Magnetar

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

Radio disappearance of the magnetar xte j1810–197 and continued x-ray timing

Abstract: We report on timing, flux density, and polarimetric observations of the transient magnetar and 5.54 s radio pulsar XTE J1810-197 using the GBT, Nancay, and Parkes radio telescopes beginning in early 2006, until its sudden disappearance as a radio source in late 2008. Repeated observations through 2016 have not detected radio pulsations again. The torque on the neutron star, as inferred from its rotation frequency derivative f-dot, decreased in an unsteady manner by a factor of 3 in the first year of radio monitoring. In contrast, during its final year as a detectable radio source, the torque decreased steadily by only 9%. The period-averaged flux density, after decreasing by a factor of 20 during the first 10 months of radio monitoring, remained steady in the next 22 months, at an average of 0.7+/-0.3 mJy at 1.4 GHz, while still showing day-to-day fluctuations by factors of a few. There is evidence that during this last phase of radio activity the magnetar had a steep radio spectrum, in contrast to earlier behavior. There was no secular decrease that presaged its radio demise. During this time the pulse profile continued to display large variations, and polarimetry indicates that the magnetic geometry remained consistent with that of earlier times. We supplement these results with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the first 4 years, XTE J1810-197 experienced non-monotonic excursions in f-dot by at least a factor of 8. But since 2007, its f-dot has remained relatively stable near its minimum observed value. The only apparent event in the X-ray record that is possibly contemporaneous with the radio shut-down is a decrease of ~20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However, the permanence of the high-amplitude, thermal X-ray pulse, even after the radio demise, implies continuing magnetar activity.

Radio spectrum of the AXP J1810 197 and of its profile components

Abstract: As part of a European Pulsar Network (EPN) multitelescope observing campaign, we performed simultaneous multifrequency observations at 1.4, 4.9 and 8.4 GHz during 2006 July and quasi-simultaneous multifrequency observations from 2006 December until 2007 July at 2.7, 4.9, 8.4, 14.6 and 32 GHz, in order to obtain flux density measurements and spectral features of the 5.5 s radio-emitting magnetar AXP J1810−197. We monitored the spectral evolution of its pulse shape which consists of a main pulse (MP) and an interpulse (IP). We present the flux density spectrum of the average profile and of the separate pulse components of this first-known radio-emitting transient anomalous X-ray pulsar. We observe a decrease in the flux density by a factor of 10 within 8 m and follow the disappearance of one of the two main components. Although the spectrum is generally flat, we observe large fluctuations of the spectral index with time. For that reason, we have made some measurements of modulation indices for individual pulses in order to investigate the origin of these fluctuations.

Are gravitational waves from giant magnetar flares observable

Abstract: Are giant flares in magnetars viable sources of gravitational radiation? Few theoretical studies have been concerned with this problem, with the small number using either highly idealized models or assuming a magnetic field orders of magnitude beyond what is supported by observations We perform nonlinear general-relativistic magnetohydrodynamics simulations of large-scale hydromagnetic instabilities in magnetar models We utilise these models to find gravitational wave emissions over a wide range of energies, from 10^40 to 10^47 erg This allows us to derive a systematic relationship between the surface field strength and the gravitational wave strain, which we find to be highly nonlinear In particular, for typical magnetar fields of a few times 10^15 G, we conclude that a direct observation of f-modes excited by global magnetic field reconfigurations is unlikely with present or near-future gravitational wave observatories, though we also discuss the possibility that modes in a low-frequency band up to 100 Hz could be sufficiently excited to be relevant for observation

The X-Ray Polarization Signature of Quiescent Magnetars: Effect of Magnetospheric Scattering and Vacuum Polarization

Abstract: In the magnetar model, the quiescent non-thermal soft X-ray emission from anomalous X-ray pulsars and soft gamma repeaters is thought to arise from resonant Comptonization of thermal photons by charges moving in a twisted magnetosphere. Robust inference of physical quantities from observations is difficult, because the process depends strongly on geometry, and current understanding of the magnetosphere is not very deep. The polarization of soft X-ray photons is an independent source of information, and its magnetospheric imprint remains only partially explored. In this paper, we calculate how resonant cyclotron scattering would modify the observed polarization signal relative to the surface emission, using a multidimensional Monte Carlo radiative transfer code that accounts for the gradual coupling of polarization eigenmodes as photons leave the magnetosphere. We employ a globally twisted, self-similar, force-free magnetosphere with a power-law momentum distribution, assume a blackbody spectrum for the seed photons, account for general relativistic light deflection close to the star, and assume that vacuum polarization dominates the dielectric properties of the magnetosphere. The latter is a good approximation if the pair multiplicity is not much larger than unity. Phase-averaged polarimetry is able to provide a clear signature of the magnetospheric reprocessing of thermal photons and to constrain mechanisms generating the thermal emission. Phase-resolved polarimetry, in addition, can characterize the spatial extent and magnitude of the magnetospheric twist angle at ~100 stellar radii, and discern between uni- or bidirectional particle energy distributions, almost independently of every other parameter in the system. We discuss prospects for detectability with the Gravity and Extreme Magnetism (GEMS) mission.

X-ray Observations of a New Unusual Magnetar Swift J1834.9-0846

Abstract: We present X-ray observations of the new transient magnetar Swift J1834.9-0846, discovered with Swift BAT on 2011 August 7. The data were obtained with Swift, RXTE, CXO, and XMM-Newton both before and after the outburst. Timing analysis reveals singe peak pulsations with a period of 2.4823 s and an unusually high pulsed fraction, 85+/-10%. Using the RXTE and CXO data, we estimated the period derivative, dot{P}=8\times 10^{-12} s/s, and confirmed the high magnetic field of the source, B=1.4\times 10^{14} G. The decay of the persistent X-ray flux, spanning 48 days, is consistent with a power law, t^{-0.5}. In the CXO/ACIS image, we find that the highly absorbed point source is surrounded by extended emission, which most likely is a dust scattering halo. Swift J1834.9-0846 is located near the center of the radio supernova remnant W41 and TeV source HESS J1834-087. An association with W41 would imply a source distance of about 4 kpc; however, any relation to the HESS source remains unclear, given the presence of several other candidate counterparts for the latter source in the field. Our search for an IR counterpart of Swift J1834.9-0846 revealed no source down to K_s=19.5 within the 0.6' CXO error circle.