TITLE:   GCN CIRCULAR
NUMBER:  24257
SUBJECT: LIGO/Virgo S190426c: Public DECam Observations
DATE:    19/04/27 01:38:15 GMT
FROM:    Daniel Goldstein at Caltech  <danny@caltech.edu>

Daniel A. Goldstein (Caltech), Igor Andreoni (Caltech), Michael
Coughlin (Caltech), Mansi M. Kasliwal (Caltech), Peter E. Nugent
(LBNL), Joshua S. Bloom (UC Berkeley), Keming Zhang (UC Berkeley),
Shreya Anand (Caltech), Jennifer Barnes (Columbia), S. Bradley Cenko
(NASA GSFC), Jeffrey Cooke (Swinburne), Jorge Martínez Palomera (UC
Berkeley), Leo P. Singer (NASA GSFC), on behalf of the Global Relay of
Observatories Watching Transients Happen (GROWTH) and ZTF
collaborations:

We are observing the ecliptic lobe and southern regions of the
northern lobe of the localization region of the gravitational wave
trigger S190426c (LIGO Scientific Collaboration and the Virgo
Collaboration, GCN #24237) with the Victor M. Blanco 4m Telescope at
Cerro Tololo Inter-American Observatory, equipped with the Dark Energy
Camera (DECam). An observational tiling for the event was
automatically and optimally determined and triggered using the GROWTH
Target of Opportunity marshal (Coughlin et al. 2019a, Kasliwal et al.
2019b). We plan to observe 35% of the integrated probability and more
than 800 square degrees with 30 second visits in r and 50 in z. Our
limiting magnitudes are expected to be ~22.9 in r and ~22.4 in z,
based on the DECam exposure time calculator
(http://www.ctio.noao.edu/noao/sites/default/files/DECam/DECam_ETC-ARW-RCS7.xls).

The data from this program are immediately public and we invite anyone
interested to search the images for optical counterparts. We are
searching the images in real time for optical counterpart candidates
using an image subtraction pipeline written for this program. We
invite anyone interested to download the images. The images are
available under proposal ID 2019A-0205 from the NOAO archive
(archive.noao.edu). For any questions on the data or the observations,
please contact the PIs of this program, Danny Goldstein and Igor
Andreoni (danny@caltech.edu, andreoni@caltech.edu).

GROWTH and ZTF 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; TTU, USA; LANL USA;
Tokyo Tech, Japan; IIT-B, India; IIA, India; LJMU, UK 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
co-ordination is being undertaken by the GROWTH marshal system
(Kasliwal et al. 2019).