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GCN Circular 33826

LIGO/Virgo S230518h: AGILE/MCAL observations
2023-05-19T11:54:04Z (20 days ago)
Francesco Verrecchia at SSDC,INAF-OAR <>
F. Verrecchia (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS, and Univ. Roma Tor Vergata), A. Ursi (ASI), C. Pittori (SSDC, and INAF/OAR), M. Cardillo, C. Casentini, L. Foffano, G. Piano (INAF/IAPS), F. Lucarelli (SSDC, and INAF/OAR), L. Baroncelli, A. Bulgarelli, A. Ciabattoni, A. Di Piano, V. Fioretti, G. Panebianco, 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 S230518h at T0 = 2023-05-18 12:59:08.167 (UT), a preliminary analysis of the AGILE minicalorimeter (MCAL) triggered data found no significant event candidates within a time interval covering -/+ 2 sec from the LIGO/Virgo T0. At the T0, about 25% of the S230518h 90% c.l. localization region (LR) was accessible to the AGILE/MCAL. Three-sigma upper limits (ULs) are obtained in the 0.4-1 MeV energy range, for a 1 s integration time at different celestial positions within the accessible S230518h LR, from a minimum of 1.4E-06 erg cm^-2 to a maximum of 6.6E-06 erg cm^-2 (assuming as spectral model a single power-law with photon index 1.5). An independent procedure based on photon counting statistics provides UL fluences in the range 0.4-1 MeV, for a 300 microseconds integration time, from a minimum of 1.1E-08 erg cm^-2 to a maximum of 4.4E-08 erg cm^-2. We notice the detection of a short pulse in the energy range 0.4-1.4 MeV with S/N 5.7 at time T0+10.77 s. The AGILE/MCAL detector is a CsI detector with a 4 pi FoV, sensitive in the energy range 0.4-100 MeV. Additional analysis of AGILE data is in progress.
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