Showing papers on "Magnetar published in 1999"
TL;DR: The soft gamma repeater SGR 1900+14 became active again in June 1998 after a long period of quiescence; it remained at a low state of activity until August 1998, when it emitted a series of extraordinarily intense outbursts.
Abstract: The soft gamma repeater SGR 1900+14 became active again in June 1998 after a long period of quiescence; it remained at a low state of activity until August 1998, when it emitted a series of extraordinarily intense outbursts. We have observed the source with the Rossi X-Ray Timing Explorer twice, during the onset of each active episode. We confirm the pulsations at the 5.16 s period reported earlier from SGR 1900+14. Here we report the detection of a secular spin-down of the pulse period at an average rate of 1.1 x 10(exp -10)s/s. In view of the strong similarities between SGRs, we attribute the spin-down of SGR 1900+14 to magnetic dipole radiation, possibly accelerated by a quiescent flux, as in the case of SGR 1806-20. This allows an estimate of the pulsar dipolar magnetic field, which is (2-8) x 10(exp 14) G. Our results confirm that SGRs are magnetars.
387 citations
TL;DR: In this paper, the authors 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.
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.
343 citations
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TL;DR: It is found that if SGR 1806-20 puts out a continuous particle wind of 1037 ergs s-1, then the pulsar age is consistent with that of the supernova remnant, but the derived surface dipole magnetic field is only 3x1013 G, in the range of normal radio pulsars.
Abstract: We examine the effects of a relativistic wind on the spin-down of a neutron star and apply our results to the study of soft gamma repeaters (SGRs), which are thought to be neutron stars with magnetic fields greater than 1014 G. We derive a spin-down formula that includes torques from both dipole radiation and episodic or continuous particle winds. We find that if SGR 1806-20 puts out a continuous particle wind of 1037 ergs s-1, then the pulsar age is consistent with that of the supernova remnant, but the derived surface dipole magnetic field is only 3x1013 G, in the range of normal radio pulsars. If instead the particle wind flows are episodic with small duty cycle, then the observed period derivatives imply magnetar-strength fields, while still allowing characteristic ages within a factor of 2 of the estimated supernova remnant age. Close monitoring of the periods of SGRs will allow us to establish or place limits on the wind duty cycle and thus the magnetic field and age of the neutron star.
185 citations
TL;DR: In this article, the physical implications of the rapid spindown of Soft Gamma Repeater 1900+14, and of the apparent "braking glitch", \Delta P/P = l x 10^-4, that was concurrent with the Aug. 27th giant flare are considered.
Abstract: We consider the physical implications of the rapid spindown of Soft Gamma Repeater 1900+14, and of the apparent "braking glitch", \Delta P/P = l x 10^-4, that was concurrent with the Aug. 27th giant flare. A radiation-hydrodynamical outflow associated with the flare could impart the required torque, but only if the dipole magnetic field is stronger than ~ 10^14 G and the outflow lasts longer and/or is more energetic than the observed X-ray flare. A positive period increment is also a natural consequence of a gradual, plastic deformation of the neutron star crust by an intense magnetic field, which forces the neutron superfluid to rotate more slowly than the crust. Sudden unpinning of the neutron vortex lines during the August 27th event would then induce a glitch opposite in sign to those observed in young pulsars, but of a much larger magnitude as a result of the slower rotation.
The change in the persistent X-ray lightcurve following the August 27 event is ascribed to continued particle heating in the active region of that outburst. The enhanced X-ray output can be powered by a steady current flowing through the magnetosphere, induced by the twisting motion of the crust. The long term rate of spindown appears to be accelerated with respect to a simple magnetic dipole torque. Accelerated spindown of a seismically-active magnetar will occur when its persistent output of Alfven waves and particles exceeds its spindown luminosity. We suggest that SGRs experience some episodes of relative inactivity, with diminished spindown rates, and that such inactive magnetars are observed as Anomalous X-ray Pulsars (AXPs). The rapid reappearence of persistent X-ray emission following August 27 flare gives evidence against accretion-powered models.
133 citations
TL;DR: In this article, the rotational, magnetic, and thermal evolution of an ultra-magnetized neutron star, or magnetar, with available data on the anomalous X-ray Pulsars (AXPs) was studied.
