GCN Circular 32643
Subject
Swift J1913.1+1946 : Pre-discovery limits from ZTF
Date
2022-10-10T04:06:07Z (2 years ago)
From
Viraj Karambelkar at Indian Inst of Tech,Bombay <karambelkarvraj21197@gmail.com>
Viraj Karambelkar (Caltech), Igor Andreoni (Univ. of Maryland), Eric Bellm
(University of Washington), Daniel Perley (LJMU), Harsh Kumar (IIT Bombay)
on behalf of the ZTF collaboration
We performed forced photometry on ~1400 Zwicky Transient Facility (ZTF)
images dating back to 2018-03-27 at the location of the bright hard X-ray
and optical transient Swift J1913.1+1946 (Dichiara et al., GCN 32632;
Lipunov et al., GCN 32634; Perley et al. GCN 32638; Broens et al. GCN
32640). We used the ZTF point-spread-function (PSF) forced photometry
service (Masci et al., 2018) on images processed through the ZTF reduction
and image subtraction pipelines at IPAC (Masci et al., 2019)
No source is detected in the archival ZTF images, which reached a median
5-sigma depth of ~21 mag (AB) in the g, r and i filters.
ZTF last observed the field of this transient on JD 2459861.68 in the
g-band, and on JD 2459860.59 in the r-band -- 0.4 and 1.5 days prior to the
Swift BAT discovery respectively. No source was detected in these images,
and the following 5-sigma upper limits were measured -
+----------------------+------------+------------------------+--------+----------+
| Date [UT] | JD | days_before_discovery | Filter | mag
(AB) |
|
---------------------+------------+------------------------+--------+----------+
| 2022-10-09 04:19:12 | 2459861.68 | 0.4 | ZTF-g |
>20.1 |
| 2022-10-08 02:09:36 | 2459860.59 | 1.5 | ZTF-r |
>22.0 |
+----------------------+------------+------------------------+--------+----------+
The reported limits are not corrected for Galactic extinction.
ZTF is a project led by PI S. R. Kulkarni at Caltech (see ATEL #11266), and
includes IPAC; WIS, Israel; OKC, Sweden; JSI/UMd, USA; UW, USA; DESY,
Germany; NSTC, Taiwan; UW Milwaukee, USA and LANL USA. ZTF acknowledges the
generous support of the NSF under AST MSIP Grant No 1440341. Alert
distribution service provided by DIRAC@UW. The ZTF forced-photometry
service was funded under the Heising-Simons Foundation grant #12540303 (PI:
Graham)