First detection of Gravitational Waves and Gamma-rays from a Binary Neutron Star Merger: GW170817 and GRB170817A
On 17 August, a burst of gamma rays lit up in space for almost two seconds. It was
promptly recorded by INTEGRAL and NASA's Fermi satellite. Such short gamma-ray
bursts are not uncommon: INTEGRAL catches about 20 every year.
But this one was special: just seconds before the two satellites saw the blast, an
entirely different instrument was triggered on Earth: the detectors of the Laser
Interferometer Gravitational-wave Observatory (LIGO) experiment, in the USA, recorded
the passage of gravitational waves – fluctuations in the fabric of spacetime caused
by powerful cosmic events.
This is a ground-breaking discovery, revealing for the first time gravitational waves
and highly energetic light released by the same cosmic source.
The Figure shows the joint, multimessenger detection of GW170817 and GRB170817A. Top:
The summed Fermi/GBM lightcurve for sodium iodide (NaI) detectors 1, 2, and 5 for
GRB170817A between 50 and 300 keV, matching the 100 ms time bins of SPI-ACS data shown at
the bottom. Middle: The time-frequency map of GW170817 was obtained by coherently combining
LIGO-Hanford and LIGO-Livingston data. Bottom: The SPI-ACS lightcurve with the energy
range starting approximately at 100 keV and with a high energy limit of least 80 MeV.
All times here are referred to the GW170817 trigger time, T0GW.
This is the closest (i.e., about 40 Mpc) short gamma-ray burst detected among the ones for
which we've measured the distance, and by far the dimmest one - nearly a million times less
bright than average. The unusual properties of this source suggest that the powerful jets
that arise in the cosmic clash of the neutron stars are not pointing straight towards us,
as happens in the majority of gamma-ray bursts detected.
When the LIGO/Virgo experiments start their observations again, with improved sensitivity,
in late 2018, it is crucial that as many gamma-ray satellites as possible are active
to check on the electro-magnetic gamma-ray radiation coincident with the gravitational wave
detections. With the high sensitivity to gamma-rays and almost full-sky coverage for brief
events, INTEGRAL is among the best astronomical facilities for keeping an eye on these
gamma-ray bursts.
"Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB 170817A",
LIGO/Virgo collaboration, Fermi collaboration, INTEGRAL collaboration
The Astrophysical Journal Letters, Volume 848, Number 2
http://iopscience.iop.org/article/10.3847/2041-8213/aa920c/meta
"INTEGRAL Detection of the First Prompt Gamma-Ray Signal Coincident with the Gravitational-wave Event GW170817",
The INTEGRAL collaboration
The Astrophysical Journal Letters, Volume 848, Number 2
http://iopscience.iop.org/article/10.3847/2041-8213/aa8f94/meta