TITLE:   GCN CIRCULAR
NUMBER:  21498
SUBJECT: LIGO/Virgo G297595: INAF VST-ESO PARANAL observations
DATE:    17/08/16 16:49:09 GMT
FROM:    Giuseppe Greco at U degli Studi di Urbino  <giuseppe.greco@uniurb.it>

G. Greco (Urbino University/INFN Firenze), A. Grado (INAF-OAC), F. Getman
(INAF-OAC), E. Cappellaro (INAF-OAPD), M. Branchesi (GSSI), S. Covino
(INAF-OAB), P. D'Avanzo (INAF-OAB), A. Melandri (INAF-OAB), L. Amati
(INAF-IASF Bo), L. A. Antonelli, (INAF-OAR), S. Ascenzi (INAF-OAR), S.
Benetti (INAF-OAPD), M.T. Botticella (INAF-OAC),  S. Campana (INAF-OAB), V.
D'Elia (INAF-ASDC), D. Fugazza, L. Limatola (INAF-OAC), M. Lisi (INAF-OAR),
L. Nicastro (INAF-IASF Bo), E. Palazzi (INAF-IAFS Bo), E. Pian (SNS-Pisa),
S. Piranomonte (INAF-OAR), L. Pulone (INAF-OAR), A. Rossi (INAF-IASF Bo), P.
Schipani (INAF-OAC), G. Stratta (Urbino University/INFN Firenze), G.
Tagliaferri (INAF-OAB), V. Testa (INAF-OAR), L . Tomasella (INAF-OAPD), S.
Yang (INAF-OAPD), E. Brocato (INAF-OAR) on behalf of GRavitational Wave
Inaf TeAm report:



Observations of 81 square degrees of the skymap of the Advanced LIGO and
Virgo trigger G297595 (LVC GCN Circ. 21474) were performed with the VLT
Survey Telescope (VST - Proposal ID ESO 099.D-0568) at ESO-Paranal equipped
with OMEGACAM (FOV=1 square degree). The observations are divided in 9
regions, 3 x 3 square degrees each, centered on the following  coordinates
RA, Dec (ICRSd):



41.06842   -45.48795

36.78869   -45.48795

45.34815   -45.48795

42.42450   -42.48795

42.42450   -39.48795

39.71234   -48.48795

44.97423   -36.48795

46.17326   -33.80461

37.32240   -51.48795



The sequence of the VST pointings was generated using the GWsky script (
https://github.com/ggreco77/GWsky). Starting from the high probability
region of the skymap, the sequence was defined to maximize the contained
localization probability, to limit the airmass to 2, and to use the
available reference images. Fields with bright stars were excluded.



The images were taken in the r_SDSS filter with an exposure of 80s (split
in two dithered exposures of 40 s each). The observations started at
2017-08-15T 04:44:22 UTC and finished at 2017-08-15T 09:03:15 UTC.

The contained probability of the initial BAYESTAR sky map (LVC GCN Circ.
21474) covered by the VST observations is about 75%, while for the
LALinference sky map (LVC GCN Circ. 21493) it is about  25%.



Automatic data reduction with the VSTTube pipeline (Grado et al. 2012
Mem.SAIt 19, 362 ) was completed. The image analysis is ongoing. Further
observations of these fields are planned.