scholarly journals On the Energetics of a Possible Relativistic Jet Associated with the Binary Neutron Star Merger Candidate S190425z

2020 ◽  
Vol 891 (2) ◽  
pp. 130 ◽  
Author(s):  
M. Saleem ◽  
L. Resmi ◽  
K. G. Arun ◽  
S. Mohan
Keyword(s):  
Neutron Star ◽  
Binary Neutron Star ◽  
Relativistic Jet

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 Compact radio emission indicates a structured jet was produced by a binary neutron star merger

Science ◽  
2019 ◽  
Vol 363 (6430) ◽  
pp. 968-971 ◽  
Author(s):  
G. Ghirlanda ◽  
O. S. Salafia ◽  
Z. Paragi ◽  
M. Giroletti ◽  
J. Yang ◽  
...  
Keyword(s):  
Neutron Star ◽  
Very Long Baseline Interferometry ◽  
High Spatial Resolution ◽  
Apparent Size ◽  
Source Size ◽  
Global Network ◽  
Binary Neutron Star ◽  
Long Baseline ◽  
Relativistic Jet ◽  
Merger Event

The binary neutron star merger event GW170817 was detected through both electromagnetic radiation and gravitational waves. Its afterglow emission may have been produced by either a narrow relativistic jet or an isotropic outflow. High-spatial-resolution measurements of the source size and displacement can discriminate between these scenarios. We present very-long-baseline interferometry observations, performed 207.4 days after the merger by using a global network of 32 radio telescopes. The apparent source size is constrained to be smaller than 2.5 milli–arc seconds at the 90% confidence level. This excludes the isotropic outflow scenario, which would have produced a larger apparent size, indicating that GW170817 produced a structured relativistic jet. Our rate calculations show that at least 10% of neutron star mergers produce such a jet.

scholarly journals Late Time Afterglow Observations Reveal a Collimated Relativistic Jet in the Ejecta of the Binary Neutron Star Merger GW170817

2018 ◽  
Vol 120 (24) ◽  
Author(s):  
Davide Lazzati ◽  
Rosalba Perna ◽  
Brian J. Morsony ◽  
Diego Lopez-Camara ◽  
Matteo Cantiello ◽  
...  
Keyword(s):  
Neutron Star ◽  
Late Time ◽  
Binary Neutron Star ◽  
Relativistic Jet

scholarly journals Multimessenger Binary Mergers Containing Neutron Stars: Gravitational Waves, Jets, and γ-Ray Bursts

2021 ◽  
Vol 8 ◽  
Author(s):  
Milton Ruiz ◽  
Stuart L. Shapiro ◽  
Antonios Tsokaros
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Essential Feature ◽  
Theoretical Understanding ◽  
Binary Neutron Star ◽  
Relativistic Jet ◽  
Binary Mergers ◽  
Γ Ray ◽  
Magnetohydrodynamic Simulations ◽  
The One

Neutron stars (NSs) are extraordinary not only because they are the densest form of matter in the visible Universe but also because they can generate magnetic fields ten orders of magnitude larger than those currently constructed on earth. The combination of extreme gravity with the enormous electromagnetic (EM) fields gives rise to spectacular phenomena like those observed on August 2017 with the merger of a binary neutron star system, an event that generated a gravitational wave (GW) signal, a short γ-ray burst (sGRB), and a kilonova. This event serves as the highlight so far of the era of multimessenger astronomy. In this review, we present the current state of our theoretical understanding of compact binary mergers containing NSs as gleaned from the latest general relativistic magnetohydrodynamic simulations. Such mergers can lead to events like the one on August 2017, GW170817, and its EM counterparts, GRB 170817 and AT 2017gfo. In addition to exploring the GW emission from binary black hole-neutron star and neutron star-neutron star mergers, we also focus on their counterpart EM signals. In particular, we are interested in identifying the conditions under which a relativistic jet can be launched following these mergers. Such a jet is an essential feature of most sGRB models and provides the main conduit of energy from the central object to the outer radiation regions. Jet properties, including their lifetimes and Poynting luminosities, the effects of the initial magnetic field geometries and spins of the coalescing NSs, as well as their governing equation of state, are discussed. Lastly, we present our current understanding of how the Blandford-Znajek mechanism arises from merger remnants as the trigger for launching jets, if, when and how a horizon is necessary for this mechanism, and the possibility that it can turn on in magnetized neutron ergostars, which contain ergoregions, but no horizons.

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 afterglow and kilonova of the short GRB 160821B

2019 ◽  
Author(s):  
E Troja ◽  
A J Castro-Tirado ◽  
J Becerra González ◽  
Y Hu ◽  
G S Ryan ◽  
...  
Keyword(s):  
Neutron Star ◽  
Gamma Ray ◽  
Surrounding Medium ◽  
Rapid Evolution ◽  
Radioactive Decay ◽  
Reverse Shock ◽  
Binary Neutron Star ◽  
Global Properties ◽  
Relativistic Jet ◽  
Low Mass

Abstract GRB 160821B is a short duration gamma-ray burst (GRB) detected and localized by the Neil Gehrels Swift Observatory in the outskirts of a spiral galaxy at z=0.1613, at a projected physical offset of ≈16 kpc from the galaxy’s center. We present X-ray, optical/nIR and radio observations of its counterpart and model them with two distinct components of emission: a standard afterglow, arising from the interaction of the relativistic jet with the surrounding medium, and a kilonova, powered by the radioactive decay of the sub-relativistic ejecta. Broadband modeling of the afterglow data reveals a weak reverse shock propagating backward into the jet, and a likely jet-break at ≈3.5 d. This is consistent with a structured jet seen slightly off-axis (θview ∼ θcore) while expanding into a low-density medium (n ≈ 10−3 cm−3). Analysis of the kilonova properties suggests a rapid evolution toward red colors, similar to AT2017gfo, and a low nIR luminosity, possibly due to the presence of a long-lived neutron star. The global properties of the environment, the inferred low mass (Mej ≲ 0.006 M⊙) and velocities (vej ≳ 0.05c) of lanthanide-rich ejecta are consistent with a binary neutron star merger progenitor.

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