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Register a new userA deep search for the optical counterpart to the anomalous X-ray pulsar 1E 2259+58.6
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F. Hulleman
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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.
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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.
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.
We have carried out a search for the optical and infrared counterpart of the Anomalous X-ray Pulsar 1E 1841-045, which is located at the center of the supernova remnant Kes73. We present the first deep optical and infrared images of the field of 1E 1841-045, as well as optical spectroscopy results that exclude the brightest objects in the error circle as possible counterparts. A few of the more reddened objects in this region can be considered as particularly interesting candidates, in consideration of the distance and absorption expected from the association with Kes73. The strong interstellar absorption in the direction of the source does not allow to completely exclude the presence of main sequence massive companions.
We report our discovery of the likely near-infrared counterpart to the anomalous X-ray pulsar (AXP) 1E1048.1-5937, using observations from the 6.5-m Baade (Magellan-I) telescope in Chile. We derived a precise position for the X-ray source using archival data from the Chandra X-Ray Observatory. This position is inconsistent with a position reported earlier from XMM-Newton, but we show that the originally reported XMM-Newton position suffered from attitude reconstruction problems. Only two of the infrared objects in a 17 arcsec x 17 arcsec field containing the target have unusual colors, and one of these has colors consistent with those of the identified counterparts of two other AXPs. The latter object is also the only source detected within the 0.6 arcsec Chandra error circle, and we identify it as the counterpart to 1E1048.1-5937. This is the first AXP counterpart detected in multiple infrared bands, with magnitudes J=21.7(3), H=20.8(3), and K=19.4(3). There is marginal evidence for spectral flattening at longer wavelengths.
The energy source of the anomalous X-ray pulsars is not well understood, hence their designation as anomalous. Unlike binary X-ray pulsars, no companions are seen, so the energy cannot be supplied by accretion of matter from a companion star. The loss of rotational energy, which powers radio pulsars, is insufficient to power AXPs. Two models are generally considered: accretion from a large disk left over from the birth process, or decay of a very strong magnetic field (10^15 G) associated with a magnetar. The lack of counterparts at other wavelengths has hampered progress in our understanding of these objects. Here, we present deep optical observations of the field around 4U 0142+61, which is the brightest AXP in X-rays. We find an object with peculiar optical colours at the position of the X-ray source, and argue that it is the optical counterpart. The optical emission is too faint to admit the presence of a large accretion disk, but may be consistent with magnetospheric emission from a magnetar.
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