Abstract: We confront theoretical models for the rotational, magnetic, and thermal evolution of an ultra-magnetized neutron star, or magnetar, with available data on the Anomalous X-ray Pulsars (AXPs). We argue that, if the AXPs are interpreted as magnetars, their clustering of spin periods between 6 and 12 seconds, observed at present in this class of objects, their period derivatives, their thermal X-ray luminosities, and the association of two of them with young supernova remnants, can only be understood globally if the magnetic field in magnetars decays significantly on a time scale of the order of 10^4 years.
106 citations
TL;DR: The frequency derivative for 1E 2259+586 is inconsistent with that inferred from incoherent frequency observations made over the last 20 yr, consistent with the magnetar hypothesis and make binary accretion scenarios appear unlikely.
Abstract: We report on long-term X-ray timing of two anomalous X-ray pulsars, 1RXS J170849.0-400910 and 1E 2259+586, using the Rossi X-Ray Timing Explorer. In monthly observations made over 1.4 and 2.6 yr for the two pulsars, respectively, we have obtained phase-coherent timing solutions which imply that these objects have been rotating with great stability throughout the course of our observations. For 1RXS J170849.0-400910, we find a rotation frequency of 0.0909169331(5) Hz and frequency derivative -15.687(4) × 10-14 Hz s-1 for epoch MJD 51215.931. For 1E 2259+586, we find a rotation frequency of 0.1432880613(2) Hz and frequency derivative -1.0026(7) × 10-14 Hz s-1 for epoch MJD 51195.583. The rms phase residuals from these simple models are only ~0.01 cycles for both sources. We show that the frequency derivative for 1E 2259+586 is inconsistent with that inferred from incoherent frequency observations made over the last 20 yr. Our observations are consistent with the magnetar hypothesis and make binary accretion scenarios appear unlikely.
101 citations
TL;DR: In this paper, it was shown that if anomalous X-ray pulsars are nonaccreting magnetars, i.e., isolated neutron stars with surface magnetic fields B0 1010 T, then they spin down electromagnetically in exactly the manner observed, because of an effect called "radiative precession."
Abstract: The two anomalous X-ray pulsars (AXPs) with well-sampled timing histories, 1E 1048.1-5937 and 1E 2259+586, are known to spin down irregularly, with "bumps" superposed on an overall linear trend. Here we show that if AXPs are nonaccreting magnetars, i.e., isolated neutron stars with surface magnetic fields B0 1010 T, then they spin down electromagnetically in exactly the manner observed, because of an effect called "radiative precession." Internal hydromagnetic stresses deform the star, creating a fractional difference = (I3 - I1)/I1 ~ 10-8 between the principal moments of inertia I1 and I3; the resulting Eulerian precession couples to an oscillating component of the electromagnetic torque associated with the near-zone radiation fields, and the star executes an anharmonic wobble with period τpr ~ 2π/Ω(t) ~ 10 yr, where Ω(t) is the rotation frequency as a function of time t. We solve Euler's equations for a biaxial magnet rotating in vacuo, show that the computed Ω(t) matches the measured timing histories of 1E 1048.1-5937 and 1E 2259+586, predict Ω(t) for the next 20 years for both objects, predict a statistical relation between dΩ/dt and τpr, to be tested as the population of known AXPs grows, and hypothesize that radiative precession will be observed in future X-ray timing of soft gamma-ray repeaters.
96 citations
TL;DR: In this article, the authors explore the implications of this evidence on magnetar and propeller-based models for the rapid spin-down of soft gamma-ray repeaters (SGRs) and anomalous x-ray pulsars (AXPs) with typical ages <30 kyr.
Abstract: Soft gamma-ray repeaters (SGRs) and anomalous x-ray pulsars (AXPs) are young and radio-quiet x-ray pulsars which have been rapidly spun-down to slow spin periods clustered in the range 5-12 s. Most of these unusual pulsars also appear to be associated with supernova shell remnants (SNRs) with typical ages <30 kyr. By examining the sizes of these remnants versus their ages, we demonstrate that the interstellar media which surrounded the SGR and AXP progenitors and their SNRs were unusually dense compared to the environments around most young radio pulsars and SNRs. We explore the implications of this evidence on magnetar and propeller-based models for the rapid spin-down of SGRs and AXPs. We find that evidence of dense environments is not consistent with the magnetar model unless a causal link can be shown between the development of magnetars and the external ISM. Propeller-driven spin-down by fossil accretion disks for SGRs and AXPs appears to be consistent with dense environments since the environment can facilitate the formation of such a disk. This may occur in two ways: 1) formation of a ``pushback'' disks from the innermost ejecta pushed back by prompt reverse shocks from supernova remnant interactions with massive progenitor wind material stalled in dense surrounding gas, or 2) acquisition of disks by a high velocity neutron stars, which may be able to capture a sufficient amounts of co-moving outflowing ejecta slowed by the prompt reverse shocks in dense environments.
