A Tour of GW170817

Narrator (April Hobart, CXC): Astronomers have used NASA's Chandra X-ray Observatory to make the first X-ray detection of a gravitational wave source. Chandra was one of multiple observatories to detect the aftermath of this gravitational wave event, the first to produce an electromagnetic signal of any type. This discovery represents the beginning of a new era in astrophysics.

The gravitational wave source, GW170817, was detected with the advanced Laser Interferometer Gravitational-Wave Observatory, or LIGO, at 8:41am EDT on Thursday August 17, 2017. Two seconds later NASA’s Fermi Gamma-ray Burst Monitor detected a weak pulse of gamma rays. Later that morning, LIGO scientists announced that GW170817 had the characteristics of a merger of two neutron stars.

During the evening of August 17, multiple teams of astronomers using ground-based telescopes reported a detection of a new source of optical and infrared light in the galaxy NGC 4993, a galaxy located about 130 million light years from Earth.

Over the following two weeks, Chandra observed NGC 4993 and the source GW170817 four separate times. In the first observation on August 19th, no X-rays were detected at the location of GW170817. This observation was obtained remarkably quickly, only 2.3 days after the gravitational source was detected.

On August 26, Chandra observed GW170817 again and this time, X-rays were seen for the first time. This new X-ray source was located at the exact position of the optical and infrared source.

All of these pieces of information indicate that this event was produced by the merger of two neutron stars, which, in turn, set off a gamma-ray burst that produced a jet pointing away from Earth. The combination of gravitational wave signals with light detected by various telescopes including Chandra represents a new era in astrophysics.