Gravitational waves from mountains in newly born millisecond magnetars

ABSTRACT In this paper, we study the spin-evolution and gravitational-wave luminosity of a newly born millisecond magnetar, formed either after the collapse of a massive star or after the merger of two neutron stars. In both cases, we consider the effect of fallback accretion; and consider the evolution of the system due to the different torques acting on the star, namely the spin-up torque due to accretion and spin-down torques due to magnetic dipole radiation, neutrino emission, and gravitational-wave emission linked to the formation of a ‘mountain’ on the accretion poles. Initially, the spin period is mostly affected by the dipole radiation, but at later times, accretion spin the star up rapidly. We find that a magnetar formed after the collapse of a massive star can accrete up to 1 M⊙, and survive on the order of 50 s before collapsing to a black hole. The gravitational-wave strain, for an object located at 1 Mpc, is hc ∼ 10−23 at kHz frequencies, making this a potential target for next-generation ground-based detectors. A magnetar formed after a binary neutron star merger, on the other hand, accretes at the most 0.2 M⊙ and emits gravitational waves with a lower maximum strain of the order of hc ∼ 10−24, but also survives for much longer times, and may possibly be associated with the X-ray plateau observed in the light curve of a number of short gamma-ray burst.

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Interpreting the X-ray afterglows of gamma-ray bursts with radiative losses and millisecond magnetars

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3090 ◽

2020 ◽

Vol 499 (4) ◽

pp. 5986-5992

Author(s):

Nikhil Sarin ◽

Paul D Lasky ◽

Gregory Ashton

Keyword(s):

Gravitational Wave ◽

Gamma Ray ◽

Gamma Ray Bursts ◽

Dipole Radiation ◽

X Ray ◽

Radiative Efficiency ◽

Central Engine ◽

Radiative Losses ◽

Wave Emission ◽

Prompt Emission

ABSTRACT The spin-down energy of millisecond magnetars has been invoked to explain X-ray afterglow observations of a significant fraction of short and long gamma-ray bursts. Here, we extend models previously introduced in the literature, incorporating radiative losses with the spin-down of a magnetar central engine through an arbitrary braking index. Combining this with a model for the tail of the prompt emission, we show that our model can better explain the data than millisecond-magnetar models without radiative losses or those that invoke spin-down solely through vacuum dipole radiation. We find that our model predicts a subset of X-ray flares seen in some gamma-ray bursts. We can further explain the diversity of X-ray plateaus by altering the radiative efficiency and measure the braking index of newly born millisecond magnetars. We measure the braking index of GRB061121 as $n=4.85^{+0.11}_{-0.15}$ suggesting the millisecond-magnetar born in this gamma-ray burst spins down predominantly through gravitational-wave emission.

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Constraints from LIGO O3 Data on Gravitational-wave Emission Due to R-modes in the Glitching Pulsar PSR J0537–6910

The Astrophysical Journal ◽

10.3847/1538-4357/ac0d52 ◽

2021 ◽

Vol 922 (1) ◽

pp. 71

Author(s):

R. Abbott ◽

T. D. Abbott ◽

S. Abraham ◽

F. Acernese ◽

K. Ackley ◽

...

Keyword(s):

Energy Conservation ◽

Gravitational Wave ◽

Gravitational Waves ◽

Theoretical Models ◽

X Ray ◽

Spin Evolution ◽

Upper Limits ◽

Wave Emission ◽

Using Data

Abstract We present a search for continuous gravitational-wave emission due to r-modes in the pulsar PSR J0537–6910 using data from the LIGO–Virgo Collaboration observing run O3. PSR J0537–6910 is a young energetic X-ray pulsar and is the most frequent glitcher known. The inter-glitch braking index of the pulsar suggests that gravitational-wave emission due to r-mode oscillations may play an important role in the spin evolution of this pulsar. Theoretical models confirm this possibility and predict emission at a level that can be probed by ground-based detectors. In order to explore this scenario, we search for r-mode emission in the epochs between glitches by using a contemporaneous timing ephemeris obtained from NICER data. We do not detect any signals in the theoretically expected band of 86–97 Hz, and report upper limits on the amplitude of the gravitational waves. Our results improve on previous amplitude upper limits from r-modes in J0537-6910 by a factor of up to 3 and place stringent constraints on theoretical models for r-mode-driven spin-down in PSR J0537–6910, especially for higher frequencies at which our results reach below the spin-down limit defined by energy conservation.