95 citations
TL;DR: In this article, the authors presented a spin chronology of the pulsar using additional Ginga, ASCA, RXTE, and BeppoSAX data sets spanning over a decade.
Abstract: In previous papers, we presented the discovery of a 12 s X-ray pulsar in the supernova remnant Kes 73, providing the first direct evidence for an ultramagnetized neutron star, a magnetar, with an equivalent dipole field of nearly 20 times the quantum critical magnetic field (me2c3/e). Our conclusions were based on two epochs of the measurement of the spin, along with an age estimate of the host supernova remnant. Herein, we present a spin chronology of the pulsar using additional Ginga, ASCA, RXTE, and BeppoSAX data sets spanning over a decade. The timing and spectral analyses confirm our initial results and severely limit an accretion origin for the observed flux. Over the 10 yr baseline, the pulsar is found to undergo a rapid, constant spin-down while maintaining a steady flux and an invariant pulse profile. Within the measurement uncertainties, no systematic departures from a linear spin-down are found—departures as in the case of glitches or simply stochastic fluctuations in the pulse times of arrival (e.g., red timing noise). We suggest that this pulsar is akin to the soft γ-ray repeaters; however, it is remarkably stable and has yet to display similar outbursts. Future γ-ray activity from this object is likely.
93 citations
TL;DR: It is concluded that anomalous X-ray pulsars (AXPs) are young ( less, similar10,000 yr) objects and that they are produced in at least 5% of core-collapse supernovae.
Abstract: We report on Very Large Array observations in the direction of the recently discovered slow X-ray pulsar AX J1845-0258. In the resulting images, we find a 5a shell of radio emission; the shell is linearly polarized with a nonthermal spectral index. We classify this source as a previously unidentified, young (<8000 yr) supernova remnant (SNR), G29.6+0.1, which we propose is physically associated with AX J1845-0258. The young age of G29.6+0.1 is then consistent with the interpretation that anomalous X-ray pulsars (AXPs) are isolated, highly magnetized neutron stars ("magnetars"). Three of the six known AXPs can now be associated with SNRs; we conclude that AXPs are young ( less, similar10,000 yr) objects and that they are produced in at least 5% of core-collapse supernovae.
87 citations
TL;DR: In this paper, a gigantic periodic flare from the soft γ repeater SGR 1900+14 produced enhanced ionization at ionospheric altitudes of 30 to 90 km, which was observed as unusually large amplitude and phase changes of very low frequency (VLF) signals propagating in the Earth-ionosphere waveguide.
Abstract: A gigantic periodic flare from the soft γ repeater SGR 1900+14 produced enhanced ionization at ionospheric altitudes of 30 to 90 km, which was observed as unusually large amplitude and phase changes of very low frequency (VLF) signals propagating in the Earth-ionosphere waveguide. The VLF signals remained perturbed for ∼5 min and exhibited the 5.16 s periodicity of the giant flare detected on the Ulysses spacecraft [Hurley et al., 1999]. Quantitative analysis indicates the presence of an intense initial low energy (3–10 keV) photon component that was not detectable by the Ulysses instrument.
TL;DR: In this paper, the authors presented a spin chronology of the pulsar using additional GINGA, ASCA, XTE, and SAX datasets spanning over a decade.
Abstract: In previous papers, we presented the discovery of a 12-s X-ray pulsar in the supernova remnant Kes 73, providing the first direct evidence for an ultramagnetized neutron star, a magnetar, with an equivalent dipole field of nearly twenty times the quantum critical magnetic field. Our conclusions were based on two epochs of measurement of the spin, along with an age estimate of the host supernova remnant. Herein, we present a spin chronology of the pulsar using additional GINGA, ASCA, XTE, & SAX datasets spanning over a decade. Timing and spectral analysis confirms our initial results and severely limit an accretion origin for the observed flux. Over the 10 year baseline, the pulsar is found to undergo a rapid, constant spindown, while maintaining a steady flux and an invariant pulse profile. Within the measurement uncertainties, no systematic departures from a linear spin-down are found - departures as in the case of glitches or simply stochastic fluctuations in the pulse times-of-arrival (e.g. red timing noise). We suggest that this pulsar is akin to the soft gamma-ray repeaters, however, it is remarkably stable and has yet to display similar outbursts; future gamma-ray activity from this object is likely.
