LIGO/Virgo S190915ak: Upper Limits from AGILE-GRID observations

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.