[vsnet-grb-info 24697] LIGO/Virgo S200114f: ZTF Forced Photometry of the Swift Source S200114f_X2

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  26796
SUBJECT: LIGO/Virgo S200114f: ZTF Forced Photometry of the Swift Source S200114f_X2
DATE:    20/01/17 06:19:19 GMT
FROM:    Igor Andreoni at Caltech  <igor.andreoni at gmail.com>

Igor Andreoni (Caltech), Mansi M. Kasliwal (Caltech), Matthew Graham (Caltech), Frank Masci (IPAC)
On behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations

The Zwicky Transient Facility (ZTF; Graham et al. 2019, Bellm et al. 2019) has repeatidly observed the location of Source S200114f_X2 (Evans et al., GCN #26787, GCN #26791), an X-ray transient candidate possibly associated with the gravitational wave event S200114f (LVC, GCN #26734). We used the Kowalski infrastructure (Duev et al., 2019) to query the ZTF database. Only one source, ZTF19aaehfwn, was found in ZTF data that generated >5sigma alerts within a 21-arcsec radius from Source S200114f_X2, whose position was reported with 7 arcsec uncertainty (Evans et al., GCN #26787, GCN #26791). ZTF19aaehfwn is spatially coincident with the candidate quasar WISEA J072127.41+170205.7 (Assef et al., 2018), that is consistent with the location of Source S200114f_X2 as previously noted by Evans et al. (GCN #26787, GCN #26791). ZTF19aaehfwn/WISEA J072127.41+170205.7 is located 3.9 arcsec away from Source S200114f_X2.

We performed forced photometry on 57 ZTF images acquired between 2018-11-17 and 2020-01-14 08:23:13, with the last image taken about 6 hours after the S200114f detection time. Forced photometry was performed on images processed through the ZTF reduction and image subtraction pipelines at IPAC (Masci et al. 2019).

The light curve of ZTF19aaehfwn shows possible long and short timescale variability, with upper limits at about r>20 before September 2019, followed by several detections at roughly 19.5 < r < 20.5 and 19.6 < g < 20.1. The light curve behavior does not appear atypical for an AGN and there is no evidence of strong flares. A decline in brightness is measured in the first hours after S200114f, as shown in the table below presenting the latest data points available.

+---------------------+--------+----------+------+
| Date (UTC)          | filter | mag (AB) | err  |
+---------------------+--------+----------+------+
| 2020-01-12 07:51:20 | r      | 19.52    | 0.19 |
| 2020-01-14 08:22:34 | r      | 19.70    | 0.11 |
| 2020-01-14 08:23:13 | r      | 20.28    | 0.18 |
+---------------------+--------+----------+------+


The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: Graham). 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.