From first speculations to first multimessenger spectra

Waiting for the impending one shot Large Hadron Merger (and its neutron star-killing black-hole? ;-)

30 years ago a polish astronomer would carefully speculate about the astrophysical origin of gamma ray bursts:

Gamma-ray bursters are known to have a duration of about a second, their distribution on the sky is isotropic, their number density increases slowly with the decreasing burst intensity ..., their spectra peak at the energy above mec² , and they have no convincing spectral lines... A strong gamma-ray burst reaches an observed flux of 10^-4ergs s^-1cm-² for a duration of about 1 s. The detection limit is 10“7 ergs s -1 cm-2 . The burst spectra have broad maxima between 0.5 MeV (e.g., 1972 May 14 event) and 5 MeV (e.g., 1982 January 25 event)...  

Let us use strictly astronomical criteria to estimate typical distances of the unknown objects. If their distribution is isotropic then characteristic distances in the range between 1 kpc and 30 Mpc seem to be excluded. The unusual slope of the log V-log S relation implies that they are not uniformly distributed in Euclidean space. This leaves us with two possibilities: either the objects are very local indeed, associated with our solar system (e.g., with the Oort cloud of comets; Milgrom 1986), or they are at cosmological distances like quasars. No specific phenomenon was ever proposed for either of these distances. Here we shall look into the second possibility...  

There are two coincidences that make the cosmological hypothesis not unreasonable: the observed energies and the observed spectra. A gamma-ray burst that brings about 10“6 ergs cm-2 at Earth, requires a total energy release of 10⁵¹ ergs if the source is at a Hubble distance of c/H0≈ 10²⁸ cm. This is like a supernova energy, and this is the first coincidence. It suggests that gamma-ray bursts may be related to some violent events on neutron stars which are far away. If all this energy is to be radiated away in 1 s from a surface with a radius of 10 km then the required effective temperature is about 3.10¹⁰K, and it peaks around 8 MeV. With a modest cosmological redshift this falls into the range of observed peak energies, and this is the second coincidence. These two very rough coincidences encourage a more detailed analysis of the following proposition: suppose that some unknown process releases 10⁵¹ ergs, or even more, in a small volume of space within 1s or so. What would be the consequences? 

As an example we may take an object as big as a neutron star, just to be specific. However, our considerations do not assume or require the presence of a neutron star. A hypothesis that gamma-ray bursters are at cosmological distances was initiated because of two rather loose coincidences, which indicated that the bursts may be related to neutron stars which are far away. However, there is no direct evidence that there is such a relation, and it may well be that the origin of gamma-ray bursts is not related to neutron stars at all... 

Are there any phenomena on a supernova energy scale that are expected to involve bare neutron stars, so that the apparent temperatures could be in the gamma-ray region? Is there any possibility of finding convincing observational evidence that at least some gamma-ray bursters are at cosmological distances? 

On various occasions very energetic phenomena that involved bare neutron stars were suggested for a variety of reasons. Haensel and Schaeffer (1982) calculated models of neutron stars with a phase transition in their structure leading to a release of 10⁴⁸ ergs in a small fraction of a second and noticed a possibility of even more powerful events. Ostriker (1979) considered the fate of the inner cores of globular clusters where the dominant constituents may be neutron stars. From time to time neutron stars will collide, releasing up to 10⁵³ ergs per event. The binary radio pulsar PSR 1913+16 will coalesce with its neutron star companion within about 10⁸ yr as a result of gravitational radiation losses (Taylor and Weisberg 1982). The final stage is likely to be very violent, and again of the order of 10⁵²or 10⁵³ergs will be released. In all of these cases the details of a violent energy release are not known, and it is not clear at all that a significant fraction of energy will be radiated in the gamma-ray region. But it is not unreasonable to expect that some of these, or perhaps some other rare phenomena may generate enough gamma-ray energy. The frequency of events required by the available observations is very low: perhaps 1000 bursts per year per 10¹¹ galaxies.

GAMMA-RAY BURSTERS AT COSMOLOGICAL DISTANCES Bohdan Paczyñski Princeton University Observatory, Received 1986 May 12; accepted 1986 June 23

 130 million light-years back in far spacetime (to be continued... in a few hours now)

On August 17, 2017 at 12∶41:04 UTC the Advanced LIGO and Advanced Virgo gravitational-wave detectors made their first observation of a binary neutron star inspiral. The signal, GW170817, was detected with a combined signal-to-noise ratio of 32.4 and a false-alarm-rate estimate of less than one per 8.0 × 10^4 years. We infer the component masses of the binary to be between 0.86 and 2.26 M⊙, in agreement with masses of known neutron stars. Restricting the component spins to the range inferred in binary neutron stars, we find the component masses to be in the range 1.17–1.60 M⊙, with the total mass of the system 2.74+0.04 −0.01M⊙. The source was localized within a sky region of 28 deg^2 (90% probability) and had a luminosity distance of 40+8 −14 Mpc, the closest and most precisely localized gravitational-wave signal yet. The association with the γ-ray burst GRB 170817A, detected by Fermi-GBM 1.7 s after the coalescence, corroborates the hypothesis of a neutron star merger and provides the first direct evidence of a link between these mergers and short γ-ray bursts. Subsequent identification of transient counterparts across the electromagnetic spectrum in the same location further supports the interpretation of this event as a neutron star merger. This unprecedented joint gravitational and electromagnetic observation provides insight into astrophysics, dense matter, gravitation, and cosmology.

GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral

LIGO Scientific Collaboration and Virgo Collaboration

(Received 26 September 2017; revised manuscript received 2 October 2017; published 16 October 2017)

The first X ray signal from a gravitational wave source by Chandra Observatory! (live)

The first radio signal from a gravitational wave source by Karl G. Jansky Very Large Array! (live)

On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of - + 40 8 8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M⊙. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the OneMeter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ∼10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

Multi-messenger Observations of a Binary Neutron Star Merger 

LIGO Scientific Collaboration and Virgo Collaboration, Fermi GBM, INTEGRAL, IceCube Collaboration, AstroSat Cadmium Zinc Telluride Imager Team, IPN Collaboration, The Insight-Hxmt Collaboration, ANTARES Collaboration, The Swift Collaboration, AGILE Team, The 1M2H Team, The Dark Energy Camera GW-EM Collaboration and the DES Collaboration, The DLT40 Collaboration, GRAWITA: GRAvitational Wave Inaf TeAm, The Fermi Large Area Telescope Collaboration, ATCA: Australia Telescope Compact Array, ASKAP: Australian SKA Pathfinder, Las Cumbres Observatory Group, OzGrav, DWF (Deeper, Wider, Faster Program), AST3, and CAASTRO Collaborations, The VINROUGE Collaboration, MASTER Collaboration, J-GEM, GROWTH, JAGWAR, CaltechNRAO, TTU-NRAO, and NuSTAR Collaborations, Pan-STARRS, The MAXI Team, TZAC Consortium, KU Collaboration, Nordic Optical Telescope, ePESSTO, GROND, Texas Tech University, SALT Group, TOROS: Transient Robotic Observatory of the South Collaboration, The BOOTES Collaboration, MWA: Murchison Widefield Array, The CALET Collaboration, IKI-GW Follow-up Collaboration, H.E.S.S. Collaboration, LOFAR Collaboration, LWA: Long Wavelength Array, HAWC Collaboration, The Pierre Auger Collaboration, ALMA Collaboration, Euro VLBI Team, Pi of the Sky Collaboration, The Chandra Team at McGill University, DFN: Desert Fireball Network, ATLAS, High Time Resolution Universe Survey, RIMAS and RATIR, and SKA South Africa/MeerKAT

Timeline of the discovery of GW170817, GRB 170817A, SSS17a/AT 2017gfo, and the follow-up observations are shown by messenger and wavelength relative to the time tc of the gravitational-wave event. Two types of information are shown for each band/messenger. First, the shaded dashes represent the times when information was reported in a Gamma Ray Coordinate Network Circular. The names of the relevant instruments, facilities, or observing teams are collected at the beginning of the row. Second, representative observations (see Table 1) in each band are shown as solid circles with their areas approximately scaled by brightness; the solid lines indicate when the source was detectable by at least one telescope. Magnification insets give a picture of the first detections in the gravitational-wave, gamma-ray, optical, X-ray, and radio bands. They are respectively illustrated by the combined spectrogram of the signals received by LIGO-Hanford and LIGO-Livingston (see Section 2.1), the Fermi-GBM and INTEGRAL/SPI-ACS lightcurves matched in time resolution and phase (see Section 2.2), 1 5 × 1 5 postage stamps extracted from the initial six observations of SSS17a/AT 2017gfo and four early spectra taken with the SALT (at tc + 1.2 days; Buckley et al. 2017; McCully et al. 2017b), ESO-NTT (at tc + 1.4 days; Smartt et al. 2017), the SOAR 4 m telescope (at tc + 1.4 days; Nicholl et al. 2017d), and ESO-VLT-XShooter (at tc + 2.4 days; Smartt et al. 2017) as described in Section 2.3, and the first X-ray and radio detections of the same source by Chandra (see Section 3.3) and JVLA (see Section 3.4). In order to show representative spectral energy distributions, each spectrum is normalized to its maximum and shifted arbitrarily along the linear y-axis (no absolute scale). The high background in the SALT spectrum below 4500 Å prevents the identification of spectral features in this band (for details McCully et al. 2017b). (Source)

Detection Papers

GW170817

Discovery paper
GW170817: Observation of Gravitational Waves from a Binary Neutron Star Inspiral (open access)
Published in Phys. Rev. Lett. 119, 161101 (2017)
GW170817 Data Release

Related papers
Multi-Messenger Observations of a Binary Neutron Star Merger (open access)
Published in Astrophys. J. Lett.
Gravitational Waves and Gamma-Rays from a Binary Neutron Star Merger: GW170817 and GRB170817A(open access)
Published in Astrophys. J. Lett.
A Gravitational-Wave Standard Siren Measurement of the Hubble Constant (currently free to read)
Published in Nature
Estimating the Contribution of Dynamical Ejecta in the Kilonova Associated with GW170817
Accepted by Astrophys. J. Lett.
GW170817: Implications for the Stochastic Gravitational-Wave Background from Compact Binary Coalescences
Submitted to Phys. Rev. Lett.
On the Progenitor of Binary Neutron Star Merger GW170817
Accepted by Astrophys. J. Lett.
Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory (authored by the ANTARES, IceCube, Pierre Auger, LIGO Scientific, and Virgo Collaborations) Submitted to Astrophys. J. Lett.