INTEGRAL's unique payload, comprised of a set of large and heavy
detectors, allows it to detect the elusive weakly interacting low-energy
gamma-ray photons from any direction of the sky at a given
moment. Coupled with an exceptionally stable background owing to the
elongated orbit mostly far from the Earth's violent magnetosphere, this
makes it an ideal instrument to search for electromagnetic counterparts
to sources of various impulsive transients, such as gravitational
waves events (see also
Gamma-ray observatory INTEGRAL reloaded,
by E.P.J. van den Heuvel). Thanks to
the large Field of View of its sensitive X-ray and gamma-ray detectors
it may pinpoint and accurately characterize properties of any possible
counterpart, if detected.
LIGO/Virgo trigger LVT151012 was of one the three binary black-hole
merger events observed by LIGO in the first breakthrough scientific run
of 2015/2016. Unlike the other two events (GW150914 and GW151226),
LVT151012 had a slightly lower LIGO detection certainty: it had just
over 90% change of being of astrophysical origin. If astrophysical, it
corresponds to a merger of two black holes of 13 and 23
M☉, releasing gravitational wave radiation equivalent
to rest energy of 1.5 M☉ in a fraction of a second.
Gravitational wave event localizations provided by LIGO are still
quite approximate, and the location of LVT151012 could only be limited
to two very elongated arcs, spanning each over 60 degrees in the
sky. Luckily, a large fraction of the LIGO localization of LVT151012 was
in the Field of View of the most sensitive INTEGRAL instruments at the
time of occurrence of the LIGO/Virgo event. This enabled to join JEM-X,
IBIS, and SPI measurements together, in order to derive a
high-sensitivity over more than 3 decades in photon energy: from 3 keV
to 10 MeV.
Observation of the complete, extended, localization of LVT151012 could
only be achieved by combining the complementary contributions of
both the INTEGRAL high-energy detectors and their active shields, i.e.,
of SPI (including SPI-ACS), IBIS (ISGRI, PICsIT, and IBIS/Veto). This
allowed to derive the most stringent upper limit in a truly all-sky
observation, constraining the ratio of energy released in gamma-rays to
the gravitational wave energy to less than 4.4e-5.
Reference:
"INTEGRAL IBIS, SPI, and JEM-X observations of LVT151012",
Savchenko, V.; Bazzano, A.; Bozzo, E.; Brandt, S.; Chenevez, J.;
Courvoisier, T. J.-L.; Diehl, R.; Ferrigno, C.; Hanlon, L.; von Kienlin, A.;
Kuulkers, E.; Laurent, P.; Lebrun, F.; Lutovinov, A.;
Martin-Carrillo, A.; Mereghetti, S.; Natalucci, L.; Roques, J. P.;
Siegert, T.; Sunyaev, R.; Ubertini, P.,
2017, A&A, in press
http://adsabs.harvard.edu/abs/2017arXiv170401633S
