TITLE: GCN CIRCULAR NUMBER: 20743 SUBJECT: LIGO/Virgo G275404: AGILE-GRID preliminary analysis DATE: 17/02/26 01:06:17 GMT FROM: Francesco Verrecchia at ASDC, INAF-OAR M. Pilia (INAF/OA-Cagliari), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), P. Munar-Adrover, M. Cardillo (INAF/IAPS), F. Verrecchia (ASDC and INAF/OAR), A. Bulgarelli, V. Fioretti, A. Zoli , N. Parmiggiani (INAF/IASF-Bo), C. Pittori (ASDC and INAF/OAR), I. Donnarumma, G. Piano (INAF/IAPS), F.Lucarelli (ASDC and INAF/OAR), A. Giuliani (INAF/IASF-Mi), F. Longo (Univ. Trieste and INFN Trieste), A. Ursi (INAF/IAPS), F. Fuschino (INAF/IASF-Bo), Y. Evangelista (INAF/IAPS), M. Marisaldi (INAF/IASF-Bo and Bergen University)(INAF/IAPS), A. Argan, G. Minervini (INAF/IAPS), A. Trois (INAF/OA-Cagliari), report on behalf of the AGILE Team: In response to the LIGO/Virgo GW trigger G275404 we performed an analysis of the AGILE Gamma-Ray Imaging Detector (GRID) data on different timescales. On LIGO trigger time (T0=2017-02-25 18:30:21.374 UT) the GRID exposure covered about 30% of the LIGO localization region (in the time interval T0-100s, T0+100s) that was observed with off-axis angles between 10 and 70 deg. An analysis of the data in the energy range 50 MeV - 10 GeV was performed on timescales from 2 to 100 sec centered at T0. Preliminary values of 3-sigma upper limits obtained within the accessible G275404 localization region are reported below: 1.8e-06 erg cm^-2 s^-1 for integration time of 2s, 1.5e-07 erg cm^-2 s^-1 for integration time of 20s, 3.5e-08 erg cm^-2 s^-1 for integration time of 100s. These ULs apply to a large fraction of the GRID-exposed LIGO localization region. We are currently analyzing the significance of a gamma-ray source candidate within that region. These measurements were obtained with AGILE observing a large portion of the sky in spinning mode. Additional analysis of AGILE data is in progress.