scholarly journals Binary Neutron Star (BNS) Merger: What We Learned from Relativistic Ejecta of GW/GRB 170817A

Physics ◽  
2019 ◽  
Vol 1 (2) ◽  
pp. 194-228 ◽  
Author(s):  
Houri Ziaeepour
Keyword(s):  
Neutron Star ◽  
Gravitational Waves ◽  
Gamma Ray ◽  
Lorentz Factor ◽  
Prompt Gamma ◽  
External Shocks ◽  
Binary Neutron Star ◽  
Tidal Forces ◽  
Relativistic Jet ◽  
Short Grbs

Gravitational Waves (GW) from coalescence of a Binary Neutron Star (BNS) and its accompanying short Gamma-Ray Burst (GRB) GW/GRB 170817A confirmed the presumed origin of these puzzling transients and opened up the way for relating properties of short GRBs to those of their progenitor stars and their surroundings. Here we review an extensive analysis of the prompt gamma-ray and late afterglows of this event. We show that a fraction of polar ejecta from the merger had been accelerated to ultra-relativistic speeds. This structured jet had an initial Lorentz factor of about 260 in our direction, which was O ( 10 ∘ ) from the jet’s axis, and was a few orders of magnitude less dense than in typical short GRBs. At the time of arrival to circum-burst material the ultra-relativistic jet had a close to Gaussian profile and a Lorentz factor ≳ 130 in its core. It had retained in some extent its internal collimation and coherence, but had extended laterally to create mildly relativistic lobes—a cocoon. Its external shocks on the far from center inhomogeneous circum-burst material and low density of colliding shells generated slowly rising afterglows, which peaked more than 100 days after the prompt gamma-ray. The circum-burst material was somehow correlated with the merger. As non-relativistic outflows or tidally ejected material during BNS merger could not have been arrived to the location of the external shocks before the relativistic jet, circum-burst material might have contained recently ejected materials from resumption of internal activities, faulting and mass loss due to deformation and breaking of stars crusts by tidal forces during latest stages of their inspiral but well before their merger. By comparing these findings with the results of relativistic Magneto-Hydro-Dynamics (MHD) simulations and observed gravitational waves we conclude that progenitor neutron stars were most probably old, had close masses and highly reduced magnetic fields.

scholarly journals Jet Propagation in Neutron Star Mergers and GW170817

2019 ◽  
Author(s):  
Hamid Hamidani ◽  
Kenta Kiuchi ◽  
Kunihito Ioka
Keyword(s):  
Neutron Star ◽  
Numerical Simulations ◽  
Gamma Ray ◽  
Galactic Nuclei ◽  
Expansion Velocity ◽  
Analytic Model ◽  
Binary Neutron Star ◽  
Central Engine ◽  
Relativistic Jet ◽  
Wave Event

Abstract The gravitational wave event from the binary neutron star (BNS) merger GW170817 and the following multi-messenger observations present strong evidence for i) merger ejecta expanding with substantial velocities and ii) a relativistic jet which had to propagate through the merger ejecta. The ejecta’s expansion velocity is not negligible for the jet head motion, which is a fundamental difference from the other systems like collapsars and active galactic nuclei. Here we present an analytic model of the jet propagation in an expanding medium. In particular, we notice a new term in the expression of the breakout time and velocity. In parallel, we perform a series of over a hundred 2D numerical simulations of jet propagation. The BNS merger ejecta is prepared based on numerical relativity simulations of a BNS merger with the highest-resolution to date. We show that our analytic results agree with numerical simulations over a wide parameter space. Then we apply our analytic model to GW170817, and obtain two solid constraints on: i) the central engine luminosity as Liso, 0 ∼ 3 × 1049 − 2.5 × 1052 erg s−1, and on ii) the delay time between the merger and engine activation t0 − tm < 1.3 s. The engine power implies that the apparently-faint short gamma-ray burst (sGRB) sGRB 170817A is similar to typical sGRBs if observed on-axis.

scholarly journals Prospects of joint detections of neutron star mergers and short GRBs with Gaussian structured jets

2020 ◽  
Vol 493 (2) ◽  
pp. 1633-1639
Author(s):  
M Saleem
Keyword(s):  
Neutron Star ◽  
Joint Detection ◽  
Detection Rates ◽  
Binary Neutron Star ◽  
The Core ◽  
Relativistic Jet ◽  
Inclination Angles ◽  
Γ Ray ◽  
Short Grbs ◽  
Lower Inclination

