On September 14, 2015 at 09:50:45 UTC the two detectors of the Laser Interferometer Gravitational-Wave Observatory simultaneously observed a transient gravitational-wave signal. The signal sweeps upwards in frequency from 35 to 250 Hz with a peak gravitational-wave strain of 1.0×10(-21). It matches the waveform predicted by general relativity for the inspiral and merger of a pair of black holes and the ringdown of the resulting single black hole. The signal was observed with a matched-filter signal-to-noise ratio of 24 and a false alarm rate estimated to be less than 1 event per 203,000 years, equivalent to a significance greater than 5.1σ. The source lies at a luminosity distance of 410(-180)(+160)  Mpc corresponding to a redshift z=0.09(-0.04)(+0.03). In the source frame, the initial black hole masses are 36(-4)(+5)M⊙ and 29(-4)(+4)M⊙, and the final black hole mass is 62(-4)(+4)M⊙, with 3.0(-0.5)(+0.5)M⊙c(2) radiated in gravitational waves. All uncertainties define 90% credible intervals. These observations demonstrate the existence of binary stellar-mass black hole systems. This is the first direct detection of gravitational waves and the first observation of a binary black hole merger.

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The Observation of Gravitational Waves from a Binary Black Hole Merger

The North American Nanohertz Observatory for Gravitational Waves is a collaboration of researchers who are actively engaged in using North American radio telescopes to detect and study gravitational waves (GWs) via pulsar timing. To achieve this goal, we regularly observe millisecond pulsars with the Arecibo and Green Bank telescopes and develop and implement new instrumentation and algorithms for searching for and observing pulsars, calculating arrival times, understanding and correcting for propagation delays and sources of noise in our data and detecting and characterizing a variety of GW sources. We collaborate on these activities with colleagues in the International Pulsar Timing Array. We also educate students of all levels and the public about the detection and study of GWs via pulsar timing.

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Bow-Shock Pulsar Wind Nebulae Searches Aided by the North American Nanohertz Observatory for Gravitational Waves

Oscillons are massive, long-lived, localized excitations of a scalar field. We show that in a class of well-motivated single-field models, inflation is followed by self resonance, leading to copious oscillon generation and a lengthy period of oscillon domination. These models are characterized by an inflaton potential which has a quadratic minimum and is shallower than quadratic away from the minimum. This set includes both string monodromy models and a class of supergravity inspired scenarios and is in good agreement with the current central values of the concordance cosmology parameters. We assume that the inflaton is weakly coupled to other fields so as not to quickly drain energy from the oscillons or prevent them from forming. An oscillon-dominated universe has a greatly enhanced primordial power spectrum on very small scales relative to that seen with a quadratic potential, possibly leading to novel gravitational effects in the early Universe.

Oscillons after Inflation

We present extensive radio and millimeter observations of the unusually bright GRB 130427A at z = 0.340, spanning 0.67-12 days after the burst. We combine these data with detailed multi-band UV, optical, NIR, and Swift X-ray observations and find that the broadband afterglow emission is composed of distinct reverse shock and forward shock contributions. The reverse shock emission dominates in the radio/millimeter and at 0.1 days in the UV/optical/NIR, while the forward shock emission dominates in the X-rays and at 0.1 days in the UV/optical/NIR. We further find that the optical and X-ray data require a wind circumburst environment, pointing to a massive star progenitor. Using the combined forward and reverse shock emission, we find that the parameters of the burst include an isotropic kinetic energy of E K, iso 2 × 1053 erg, a mass loss rate of M ☉ yr–1 (for a wind velocity of 1000 km s–1), and a Lorentz factor at the deceleration time of Γ(200 s) 130. Due to the low density and large isotropic energy, the absence of a jet break to 15 days places only a weak constraint on the opening angle, θj 2.°5, and therefore a total energy of E γ + EK 1.2 × 1051 erg, similar to other gamma-ray bursts (GRBs). The reverse shock emission is detectable in this burst due to the low circumburst density, which leads to a slow cooling shock. We speculate that this property is required for the detectability of reverse shocks in radio and millimeter bands. Following on GRB 130427A as a benchmark event, observations of future GRBs with the exquisite sensitivity of the Very Large Array and ALMA, coupled with detailed modeling of the reverse and forward shock contributions, will test this hypothesis.

A Reverse Shock in GRB 130427A

The main criticism of my piece in ref (2) seems to be that my calculations rely on testing a point null hypothesis, i.e. the hypothesis that the true effect size is zero. He objects to my contention that the true effect size can be zero, "just give the same pill to both groups", on the grounds that two pills can't be exactly identical. He then says "I understand that this criticism may come across as frivolous semantic pedantry of no practical consequence: of course that the author meant to say 'pills with the same contents' as everybody would have understood". Yes, that is precisely how it comes across to me. I shall try to explain in more detail why I think that this criticism has little substance.

A response to O. Arandjelovic's critique of "The reproducibility of research and the misinterpretation of p-values"

Astroparticle physics is undergoing a profound transformation, due to a series of extraordinary new results, such as the discovery of high-energy cosmic neutrinos with IceCube, the direct detection of gravitational waves with LIGO and Virgo, and many others. This white paper is the result of a collaborative effort that involved hundreds of theoretical astroparticle physicists and cosmologists, under the coordination of the European Consortium for Astroparticle Theory (EuCAPT). Addressed to the whole astroparticle physics community, it explores upcoming theoretical opportunities and challenges for our field of research, with particular emphasis on the possible synergies among different subfields, and the prospects for solving the most fundamental open questions with multi-messenger observations.

C.G. Böhmer

Papers

EuCAPT White Paper: Opportunities and Challenges for Theoretical Astroparticle Physics in the Next Decade