National Aeronautics and Space Administration

The Amazing Year 2017 in High-Energy Astrophysics

Note: These items are extracted from the HEASARC's Brief History of High-Energy (X-ray & Gamma-Ray) Astronomy website.

2017 Jun 1	At a press conference, it is announced that the Laser Interferometer Gravitational-wave Observatory (LIGO) has detected a third transient gravitational wave source, GW 170104. The waveform of this event detected on January 4th, 2017 was (like the previous two gravitational wave sources GW 151226 and GW 150914) consistent with that predicted to be produced by the merger of two black holes into a single, more massive, spinning black hole. The masses of the merging black holes in this third confirmed event were 32 and 19 solar masses, and the mass of the final black hole is 49 solar masses, with the "missing" 2 solar masses having been converted into gravitational waves. This most recent detection appears to be the farthest yet, with the black holes located about 3 billion light-years away. See Abbott et al. (2017, PRL, 118, 21101) for more details on this tremendously energetic merger event.
2017 Jun 15, 03:00 UTC	Launch of the Chinese Hard X-ray Modulation Telescope (HXMT, now renamed to Huiyan or "Insight") mission on a Long March 4B rocket from the Jiuquan Satellite Launch Center. This observatory will perform the most sensitive all-sky survey to date in the hard X-ray (20 - 250 keV) energy band. It will also have soft and medium X-ray (1 - 30 keV) detectors for pointed observations of such objects as X-ray binary systems containing black holes or neutron stars, active galactic nuclei (AGN), supernova remnants, soft gamma repeaters (SGRs), and clusters of galaxies.
2017 Jun 30	Mission completion for the ESA (with NASA participation) LISA Pathfinder (LPF) mission. After sixteen months of science operations, LISA Pathfinder successfully demonstrated the technology that will be required for ESA's future space observatory of gravitational waves, the Laser Interferometer Space Antenna (LISA). This latter mission will consist of a "constellation" of 3 spacecraft that are currently planned to be launched in 2034. LISA will study the low-frequency (0.1 mHz to 1 Hz) gravitational waves produced by the mergers of supermassive black holes sitting at the centers of galaxies. LPF demonstrated a precision in the 60 mHz to 1 Hz range that surpasses the level required by LISA by a factor of more than 100 (!), and a precision in the 0.1 mHz to 60 mHz range that is within a factor of several of meeting LISA's requirements. See Armano et al. 2016, PRL, 116, 231101 for the initial results from LPF.
2017 Aug 14, 12:31 pm EDT	Launch on a SpaceX Dragon spacecraft of the ISS-CREAM (International Space Station Cosmic Ray Energetics And Mass) payload that will be subsequently attached robotically to the International Space Station and, starting in Fall 2017, will be used to to extend the energy reach of direct measurements of cosmic rays to the highest energy possible to probe their origin, acceleration and propagation. ISS-CREAM, a collaboration of US, Korean, French and Mexican institutions, will (1) determine how the observed spectral differences of protons and heavier nuclei evolve at higher energies approaching the knee; (2) be capable of measuring potential changes in the spectra of secondary nuclei resulting from interactions of primary cosmic rays with the interstellar medium; (3) conduct a sensitive search for spectral features, such as a bend in proton and helium spectra; and (4) measure electrons with sufficient accuracy and statistics to determine whether or not a nearby cosmic-ray source exists. It will also contribute indirectly to the dark matter search by measuring electrons in addition to nuclei at energies beyond where current direct measurements exist.
2017 Sep 27	The fourth transient gravitational wave detection, GW 170814 is announced by the LIGO Scientific Collaboration and the Virgo collaboration. This is the first joint detection of gravitational waves by both LIGO and Virgo detectors, and as a result has by far the best localization (60 square degrees) on the sky of the 4 GW detections. The waveform of the event detected on August 14th, 2017 was (like the previous three gravitational wave source detections, GW 151226, GW 150914 and GW170104) consistent with that predicted from the merger of two black holes into a single, more massive, spinning black hole. The masses of the merging black holes in this third confirmed event were 31 and 25 solar masses, and the mass of the final black hole is 53 solar masses, with the "missing" 3 solar masses having been converted into gravitational waves. See Abbott et al. (2017, PRL, in press) for more details on this merger event.
