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GCN Circular 27737

Subject
GRB200514B: Zwicky Transient Facility Follow-Up of a Fermi Short GRB (Trigger 611140062)
Date
2020-05-14T18:20:05Z (4 years ago)
From
Tomas Ahumada at U. of Maryland <tahumada@astro.umd.edu>
Tomas Ahumada (UMD), Shreya Anand (Caltech), Igor Andreoni (Caltech),
Michael Coughlin (UMN), Erik Kool (OKC), Simeon Reusch (DESY), Ana Sagu��s
Carracedo (OKC), Robert Stein (DESY)

on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of
Observatories Watching Transients Happen (GROWTH) collaborations

We observed the localization region of the short GRB200514B (trigger
611140062) 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 g-
and r-band images covering 519.3 square degrees beginning at 10:01 UT on
2020 May 14 (0.9 hours after the burst trigger time). This corresponds to
~49% of the probability enclosed in the GRB localization map (GCN 27736).
Each exposure was 300s, reaching a g-band median depth of 21.8 mag and
r-band median depth of 22.0 mag. The images were processed in real-time
through the ZTF reduction and image subtraction pipelines at IPAC (Masci et
al. 2019).

We queried the ZTF alert stream using Kowalski (Duev et al. 2019) and AMPEL
(Nordin et al. 2019). We required at least 2 detections separated by at
least 15 minutes to select against moving objects. Furthermore, we
cross-matched our candidates with the Minor Planet Center to flag known
asteroids, reject stellar sources (Tachibana and Miller 2018), and apply
machine learning algorithms (Mahabal et al. 2019). We require no spatially
coincident ZTF alert to be issued before the detection time of the GBM
trigger. The candidates within the 90% probability contour of the GRB
localization map that passed the automatic selection criteria and human
vetting are presented in the table below.


+----------------------------------------------------------------------------------------------------+
| ZTF Name     | IAU Name   | RA (deg)    | DEC (deg)   | Filter | Mag   |
MagErr | MJD      | Notes |
+----------------------------------------------------------------------------------------------------+
| ZTF20aazpphd | AT 2020jww | 242.7149675 | +27.1616870 | r      | 19.6  |
0.05   | 58983.49 |       |
| ZTF20aazppnv | AT 2020jxa | 238.1438691 | +25.5764946 | r      | 21.1  |
0.17   | 58983.49 | (b,c) |
| ZTF20aazprjq | AT 2020jxb | 233.5213585 | +43.3298714 | r      | 21.3  |
0.13   | 58983.47 | (a,d) |
| ZTF20aazptlp | AT 2020jxd | 229.007524  | +48.774925  | r      | 21.5  |
0.19   | 58983.48 | (a,e) |
| ZTF20aazptnn | AT 2020jxc | 237.2967278 | +47.271954  | r      | 21.6  |
0.17   | 58983.48 | (a,f) |
| ZTF20aazpnst | AT 2020jxn | 254.0989833 | +34.4655542 | r      | 22.0  |
0.20   | 58983.47 | (a,g) |
| ZTF20aazpofi | AT 2020jxm | 236.929525  | +46.9809542 | r      | 21.5  |
0.13   | 58983.48 | (a,h) |
+----------------------------------------------------------------------------------------------------+

We highlight ZTF20aazpphd, as it is offset 12 arcseconds from the center of
a galaxy at 160 Mpc and was not detected 2.15 days earlier with a limiting
magnitude of g > 20.53. The host spectroscopic redshift is z = 0.04573,
which would imply a g-band absolute magnitude of -17.23.

Notes:
(a) Offset from faint host
(b) Nuclear
(c) SDSS photoz = 0.170 +- 0.03
(d) SDSS photoz = 0.226 +- 0.04
(e) SDSS photoz = 0.402 +- 0.11
(f) SDSS photoz = 0.261 +- 0.06
(g) SDSS photoz = 0.188 +- 0.05
(h) SDSS photoz = 0.464 +- 0.08


ZTF and GROWTH are worldwide collaborations comprising Caltech, USA; IPAC,
USA, WIS, Israel; OKC, Sweden; JSI/UMd, USA; U Washington, USA; DESY,
Germany; MOST, Taiwan; UW Milwaukee, USA; LANL USA; Tokyo Tech, Japan;
IITB, India; IIA, India; LJMU, UK; TTU, USA; SDSU, USA and USyd, Australia.
ZTF acknowledges the generous support of the NSF under AST MSIP Grant No
1440341.
GROWTH acknowledges generous support of the NSF under PIRE Grant No 1545949.
Alert distribution service provided by DIRAC@UW (Patterson et al. 2019).
Alert database searches are done by AMPEL (Nordin et al. 2019) and Kowalski
(Duev et al. 2019).
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