ABSTRACT GW170817 was the first ever joint detection of gravitational waves (GW) from a binary neutron star (BNS) merger with the detections of short γ-ray burst (SGRB) counterparts. Analysis of the multiband afterglow observations of over more than a year revealed that the outflow from the merger end product was consistent with structured relativistic jet models with the core of the jet narrowly collimated to half-opening angles ∼5○. In this work, assuming that all the BNS mergers produce Gaussian structured jets with properties as inferred for GW170817, we explore the prospects of joint detections of BNS mergers and prompt γ-ray emission, expected during the current and upcoming upgrades of LIGO–Virgo–KAGRA detectors. We discuss three specific observational aspects: 1) the distribution of detected binary inclination angles, 2) the distance reach, and 3) the detection rates. Unlike GW-only detections, the joint detections are greatly restricted at large inclination angles, due to the structure of the jets. We find that at lower inclination angles (say below 20○), the distance reach as well as the detection rates of the joint detections are limited by GW detectability while at larger inclinations (say above 20○), they are limited by the γ-ray detectability.

scholarly journals Properties of jet and surrounding material of GW/GRB 170817A

2019 ◽  
Vol 490 (2) ◽  
pp. 2822-2837 ◽  
Author(s):  
Houri Ziaeepour
Keyword(s):  
Gamma Ray ◽  
Broad Band ◽  
Lorentz Factor ◽  
Published Data ◽  
Prompt Gamma ◽  
External Shocks ◽  
Long Distance ◽  
X Ray ◽  
Slow Rise ◽  
Gamma Ray Emission

ABSTRACT We use published data in radio, optical, and X-ray bands to analyse and model afterglows of GW/GRB 170817A. Our analysis is based on a phenomenological gamma-ray burst generator model, which we previously used to study the prompt gamma-ray emission of this important transient. We find a multicomponent model and a few of its variants that are consistent with broad-band ∼1 yr observations of afterglows, once the contribution of kilonova in optical/IR band is taken into account. Considering beaming and off-axis view of relativistic outflows, we interpret the components of the model as approximately presenting the profile of a relativistic structured jet with a rapidly declining Lorentz factor from our line of sight, where it had a Lorentz factor of $\mathcal {O}(100)$, to outer boundaries, where it became a mildly relativistic cocoon with a relative velocity to light of ∼0.4–0.97. Properties of the ultra-relativistic core of the jet obtained here are consistent with conclusions from analysis of the prompt gamma-ray emission. In particular, our results show that after prompt internal shocks the remnant of the jet retained in some extent its internal collimation and coherence. Slow rise of the afterglows can be associated to low density of circumburst material and low column density of the jet. The long distance of external shocks from the merger, which could have been in part responsible for extensive thinning of the jet through expansion and energy dissipation before occurrence of external shocks, is responsible for the peak of emission being at ≳110 d after the merger. We discuss implications of these observations for origin and properties of circumburst material around binary neutron stars. This analysis confirms our previous results showing that an outflow with a Lorentz factor of ∼2–5 cannot explain observed afterglows without an additional X-ray source or significant absorption of optical/IR photons.

scholarly journals Gravitational waves from post-merger radially oscillating millisecond pulsars

2019 ◽  
Vol 622 ◽  
pp. A194 ◽  
Author(s):  
Z. G. Dai
Keyword(s):  
Neutron Star ◽  
Gravitational Waves ◽  
High Frequency ◽  
Gamma Ray ◽  
Magnitude Estimate ◽  
Compact Objects ◽  
Millisecond Pulsars ◽  
Binary Neutron Star ◽  
Order Of Magnitude ◽  
Negligible Contribution

Observations of short-duration gamma-ray bursts and their afterglows show that a good fraction (perhaps ≳50%) of binary neutron star mergers lead to strongly magnetized, rapidly rotating pulsars (including millisecond magnetars), no matter whether the pulsar remnants are short- or long-lived. Such compact objects are very likely to have significant radial oscillations and high interior temperatures, as indicated in recent numerical simulations. In this paper, we have investigated rotation-induced gravitational radiation from possibly existing, radially oscillating pulsars after binary neutron star mergers, and find that this mechanism can efficiently damp the radial oscillations. The resulting gravitational waves (GWs) could have a non-negligible contribution to the high-frequency spectrum. We provide an order-of-magnitude estimate of the event rate and suggest that such GW events would be detectable with the advanced LIGO/Virgo or next-generation detectors. Our discussion can also be applied to newborn, radially oscillating, millisecond pulsars formed through the other astrophysical processes.

