TITLE: GCN CIRCULAR NUMBER: 24246 SUBJECT: LIGO/Virgo S190426c: AGILE-GRID Observations DATE: 19/04/26 20:04:13 GMT FROM: Giovanni Piano at INAF-IAPS G. Piano, M. Cardillo (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), F. Verrecchia (SSDC, and INAF/OAR), A. Ursi, C. Casentini (INAF/IAPS), F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, N. Parmiggiani (INAF/OAS-Bologna), M. Pilia (INAF/OA-Cagliari), F. Longo (Univ. Trieste, and INFN Trieste), report on behalf of the AGILE Team: In response to the LIGO-Virgo GW event S190426c at T0 = 2019-04-26 15:21:55.337 (UT), we performed a preliminary analysis of the AGILE Gamma-Ray Imaging Detector (GRID) at different timescales in the energy range 50 MeV - 10 GeV. At T0 the accessible LIGO/Virgo 90% c.l. localization region (LR), which includes the Celestial North Pole, was observed at off-axis angles between 10 and 70 deg. Preliminary values of 3-sigma upper limits (UL) obtained at LIGO/Virgo trigger time (T0) are: (1) from 5.5e-7 to 3.2e-6 erg cm^-2 s^-1 for an integration time of 5s starting from T0, with the GRID exposure covered nearly 75% of this part of the LR. (2) from 2.8e-7 to 1.6e-6 erg cm^-2 s^-1 for an integration time of 10s starting from T0, with the GRID exposure covered nearly 80% of this part of the LR. (3) from 3.9e-8 to 1.6e-7 erg cm^-2 s^-1 for an integration time of 100s starting from T0, with the GRID exposure covered 100% of this part of the LR. The other part of the LR (R.A. in the approximate range between 10 - 16 hr) was partly occulted by the Earth at T0, and is currently in the region not accessible by the GRID because of solar panel constraints. These measurements were obtained with AGILE observing a large portion of the sky in spinning mode. Additional analysis of AGILE data is in progress.