Tavani, M.M.TavaniPittori, CarlottaCarlottaPittoriVerrecchia, FrancescoFrancescoVerrecchiaLucarelli, FabrizioFabrizioLucarelliAntonelli, Lucio AngeloLucio AngeloAntonelliPicozza, P.P.PicozzaGiommi, PaoloPaoloGiommi2020-09-172020-09-172016-07-01https://hdl.handle.net/20.500.13025/4771The Astrophysical Journal Letters, Volume 825, Issue 1, (2016).We report the results of an extensive search through the AGILE data for a gamma-ray counterpart to the LIGO gravitational-wave (GW) event GW150914. Currently in spinning mode, AGILE has the potential of cover 80% of the sky with its gamma-ray instrument, more than 100 times a day. It turns out that AGILE came within a minute of the event time of observing the accessible GW150914 localization region. Interestingly, the gamma-ray detector exposed ~65% of this region during the 100 s time intervals centered at −100 and +300 s from the event time. We determine a 2σ flux upper limit in the band 50 MeV–10 GeV, UL = 1.9 × 10−8 erg cm−2 s−1, obtained ~300 s after the event. The timing of this measurement is the fastest ever obtained for GW150914, and significantly constrains the electromagnetic emission of a possible high-energy counterpart. We also carried out a search for a gamma-ray precursor and delayed emission over five timescales ranging from minutes to days: in particular, we obtained an optimal exposure during the interval −150/−30 s. In all these observations, we do not detect a significant signal associated with GW150914. We do not reveal the weak transient source reported by Fermi-GBM 0.4 s after the event time. However, even though a gamma-ray counterpart of the GW150914 event was not detected, the prospects for future AGILE observations of GW sources are decidedly promising.gamma rays generalgravitational wavesjournal article10.3847/2041-8205/825/1/L4https://iopscience.iop.org/article/10.3847/2041-8205/825/1/L4/meta2016ApJ...825L...4T