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bluecrab The Crab Nebula is the archetypal filled-center supernova remnant,or plerion. A central pulsar presumably powers each filled-center supernova remnant. Thus, the inner nebula of a plerion is particularly interesting, since it is the site of conversion of pulsar-supplied energy into synchrotron-emitting electrons.

The Chandra X-Ray Observatory first observed the Crab Nebula and pulsar during orbital calibration. Zeroth-order images with the High-Energy Transmission Grating (HETG) readout by the Advanced CCD Imaging Spectrometer spectroscopy array (ACIS-S) show a striking richness of X-ray structure at a resolution comparable to that of the best ground-based visible-light observations. The HETG-ACIS-S images (Below) reveal, for the first time, an X-ray inner ring within the X-ray torus, the suggestion of a hollow-tube structure for the torus, and X-ray knots along the inner ring and perhaps along the inward extension of the X-ray jet. Spectrometric analysis shows systematic variations of the X-ray spectrum throughout the nebula. These observations are described in detail in this paper.


Detailed studies with the Hubble Space Telescope (HST above left) illustrate the rich structure of the Crab Nebula's synchrotron emission, on scales down to 0.2 arcseconds. These are also evident in the X-ray image shown on the same scale at right. Especilly intriguing are the structures of the inner nebula near the pulsar--wisps, knots, and fibrous texture--which exhibit cylindrical symmetry. HST observations also show that wisps form and dissipate over a few weeks while moving outward at about 0.5c. (See links below)

Within the center of the Crab Nebula is, of course, the Crab Pulsar.The Crab pulsar (P = 33.5 ms) is the best studied, young (t = 10³ yr) rotation-powered pulsar. We obtained phase-resolved observations of the Crab pulsar using the Chandra X-Ray Observtory to determine its pulse profile and to search for thermal emission from the underlying neutron star. Due to the high surface brightness of the nebula, Chandra's unprecedented angular resolution (<1") is essential for achieving the required sensitivity.
We obtained two observations of the Crab Nebula and Pulsar, utilizing the Chandra Low-Energy Transimission Grating Spectrometer(LETGS)--the LETG with the High-Resolution Camera Spectroscopy (HRC-S) detector. The observations acquired 100 and 50 ks of data on 2000 January 31 and February 2, respectively. The details of these observations are described in this paper.

X-ray pulse profiles of the Crab pulsar (Figure above to the right), in 250 phase bins. The top panel diplays the ROSAT HRI observation, with the spline fitted to the data. The middle panel shows the Chandra simulation for 2 ms filter, compared to ROSAT-derived template with adjusted phase, DC offset, and normalization. The bottom panel gives actual Chandra data from ObsID 758, after application of a 2 ms filter, compared with a ROSAT derived template with adjusted phase, DC offset, and normalization. The Chandra-measured, 2 ms-filtered profile (bottom panel of figure above right) shows significant flux at pulse minimum. This discovery is even more manifest in the image itself (below).
The figure below Shows the 2 ms-filtered, LETGS zeroth-order image at pulse maximum and at pulse minimum.
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