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Register a new userChandra Observations of the Anomalous X-ray Pulsar 1E 2259+58.6
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We present X-ray imaging, timing, and phase resolved spectroscopy of the anomalous X-ray pulsar 1E 2259+58.6 using the Chandra X-ray Observatory. The spectrum is well described by a power law plus blackbody model with power law index = 3.6(1), kT_BB = 0.412(6) keV, and N_H=0.93(3) x 10^{22} cm^{-2}; we find no evidence for spectral features (0.5-7.0 keV). We derive a new, precise X-ray position for the source and determine its spin period, P=6.978977(24) s. Time resolved X-ray spectra show no significant variation as a function of pulse phase. We have detected excess emission beyond 4 arcsec from the central source extending to beyond 100 arcsec, due to the supernova remnant and possibly dust scattering from the interstellar medium.
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We present Keck R and I band images of the field of the anomalous X-ray pulsar 1E 2259+58.6. We derive an improved X-ray position from archival ROSAT HRI observations by correcting for systematic (boresight) errors. Within the corresponding error circle, no object is found on the Keck images, down to limiting magnitudes R = 25.7 and I = 24.3. We discuss the constraints imposed by these limits, and conclude that it is unlikely that 1E 2259+58.6 is powered by accretion from a disk, irrespective of whether it is in a binary or not, unless the binary is extremely compact.
We present an analysis of five X-ray Multi-Mirror Mission (XMM) observations of the anomalous X-ray pulsar (AXP) 1E 2259+586 taken in 2004 and 2005 during its relaxation following its 2002 outburst. We compare these data with those of five previous XMM observations taken in 2002 and 2003, and find the observed flux decay is well described by a power-law of index -0.69+/-0.03. As of mid-2005, the source may still have been brighter than preoutburst, and was certainly hotter. We find a strong correlation between hardness and flux, as seen in other AXP outbursts. We discuss the implications of these results for the magnetar model.
We present the results of a near-infrared monitoring program of the Anomalous X-ray Pulsar 1E 2259+586, performed at the Gemini Observatory. This program began three days after the pulsars 2002 June outburst, and spans ~1.5 years. We find that after an initial increase associated with the outburst, the near-infrared flux decreased continually and reached the pre-burst quiescent level after about one year. We compare both the near-infrared flux enhancement and its decay to those of the X-ray afterglow, and find them to be remarkably consistent. Fitting simple power laws to the RXTE pulsed flux and near-infrared data for t>1 day post-burst, we find the following decay indices: alpha=-0.21+/-0.01 (X-ray), alpha=-0.21+/-0.02 (near-infrared), where flux is a function of time such that F is proportional to t^alpha. This suggests that the enhanced infrared and X-ray fluxes have a physical link post-outburst, most likely from the neutron-star magnetosphere.
We present near-infrared and optical observations of the field of the Anomalous X-ray Pulsar 1E 2259+58.6 taken with the Keck telescope. We derive a subarcsecond Chandra position and tie it to our optical reference frame using other stars in the field. We find a very faint source, Ks = 21.7pm0.2 mag, with a position coincident with the Chandra position. We argue that this is the counterpart. In the J, I, and R bands, we derive (2 sigma) limits of 23.8, 25.6 and 26.4 mag, respectively. As with 4U 0142+61, for which a counterpart has previously been found, our results are inconsistent with models in which the source is powered by accretion from a disk, but may be consistent with the magnetar model.
Magnetic field geometry is expected to play a fundamental role in magnetar activity. The discovery of a phase-variable absorption feature in the X-ray spectrum of SGR 0418+5729, interpreted as cyclotron resonant scattering, suggests the presence of very strong non-dipolar components in the magnetic fields of magnetars. We performed a deep XMM-Newton observation of pulsar 1E 2259+586, to search for spectral features due to intense local magnetic fields. In the phase-averaged X-ray spectrum, we found evidence for a broad absorption feature at very low energy (0.7 keV). If the feature is intrinsic to the source, it might be due to resonant scattering/absorption by protons close to star surface. The line energy implies a magnetic field of ~ 10^14 G, roughly similar to the spin-down measure, ~ 6x10^13 G. Examination of the X-ray phase-energy diagram shows evidence for a further absorption feature, the energy of which strongly depends on the rotational phase (E >~ 1 keV ). Unlike similar features detected in other magnetar sources, notably SGR 0418+5729, it is too shallow and limited to a small phase interval to be modeled with a narrow phase-variable cyclotron absorption line. A detailed phase-resolved spectral analysis reveals significant phase-dependent variability in the continuum, especially above 2 keV. We conclude that all the variability with phase in 1E 2259+586 can be attributed to changes in the continuum properties which appear consistent with the predictions of the Resonant Compton Scattering model.
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