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تسجيل مستخدم جديدPhase-Resolved Spectroscopy of the Magnetar SGR J1745-2900 Based on Data from the NuSTAR Observatory
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The magnetar SGR J1745-2900 located in the vicinity of the supermassive black hole Sgr A$^{star}$ was detected during its X-ray outburst with the Swifht/XRT telescope in April 2013. For several months after its detection the source was observed with the NuSTAR observatory, which allowed pulsations with a period $sim3.76$ s to be recorded. Using these observations, we have studied in detail the dependence of the pulse profile and the pulsed fraction on the energy and intensity of the magnetar. The pulsed fraction in the 3-5 and 5-10 keV energy bands is shown to be 40-50%, slightly increasing with decreasing flux. We have performed phase-resolved spectroscopy for the source in the energy band from 3 to $sim$40 keV and show that the temperature of the emitting regions remains fairly stable during the pulse, while their apparent size changes significantly with phase.
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We present radio continuum light curves of the magnetar SGR J1745$-$2900 and Sgr A* obtained with multi-frequency, multi-epoch Very Large Array observations between 2012 and 2014. During this period, a powerful X-ray outburst from SGR J1745$-$2900 oc
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We present the X-ray timing and spectral evolution of the Galactic Center magnetar SGR J1745-2900 for the first ~4 months post-discovery using data obtained with the Nuclear Spectroscopic Telescope Array (NuSTAR)} and Swift observatories. Our timing
analysis reveals a large increase in the magnetar spin-down rate by a factor of 2.60 +/- 0.07 over our data span. We further show that the change in spin evolution was likely coincident with a bright X-ray burst observed in 2013 June by Swift, and if so, there was no accompanying discontinuity in the frequency. We find that the source 3-10 keV flux has declined monotonically by a factor of ~2 over an 80-day period post-outburst accompanied by a ~20% decrease in the sources blackbody temperature, although there is evidence for both flux and kT having levelled off. We argue that the torque variations are likely to be magnetospheric in nature and will dominate over any dynamical signatures of orbital motion around Sgr A*.
We report on simultaneous observations of the magnetar SGR J1745-2900 at frequencies $ u = 2.54$ to $225,rm{GHz}$ using the Nancay 94-m equivalent, Effelsberg 100-m, and IRAM 30-m radio telescopes. We detect SGR J1745-2900 up to 225 GHz, the highest
radio frequency detection of pulsed emission from a neutron star to date. Strong single pulses are also observed from 4.85 up to 154 GHz. At the millimetre band we see significant flux density and spectral index variabilities on time scales of tens of minutes, plus variability between days at all frequencies. Additionally, SGR J1745-2900 was observed at a different epoch at frequencies 296 to 472 GHz using the APEX 12-m radio telescope, with no detections. Over the period MJD 56859.83-56862.93 the fitted spectrum yields a spectral index of $left<alpharight> = -0.4 pm 0.1$ for a reference flux density $left< S_{154} right> = 1.1 pm 0.2rm{,mJy}$ (with $S_{ u} propto { u}^{alpha})$, a flat spectrum alike those of the other radio-loud magnetars. These results show that strongly magnetized neutron stars can be effective radio emitters at frequencies notably higher to what was previously known and that pulsar searches in the Galactic Centre are possible in the millimetre band.
In Torne et al. (2015), we showed detections of SGR J1745-2900 up to 225 GHz (1.33 mm); at that time the highest radio frequency detection of pulsar emission. In this work, we present the results of new observations of the same magnetar with detectio
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We report on 3.5 years of Chandra monitoring of the Galactic Centre magnetar SGR J1745-2900 since its outburst onset in April 2013. The magnetar spin-down has shown at least two episodes of period derivative increases so far, and it has slowed down r
egularly in the past year or so. We observed a slightly increasing trend in the time evolution of the pulsed fraction, up to about 55 per cent in the most recent observations. SGR J1745-2900 has not reached the quiescent level yet, and so far the overall outburst evolution can be interpreted in terms of a cooling hot region on the star surface. We discuss possible scenarios, showing in particular how the presence of a shrinking hot spot in this source is hardly reconcilable with internal crustal cooling and favors the untwisting bundle model for this outburst. Moreover, we also show how the emission from a single uniform hot spot is incompatible with the observed pulsed fraction evolution for any pair of viewing angles, suggesting an anisotropic emission pattern.
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