TITLE:   GCN CIRCULAR
NUMBER:  26767
SUBJECT: LIGO/Virgo S200115j: Candidates from the Zwicky Transient Facility
DATE:    20/01/15 10:37:04 GMT
FROM:    Varun Bhalerao at Indian Inst of Tech  <varunb@iitb.ac.in>

Shreya Anand (Caltech), Harsh Kumar (IITB), Simeon Reusch (DESY), Varun Bhalerao (IITB), Leo Singer (NASA-GSFC), Michael Coughlin (UMinn), Igor Andreoni (Caltech), Matthew Graham (Caltech), Brad Cenko (UMD), David Kaplan (UWM), Mansi Kasliwal (Caltech)

on behalf of the Zwicky Transient Facility (ZTF) and Global Relay of Observatories Watching Transients Happen (GROWTH) collaborations.

We observed the localization region of the gravitational wave trigger S200115j, in the initial bayestar.fits.gz,2 skymap (LVC, GCN #26759) with the Palomar 48-inch telescope equipped with the 47 square degree Zwicky Transient Facility camera (ZTF, Bellm et al. 2019, Graham et al. 2019).

The tiling was optimally determined and triggered using the GROWTH Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et al. 2019b). We started obtaining target-of-opportunity observations in the g-band and r-band beginning at 2020-01-15 06:28 UT. In our triggered 300s observations, we covered 36% of the enclosed probability to a median depth of 21.2 mag.

The images were processed in real-time through the ZTF reduction and image subtraction pipelines at IPAC to search for potential counterparts (Masci et al. 2019). Alert filtering and follow-up coordination was undertaken by the GROWTH Marshal system (Kasliwal et al. 2019). The ZTF alert stream was also queried using the Kowalski infrastructure (Duev et al., 2019) and with AMPEL (Nordin et al. 2019).

Two of our candidates were located near galaxies detected in the PanSTARRs survey (Chambers et al. 2016). Phot-z estimates for these were based on ANNz2 (Sadeh et al. 2016).

We identified the following candidates:
±-------------±---------±------------±-------------±-------±-----±---------±------±------+
| Name | IAU Name | RA | Dec | filter | mag | MJD | b_Gal | Notes |
±-------------±---------±------------±-------------±-------±-----±---------±------±------+
| ZTF20aafqpum | AT2020yo | 03:06:06.50 | +13:54:48.4 | g | 20.8 | 58863.27 | -37.5 | (a) |
| ZTF20aafqulk | AT2020yp | 03:39:45.43 | +27:44:05.4 | g | 21.1 | 58863.29 | -21.9 | (b) |
| ZTF20aafqvyc | AT2020yq | 03:47:58.21 | +38:26:31.8 | g | 20.9 | 58863.30 | -12.5 | |
±-------------±---------±------------±-------------±-------±-----±---------±------±------+
(a) Offset from possible host galaxy at redshift photz = 0.12 +/- 0.03
(b) Offset from possible host galaxy at redshift photz = 0.27 +/- 0.04

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 filtering and follow-up coordination is being undertaken by the GROWTH marshal system (Kasliwal et al. 2019). Alert database searches are done with using the Kowalski infrastructure (Duev et al., 2019) and with AMPEL (Nordin et al. 2019).