[vsnet-grb-info 22527] LIGO-Virgo S190521g: Upper Limits from AGILE-GRID observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24626
SUBJECT: LIGO-Virgo S190521g: Upper Limits from AGILE-GRID observations
DATE:    19/05/21 06:34:26 GMT
FROM:    Francesco Verrecchia at ASDC  <francesco.verrecchia at ssdc.asi.it>

F. Verrecchia (SSDC, and INAF-OAR), C. Casentini (INAF/IAPS), M. Tavani (INAF/IAPS,
and Univ. Roma Tor Vergata),  F. Lucarelli, C. Pittori (SSDC, and INAF-OAR),
M. Cardillo (INAF/IAPS), G. Piano A. Ursi (INAF/IAPS), 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 S190521g at T0 = 2019-05-21 03:02:29.47
UTC (GCN #24621) a preliminary analysis of the AGILE exposure at T0 showed
the S190521g 90% c.l. localization region (LR) was not exposed
by the Gamma-Ray Imaging Detector (GRID), the nearest exposure in time occurred
at T0-15s covering about 60% of the LR near the Galactic north pole at off-axis
angles between 15 and 60 deg.

We performed an analysis of the GRID data in the energy range 50 MeV - 10 GeV
over three time intervals before and after T0, when good exposure of
the S190521g 90% c.l. LR was available.

The following preliminary GRID 3-sigma upper limit (UL) values are obtained
over a large area of the exposed LR:

(T0-15s; T0-5s ): from 2.7e-07 to 1.4e-06 erg cm^-2 s^-1;

(T0-100s; T0 ): from 4.5e-08 to 5.4e-07 erg cm^-2 s^-1;

(T0+900s; T0+1000s): from 3.0e-08 to 5.0e-07 erg cm^-2 s^-1.

An image of the AGILE-GRID 10s exposure near T0 is available at the site
https://tools.ssdc.asi.it/ImgView/Agile/S190521g_T0-15s_d10s_bayest_fv70a75off13

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