Formation of very strongly magnetized neutron stars - Implications for gamma-ray bursts
TL;DR: In this article, it is argued that a convective dynamo can also generate a very strong dipole field after the merger of a neutron star binary, but only if the merged star survives for as long as about 10-100 ms.
Abstract: It is proposed that the main observational signature of magnetars, high-field neutron stars, is gamma-ray bursts powered by their vast reservoirs of magnetic energy. If they acquire large recoils, most magnetars are unbound from the Galaxy or reside in an extended, weakly bound Galactic corona. There is evidence that the soft gamma repeaters are young magnetars. It is argued that a convective dynamo can also generate a very strong dipole field after the merger of a neutron star binary, but only if the merged star survives for as long as about 10-100 ms. Several mechanisms which could impart a large recoil to these stars at birth, sufficient to escape from the Galactic disk, are discussed.
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TL;DR: The successes, as well as the limits, of perturbation theory are presented, and its role in the emerging era of numerical relativity and supercomputers is discussed.
Abstract: Perturbations of stars and black holes have been one of the main topics of relativistic astrophysics for the last few decades. They are of particular importance today, because of their relevance to gravitational wave astronomy. In this review we present the theory of quasi-normal modes of compact objects from both the mathematical and astrophysical points of view. The discussion includes perturbations of black holes (Schwarzschild, Reissner-Nordstrom, Kerr and Kerr-Newman) and relativistic stars (non-rotating and slowly-rotating). The properties of the various families of quasi-normal modes are described, and numerical techniques for calculating quasi-normal modes reviewed. The successes, as well as the limits, of perturbation theory are presented, and its role in the emerging era of numerical relativity and supercomputers is discussed.
1,569 citations
Cites background from "Formation of very strongly magnetiz..."
...This is an interesting possibility considering the recent discovery of so-called magnetars: Neutron stars with extreme magnetic fields [81]....
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TL;DR: In this article, the decay rate of the core field is a very strong function of temperature and therefore of the magnetic flux density, which is not present in the decay of the weaker fields associated with ordinary radio pulsars.
Abstract: We calculate the quiescent X-ray, neutrino, and Alfven wave emission from a neutron star with a very strong magnetic field, Bdipole ~ 1014 − 1015 G and Binterior ~ (5–10) × 1015 G. These results are compared with observations of quiescent emission from the soft gamma repeaters and from a small class of anomalous X-ray pulsars that we have previously identified with such objects. The magnetic field, rather than rotation, provides the main source of free energy, and the decaying field is capable of powering the quiescent X-ray emission and particle emission observed from these sources. New features that are not present in the decay of the weaker fields associated with ordinary radio pulsars include fracturing of the neutron star crust, strong heating of its core, and effective suppression of thermal conduction perpendicular to the magnetic field. As the magnetic field is forced through the crust by diffusive motions in the core, multiple small-scale fractures are excited, as well as a few large fractures that can power soft gamma repeater bursts. The decay rate of the core field is a very strong function of temperature and therefore of the magnetic flux density. The strongest prediction of the model is that these sources will show no optical emissions associated with X-ray heating of an accretion disk.
1,128 citations
TL;DR: A review of nearly a decade of short gamma-ray bursts and their afterglow and host-galaxy observations is presented in this article, where the authors use this information to shed light on the nature and properties of their progenitors, the energy scale and collimation of the relativistic outflow, and the properties of the circumburst environments.
Abstract: Gamma-ray bursts (GRBs) display a bimodal duration distribution with a separation between the short- and long-duration bursts at about 2 s. The progenitors of long GRBs have been identified as massive stars based on their association with Type Ic core-collapse supernovae (SNe), their exclusive location in star-forming galaxies, and their strong correlation with bright UV regions within their host galaxies. Short GRBs have long been suspected on theoretical grounds to arise from compact object binary mergers (neutron star–neutron star or neutron star–black hole). The discovery of short GRB afterglows in 2005 provided the first insight into their energy scale and environments, as well as established a cosmological origin, a mix of host-galaxy types, and an absence of associated SNe. In this review, I summarize nearly a decade of short GRB afterglow and host-galaxy observations and use this information to shed light on the nature and properties of their progenitors, the energy scale and collimation of the relativistic outflow, and the properties of the circumburst environments. The preponderance of the evidence points to compact object binary progenitors, although some open questions remain. On the basis of this association, observations of short GRBs and their afterglows can shed light on the on- and off-axis electromagnetic counterparts of gravitational wave sources from the Advanced LIGO/Virgo experiments.
1,061 citations
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...…discovery of neutron stars with masses of about 2 M⊙ (Demorest et al. 2010, Antoniadis et al. 2013), suggest that some mergers may lead instead to a transitory or stable rapidly-spinning and highly-magnetized neutron star (a magnetar;Duncan & Thompson 1992; Metzger, Quataert & Thompson 2008)....
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TL;DR: The gamma-ray burst of GRB 970508 (z = 0.835) was a few hundred times more luminous than any supernova as discussed by the authors, and the name "hypernova" was proposed for the whole GRB/afterglow event.
Abstract: The optical afterglow of the gamma-ray burst GRB 970508 (z=0.835) was a few hundred times more luminous than any supernova. Therefore, the name "hypernova" is proposed for the whole GRB/afterglow event. There is tentative evidence that the GRBs 970228, 970508, and 970828 were close to star-forming regions. If this case is strengthened with future afterglows, then the popular model in which GRBs are caused by merging neutron stars will have to be abandoned, and a model linking GRBs to cataclysmic deaths of massive stars will be favored. The presence of X-ray precursors, first detected with Ginga, is easier to understand within a framework of a "dirty" rather than a "clean" fireball. A very energetic explosion of a massive star is likely to create a dirty fireball rather than a clean one. A specific speculative example of such an explosion is proposed: a microquasar. Its geometrical structure is similar to the "failed supernova" of Woosley: the inner core of a massive, rapidly rotating star collapses into a ~10 M☉ Kerr black hole with ~5×1054 ergs of rotational energy, while the outer core forms a massive disk/torus. A superstrong ~1015 G magnetic field is needed to make the object operate as a microquasar similar to the Blandford & Znajek model. Such events must be vary rare, 104-105 times less common than ordinary supernovae, if they are to account for the observed GRBs.
1,047 citations
Cites background from "Formation of very strongly magnetiz..."
...…is not clear how a superstrong field is generated, even though it has become popular in theoretical papers over the last few years Paczyński 1991, Duncan & Thompson 1992, Narayan, Paczyński & Piran 1992, Usov 1992, Paczyński 1993, Woosley 1993a,b, Hartmann & Woosley 1995, Woosley 1995, .....,…...
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