A CANDIDATE NEUTRON STAR ASSOCIATED WITH GALACTIC CENTER SUPERNOVA REMNANT SAGITTARIUS A EAST

摘要

We present imaging and spectral studies of the supernova remnant (SNR) Sagittarius (Sgr) A East from deep observations with Chandra. The spatially resolved spectral analysis of Sgr A East reveals the presence of a two-temperature thermal plasma (kT ? 1 and 5 keV) near the center of the SNR. The central region is dominated by emission from highly ionized Fe-rich ejecta. We estimate a conservative upper limit to the total Fe ejecta mass of the SNR, M_(Fe) < 0.27 solar mass Comparisons with standard SN nucleosynthesis models suggest that this Fe mass limit is consistent with a Type Ⅱ SN explosion for the origin of Sgr A East. On the other hand, the soft X-ray emission extending toward the north of the SNR can be described by a single-temperature (kT ～ 1.3 keV) thermal plasma with normal chemical composition. This portion of the SNR is thus X-ray emission from the heated interstellar medium rather than the metal-rich stellar ejecta. We point out that a hard pointlike source CXOGC J174545.5-285829 (the so-called cannonball) at the northern edge of the SNR shows X-ray characteristics unusual among other Galactic center sources. The morphological, spectral, and temporal characteristics of this source suggest identification as a high-velocity neutron star. Based on the suggested Type Ⅱ origin for the SNR Sgr A East and the proximity between the two, we propose that CXOGC J174545.5-285829 is a high-velocity neutron star candidate, born from the core-collapse SN that also created the SNR Sgr A East.