1
(Chambers et al. 2016) finds no detection in the r-band to r > 22.6 mag and
a bright detection in z-band at z ~ 20.8,corresponding to M_Z ~ -17.2 at
z=0.093 (Cenko et al. GCN24430). The z-band luminosity is higher than
GW170817 at this phase. The red color at this phase is plausible for a
kilonova but we cannot definitively rule out unrelated, nuclear activity.
We further caution that the INT and PS1 have different filter transmission
curves in z-band. We encourage follow-up to confirm or refute the
association of this source with the GW event S190426c (LVC et al. GCN
24237,  GCN 24411).

We thank the INT observers, Lord Dover and Tarik Zegmott for facilitating
these observations.