TL;DR: In this paper, the influence of strong magnetic fields on the properties and internal structure of magnetized neutron stars (magnetars) was investigated and properties of a degenerate equilibrium ideal neutron-proton-electron (npe) gas with and without the effects of the anomalous nucleon magnetic moments in a magnetic field.
Abstract: Neutron stars with very strong surface magnetic fields have been suggested as the site for the origin of observed soft gamma repeaters (SGRs). In this paper we investigate the influence of such strong magnetic fields on the properties and internal structure of these magnetized neutron stars (magnetars). We study properties of a degenerate equilibrium ideal neutron-proton-electron (npe) gas with and without the effects of the anomalous nucleon magnetic moments in a magnetic field. The presence of a sufficiently strong magnetic field changes the ratio of protons to neutrons as well as the neutron drip density. We also study the appearance of muons as well as pion condensation in strong magnetic fields. We discuss the possibility that boson condensation in the interior of magnetars might be a source of SGRs.
TL;DR: In this paper, the authors report on very large array observations in the direction of the recently-discovered slow X-ray pulsar AX J1845-0258.1 and find a 5-arcmin shell of radio emission; the shell is linearly polarized with a non-thermal spectral index.
Abstract: We report on Very Large Array observations in the direction of the recently-discovered slow X-ray pulsar AX J1845-0258. In the resulting images, we find a 5-arcmin shell of radio emission; the shell is linearly polarized with a non-thermal spectral index. We class this source as a previously unidentified, young (< 8000 yr), supernova remnant (SNR), G29.6+0.1, which we propose is physically associated with AX J1845-0258. The young age of G29.6+0.1 is then consistent with the interpretation that anomalous X-ray pulsars (AXPs) are isolated, highly magnetized neutron stars ("magnetars"). Three of the six known AXPs can now be associated with SNRs; we conclude that AXPs are young (~<10 000 yr) objects, and that they are produced in at least 5% of core-collapse supernovae.
TL;DR: The spin evolution of the binary X-ray pulsar 2S 0114+650 is investigated and results present support for magnetic field decay predicted by the magnetar model.
Abstract: We investigate the spin evolution of the binary X-ray pulsar 2S 0114+650, which possesses the slowest known spin period: ~2.7 hr. We argue that, to interpret such a long spin period, the magnetic field strength of this pulsar must be initially 1014 G; that is, it was born as a magnetar. Since the pulsar currently has a normal magnetic field of ~1012 G, our results present support for magnetic field decay predicted by the magnetar model.
TL;DR: In 1998 June-July, the Konus-Wind burst spectrometer observed a series of bursts from the new soft gamma repeater SGR 1627-41 as discussed by the authors.
Abstract: In 1998 June-July, the Konus-Wind burst spectrometer observed a series of bursts from the new soft gamma repeater SGR 1627-41. Time histories and energy spectra of the bursts have been studied, revealing fluences and peak fluxes in the ranges 3 × 10-7 to 7.5 × 10-6 ergs cm-2 and 10-5 to 10-4 ergs cm-2 s-1, respectively. One event, 18 June 6153.5 s UT, stands out dramatically from this series. Its fluence is ~7 × 10-4 ergs cm-2, and its peak flux is ~2 × 10-2 ergs cm-2 s-1. These values from a source at a distance of 5.8 kpc yield an energy output of ~3 × 1042 ergs and a maximum luminosity of ~8 × 1043 ergs s-1 for isotropic emission, similar to the values for the famous 1979 March 5 and 1998 August 27 events. In terms of energy, this event is another giant outburst seen in a third soft gamma repeater! However, this very energetic burst differs significantly from the other giant outbursts. It exhibits no separate initial pulse with a fast rise time, no extended tail, and no pulsations. It is rather similar to ordinary repeated bursts, but is a few hundred times stronger in intensity. According to the magnetar model by Thompson & Duncan, such a burst may be initiated by a strong starquake when a crust fracture propagates over the whole surface of a neutron star.
TL;DR: In this article, the Konus-Wind burst spectrometer observed a series of bursts from the new soft gamma repeater SGR1627-41.5sUT.
