Magnetar

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

Implications For The Origin Of GRB 051103 From LIGO Observations

Abstract: We present the results of a LIGO search for gravitational waves (GWs) associated with GRB 051103, a short-duration hard-spectrum gamma-ray burst (GRB) whose electromagnetically determined sky position is coincident with the spiral galaxy M81, which is 3.6 Mpc from Earth. Possible progenitors for short-hard GRBs include compact object mergers and soft gamma repeater (SGR) giant flares. A merger progenitor would produce a characteristic GW signal that should be detectable at the distance of M81, while GW emission from an SGR is not expected to be detectable at that distance. We found no evidence of a GW signal associated with GRB 051103. Assuming weakly beamed gamma-ray emission with a jet semi-angle of 30 deg we exclude a binary neutron star merger in M81 as the progenitor with a confidence of 98%. Neutron star-black hole mergers are excluded with > 99% confidence. If the event occurred in M81 our findings support the the hypothesis that GRB 051103 was due to an SGR giant flare, making it the most distant extragalactic magnetar observed to date.

Magneto-elastic oscillations of neutron stars: exploring different magnetic field configurations

Abstract: We study magneto-elastic oscillations of highly magnetized neutron stars (magnetars) which have been proposed as an explanation for the quasi-periodic oscillations (QPOs) appearing in the decaying tail of the giant flares of soft gamma-ray repeaters (SGRs). We extend previous studies by investigating various magnetic field configurations, computing the Alfv´ en spectrum in each case and performing magneto-elastic simulations for a selected number of models. By identifying the observed frequencies of 28 Hz (SGR 1900+14) and 30 Hz (SGR 1806-20) with the fundamental Alfv´ en QPOs, we estimate the required surface magnetic field strength. For the magnetic field configurations investigated (dipole-like poloidal, mixed toroidal-poloidal with a dipole-like poloidal component and a toroidal field confined to the region of field lines closing inside the star, and for poloidal fields with an additional quadrupole-like component) the estimated dipole spin-down magnetic fields are between 8 10 14 G and 4 10 15 G, in broad agreement with spin-down estimates for the SGR sources producing giant flares. A number of these models exhibit a rich Alfv´ en continuum revealing new turning points which can produce QPOs. This allows one to explain most of the observed QPO frequencies as associated with magneto-elastic QPOs. In particular, we construct a possible configuration with two turning points in the spectrum which can explain all observed QPOs of SGR 1900+14. Finally, we find that magnetic field configurations which are entirely confined in the crust (if the core is assumed to be a type I superconductor) are not favoured, due to difficulties in explaining the lowest observed QPO frequencies (f . 30 Hz).

Timing analysis of the isolated neutron star RX J0720.4-3125

Abstract: We present a combined analysis of XMM-Newton, Chandra and ROSAT observations of the isolated neutron star RX J0720.4-3125, spanning a total period of similar to7 yr. We develop a maximum likelihood periodogram for our analysis based on the DeltaC statistic and the maximum likelihood method, which are appropriate for the treatment of sparse event lists. Our results have been checked a posteriori by folding a further BeppoSAX data set with the period predicted at the time of that observation: the phase is found to be consistent.The study of the spin history and the measure of the spin-down rate are of extreme importance in discriminating between the possible mechanisms suggested for the nature of the X-ray emission. The value of P., here measured for the first time, is approximate to10 (-14) s s(-1). This value cannot be explained in terms of torque from a fossil disc. When interpreted in terms of dipolar losses, it gives a magnetic field of B approximate to10(13) G, making it also implausible that the source is accreting from the underdense surroundings. On the other hand, we also find it unlikely that the field decayed from a much larger value (B approximate to10(15) G, as expected for a magnetar powered by dissipation of a superstrong field) since this scenario predicts a source age of approximate to10(4) yr, too young to match the observed X-ray luminosity. The observed properties are more compatible with a scenario in which the source is approximate to10(6) yr old, and its magnetic field has not changed substantially over the lifetime.

Search for gamma-ray emission from magnetars with the Fermi Large Area Telescope

Abstract: We report on the search for 0.1-10 GeV emission from magnetars in 17 months of Fermi Large Area Telescope (LAT) observations. No significant evidence for gamma-ray emission from any of the currently-known magnetars is found. The most stringent upper limits to date on their persistent emission in the Fermi-LAT energy range are estimated between ~10^{-12}-10^{-10} erg/s/cm2, depending on the source. We also searched for gamma-ray pulsations and possible outbursts, also with no significant detection. The upper limits derived support the presence of a cut-off at an energy below a few MeV in the persistent emission of magnetars. They also show the likely need for a revision of current models of outer gap emission from strongly magnetized pulsars, which, in some realizations, predict detectable GeV emission from magnetars at flux levels exceeding the upper limits identified here using the Fermi-LAT observations.

Anomalous X-Ray Pulsars and Soft Gamma-Ray Repeaters: Spectral Fits and the Magnetar Model

Abstract: The energy source powering the X-ray emission from anomalous X-ray pulsars (AXPs) and soft γ-ray repeaters (SGRs) is still uncertain. In one scenario, the presence of an ultramagnetized neutron star, or "magnetar," with B 1014-1015 G is invoked. To investigate this hypothesis, we have analyzed archival ASCA data for several known AXPs and SGRs and fitted them with a model in which all or part of the X-ray flux originates as thermal emission from a magnetar. Our magnetar spectral model includes the effects of the anisotropy of the heat flow through an ultramagnetized neutron star envelope, reprocessing by a light-element atmosphere, and general relativistic corrections to the observed spectrum. We obtain good fits to the data with radii for the emitting areas that are generally consistent with those expected for neutron stars, in contrast to blackbody (BB) fits, which imply much smaller radii. Furthermore, the inclusion of atmospheric effects results in inferred temperatures lower than those implied by BB fits, but still too high to be accounted for by thermal cooling alone. An extra source of heating (possibly resulting from magnetic field decay) is needed. Despite the harder tail in the spectrum produced by reprocessing of the outgoing flux through the atmosphere, spectral fits still require a considerable fraction of the flux to be in a power-law component, probably produced in the magnetosphere of the star.