Updated imaging and photometric results from Chandra observations of SN 1987A, covering the last 16 years, are presented. We find that the 0.5-2 keV light curve has remained constant at ∼8 × 10 −12 erg s −1 cm −2 since 9500 days, with the 3-8 keV light curve continuing to increase until at least 10000 days. The expansion rate of the ring is found to be energy dependent, such that after day 6000 the ring expands faster in the 2-10 keV band than it does at energies < 2 keV. Images show a reversal of the east-west asymmetry between 7000 and 8000 days after the explosion. The latest images suggest the southeastern side of the equatorial ring is beginning to fade. Consistent with the latest optical and infrared results, our Chandra analysis indicates the blast wave is now leaving the dense equatorial ring, which marks the beginning of a major change in the evolutionary phase of the supernova remnant 1987A.

We report on the results of our monitoring program of the remnant of SN 1987A with the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-ray Observatory. Two new observations have been performed in AO2, bringing the total to four monitoring observations over the past two years. Over this time period, new techniques for correction of "Charge Transfer Inefficiency (CTI)" and for use of charge spreading to provide angular resolution somewhat better than the pixel size of the CCD detector have become available at Penn State. We have processed all four observations using sub-pixel resolution to obtain the highest possible angular resolution, and using our CTI correction software to provide more reliable spectral analysis and flux estimations.The high angular resolution images indicate that the X-ray bright knots are convincingly correlated with the optical spots, primarily at ∼ <1 keV, while higher energy photons are very well correlated with radio images. Our data also provide marginal evidence for radial expansion of the X-ray remnant at a rate of 5200 ± 2100 km s −1 . The X-ray flux appears to linearly increase by ∼60% over the 18 month period of these observations. The spectrum is dominated by broad complexes of atomic emission lines and can be fit with a simple model of a planeparallel shock with electron temperatures of kT ∼ 2 − 4 keV and a postshock electron density of n e ∼ 210 − 420 cm −3 . The implied 0.5 − 10 keV band luminosity in 2001 April is ∼1.3 × 10 35 ergs s −1 ; as of that date, we still observe no direct evidence for the central point source, with an upper limit on the observed luminosity of L X ∼ 5.5 × 10 33 ergs s −1 in the 2 − 10 keV band.

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 ( f X $ 6 ; 10 À13 ergs cm À2 s À1 ) 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 (n e $ 235 cm À3 for the fast shock and n e $ 7500 cm À3 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 (L X 1:5 ; 10 34 ergs s À1 ) in the 2-10 keV band. The X-ray remnant continues to expand linearly at a rate of 4167 km s À1 .

We present an extended analysis of the deep Chandra LETG and HETG observations of the supernova remnant 1987A ( SNR 1987A ) carried out in 2007. The global fits to the grating spectra show that the temperature of the X-ray emitting plasma in the slower shocks in this system has remained stable for the last three years, while that in the faster shocks has decreased. This temperature evolution is confirmed by the first light curves of strong X-ray emission lines and their ratios. On the other hand, bulk gas velocities inferred from the X-ray line profiles are too low to account for the post-shock plasma temperatures inferred from spectral fits. This suggests that the X-ray emission comes from gas that has been shocked twice, first by the blast wave and again by shocks reflected from the inner ring of SNR 1987A . A new model that takes these considerations into account gives support to this physical picture.