GCN Circular 22739

Michael. W. Coughlin (Caltech), Leo P. Singer (NASA GSFC), S. Bradley Cenko (NASA GSFC), Mansi M. Kasliwal (Caltech),��Daniel A. Perley (LJMU),��Eric Burns (NASA GSFC), and��V. Zach Golkhou (U. Wash.) report on behalf of the ZTF project and the GROWTH collaboration:

We observed the localization region of the short GRB 180523B (trigger 548793993) detected by the Gamma-Ray Burst Monitor (GBM) on the Fermi satellite with the Palomar 48 inch telescope equipped with the 47 square degree Zwicky Transient Facility camera. ��We obtained a series of r- and g-band images covering 2900 square degrees beginning at 3:51 UT on 2018 May 24 (9.1 hours after the burst trigger time), corresponding to ~ 70% of the probability enclosed in the localization region. ��

The images were processed though the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts. ��121 high-significance transient and variable candidates were identified by our pipeline in this area, all of which had previous detections with ZTF in the days and weeks prior to the GRB trigger time (e.g., supernovae, active galactic nuclei). ��No viable optical counterparts were thus identified. ��The median 5 sigma upper limit for an isolated point source in our images was r > 20.3 and g > 20.6 mag.

Further observations of the field are planned.

ZTF (http://ztf.caltech.edu) acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. All alerts were filtered, vetted and follow-up co-ordinated by the GROWTH (http://growth.caltech.edu) project marshal system with generous support of the NSF under PIRE Grant No 1545949.