Impact of an off-centred dipole on neutron star binaries

ABSTRACT Neutron stars are strongly magnetized rotating compact objects. Therefore, they also produce huge electric fields accelerating particles to ultrarelativistic energies. The simplest magnetic topology is a dipole traditionally located at the stellar centre. In this paper, we re-investigate the consequences of an off-centred rotating magnetic dipole, showing accurate magnetic field line geometries, the associated spin-down luminosity as well as the corresponding electromagnetic kick and torque imprinted to the neutron star. Results are obtained by time-dependent numerical simulations of Maxwell equations in vacuum using pseudo-spectral methods. We compare our results to known analytical expressions available to lowest order in the parameter ϵ = d/R, where d is the displacement of the dipole from the stellar centre and R the neutron star radius. We found good agreement between our numerical computations and our analytical approximations even for well off-centred dipoles having large displacements with a sizeable fraction of the radius, i.e. ϵ ≲ 1. An explanation for binary neutron star eccentricity distribution functions is given with an emphasize on highly eccentric systems as an alternative scenario to traditional binary formation.

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Gravitational waves from post-merger radially oscillating millisecond pulsars

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834552 ◽

2019 ◽

Vol 622 ◽

pp. A194 ◽

Cited By ~ 2

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.

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Prospects for observing and localizing gravitational-wave transients with Advanced LIGO, Advanced Virgo and KAGRA

Living Reviews in Relativity ◽

10.1007/s41114-020-00026-9 ◽

2020 ◽

Vol 23 (1) ◽

Cited By ~ 1

Author(s):

B. P. Abbott ◽

◽

R. Abbott ◽

T. D. Abbott ◽

S. Abraham ◽

...

Keyword(s):

Black Hole ◽

Neutron Star ◽

Gravitational Wave ◽

Binary Systems ◽

Compact Objects ◽

Binary Neutron Star ◽

Binary Black Hole ◽

Credible Region ◽

Binary Mergers ◽

Black Hole Binary

AbstractWe present our current best estimate of the plausible observing scenarios for the Advanced LIGO, Advanced Virgo and KAGRA gravitational-wave detectors over the next several years, with the intention of providing information to facilitate planning for multi-messenger astronomy with gravitational waves. We estimate the sensitivity of the network to transient gravitational-wave signals for the third (O3), fourth (O4) and fifth observing (O5) runs, including the planned upgrades of the Advanced LIGO and Advanced Virgo detectors. We study the capability of the network to determine the sky location of the source for gravitational-wave signals from the inspiral of binary systems of compact objects, that is binary neutron star, neutron star–black hole, and binary black hole systems. The ability to localize the sources is given as a sky-area probability, luminosity distance, and comoving volume. The median sky localization area (90% credible region) is expected to be a few hundreds of square degrees for all types of binary systems during O3 with the Advanced LIGO and Virgo (HLV) network. The median sky localization area will improve to a few tens of square degrees during O4 with the Advanced LIGO, Virgo, and KAGRA (HLVK) network. During O3, the median localization volume (90% credible region) is expected to be on the order of $$10^{5}, 10^{6}, 10^{7}\mathrm {\ Mpc}^3$$ 10 5 , 10 6 , 10 7 Mpc 3 for binary neutron star, neutron star–black hole, and binary black hole systems, respectively. The localization volume in O4 is expected to be about a factor two smaller than in O3. We predict a detection count of $$1^{+12}_{-1}$$ 1 - 1 + 12 ($$10^{+52}_{-10}$$ 10 - 10 + 52 ) for binary neutron star mergers, of $$0^{+19}_{-0}$$ 0 - 0 + 19 ($$1^{+91}_{-1}$$ 1 - 1 + 91 ) for neutron star–black hole mergers, and $$17^{+22}_{-11}$$ 17 - 11 + 22 ($$79^{+89}_{-44}$$ 79 - 44 + 89 ) for binary black hole mergers in a one-calendar-year observing run of the HLV network during O3 (HLVK network during O4). We evaluate sensitivity and localization expectations for unmodeled signal searches, including the search for intermediate mass black hole binary mergers.

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Off-centred force-free neutron star magnetospheres

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3909 ◽

2020 ◽

Author(s):

J Pétri

Keyword(s):

Neutron Star ◽

Charged Particles ◽

Zeroth Order ◽

Free Neutron ◽

Field Geometry ◽

The Impact ◽

Pseudo Spectral ◽

Analytical Expressions ◽

Free Plasma ◽

Neutron Star Radius

Abstract Neutron star electromagnetic activity produces pairs that fill their magnetosphere represented to the zeroth order by the force-free approximation. Neither dissipation nor acceleration nor radiation from charged particles is expected from this simplified model. So far, only centred dipole magnetic fields have been studied in this limit. In this paper, we explore the consequences of a rotating off-centred dipole on the force-free magnetosphere, showing the new magnetic field geometry, its spin-down luminosity as well as the electromagnetic kick and torque felt by the neutron star. Solutions are obtained by time-dependent numerical simulations of the force-free regime using our pseudo-spectral code written in spherical coordinates. Our results are also compared to known analytical expressions found for the off-centred vacuum dipole by an expansion to lowest order in the parameter ε = d/R, where d is the displacement of the dipole from the stellar centre and R the neutron star radius. The presence of a force-free plasma enhances the spin-down luminosity as well as the electromagnetic kick and torque with respect to a centred force-free dipole. The impact on isolated and binary neutron stars is revised in light of these new results.

