GCN Circular 25821

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.



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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
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e-mail:francesco.verrecchia@ssdc.asi.it
phone:+39 068567 882
e-mail OAR:francesco.verrecchia@oa-roma.inaf.it
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