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Protomagnetar research through an analysis of the X-ray plateau in the multi-messengar era

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936671 ◽

2020 ◽

Vol 641 ◽

pp. A56

Author(s):

Xiaoxiao Ren ◽

Daming Wei ◽

Zhenyu Zhu ◽

Yan Yan ◽

Chengming Li

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Gravitational Wave ◽

Gamma Ray ◽

Equations Of State ◽

Electromagnetic Emission ◽

Gamma Ray Bursts ◽

Gamma Ray Burst ◽

X Ray ◽

Binary Neutron Star

The joint detection of the gravitational wave signal and the electromagnetic emission from a binary neutron star merger can place unprecedented constraint on the equation of state of supranuclear matter. Although a variety of electromagnetic counterparts have been observed for GW170817, including a short gamma-ray burst, kilonova, and the afterglow emission, the nature of the merger remnant is still unclear, however. The X-ray plateau is another important characteristics of short gamma-ray bursts. This plateau is probably due to the energy injection from a rapidly rotating magnetar. We investigate what we can learn from the detection of a gravitational wave along with the X-ray plateau. In principle, we can estimate the mass of the merger remnant if the X-ray plateau is caused by the central magnetar. We selected eight equations of state that all satisfy the constraint given by the gravitational wave observation, and then calculated the mass of the merger remnants of four short gamma-ray bursts with a well-measured X-ray plateau. If, on the other hand, the mass of the merger remnant can be obtained by gravitational wave information, then by comparing the masses derived by these two different methods can further constrain the equation of state. We discuss the possibility that the merger product is a quark star. In addition, we estimate the possible mass range for the recently discovered X-ray transient CDF-S XT2 that probably originated from a binary neutron star merger. Finally, under the assumption that the post-merger remnant of GW170817 was a supramassive neutron star, we estimated the allowed parameter space of the supramassive neutron star and find that in this case, the magnetic dipole radiation energy is so high that it may have some effects on the short gamma-ray burst and kilonova emission. The lack of detection of these effects suggests that the merger product of GW170817 may not be a supermassive neutron star.

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

Galaxies ◽

10.3390/galaxies6040119 ◽

2018 ◽

Vol 6 (4) ◽

pp. 119 ◽

Cited By ~ 4

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.

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The confrontation between general relativity and experiment

Proceedings of the International Astronomical Union ◽

10.1017/s174392130999038x ◽

2009 ◽

Vol 5 (S261) ◽

pp. 198-199

Author(s):

Clifford M. Will

Keyword(s):

General Relativity ◽

Gravitational Wave ◽

Equivalence Principle ◽

Gamma Ray ◽

Strong Field ◽

Weak Field ◽

X Ray ◽

Spacetime Geometry ◽

Tests Of General Relativity ◽

Laser Interferometric

AbstractWe review the experimental evidence for Einstein's general relativity. A variety of high precision null experiments confirm the Einstein Equivalence Principle, which underlies the concept that gravitation is synonymous with spacetime geometry, and must be described by a metric theory. Solar system experiments that test the weak-field, post-Newtonian limit of metric theories strongly favor general relativity. Binary pulsars test gravitational-wave damping and aspects of strong-field general relativity. During the coming decades, tests of general relativity in new regimes may be possible. Laser interferometric gravitational-wave observatories on Earth and in space may provide new tests via precise measurements of the properties of gravitational waves. Future efforts using X-ray, infrared, gamma-ray and gravitational-wave astronomy may one day test general relativity in the strong-field regime near black holes and neutron stars.

