TITLE: GCN CIRCULAR NUMBER: 25821 SUBJECT: LIGO/Virgo S190923y: Upper limits from AGILE-GRID observations DATE: 19/09/23 15:47:50 GMT FROM: Francesco Verrecchia at ASDC F. Verrecchia (SSDC, and INAF/OAR), C. Casentini (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ.Roma Tor Vergata), M. Cardillo, G. Piano, A. Ursi (INAF/IAPS), F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, V. Fioretti, 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 S190923y at T0 = 2019-09-23 12:55:59.646 UTC a preliminary analysis of the AGILE exposure at T0 shows that the Gamma-Ray Imaging Detector (GRID) exposure covered the 10% of the 90% c.l. localization region (LR) (40% of 90% c.l. localization region (LR) is occulted by Earth) at an off-axis angle of about 5 degrees. We performed an analysis of the GRID data in the energy range 50 MeV - 10 GeV on T0, where good exposure of the S190923y 90% c.l. LR was available. No candidate gamma-ray transient was detected. The following preliminary GRID values of 3-sigma upper limit (UL) are obtained: - from 7.0e-07 to 9.3e-07 erg cm^-2 s^-1, with exposure of about 10% of the LR over the time interval ( T0 - 2s ; T0 + 2s ); - from 2.9e-07 to 4.2e-07 erg cm^-2 s^-1, with exposure of about 10% of the LR over the time interval ( T0 ; T0 + 10s ); - from 6.5e-08 to 6.6e-06 erg cm^-2 s^-1, with exposure of about 11% of the LR over the time interval ( T0 ; T0 + 100s ) ; A map in Galactic coordinates showing the AGILE FoV at T0 is available at the site: https://tools.ssdc.asi.it/ImgView/Agile/AGILE_FOV_LIGO-VirgoS190923y_1909232521 These measurements were obtained with AGILE observing a large portion of the sky in spinning mode. Additional analysis of AGILE data is in progress. ========================================================================== Francesco Verrecchia ASDC - ASI Science Data Center - INAF/OAR - Istituto Nazionale di Astrofisica/ Osservatorio Astronomico di Roma - c/o ASI - Agenzia Spaziale Italiana - via del Politecnico snc, I-00133, Roma - Italy ========================================================================== e-mail:francesco.verrecchia@ssdc.asi.it phone:+39 068567 882 e-mail OAR:francesco.verrecchia@oa-roma.inaf.it ==========================================================================