GCN Circular 25757

F. Verrecchia, F. Lucarelli (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS,
and Univ.Roma Tor Vergata), C. Casentini, M. Cardillo, G. Piano, A. Ursi
(INAF/IAPS), 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 S190915ak at T0 = 2019-09-15
23:57:02.691 UTC a preliminary analysis of the AGILE exposure at T0
shows that the Gamma-Ray Imaging Detector (GRID) exposure covered the 22%
of the 90% c.l. localization region (LR) (33% of 90% c.l. localization
region (LR) is occulted by Earth) at an off-axis angle of about 70
degrees.

We performed an analysis of the GRID data in the energy range 50 MeV -
10 GeV on T0, where good exposure of the S190915ak 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 4.0e-06 to 1.0e-05 erg cm^-2 s^-1, with exposure of about 22% of
the LR over the time interval ( T0 -2s ; T0 + 2s ) at an off-axis angle
of about 70 degrees;
from 1.6e-06 to 1.0e-05 erg cm^-2 s^-1, with exposure of about 37% of
the LR over the time interval ( T0s ; T0 + 10s ) at an off-axis angle
of about 70 degrees;
from 3.9e-08 to 4.0e-07 erg cm^-2 s^-1, with exposure of about 75% of
the LR over the time interval ( T0s+ 100s ; T0 + 200s ) at an off-axis
angle between 30 and 70 degrees;

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_LIGOS190915ak_190915011120

These measurements were obtained with AGILE observing a large portion of
the sky in spinning mode. Additional analysis of AGILE data is in progress.