TITLE: GCN CIRCULAR NUMBER: 24130 SUBJECT: GRB 190406B: Zwicky Transient Facility Follow-Up of a Fermi Short GRB (Trigger 576241792) DATE: 19/04/18 22:06:52 GMT FROM: Tomas Ahumada at U. of Maryland Authors: Tomas Ahumada (UMD), S. Bradley Cenko (NASA GSFC), Michael W. Coughlin (Caltech), Eric C. Bellm (UW), Leo P. Singer (NASA GSFC), Shaon Ghosh (UWM), Mansi M. Kasliwal (Caltech), Shreya Anand (Caltech), Igor Andreoni (Caltech), Scott Adams (Caltech), Matt Hankins (Caltech), Varun Bhalerao (IITB), Harsh Kumar (IITB), V. Zach Golkhou (UW) on behalf of the ZTF and GROWTH collaborations and the KPED team We observed the localization region of the short GRB190406B (trigger 576241792) 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 (ZTF) camera. We obtained a series of r- and g-band images covering 268 square degrees beginning at 08:01 UT on 2019 April 08 (44:52 hours after the burst trigger time). This corresponds to ~ 44% of the probability enclosed in the intersection of the GBM and IPN localization regions. We revisited the region on 2019 April 11, starting at 08:03 UT (116:54 hours after the burst trigger time) and we covered the same ~ 44% of the probability region. The images were processed through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts. 240 high-significance transient and variable candidates were identified by our pipeline in the area observed, 236 of which had previous detections with ZTF in the days and weeks prior to the GRB trigger time (e.g., supernovae, active galactic nuclei). Further follow-up of 4 transients was obtained with the Kitt Peak EMCCD Demonstrator (KPED) on the Kitt Peak 84-inch telescope on April 12. Additionally, we obtained follow-up spectroscopy of 2 candidates with the Double Spectrograph (DBSP) on Palomar 200” the nights of April 12. The candidates are listed below, however no photometric evolution or spectral classification was consistent with an optical counterpart. ---------------------------------------------------------------------------------------------------------------------------- ZTF ID RA DEC last non-detection discovery KPED Class ---------------------------------------------------------------------------------------------------------------------------- deg deg date in 2019 April 08 April 12 ---------------------------------------------------------------------------------------------------------------------------- ZTF19aapgbri 275.504094 +55.964483 04-07 r<20.41 g = 21.36 g=20.76 SN Ia ZTF19aapgdcn 285.158686 +69.881810 04-04 r<19.49 g = 20.67 g=21.74 SN Ia ZTF19aapfxqv 276.915046 +65.626121 04-04 r<17.61 g=20.67 g=20.67 SN* ZTF19aapwbgo 278.519641 +57.057325 04-07 r<20.35 g=21.61 g=22.36 SN* ------------------------------------------------------------------------------------------------------------------------- *Classification from photometric data points. The median 5 sigma upper limit for an isolated point source in our images was r > 21.5 and g > 21.8 mag for the observations made on April 8 26 and r > 21.9 and g > 21.6 mag for the observations made on April 11. ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266 ), and includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW, USA; DESY, Germany; NRC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the generous support of the NSF under AST MSIP Grant No 1440341. Alert distribution service provided by DIRAC@UW. Alert filtering is being undertaken by the GROWTH marshal system, supported by NSF PIRE grant 1545949.