Magnetar

About: Magnetar is a research topic. Over the lifetime, 2905 publications have been published within this topic receiving 106806 citations.

Short Duration Gamma-Ray Bursts with Extended Emission from Proto-Magnetar Spin-Down

Abstract: Evidence is growing for a class of gamma-ray bursts (GRBs) characterized by an initial ~0.1-1 s spike of hard radiation followed, after a ~3-10 s lull in emission, by a softer period of extended emission lasting ~10-100 s. In a few well-studied cases, these ``short GRBs with extended emission'' show no evidence for a bright associated supernova (SN). We propose that these events are produced by the formation and early evolution of a highly magnetized, rapidly rotating neutron star (a ``proto-magnetar'') which is formed from the accretion-induced collapse (AIC) of a white dwarf (WD), the merger and collapse of a WD-WD binary, or, perhaps, the merger of a double neutron star binary. The initial emission spike is powered by accretion onto the proto-magnetar from a small disk that is formed during the AIC or merger event. The extended emission is produced by a relativistic wind that extracts the rotational energy of the proto-magnetar on a timescale ~10-100 s. The ~3-10 s delay between the prompt and extended emission is the time required for the newly-formed proto-magnetar to cool sufficiently that the neutrino-heated wind from its surface becomes ultra-relativistic. Because a proto-magnetar ejects little or no Ni56 (< 1e-3 M_sun), these events should not produce a bright SN-like transient. We model the extended emission from GRB060614 using spin-down calculations of a cooling proto-magnetar, finding reasonable agreement with observations for a magnetar with an initial rotation period of ~1 ms and a surface dipole field of ~3e15 G. If GRBs are indeed produced by AIC or WD-WD mergers, they should occur within a mixture of both early and late-type galaxies and should not produce strong gravitational wave emission. An additional consequence of our model is the existence of X-ray flashes unaccompanied by a bright SN.

Millisecond Magnetar Birth Connects FRB 121102 to Superluminous Supernovae and Long Duration Gamma-ray Bursts

Abstract: Sub-arcsecond localization of the repeating fast radio burst FRB 121102 revealed its coincidence with a dwarf host galaxy and a steady (`quiescent') non-thermal radio source. We show that the properties of the host galaxy are consistent with those of long-duration gamma-ray bursts (LGRB) and hydrogen-poor superluminous supernovae (SLSNe-I). Both LGRBs and SLSNe-I were previously hypothesized to be powered by the electromagnetic spin-down of newly-formed, strongly-magnetized neutron stars with millisecond birth rotation periods (`millisecond magnetars'). This motivates considering a scenario whereby the repeated bursts from FRB 121102 originate from a young magnetar remnant embedded within a young hydrogen-poor supernova remnant. Requirements on the GHz free-free optical depth through the expanding supernova ejecta (accounting for photo-ionization by the rotationally-powered magnetar nebula), energetic constraints on the bursts, and constraints on the size of the quiescent source all point to an age of less than a few decades to a century. The quiescent radio source can be attributed to synchrotron emission from the shock interaction between the fast outer layer of the supernova ejecta with the surrounding wind of the progenitor star, or from deeper within the magnetar wind nebula. Alternatively, the radio emission could be an orphan afterglow from an initially off-axis LGRB jet, though this might require the source to be too young. The young age of the source can be tested by searching for a time derivative of the dispersion measure and predicted fading of the quiescent radio source. We propose future tests of the SLSNe-I/LGRB/FRB connection, such as searches for FRBs from nearby SLSNe-I/LGRB on timescales of decades after their explosions.

Asymmetric Supernovae, Pulsars, Magnetars, and Gamma-Ray Bursts

Abstract: We outline the possible physical processes, associated timescales, and energetics that could lead to the production of pulsars, jets, asymmetric supernovae, and weak gamma-ray bursts in routine circumstances and to a magnetar and perhaps stronger gamma-ray burst in more extreme circumstances in the collapse of the bare core of a massive star. The production of a LeBlanc-Wilson MHD jet could provide an asymmetric supernova and result in a weak gamma-ray burst when the jet accelerates down the stellar density gradient of a hydrogen-poor photosphere. The matter-dominated jet would be formed promptly, but requires 5 to 10 s to reach the surface of the progenitor of a Type Ib/c supernova. During this time, the newly-born neutron star could contract, spin up, and wind up field lines or turn on an alpha-Omega dynamo. In addition, the light cylinder will contract from a radius large compared to the Alfven radius to a size comparable to that of the neutron star. This will disrupt the structure of any organized dipole field and promote the generation of ultrarelativistic MHD waves (UMHDW) at high density and Large Amplitude Electromagnetic Waves (LAEMW) at low density. The generation of the these waves would be delayed by the cooling time of the neutron star about 5 to 10 seconds, but the propagation time is short so the UMHDW could arrive at the surface at about the same time as the matter jet. In the density gradient of the star and the matter jet, the intense flux of UMHDW and LAEMW could drive shocks, generate pions by proton-proton collision, or create electron/positron pairs depending on the circumstances. The UMHDW and LAEMW could influence the dynamics of the explosion and might also tend to flow out the rotation axis to produce a collimated gamma-ray burst.

Soft gamma repeaters and anomalous X-ray pulsars: magnetar candidates

Abstract: This article is a review of Soft Gamma Repeaters and Anomalous X-ray Pulsars. It contains a brief historical record of the emergence of these classes of neutron stars, a thorough overview of the observational data, a succinct summary of the magnetar model, and suggested directions for future research in this field.

Magnetar Spindown, Hyper-Energetic Supernovae, and Gamma Ray Bursts

Abstract: The Kelvin-Helmholtz cooling epoch, lasting tens of seconds after the birth of a neutron star in a successful core-collapse supernova, is accompanied by a neutrino-driven wind. For magnetar-strength ($\sim10^{15}$ G) large scale surface magnetic fields, this outflow is magnetically-dominated during the entire cooling epoch.Because the strong magnetic field forces the wind to co-rotate with the protoneutron star,this outflow can significantly effect the neutron star's early angular momentum evolution, as in analogous models of stellar winds (e.g. Weber & Davis 1967). If the rotational energy is large in comparison with the supernova energy and the spindown timescale is short with respect to the time required for the supernova shockwave to traverse the stellar progenitor, the energy extracted may modify the supernova shock dynamics significantly. This effect is capable of producing hyper-energetic supernovae and, in some cases, provides conditions favorable for gamma ray bursts. We estimate spindown timescales for magnetized, rotating protoneutron stars and construct steady-state models of neutrino-magnetocentrifugally driven winds. We find that if magnetars are born rapidly rotating, with initial spin periods ($P$) of $\sim1$ millisecond, that of order $10^{51}-10^{52}$ erg of rotational energy can be extracted in $\sim10$ seconds. If magnetars are born slowly rotating ($P\gtrsim10$ ms) they can spin down to periods of $\sim1$ second on the Kelvin-Helmholtz timescale.