TITLE:   GCN CIRCULAR
NUMBER:  26486
SUBJECT: LIGO/Virgo S191216ap and IceCube neutrino: no counterpart candidates from AGILE-GRID observations
DATE:    19/12/18 16:56:01 GMT
FROM:    Francesco Verrecchia at SSDC,INAF-OAR  <francesco.verrecchia@ssdc.asi.it>

F. Verrecchia (SSDC, and INAF/OAR), M. Tavani (INAF/IAPS, and Univ. Roma
Tor Vergata), M. Cardillo, A. Ursi, C. Casentini, G. Piano (INAF/IAPS),
F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), M. Pilia
(INAF/OA-Cagliari), A. Bulgarelli, V. Fioretti, N. Parmiggiani
(INAF/OAS-Bologna), F. Longo (Univ. Trieste, and INFN Trieste), report on
behalf of the AGILE Team:

In response to the LIGO-Virgo GW event S191216ap at T0 = 2019-12-16
21:33:38.473 UTC and the candidate IceCube neutrino (GCN Circ. 26463),
an analysis of the AGILE exposure at T0 shows that both the GW
localization region (LR) and neutrino error circle (EC) were occulted by
the Earth.

We performed an analysis of the GRID data over time intervals before and
after T0, when good exposures of the S191216ap LR and neutrino EC were
available.

No candidate gamma-ray transient was detected.

The following preliminary GRID values of 3-sigma upper limits (ULs) in
the 100 MeV - 10 GeV energy band are obtained over the neutrino position:

- 6.9e-11 erg cm^-2 s^-1, with exposure over the time interval
(T0 - 3 days; T0);
- 4.6e-11 erg cm^-2 s^-1, with exposure over the time interval
(T0 - 7 days; T0).

As the S191216ap LR became visible, we obtained the following preliminary
GRID values of 3-sigma ULs:

from 7.7e-08 to 3.9e-07 erg cm^-2 s^-1, with exposure of about 80% of the
LR over the time interval (T0 + 1.6ks ; T0 + 1.8ks);

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