scholarly journals Recent searches for continuous gravitational waves

2017 ◽  
Vol 32 (39) ◽  
pp. 1730035 ◽  
Author(s):  
Keith Riles
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Star ◽  
Gravitational Waves ◽  
Gamma Ray ◽  
Continuous Wave ◽  
New Era ◽  
Binary Neutron Star ◽  
Binary Black Hole ◽  
Bose Einstein

Gravitational wave astronomy opened dramatically in September 2015 with the LIGO discovery of a distant and massive binary black hole coalescence. The more recent discovery of a binary neutron star merger, followed by a gamma ray burst (GRB) and a kilonova, reinforces the excitement of this new era, in which we may soon see other sources of gravitational waves, including continuous, nearly monochromatic signals. Potential continuous wave (CW) sources include rapidly spinning galactic neutron stars and more exotic possibilities, such as emission from axion Bose Einstein “clouds” surrounding black holes. Recent searches in Advanced LIGO data are presented, and prospects for more sensitive future searches are discussed.

Pan Galactic Gargle Blaster

2019 ◽  
pp. 132-137
Author(s):  
Nicholas Mee
Keyword(s):  
General Relativity ◽  
Neutron Star ◽  
Neutron Stars ◽  
Gravitational Waves ◽  
Gamma Ray ◽  
Great Accuracy ◽  
Gamma Ray Bursts ◽  
Tests Of General Relativity ◽  
Binary Neutron Star

The sources of short gamma ray bursts (GRBs) have been identified with neutron star merger events. Hulse and Taylor discovered the first binary neutron star in 1974. By monitoring the pulsar in this system the orbital characteristics of the system have been determined with great accuracy. This has led to tests of general relativity, including the first confirmation of the existence of gravitational waves. The emission of this radiation is gradually bringing the two neutron stars together. They will collide and merge in about 300 million years.

scholarly journals Binary Neutron Star and Short Gamma-Ray Burst Simulations in Light of GW170817

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 119 ◽  
Author(s):  
Antonios Nathanail
Keyword(s):  
Neutron Star ◽  
Gravitational Wave ◽  
Electromagnetic Radiation ◽  
Numerical Simulations ◽  
Gravitational Waves ◽  
Gamma Ray ◽  
Numerical Relativity ◽  
Gamma Ray Burst ◽  
Binary Neutron Star ◽  
The Status

In the dawn of the multi-messenger era of gravitational wave astronomy, which was marked by the first ever coincident detection of gravitational waves and electromagnetic radiation, it is important to take a step back and consider our current established knowledge. Numerical simulations of binary neutron star mergers and simulations of short GRB jets must combine efforts to understand such complicated and phenomenologically rich explosions. We review the status of numerical relativity simulations with respect to any jet or magnetized outflow produced after merger. We compare what is known from such simulations with what is used and obtained from short GRB jet simulations propagating through the BNS ejecta. We then review the established facts on this topic, as well as discuss things that need to be revised and further clarified.

scholarly journals A Genuinely Short Gamma-Ray Burst from Massive Star Core Collapse

2020 ◽  
Author(s):  
Binbin Zhang ◽  
Zi-Ke Liu ◽  
Zong-Kai Peng ◽  
Ye Li ◽  
H.-J. Lu ◽  
...  
Keyword(s):  
Neutron Star ◽  
Massive Star ◽  
Gamma Ray ◽  
Sensitivity Threshold ◽  
Core Collapse ◽  
Binary Neutron Star ◽  
Long Duration ◽  
Multi Wavelength ◽  
Short Grbs ◽  
Bright Emission

Abstract Gamma-ray bursts have been phenomenologically classified into long and short populations based on whether the observed duration is longer or shorter than two seconds. Multi-wavelength and multi-messenger observations in recent years have revealed that in general long GRBs originate from massive star core collapse events, whereas short GRBs originate from binary neutron star mergers. It has been known that the duration criterion is sometimes unreliable, and multi-wavelength criteria are needed to identify the physical origin of a particular GRB. Some apparently long GRBs have been suggested to have a neutron star merger origin, whereas some apparently short GRBs have been attributed to genuinely long GRBs whose short, bright emission is above the detector's sensitivity threshold. Still, there has been no known case that a GRB is genuinely short but originates from death of a massive star. Here we report the comprehensive analysis of the multi-wavelength data of a bright short GRB 200826A. This burst has a sharp 1-second spike, which is not part of an underlying long-duration event. Its other observational properties are, however, inconsistent with those of other short GRBs believed to originate from binary neutron star mergers. Rather, these properties resemble those of long GRBs. This burst presents a challenge to the traditional GRB classification scheme and reveals a class of core-collapse-origin GRBs with genuinly short durations.