Abstract: In June-July,1998 the Konus-Wind burst spectrometer observed a series of bursts from the new soft gamma repeater SGR1627-41. Time histories and energy spectra of the bursts have been studied, revealing fluences and peak fluxes in the ranges of 3x10^{-7} - 7.5x10^{-6} erg cm^{-2} and 10^{-5} - 10^{-4}erg cm^{-2}/s respectively. One event, 18 June 6153.5sUT stands out dramatically from this series. Its fluence is ~7x10^{-4} erg cm^{-2} and peak flux ~2x10^{-2} erg cm^{-2}/s. These values from a source at a distance of 5.8 kpc yield an energy output of ~3x10^{42}erg and maximum luminosity of ~8x10^{43} erg/s, similar to the values for the famous March 5, 1979 and August27,1998 events. In terms of energy, this event is another giant outburst seen in a third SGR! However, this very energetic burst differs significantly from the other giant outbursts. It exhibits no separate initial pulse with a fast rise time, no extended tail, and no pulsations. It is rather similar to ordinary repeated bursts but is a few hundred times stronger in intensity. According to the magnetar model by Thompson and Duncan (1995) such a burst may be initiated by a strong starquake when a crust fracture propagates over the whole surface of a neutron star.
TL;DR: The Rossi X-Ray Timing Explorer observations of the soft gamma-ray repeater SGR 1900+14 taken 1996 September 4-18, nearly 2 yr before the 1998 active period of the source are consistent with the mean of (6.126 ± 0.006) × 10-11 s s-1 measured during the 2 week observation as mentioned in this paper.
Abstract: We present Rossi X-Ray Timing Explorer observations of the soft gamma-ray repeater SGR 1900+14 taken 1996 September 4-18, nearly 2 yr before the 1998 active period of the source. The pulsar period (P) of 5.1558199 ± 0.0000029 s and period derivative () of (6.0 ± 1.0) × 10-11 s s-1 measured during the 2 week observation are consistent with the mean of (6.126 ± 0.006) × 10-11 s s-1 over the time up to the commencement of the active period. This is less than half that of (12.77 ± 0.01) × 10-11 s s-1 observed during and after the active period. If magnetic dipole radiation were the primary cause of the pulsar spin-down, the implied neutron star magnetic field would exceed the critical field of ≈4.4 × 1013 G by more than an order of magnitude, and such field estimates for this and other soft gamma repeaters (SGRs) have been offered as evidence that the SGRs are magnetars, in which the neutron star magnetic energy exceeds the rotational energy. The observed doubling of , however, would suggest that the pulsar magnetic field energy increased by more than 100% as the source entered an active phase, which seems very hard to reconcile with models in which the SGR bursts are powered by the release of magnetic energy. Because of this, we suggest that the spin-down of SGR 1900+14 is not driven by magnetic dipole radiation, but by some other process, most likely a relativistic wind. The , therefore, does not provide a measure of the pulsar magnetic field strength, nor evidence for a magnetar.
TL;DR: The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a period of 5.1589715(8) s from the known X-ray source of RX J190714 as discussed by the authors.
Abstract: The Advanced Satellite for Cosmology and Astrophysics (ASCA) observed the soft gamma repeater SGR 1900+14 on 1998 April 30-May 1 and discovered a pulsar with a period of 5.1589715(8) s from the known X-ray source of RX J190714.2+0919.3. Four months later, on September 16-17, ASCA observed SGR 1900+14 again just after the giant burst on 1998 August 27. Comparing the observations in September with those in April, there are several changes in characteristics. The pulse period changed to 5.160295(3) s, and thus the long-term period derivative is 1.1 × 10-10 s s-1. This strongly supports a magnetar model. The folded pulse profile in 2-10 keV largely changed from three peaks in April to one simple peak, while the steady intensity increased by a factor of 2. Finally, we successfully determined the accurate location of SGR 1900+14 by the bursts with an accuracy of 15 in diameter.
TL;DR: In this paper, the authors present RXTE observations of the soft gamma-ray repeater SGR 1900+14 taken September 4-18, 1996, nearly 2 years before the 1998 active period of the source.
