We suggest a revised distance to the supernova remnant ( SNR ) G109.1-1.0 ( CTB 109 ) and its associated anomalous X-ray pulsar ( AXP ) 1E 2259+586 by analyzing 21cm HI-line and ^ { 12 } CO-line spectra of CTB 109 , HII region Sh 152 , and the adjacent molecular cloud complex .
CTB 109 has been established to be interacting with a large molecular cloud ( recession velocity at v = - 55 km s ^ { -1 } ) .
The highest radial velocities of absorption features towards CTB 109 ( - 56 km s ^ { -1 } ) and Sh 152 ( - 65 km s ^ { -1 } ) are larger than the recombination line velocity ( - 50 km s ^ { -1 } ) of Sh 152 demonstrating the velocity reversal within the Perseus arm .
The molecular cloud has cold HI column density large enough to produce HI self-absorption ( HISA ) and HI narrow self-absorption ( HINSA ) if it was at the near side of the velocity reversal .
Absence of both HISA and HINSA indicates that the cloud is at the far side of the velocity reversal within the Perseus Arm , so we obtain a distance for CTB 109 of 4 \pm 0.8 kpc .
The new distance still leads to a normal explosion energy for CTB 109/AXP 1E 2259+586 .