Abstract
We present an update on the results of our monitoring observations of the X-ray remnant of supernova (SN) 1987A with Chandra. As of 2002 December, we have performed a total of seven observations of SN 1987A, which allows us to monitor the details of the earliest stage of the supernova remnant evolution in X-rays. The high angular resolution images from the latest data reveal developments of new X-ray-bright spots in the northwestern and the southwestern portions of the remnant, as well as changes on the eastern side. The observed soft X-ray flux is increasing more rapidly than ever, and the latest 0.5-2 keV band flux (fX ~ 6 × 10-13 ergs cm-2 s-1) is 4 times brighter than 3 yr earlier, when this monitoring began. The overall X-ray emission is primarily from the blast wave shock with kT ~ 2.4 keV. As the blast wave approaches the dense circumstellar material, the contribution from the decelerated slow shock (kT ~ 0.22 keV) to the observed X-ray emission is becoming significant. The increase of this slow shock contribution over the last 2 yr is particularly noticeable in the western half of the remnant. These results indicate that the shock front is now reaching the main body of the inner circumstellar ring and that SN 1987A will be a complete ring with dramatic brightening in coming years. Based on the best-fit two-shock spectral model, we derive approximate densities of the X-ray-emitting regions (ne ~ 235 cm-3 for the fast shock and ne ~ 7500 cm-3 for the slow shock). There is no direct observational evidence to date for a neutron star associated with supernova remnant 1987A. We obtain an upper limit on the observed X-ray luminosity of any embedded point source (LX ≤ 1.5 × 1034 ergs s-1) in the 2-10 keV band. The X-ray remnant continues to expand linearly at a rate of 4167 km s-1.
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