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GCN Circular 33801

GRB 230513A: Zwicky Transient Facility Follow-Up of a Fermi Short GRB (Trigger 705709044)
2023-05-15T01:06:55Z (a year ago)
Tomas Ahumada at U. of Maryland <>
Harsh Kumar (IITB), Vishwajeet Swain (IITB), Anirudh Salgundi (IITB), Aswin
Suresh (IITB), Tomas Ahumada (CIT), Viraj Karambelkar (CIT), Robert Stein
(CIT), Theophile du Laz (CIT), Igor Andreoni (UMD), Michael Coughlin (UMN),
Mansi Kasliwal (CIT), Simeon Reusch (DESY), Jannis Necker (DESY), Shreya
Anand (CIT), report on behalf of the ZTF collaboration:

We observed the localization region of the short GRB 230513A (trigger
705709044, GCN 33793) 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 410 square degrees beginning at
2023-05-14T03:42:31.003 (5 hours after the burst trigger time). This
corresponds to ~72% of the probability enclosed in the Earth-occultation
corrected GRB localization map. Each exposure was 300 seconds, reaching
g-band and r-band median depths of 22.2 mag and 22.0 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) through
Fritz (Coughlin et al. 2023) 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. Close to 120 sources were
time and spatially coincident with the burst, most of them showing g-r ~ 0
mag and a slow evolution. We highlight the sources that show red colors
(i.e. g-r > 0.3 mag) in the table below, and we encourage follow up.

ZTF name , AT name , UT first alert , t-t0 , filter , mag , error
ZTF23aajklxl , AT 2023ilp , 2023-05-14 03:42:31.003 , 0.23 , r , 21.44 ,
ZTF23aajkqkc , AT 2023ilq , 2023-05-14 03:58:01.998 , 0.24 , r , 20.59 , 0.1
ZTF23aajkuyh , AT 2023ilr , 2023-05-14 04:18:53.001 , 0.25 , r , 21.56 ,
ZTF23aajlbzl , AT 2023ils , 2023-05-14 04:46:40.002 , 0.27 , g , 21.61 ,
ZTF23aajktjd , AT 2023ilt , 2023-05-14 04:13:34.003 , 0.25 , r , 21.77 ,

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
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). GROWTH India telescope is located at the Indian
Astronomical Observatory (Hanle), operated by the Indian Institute of
Astrophysics (IIA). GROWTH-India project is supported by SERB and
administered by IUSSTF, under grant number IUSSTF/PIRE
Program/GROWTH/2015-16 and IUCAA.

Tomás Ahumada (he/him)
Ph.D. Candidate
Department of Astronomy
University of Maryland, College Park
NASA <> Goddard Space Flight Center, Code 661
B.Sc. Astronomy, Pontificia Universidad Católica de Chile

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