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GCN Circular 33812

GRB 230513A: Zwicky Transient Facility continuous observations of a Fermi Short GRB (Trigger 705709044)
2023-05-18T04:32:06Z (a year ago)
Tomas Ahumada at U. of Maryland <>
Tomas Ahumada (CIT), Viraj Karambelkar (CIT), Robert Stein (CIT), Harsh
Kumar (IITB), Vishwajeet Swain (IITB), Anirudh Salgundi (IITB), Aswin
Suresh (IITB),  Theophile du Laz (CIT), Igor Andreoni (UMD), Michael
Coughlin (UMN), Mansi Kasliwal (CIT), Varun Bhalerao (IITB), Simeon Reusch
(DESY), Jannis Necker (DESY), Shreya Anand (CIT), report on behalf of the
ZTF collaboration:

We re-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 beginning at 29 and 77 hours after the burst
trigger time. For the first epoch of observations we covered 619.3 square
degrees corresponding to ~82% of the probability region and reaching a
median depth of 21.85 mag in the 300 sec r-band exposures, 22.36 mag in the
450 sec r-band exposures, and 21.82 mag in the 300 sec g-band exposures.
For the second epoch ZTF covered 671.9 square degrees, corresponding to
~85% of the region, and reaching a median depth of 21.71 mag in 300 sec
r-band exposures. 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 200 sources were
time and spatially coincident with the burst. No source showed a
photometric evolution  consistent with a GRB afterglow, including the ones
circulated on GCN 33801.

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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