scholarly journals Detectability of radio afterglows from binary neutron star mergers and implications for fast radio bursts

2020 ◽  
Vol 498 (2) ◽  
pp. 2384-2390 ◽  
Author(s):  
Haoxiang Lin ◽  
Tomonori Totani
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Small Sample ◽  
Radio Bursts ◽  
Strong Constraint ◽  
Sample Number ◽  
Binary Neutron Star ◽  
Radio Monitoring ◽  
Relativistic Jet ◽  
Detection Probabilities

ABSTRACT Binary neutron star (BNS) mergers are one of the proposed origins for both repeating and non-repeating fast radio bursts (FRBs), which associates FRBs with gravitational waves and short gamma-ray bursts (GRBs). In this work, we explore detectability of radio afterglows from BNS mergers and compare it to the observed radio limits on FRB afterglow. We calculate the afterglow flux powered by the two components: a relativistic jet and a slower isotropic ejecta, and quantify the detection probability as a function of the source redshift, observing time, and flux sensitivity. The model parameter distributions inferred from short GRB afterglows are adopted, and viewing angle distributions (uniform spherical, gravitational-wave, on-axis biased) are assumed to reflect different searching scenario. Assuming that FRBs are not strongly beamed, we make comparison to FRBs detected with reported radio limits and find the detection probabilities are 1–10 per cent in general, and hence not a strong constraint on the BNS progenitor model considering the small sample number (&lt;10). In particular for some nearby FRBs (e.g. 180916.J0158+65, 190608), we find a high chance of detection (&gt;20 per cent at 10 μJy sensitivity) for the isotropic component that would peak around ∼1–10 yr after the merger. Therefore, a long-term radio monitoring of persistent radio emission for these objects is important.

scholarly journals The Rate of Short-Duration Gamma-Ray Bursts in the Local Universe

Galaxies ◽  
2018 ◽  
Vol 6 (4) ◽  
pp. 130 ◽  
Author(s):  
Soheb Mandhai ◽  
Nial Tanvir ◽  
Gavin Lamb ◽  
Andrew Levan ◽  
David Tsang
Keyword(s):  
Neutron Star ◽  
Short Duration ◽  
Gamma Ray ◽  
Local Population ◽  
Gamma Ray Burst ◽  
Binary Neutron Star ◽  
Upper Limit ◽  
Transient Source ◽  
The Galaxy ◽  
Short Grbs

Following the faint gamma-ray burst, GRB 170817A, coincident with a gravitational wave-detected binary neutron star merger at d ∼ 40 Mpc, we consider the constraints on a local population of faint short duration GRBs (defined here broadly as T 90 < 4 s). We review proposed low-redshift short-GRBs and consider statistical limits on a d ≲ 200 Mpc population using Swift/Burst Alert Telescope (BAT), Fermi/Gamma-ray Burst Monitor (GBM), and Compton Gamma-Ray Observatory (CGRO) Burst and Transient Source Experiment (BATSE) GRBs. Swift/BAT short-GRBs give an upper limit for the all-sky rate of < 4 y − 1 at d < 200 Mpc, corresponding to < 5% of SGRBs. Cross-correlation of selected CGRO/BATSE and Fermi/GBM GRBs with d < 100 Mpc galaxy positions returns a weaker constraint of ≲ 12 y − 1 . A separate search for correlations due to SGR giant flares in nearby ( d < 11 Mpc) galaxies finds an upper limit of < 3 y − 1 . Our analysis suggests that GRB 170817A-like events are likely to be rare in existing SGRB catalogues. The best candidate for an analogue remains GRB 050906, where the Swift/BAT location was consistent with the galaxy IC 0327 at d ≈ 132 Mpc. If binary neutron star merger rates are at the high end of current estimates, then our results imply that at most a few percent will be accompanied by detectable gamma-ray flashes in the forthcoming LIGO/Virgo science runs.

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