[vsnet-grb-info 22087] LIGO/Virgo S190425z: AGILE-GRID Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  24186
SUBJECT: LIGO/Virgo S190425z: AGILE-GRID Observations
DATE:    19/04/25 15:41:12 GMT
FROM:    Giovanni Piano at INAF-IAPS  <giovanni.piano at inaf.it>

G. Piano, C. Casentini (INAF/IAPS), F. Verrecchia (SSDC, and INAF/OAR), A.
Ursi, M.Cardillo (INAF/IAPS), M. Tavani (INAF/IAPS, and Univ. Roma Tor
Vergata), F. Lucarelli, C. Pittori (SSDC, and INAF/OAR), A. Bulgarelli, 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 S190425z at T0 = 2019-04-25 08:18:05
(UT), we performed a preliminary analysis of the AGILE Gamma-Ray Imaging
Detector (GRID). We divided the LIGO/Virgo localization region (LR) 90%
c.l. into two parts:
the first with R.A. in the approximate range between 1 - 8 hr, the second
with R.A. in the approximate range between 12 - 20 hr.

For the first part of the LR, we analyzed the first interval available with
a good coverage, between T0+100s and T0+200s. In this time interval, the
GRID exposure covered nearly 60% of the first part of the LR, observed at
off-axis angles between 25 deg and 70 deg. An analysis of the data in the
energy range 50 MeV - 10 GeV in this integration time was performed and
preliminary 3-sigma upper limits (ULs) values within the accessible
LIGO/Virgo LR are: from 4.1e-8 erg cm^-2 s^-1 to 4.5e-7 erg cm^-2 s^-1 for an
integration time of 100s.
In the time interval between T0-200 and T0+300, the GRID exposure covered
nearly 100% of the first part of the LR, observed at off-axis angles between
0 deg and 70 deg. An analysis of the data in the energy range 50 MeV - 10
GeV in this integration time was performed and preliminary 3-sigma ULs are:
from 1.4e-8 erg cm^-2 s^-1 to 3.2e-8 erg cm^-2 s^-1 for an integration time
of 500s.

Between T0+700s and T0+800s the GRID exposure covered nearly 15% of the
second part of the LR, observed at off-axis angles between 40 deg and 70
deg. An analysis of the data in the energy range 50 MeV - 10 GeV in this
integration time was performed and preliminary 3-sigma ULs are: from 4.2e-8
erg cm^-2 s^-1 to 2.3e-7 erg cm^-2 s^-1 for an integration time of 100s.
In the time interval between T0+700 and T0+2000, the GRID exposure covered
nearly 95% of the second part of the LR, observed at off-axis angles
between 40 deg and 70 deg. An analysis of the data in the energy range 50
MeV - 10 GeV in this integration time was performed and preliminary 3-sigma
ULs are: from 7.8e-9 erg cm^-2 s^-1 to 4.3e-8 erg cm^-2 s^-1 for an
integration time of 1300s.

These measurements were obtained with AGILE observing a large portion of
the sky in spinning mode.