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GCN Circular 33898

LIGO/Virgo/KAGRA S230527ch: Zwicky Transient Facility observations
2023-05-31T03:32:27Z (a year ago)
Viraj Karambelkar at Indian Inst of Tech,Bombay <>
Akash Anumarlapudi (UWM), Tomas Ahumada (CIT), Viraj Karambelkar (CIT),
Robert Stein (CIT), Gaurav Waratkar (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),
D. Perley (LJMU), D. Kaplan (UWM), S.B. Cenko (UMD) report on behalf of the
ZTF and GROWTH collaborations:

We observed the localization region of LVC trigger S230527ch 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 ~9 hours after the burst trigger time and covering ~20% of the
probability enclosed in the localization region (18 % with galactic
latitude |b|>10, 2 % with |b|<10).

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

Two sources passed our criteria and are inside the 95% error region:

| id           | alias                |       ra  |     dec      |     mjd
    | mag±err (ab)   | filter   | comments                      |
| ZTF23aamnsjs | AT2023jtu            | 280.2040  | -20.6598     |
60094.23830 | 19.20±0.14     | r        |
| ZTF23aamdode | AT2023jpc            | 257.1902  | 8.9143       |
60092.3303  | 17.83±0.01     | r        | likely a CV based on spectrum    |

We obtained a spectrum of AT2023jpc with the SEDM spectrograph on the
60-inch telescope at Palomar Observatory (Blagorodnova et al. 2017). The
spectrum shows a blue, featureless continuum indicating that this transient
is a cataclysmic variable (CV).

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.

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