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X-ray spatial structures and spectral mapping of the supernova remnant CTB 109 (G109.1-1.0) have been obtained by a 34,000 s ROSAT PSPC observation. CTB 109 appears a partial eastern X-ray shell surrounding the X-ray-bright central pulsar 1E 2259+586. There is no X-ray shell on the western side due to the interaction with a molecular cloud. The count rates of the entire diffuse part and the pulsar are 8.13 $\pm0.02$ cts s$^{-1}$ and 1.30 $\pm$0.004 cts s $^{-1}$, respectively. Soft X-rays (E $<$ 0.5 keV) were weakly detected, in particular from a jet-like structure and the pulsar.
The spectra of the shell are well fit by a one-temperature Raymond-Smith model with a temperature range of (0.24 - 0.33) $\pm 0.05 $ keV. The jet-like structure which is between the pulsar and the shell has thermal emission with no evidence of synchrotron radiation, indicating it is probably not powered by the central pulsar. The jet requires a second, low temperature component, kT= 0.14 $\pm 0.05 $ keV. Additionally, a BBXRT observation reveals part of south shell has two temperature components of 0.26 $\pm 0.08 $ keV and 2.7$^{+1.0}_{-0.6}$ keV. The simultaneous fit of BBXRT and PSPC for the part of the south shell shows the shocked plasma has not yet reached ionization equilibrium. The best non-equilibrium fit yields the shock temperature of 5.6 $\times$ 10$^7$ K, the ionization parameter $\eta$ = n$_o^2$ E of 10$^{49}$ erg cm$^{-6}$ and the ionization timescale nt of 200 - 300 cm$^{-3}$yr, suggesting extreme departure from ionization equilibrium. The absorbing column density gradually decreases from the north to the south. The north has N$_H$=1.02 $\pm 0.1 \times 10^{22}$cm$^{-2}$ and the south has N$_H$=0.77 $\pm 0.1 \times 10^{22}$cm$^{-2}$. The average photon energy is higher in north than in south, and the hardness map (1.3-2.2 keV/0.3-1.3 keV) shows that a CO arm extending across the remnant and eastern shell are harder and the jet is softer than elsewhere. The CO arm region, where X-rays are faint, has lower absorbing column density than the surrounding jet-like structure, indicating the lack of X-rays is not due to absorption alone. It may be due to the interaction with the molecular cloud: where the shock crosses the clouds, it becomes radiative and emits less X-rays.