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Implications of the search for optical counterparts during the second part of the Advanced LIGO’s and Advanced Virgo’s third observing run: lessons learned for future follow-up observations

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa1925 ◽

2020 ◽

Vol 497 (1) ◽

pp. 1181-1196 ◽

Cited By ~ 2

Author(s):

Michael W Coughlin ◽

Tim Dietrich ◽

Sarah Antier ◽

Mouza Almualla ◽

Shreya Anand ◽

...

Keyword(s):

Neutron Star ◽

Binary Systems ◽

Lessons Learned ◽

Compact Objects ◽

Binary Neutron Star ◽

The Third ◽

Compact Binary ◽

Compact Binary Systems ◽

Optical Telescopes

ABSTRACT Joint multimessenger observations with gravitational waves and electromagnetic (EM) data offer new insights into the astrophysical studies of compact objects. The third Advanced LIGO and Advanced Virgo observing run began on 2019 April 1; during the 11 months of observation, there have been 14 compact binary systems candidates for which at least one component is potentially a neutron star. Although intensive follow-up campaigns involving tens of ground and space-based observatories searched for counterparts, no EM counterpart has been detected. Following on a previous study of the first six months of the campaign, we present in this paper the next five months of the campaign from 2019 October to 2020 March. We highlight two neutron star–black hole candidates (S191205ah and S200105ae), two binary neutron star candidates (S191213g and S200213t), and a binary merger with a possible neutron star and a ‘MassGap’ component, S200115j. Assuming that the gravitational-wave (GW) candidates are of astrophysical origin and their location was covered by optical telescopes, we derive possible constraints on the matter ejected during the events based on the non-detection of counterparts. We find that the follow-up observations during the second half of the third observing run did not meet the necessary sensitivity to constrain the source properties of the potential GW candidate. Consequently, we suggest that different strategies have to be used to allow a better usage of the available telescope time. We examine different choices for follow-up surveys to optimize sky localization coverage versus observational depth to understand the likelihood of counterpart detection.

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Probing modified gravitational-wave propagation through tidal measurements of binary neutron star mergers

Physical Review D ◽

10.1103/physrevd.103.124047 ◽

2021 ◽

Vol 103 (12) ◽

Author(s):

Nan Jiang ◽

Kent Yagi

Keyword(s):

Wave Propagation ◽

Neutron Star ◽

Gravitational Wave ◽

Binary Neutron Star

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Waveform systematics in the gravitational-wave inference of tidal parameters and equation of state from binary neutron-star signals

Physical Review D ◽

10.1103/physrevd.103.124015 ◽

2021 ◽

Vol 103 (12) ◽

Author(s):

Rossella Gamba ◽

Matteo Breschi ◽

Sebastiano Bernuzzi ◽

Michalis Agathos ◽

Alessandro Nagar

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Gravitational Wave ◽

Binary Neutron Star

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3D magnetized jet break-out from neutron-star binary merger ejecta: afterglow emission from the jet and the ejecta

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab115 ◽

2021 ◽

Vol 502 (2) ◽

pp. 1843-1855

Author(s):

Antonios Nathanail ◽

Ramandeep Gill ◽

Oliver Porth ◽

Christian M Fromm ◽

Luciano Rezzolla

Keyword(s):

Neutron Star ◽

Thermal Emission ◽

Opening Angle ◽

Hollow Core ◽

Binary Neutron Star ◽

Vlbi Observations ◽

Superluminal Motion ◽

General Relativistic ◽

Star Binary ◽

Magnetohydrodynamic Simulations

ABSTRACT We perform 3D general-relativistic magnetohydrodynamic simulations to model the jet break-out from the ejecta expected to be produced in a binary neutron-star merger. The structure of the relativistic outflow from the 3D simulation confirms our previous results from 2D simulations, namely, that a relativistic magnetized outflow breaking out from the merger ejecta exhibits a hollow core of θcore ≈ 4°, an opening angle of θjet ≳ 10°, and is accompanied by a wind of ejected matter that will contribute to the kilonova emission. We also compute the non-thermal afterglow emission of the relativistic outflow and fit it to the panchromatic afterglow from GRB170817A, together with the superluminal motion reported from VLBI observations. In this way, we deduce an observer angle of $\theta _{\rm obs}= 35.7^{\circ \, \, +1.8}_{\phantom{\circ \, \, }-2.2}$. We further compute the afterglow emission from the ejected matter and constrain the parameter space for a scenario in which the matter responsible for the thermal kilonova emission will also lead to a non-thermal emission yet to be observed.

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Aspects of the Collapse of Compact Objects

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000018750 ◽

1980 ◽

Vol 4 (1) ◽

pp. 49-50

Author(s):

R. A. Gingold ◽

J. J. Monaghan

Keyword(s):

Neutron Star ◽

Neutron Stars ◽

White Dwarf ◽

Compact Objects ◽

Dwarf Star

Misner Thorne and Wheeler (1973), (page 629) suggested that a freshly formed White Dwarf star of several solar masses would, if slowly — rotating, collapse to form a neutron star pancake which would become unstable and eventually produce several, possibly colliding, neutron stars.

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