GCN Circular 33900

Viraj Karambelkar (CIT), Tomas Ahumada (CIT),  Robert Stein (CIT), Akash
Anumarlapudi (UWM), Gaurav Waratkar (IITB), Harsh Kumar (IITB), Anirudh
Salgundi (IITB), Vishwajeet Swain (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), Eric Bellm (UW), Brian Healy (UMN), S. B. Cenko (UMD), D. Kaplan
(UWM), D. Perley (LJMU) report on behalf of the ZTF and GROWTH
collaborations:


We observed the localization region of the LVC trigger S230529ay as part of
routine Zwicky Transient Facility (ZTF; Graham et al., 2019; Bellm et al.,
2019) survey operations. We obtained images in the r, i, and g bands
beginning at 2023-05-30T04:13:34.003 UT (10 hours after the LVC trigger
time), covering ~7% of the probability enclosed in the localization region.


We queried the ZTF alert stream using Kowalski (Duev et al. 2019) through
Fritz (Coughlin et al. 2023) and emgwcave (Karambelkar et al. in prep),
AMPEL (Nordin et al. 2019), and ZTFReST (Andreoni & Coughlin et al., 2021).
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 LVC trigger. We also run
forced photometry on ZTF images (Masci et al. 2019) and ATLAS images (Tonry
et al. 2018, Smith et al. 2020) and require no detections before the LVC
trigger.


One source passed our criteria and is inside the 95% error region:

|-----------------------------------------------------------------------------------------------------
| id           | alias                |       ra |     dec |        mjd  |
mag±err (ab)   | filter   |
|-----------------------------------------------------------------------------------------------------
| ZTF23aamnpce | AT2023jtt
Not found
 
 
            | 235.9839 | 15.2248 | 60094.23830 |
20.49±0.23     |  r       |
|-----------------------------------------------------------------------------------------------------


AT2023jtt
Not found
 
 
 is 0.5" from a galaxy that has a photometric redshift of
photoz=0.22±0.06 from the Legacy Survey DR8 (Duncan, 2022), suggesting that
it is probably not associated with the LVC trigger.

Further follow-up of this localization region will continue as part of
regular survey operations.


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). 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.