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X-ray and Gamma-ray Radiation from the Switched-off Radiopulsars

Symposium - International Astronomical Union ◽

10.1017/s0074180900034355 ◽

1983 ◽

Vol 101 ◽

pp. 505-507

Author(s):

A. I. Tsygan

Keyword(s):

Neutron Stars ◽

Magnetic Dipole ◽

Gamma Ray ◽

Neutral Hydrogen ◽

Dipole Radiation ◽

X Ray ◽

Electron Positron ◽

Hard Radiation ◽

Γ Ray ◽

Generate Electron

It is shown that pulsars that have ceased to generate electron-positron pairs (switched-off radiopulsars) may be the sources of X-ray and γ-ray radiation. The magnetic dipole radiation from these rotating neutron stars is transformed near the “light radius” into hard radiation by the plasma that is created due to ionization of interstellar neutral hydrogen.

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

Physics ◽

10.3390/physics1020018 ◽

2019 ◽

Vol 1 (2) ◽

pp. 194-228 ◽

Cited By ~ 1

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.

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Measuring the eccentricity of GW170817 and GW190425

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2120 ◽

2020 ◽

Vol 497 (2) ◽

pp. 1966-1971 ◽

Cited By ~ 1

Author(s):

Amber K Lenon ◽

Alexander H Nitz ◽

Duncan A Brown

Keyword(s):

Parameter Estimation ◽

Neutron Star ◽

Gravitational Wave ◽

Matched Filter ◽

Wave Frequency ◽

Limited Information ◽

Binary Neutron Star ◽

Wave Emission

ABSTRACT Two binary neutron star mergers, GW170817 and GW190425, have been detected by Advanced LIGO and Virgo. These signals were detected by matched-filter searches that assume that the star’s orbit has circularized by the time their gravitational-wave emission is observable. This suggests that their eccentricity is low, but full parameter estimation of their eccentricity has not yet been performed. We use gravitational-wave observations to measure the eccentricity of GW170817 and GW190425. We find that the eccentricity at a gravitational-wave frequency of 10 Hz is e ≤ 0.024 and e ≤ 0.048 for GW170817 and GW190425, respectively (90 per cent confidence). This is consistent with the binaries being formed in the field, as such systems are expected to have circularized to e ≤ 10−4 by the time they reach the LIGO–Virgo band. Our constraint is a factor of 2 smaller that an estimate based on GW170817 being detected by searches that neglect eccentricity. However, we caution that we find significant prior dependence in our limits, suggesting that there is limited information in the signals. We note that other techniques used to constrain binary neutron star eccentricity without full parameter estimation may miss degeneracies in the waveform, and that for future signals, it will be important to perform full parameter estimation with accurate waveform templates.

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Supernovae and Gamma-ray Bursts

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312012720 ◽

2011 ◽

Vol 7 (S279) ◽

pp. 75-82

Author(s):

Paolo A. Mazzali

Keyword(s):

Black Hole ◽

Massive Star ◽

Gamma Ray ◽

Massive Stars ◽

Observational Evidence ◽

Gamma Ray Bursts ◽

Core Collapse ◽

Broad Absorption ◽

X Ray ◽

Long Duration

AbstractThe properties of the Supernovae discovered in coincidence with long-duration Gamma-ray Bursts and X-Ray Flashes are reviewed, and compared to those of SNe for which GRBs are not observed. The SNe associated with GRBs are of Type Ic, they are brighter than the norm, and show very broad absorption lines in their spectra, indicative of high expansion velocities and hence of large explosion kinetic energies. This points to a massive star origin, and to the birth of a black hole at the time of core collapse. There is strong evidence for gross asymmetries in the SN ejecta. The observational evidence seems to suggest that GRB/SNe are more massive and energetic than XRF/SNe, and come from more massive stars. While for GRB/SNe the collapsar model is favoured, XRF/SNe may host magnetars.

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