Abstract: We present RXTE observations of the soft gamma--ray repeater SGR 1900+14 taken September 4-18, 1996, nearly 2 years before the 1998 active period of the source. The pulsar period (P) of 5.1558199 +/- 0.0000029 s and period derivative (Pdot) of (6.0 +/- 1.0) X 10^-11 s/s measured during the 2-week observation are consistent with the mean Pdot of (6.126 +/- 0.006) X 10^-11 s/s over the time up to the commencement of the active period. This Pdot is less than half that of (12.77 +/- 0.01) X 10^-11 s/s observed during and after the active period. If magnetic dipole radiation were the primary cause of the pulsar spindown, the implied pulsar magnetic field would exceed the critical field of 4.4 X 10^13 G by more than an order of magnitude, and such field estimates for this and other SGRs have been offered as evidence that the SGRs are magnetars, in which the neutron star magnetic energy exceeds the rotational energy. The observed doubling of Pdot, however, would suggest that the pulsar magnetic field energy increased by more than 100% as the source entered an active phase, which seems very hard to reconcile with models in which the SGR bursts are powered by the release of magnetic energy. Because of this, we suggest that the spindown of SGR pulsars is not driven by magnetic dipole radiation, but by some other process, most likely a relativistic wind. The Pdot, therefore, does not provide a measure of the pulsar magnetic field strength, nor evidence for a magnetar.
TL;DR: In this article, the authors examined the timing history of several anomalous X-ray pulsars and found that they exhibit spin-down irregularities that are statistically similar to those of radio pulsars.
Abstract: We examine the timing history of several anomalous X-ray pulsars (AXPs), and find that they exhibit spin-down irregularities that are statistically similar to those of radio pulsars. We propose that these irregularities are simply glitches like those of radio pulsars, and fit glitching spin-down solutions to the data available for 1E 2259+586, 1E 1048.1--5937 and 4U 0142+61. The inferred magnitude of the glitches (ΔΟ) is comparable to that exhibited in radio pulsar glitching. With these results, we argue that the three AXPs that we have studied are isolated neutron stars spinning down by magnetic dipole radiation and powered by a combination of cooling, magnetic field decay and magnetospheric particle bombardment.
TL;DR: There are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution, and an interpretation of these events in the context of the magnetar model is outlined.
Abstract: We present evidence for burst emission from SGR 1900+14 with a power-law high-energy spectrum extending beyond 500 keV. Unlike previous detections of high-energy photons during bursts from soft gamma repeaters (SGRs), these emissions are not associated with extraordinarily bright flares. Not only is the emission hard, but the spectra are better fitted by D. Band's gamma-ray burst (GRB) function rather than by the traditional optically thin thermal bremsstrahlung model. We find that the spectral evolution within these hard events obeys a hardness/intensity anticorrelation. Temporally, these events are distinct from typical SGR burst emissions in that they are longer (~1 s) and have relatively smooth profiles. Despite a difference in peak luminosity of 1011 between these bursts from SGR 1900+14 and cosmological GRBs, there are striking temporal and spectral similarities between the two kinds of bursts, aside from spectral evolution. We outline an interpretation of these events in the context of the magnetar model.
TL;DR: In this paper, the locations of the SGRs with respect to their supernova remnants suggest that they are high velocity objects, and the properties of these objects are reviewed in both X-ray and gamma-ray properties.
Abstract: Four Soft Gamma Repeaters (SGRs) have now been identified with certainty, and a fifth has possibly been detected. I will review their X-ray and gamma-ray properties in both outburst and quiescence. The magnetar model accounts fairly well for the observations of SGR1806-20 and SGR1900+14, but data are still lacking for SGR1627-41 and SGR0525-66. The locations of the SGRs with respect to their supernova remnants suggest that they are high velocity objects.
TL;DR: In this paper, the early evolution of a neutron star with a very strong magnetic field was examined, and it was shown that the electrical conductivity of the core matter is a strong function of the magnetic field, therefore the evolution of magnetizedneutron stars may be different from that of ordinary radiopulsars.
Abstract: We examine the early evolution of a neutron star with a very strong magnetic ®eld(B$ 4´10 13 G) that occupies a signi®cant fraction of the core volume. The electricalconductivity of the core matter is a strong function of the magnetic ®eld, therefore theevolutionofmagnetizedneutronstars(magnetars)maywellbedifferentfromthatofordinaryradiopulsars. We consider magnetohydrodynamic processes in the core for two possiblemodels of nuclear matter, with normal and super¯uid neutrons. In the case of the normalmatter,anenhancementoftheresistivityperpendiculartothemagnetic®eldcanresultinrapid®eld decay during the early evolutionary stage. If neutrons are in the super¯uid state, we ®ndthat the Hall effect can lead to oscillatory behaviour of the magnetic ®eld. This oscillatorybehaviouris caused bythegeneration oflarge-scale helicoid modes resulting from non-linearcoupling between the different ®eld components.Key words: MHD ± stars: magnetic ®elds ± stars: neutron ± pulsars: general. 1 INTRODUCTIONThe magnetic ®elds of relatively young pulsars, as inferred fromtheirspin-downrates,lieinanarrowrange4´ 10
TL;DR: In this paper, the authors examined the predicted change of a neutron star's spin in the accretion model, and found that it is unable to account for the steady spin-down observed in anomalous X-ray pulsars.
