TITLE:   GCN CIRCULAR
NUMBER:  27745
SUBJECT: GRB 200514B: Zwicky Transient Facility Follow-Up of a Fermi Short GRB (Trigger 611140062) - More Candidates
DATE:    20/05/15 21:42:13 GMT
FROM:    Shreya Anand at GROWTH Caltech  <sanand@caltech.edu>

Simeon Reusch (DESY), Tomas Ahumada (UMD), Shreya Anand (Caltech), Michael Coughlin (UMN), Mansi M. Kasliwal (Caltech), Erik Kool (OKC), Harsh Kumar (IIT-B), Robert Stein (DESY), Igor Andreoni (Caltech), Varun Bhalerao (IIT-B), Albert Kong (NTHU) and Leo Singer (NASA/GSFC)
on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations

We re-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 570 square degrees beginning at 09:58 UT on 2020 May 15 (24.83 hours after the burst trigger time). This corresponds to ~71% of the probability enclosed in the Earth-occultation corrected GRB localization map (GCN 27736). Each exposure was 300s, reaching g-band and r-band median depths of 22.4 and 22.2 mag respectively. 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-match 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 that no spatially coincident ZTF alerts were issued before the detection time of the GBM trigger. The candidates within the 90% probability contour of the GRB localization map that pass these selection criteria as well as human vetting are presented in the table below. The filter, magnitude and MJD columns correspond to the ZTF first alert, while the Decline Rate (D.R) is in [mag/day]. 

+----------------------------------------------------------------------------------------------------------------------+
| ZTF Name     | IAU Name   | RA (deg)    | DEC (deg)  | Filter | Mag  | MagErr | MJD      | D.R. [mag/day] | Notes    |
+----------------------------------------------------------------------------------------------------------------------+
| ZTF20aazplwp | AT 2020jzo | 234.0167814 | 41.1672761 |    r   | 21.6 |  0.15  | 58984.45 | 0.3 in g       | (a)      |
| ZTF20aazqlgx | AT 2020jzr | 246.0908608 | 34.6259478 |    r   | 22.3 |  0.19  | 58984.45 | 0.3 in r       | (c)(1)   |
| ZTF20aazphye | AT 2020jzn | 255.6577428 | 41.7013160 |    r   | 21.6 |  0.15  | 58984.47 | 0.3 in g       | (c,d)(2) |
| ZTF20aazpnxd | AT 2020kap | 255.931646  | 48.3862806 |    r   | 21.6 |  0.16  | 58984.47 | 0.3 in g       | (a)      |
| ZTF20aazpkri | AT 2020kaq | 240.7324792 | 48.5554957 |    r   | 21.3 |  0.10  | 58984.46 | 0              | (a)      |
| ZTF20aazqndp | AT 2020kal | 237.8212032 | 50.4933039 |    r   | 22.1 |  0.15  | 58984.46 | 0              | (c,d)(3) |
| ZTF20aazqpps | AT 2020kam | 252.2388065 | 41.3097433 |    r   | 21.6 |  0.14  | 58984.47 | 0              | (c,d)(4) |
+----------------------------------------------------------------------------------------------------------------------+


Notes:
(a) hostless
(b) offset from a galaxy
(c) nuclear
(d) PS1 detection at source position

(1) SDSS phot-z = 0.35 +/- 0.10
(2) SDSS phot-z = 0.26 +/- 0.04 
(3) CLU z = 0.03195
(4) SDSS phot-z = 0.2 +/- 0.03 

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).