SIMBAD references

The X-ray structure of Kepler's supernova remnant shows a rounded shape delineated by forward shocks. We measure proper motions of the forward shocks on overall rims of the remnant, by using archival Chandra data taken in two epochs with time difference of 6.09 yr. The proper motions of the forward shocks on the northern rim are measured to be 0.076" (±0.032" ±0.016") to 0.11" (±0.014" ±0.016")/yr, while those on the rest of the rims are measured to be 0.15" (±0.017" ±0.016") to 0.30" (±0.048" ±0.016")/yr; here the first-term errors are statistical uncertainties and the second-term errors are systematic uncertainties. Combining the best-estimated shock velocity of 1660±120 km/s measured for Balmer-dominated filaments in the northern and central portions of the remnant (Sankrit et al. (ref???)2005) with the proper motions derived for the forward shocks on the northern rim, we estimate a distance of 3.3^+1.6_–0.4 kpc to the remnant. We measure the expansion indices, m (defined as R∝t^m), to be 0.47-0.82 for most of the rims. These values are consistent with those expected in Type Ia SN explosion models, in which the ejecta and the circumstellar medium have power-law density profiles whose indices are 5-7 and 0-2, respectively. In addition, we should note the slower expansion on the northern rim than that on the southern rim. This is likely caused by the inhomogeneous circumstellar medium; the density of the circumstellar medium is higher in the north than that in the south of the remnant. The newly estimated geometric center, around which we believe the explosion point exists, is located at ∼5" offset to the north of the radio center.