2005ApJ...633..946K

We present the results of Chandra ACIS observations of the supernova remnant (SNR) W51C. The remnant is located in the cross section of the Sagittarius arm, and the Chandra images present a superb X-ray view of this complex region including the massive star-forming region W51B. The properties of thermal diffuse SNR emission are consistent with the results of previous studies except that an enhanced abundance of sulfur is required. It is found that the ASCA hard X-ray source CXO J192318.5+1403035, proposed to be a pulsar wind nebula, is composed of a relatively bright core surrounded by an extended (∼7.0x2.5 pc) diffuse envelope. The core contains a compact (<0.1 pc) source at the center. The X-ray spectrum of CXO J192318.5+1403035 can be fitted by a power-law emission model with Γ=1.82^+0.28_–0.29, and the implied X-ray (0.2-4.0 keV) luminosity is 5x10³³ ergs/s. The core contributes ∼20% of the total luminosity. The core-envelope structure and its spectral properties support CXO J192318.5+140305 as a pulsar-wind nebula associated with the SNR W51C. There is also enhanced radio emission coincident with the source. It is conceivable that the central compact source might harbor a pulsar. However, the large extent and the hardening of X-rays at the extreme boundaries need to be explained. We have searched for the Brγ line from the ionized gas associated with the source, but no emission was detected.