Agile Observations of the Gravitational-Wave Event GW150914

Journal
THE ASTROPHYSICAL JOURNAL LETTERS
Date Issued
2016
Author(s)
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Donnarumma, I.
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Monte, E. Del
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Zoli, A.
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Munar-Adrover, P.
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Barbiellini, G.
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Cattaneo, P. W.
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Ferrari, A.
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Longo, F.
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Morselli, A.
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Picozza, P.
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Rappoldi, A.
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Sabatini, S.
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Giommi, P.
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Colafrancesco, S.
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Galli, M.
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DOI
10.3847/2041-8205/825/1/L4
Abstract
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.
Volume
825
Issue
1
Start page
L4
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