[vsnet-grb-info 22107] LIGO/Virgo S190425z: ZTF19aarykkb Imaging from Las Cumbres Observatory

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24206
SUBJECT: LIGO/Virgo S190425z: ZTF19aarykkb Imaging from Las Cumbres Observatory
DATE:    19/04/26 03:24:29 GMT
FROM:    Jamison Burke at Las Cumbres Observatory/UCSB  <jburke at lco.global>

Jamison Burke (LCO/UCSB), Daichi Hiramatsu (LCO/UCSB), Iair Arcavi (Tel
Aviv University), D. Andrew Howell (LCO/UCSB), Curtis McCully (LCO), Craig
Pellegrino (LCO/UCSB) on behalf of the Las Cumbres GW Follow-up
Collaboration

Beginning 2019-04-25 21:34:17 we obtained 14 g-, r-, and i-band images of
the GW optical counterpart candidate ZTF19aarykkb (Kasliwal et al. 2019,
GCN 24191) with the Las Cumbres Observatory 1m telescope at the South
African Astronomical Observatory. We present the following PSF photometry
of the target:

Datetime (UT)         JD                Filter  Mag          Magerr
2019-04-25 21:34:17   2458599.3987      g       18.79        0.03
2019-04-25 21:38:04   2458599.4013      g       18.79        0.02
2019-04-25 21:42:05   2458599.4041      r       18.18        0.03
2019-04-25 21:44:31   2458599.4058      r       18.18        0.03
2019-04-25 21:47:12   2458599.4076      i       17.95        0.04
2019-04-25 21:49:39   2458599.4093      i       17.96        0.04
2019-04-25 22:15:11   2458599.4271      g       18.80        0.03
2019-04-25 22:20:38   2458599.4309      g       18.82        0.02
2019-04-25 22:26:19   2458599.4348      i       17.93        0.05
2019-04-25 22:31:46   2458599.4386      i       17.97        0.05
2019-04-25 23:25:31   2458599.4759      g       18.97        0.03
2019-04-25 23:29:18   2458599.4785      g       18.95        0.03
2019-04-25 23:33:18   2458599.4813      r       18.12        0.04
2019-04-25 23:35:45   2458599.4830      r       18.14        0.03

These values disagree with the photometry presented in Bhalerao et al. 2019
(GCN 24201) despite the observations being contemporaneous. The g- and
r-band photometry presented here is roughly 0.3 magnitudes fainter, and the
i-band photometry is almost a full magnitude fainter.