Abstract: The nature of the 5-12 s "anomalous" X-ray pulsars (AXPs) remains a mystery. Among the models that have been proposed to explain the properties of AXPs, the most likely are (1) isolated accreting neutron stars evolved from the Thorne-Żytkow objects (TŻOs) due to complete spiral-in during the common envelope (CE) evolution of high-mass X-ray binaries (HMXBs), and (2) magnetars, which are neutron stars with ultrahigh (~1014-1015 G) surface magnetic fields. We have critically examined the predicted change of a neutron star's spin in the accretion model, and found that it is unable to account for the steady spin-down observed in AXPs. A simple analysis also shows that any accretion disk around an isolated neutron star has an extremely limited lifetime. A more promising explanation for such objects is the magnetar model.
TL;DR: In this article, a process related to the inverse of photon/plasmon decay to neutrino-antineutrino pairs was considered, where the stimulated emission of photons and plasmons by the intense flux of neutrinos and antineutrinos present during the neutrini burst of a core collapse supernova was investigated.
TL;DR: In this paper, four Soft Gamma-ray Repeaters were observed with ASCA, RXTE, and BeppoSAX in X-ray and two were already identified to a pulsar of 7.47 s and 5.16 s in period.
Abstract: Four Soft Gamma-ray Repeaters were observed with ASCA, RXTE and BeppoSAX in X-ray. Two were already identified to a pulsar of 7.47 s and 5.16 s in period. The periods and the period derivatives enable us to estimate magnetic dipole moments. These are extremely strong of almost 1015 Gauss. Shortage of the rotational energy to explain the observed luminosities and the SGR activities are naturally explained by the Magnetar model by Thompson and Duncun. A possibility to explain the classical GRBs by a giant energy release at the birth of magnetars is also mentioned.
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TL;DR: In this paper, the rotation periods of three interesting classes of neutron stars, the anomalous X-ray pulsars (AXPs), the soft gamma ray repeaters (SGRs), and the dim isolated thermal neutron stars (DTNs) were investigated.
Abstract: The similarity of rotation periods from three interesting classes of neutron stars, the anomalous X-ray pulsars (AXPs), the soft gamma ray repeaters (SGRs) and the dim isolated thermal neutron stars (DTNs) suggests a common mechanism with an asymptotic spindownphase, extending through the propeller and early accretion stages. The DTNs are interpreted as sources in the propeller stage. Their low luminosities arise from frictional heating in the neutron star. SGRs and AXPs are accreting at $\dot{M} \sim 10^{15} gm/s $. The limited range of near equilibrium periods corresponds to a limited range of mass inflow rates $\dot{M}$. For lower rates the source of mass inflow may be depleted before the asymptotic stage is reached, while sources with higher $\dot{M}$ or later ages possess circumstellar material that is optically thick to electron scattering, destroying the X-ray beaming and the modulation at the rotation period. The model works with conventional magnetic fields of 10$^{11}-10^{12}$ G, obviating the need to postulate magnetars. Frequently sampled timing observations of AXPs, SGRs and DTNs can distinguish between this explanation and the magnetar model.
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TL;DR: In this article, the magnetic fields of X-ray pulsars are estimated from the cyclotron line energy, and the results are shown to be in good correspondence with the theoretical and observational values of radiopulsars.
Abstract: Estimations of magnetic fields of neutron stars, observed as radio and X-ray pulsars, are discussed. It is shown, that theoretical and observational values for different types of radiopulsars are in good correspondence. Magnetic fields of X-ray pulsars are estimated from the cyclotron line energy. In the case of Her X-1 this estimation exceeds considerably the value of its magnetic field obtained from long term observational data related to the beam structure evolution. Another interpretation of the cyclotron feature, based on the relativistic dipole radiation mechanism, could remove this discrepancy. Observational data about soft gamma repeators and their interpretation as magnetars are analyzed.