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GCN Circular 23515

GRB 181126B: Zwicky Transient Facility Follow-Up of a Fermi Short GRB (Trigger 564897175)
2018-12-07T05:14:50Z (5 years ago)
Tomas Ahumada at U. of Maryland <>
Authors: Tomas Ahumada (UMD), Michael W. Coughlin (Caltech), S. Bradley
Cenko (NASA GSFC), Leo P. Singer (NASA GSFC), Shaon Ghosh (UWM), Igor
Andreoni (Caltech), Mansi M. Kasliwal (Caltech), Eric C. Bellm (UW), V.
Zach Golkhou (UW), Ryosuke Itoh (Tokyo Tech), Anna Ho (Caltech), Yuhan Yao
(Caltech), Jacob Jencson (Caltech), Matt Hankins (Caltech), Kishalay De
(Caltech), Virginia Cunningham (UMD) on behalf of the ZTF and GROWTH
collaborations and the KPED team

We observed the localization region of the short GRB181126B (trigger
564897175) 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 two sets of 180
second r-band images covering 1400 square degrees beginning at 5:15 UT on
2018 November 26 (1 hour and 23 minutes after the burst trigger time).
Accounting for area lost to processing failures, this corresponds to
analyzing 66% of the probability enclosed. Beginning at 6:06 UT on 2018
November 27 we observed the updated IPN localization with ZTF using 300
second r-band exposures. The observations covered 709 square degrees. Once
again accounting for processing failures, 77% of the enclosed probability
was analyzed.

The images were processed through the ZTF reduction and image subtraction
pipelines at IPAC to search for potential counterparts. 394
high-significance transient and variable candidates were identified by our
pipeline in the area observed,  most (383) of which had previous detections
with ZTF in the days and weeks prior to the GRB trigger time (e.g.,
supernovae, active galactic nuclei, CV).

Further follow-up of 11 transients was obtained with the Kitt Peak EMCCD
Demonstrator (KPED) on the Kitt Peak 84-inch telescope on November 28.
Additionally, we obtained follow-up spectroscopy of 6 candidates with the
Low Resolution Imaging Spectrometer (LRIS) on Keck I, the nights of
December 1 and December 3. 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


                             deg deg date in 2018          Nov 26 Nov 28

ZTF18achtkfy     103.5113 37.0748    11-09 g<19.94 r = 19.69   r = 20.95
SN* (Rising)
ZTF18acpftxl     102.7187 29.3472     11-21 r<20.43 r = 20.11   r > 20.93
Asteroid* (1 det)
ZTF18achflqs      70.2895 23.8902   11-10 r<20.37 r = 20.74   r = 20.26 SN*
ZTF18acrkcxa     73.7605 22.6787   11-21 r<19.68 r = 21.21    r = 20.87 SN*
ZTF18acrkkpc     95.8148 10.323    11-21 r<20.17 r = 20.17    r = 19.85 SN*
ZTF18aadwfrc     94.3249 50.4844   11-25 r<19.33 r = 18.96    r = 18.13 SN
II z=0.04
ZTF18acrfond     59.8623 24.589     11-25 r<19.38 r = 19.93    r = 18.87 SN
Ia z=0.117
ZTF18acrfymv     94.5049 44.1813   11-25 r<19.13 r = 20.05    r = 19.60 S
ZTF18acptgzz     68.3852 -1.6475    11-25 r<19.22 r = 19.01   r = 19.04 SN
Ia z=0.096

ZTF18acbyrll       88.8695 29.4723 11-21   r<19.84 r = 18.79 r > 21.87
  Asteroid* (1 det)

ZTF18acrewzd    70.3221 -1.7688     11-25 r<19.17 r = 20.21   r = 19.9 SN
Ia z=0.13


*Classification from photometric data points.

The median 5-sigma upper limit for an isolated point source in ZTF images
was r > 20.5 mag for the observations made on November 26 and r > 21.1 mag
for the observations made on November 27.

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; MOST, 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.
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