2017 Oct 3	Rainer Weiss, Barry C. Barish and Kip S. Thorne are awarded the 2017 Nobel Prize in physics for their major contributions to the LIGO detector and the observations of black hole merger events that create enormous "chirps" of gravitational waves. Just 6 days previous to this announcement, the LIGO Scientific and Virgo collaborations reported the fourth such gravitational wave detection.
2017 Oct 16	The fifth transient gravitational wave detection, GW 170817 is announced by the LIGO Scientific Collaboration and the Virgo collaboration. This is the first detection of gravitational waves from the merger of neutron stars, as opposed to black holes. The waveform of the event detected on August 17th, 2017 at 08:41 EDT was consistent with that predicted from the merger of two neutron stars of roughly 1.6 and 1.1 solar masses into a single object, either a massive neutron star or (more likely) a "low-mass" black hole. Just 1.7 seconds after the GW detection, the Fermi GBM and INTEGRAL gamma-ray observatories detected a short gamma-ray burst (GRB 170817A), and follow-up multi-wavelength electro-magnetic (gamma-ray, X-ray, UV, optical, IR and radio) observations by 70 space- and ground-based telescopes over the next days and weeks pinpointed the counterpart object to be a so-called kilonova or r-process supernova in the elliptical galaxy NGC 4993. Among other ramifications, (1) the near-simultaneity of the GW and em signals confirmed that they both travel at the speed of light as predicted by Genefral Relativity, (2) the association with NGC 4993 and the properties of the GW signal provide a direct measurement of the Hubble Constant of 70 (+12, -8) km/s/Mpc that is completely consistent with that measured by the Planck mission (67.90 +/- 0.55 km/s/Mpc), and (3) the evolution of the optical and infared emission of the source over the first week or so is "dominated by the radioactive glow (known as a "kilonova") from freshly synthesized rapid neutron capture (r-process) material in the merger ejecta" (Troja et al. 2017, Nature, in press), consistent with the theoretical predictions that such events have produced most of the heavy elements (such as gold, platinum and uranium) in the Universe. See the LIGO press release, the GW discovery paper by Abbott et al. (2017, PRL, 119, 161101) and this issue of Astrophysical Journal Letters containing more than 20 papers about the multi-wavelength follow-up observations for more details on this merger event.
2017 Nov 15	The sixth transient gravitational wave detection, GW 170608 is announced by the LIGO Scientific and Virgo Collaborations. The waveform of the event detected on June 8th, 2017 at 02:01:16.5 UT was consistent with that predicted from the merger of two black holes of roughly 7 and 12 solar masses into a single black hole of 18 solar masses, meaning that energy equivalent to about 1 solar mass was emitted as gravitational waves during the collision. GW170608 is the lightest black hole binary merger that LIGO and Virgo have yet observed and so "is one of the first cases where black holes detected through gravitational waves have masses similar to black holes detected indirectly via electromagnetic radiation, such as X-rays". See Abbott et al. (2017, ApJL, submitted) for more details on this merger event.
2017 Dec 06	A new contender for the most distant quasar ever seen in the Universe, ULAS J134208.10+092838.61, is announced by Bañados et al. (2017, Nature, in press), with a measured redshift of 7.54, significantly more than the previous record-holder (ULAS J1120+0641, with a redshift of a mere 7.09). According to the authors, "the existence of this supermassive black hole when the Universe was only 690 million years old, just five per cent of its current age, reinforces early models of black hole growth that allow black holes with initial masses of more than about 104 solar masses or episodic hyper-Eddington accretion".

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