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Register a new userModeling the broadband persistent emission of magnetars
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In this paper, we discuss our first attempts to model the broadband persistent emission of magnetars within a self consistent, physical scenario. We present the predictions of a synthetic model that we calculated with a new Monte Carlo 3-D radiative code. The basic idea is that soft thermal photons (e.g. emitted by the star surface) can experience resonant cyclotron upscattering by a population of relativistic electrons threated in the twisted magnetosphere. Our code is specifically tailored to work in the ultra-magnetized regime; polarization and QED effects are consistently accounted for, as well different configurations for the magnetosphere. We discuss the predicted spectral properties in the 0.1-1000 keV range, the polarization properties, and we present the model application to a sample of magnetars soft X-ray spectra.
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Emission mechanism of the magnetars is still controversial while various observational and theoretical studies have been made. In order to investigate mechanisms of both the persistent X-ray emission and the burst emission of the magnetars, we have proposed a model that the persistent X-ray emission consists of numerous micro-bursts of various sizes. If this model is correct, intensity Root Mean Square (RMS) variations of the persistent emission exceed the values expected from the Poisson distribution. Using $Suzaku$ archive data of 11 magnetars (22 observations), the RMS intensity variations were calculated from 0.2 keV to 70 keV. As a result, we found significant excess RMS intensity variations from all the 11 magnetars. We suppose that numerous mircro-bursts constituting the persistent X-ray emission cause the observed variations, suggesting that the persistent X-ray emission and the burst emission have identical emission mechanisms. In addition, we found that the RMS intensity variations clearly increase toward higher energy bands for 4 magnetars (6 observations). The energy dependent RMS intensity variations imply that the soft thermal component and the hard X-ray component are emitted from different regions far apart from each other.
We report on radio observations of five magnetars and two magnetar candidates carried out at 1950 MHz with the Green Bank Telescope in 2006-2007. The data from these observations were searched for periodic emission and bright single pulses. Also, monitoring observations of magnetar 4U0142+61 following its 2006 X-ray bursts were obtained. No radio emission was detected was detected for any of our targets. The non-detections allow us to place luminosity upper limits (at 1950 MHz) of approximately L < 1.60 mJy kpc^2 for periodic emission and L < 7.6 Jy kpc^2 for single pulse emission. These are the most stringent limits yet for the magnetars observed. The resulting luminosity upper limits together with previous results are discussed, as is the importance of further radio observations of radio-loud and radio-quiet magnetars.
In this paper the current status of high-energy research on the hard X-ray characteristics of the persistent emission from magnetars is reviewed. Focus is put on recent intriguing results for 1RXS J1708-40, from phase resolved spectral analysis over a 2 decades wide energy band (~3-300 keV) combining contemporaneous RXTE, XMM and INTEGRAL data. For 1E 1841-045 and SGR 1806-10 we also present updated results. The perspective for future MAXI observations for this source class is also addressed.
Magnetars are young and highly magnetized neutron stars which display a wide array of X-ray activity including short bursts, large outbursts, giant flares and quasi-periodic oscillations, often coupled with interesting timing behavior including enhanced spin-down, glitches and anti-glitches. The bulk of this activity is explained by the evolution and decay of an ultrastrong magnetic field, stressing and breaking the neutron star crust, which in turn drives twists of the external magnetosphere and powerful magnetospheric currents. The population of detected magnetars has grown to about 30 objects and shows unambiguous phenomenological connection with very highly magnetized radio pulsars. Recent progress in magnetar theory includes explanation of the hard X-ray component in the magnetar spectrum and development of surface heating models, explaining the sources remarkable radiative output.
We represent noise strength analysis of Anomalous X-Ray Pulsars (AXPs) 4U 0142+61, 1RXS J170849.9-400910, 1E 1841-045, 1E 2259+586 and Soft Gamma Repeaters (SGRs) SGR J1833-0832, SWIFT J1822.3-1606 and SWIFT J1834.9-0846 together with the X-Ray binaries GX 1+4 and 4U 1907+09 for comparison with accreting sources. Using our timing solutions, we extracted residuals of pulse arrival times after removal of spin down trends and we calculated assoicated noise strength of each source. Our preliminary results indicate that the noise strength is scaling up with spin-down rate. This indicates that, increase in spin-down rate leads to more torque noise on the magnetars. In addition, we present our analysis with Bayesian statistics on the previously reported transient QPO feature of 4U 1907+09.
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