Distance to the SNR CTB109/AXP 1E 2259+586 by H I absorption and self-absorption

We suggest a revised distance to the supernova remnant G109.1-1.0 (CTB 109) and its associated anomalous X-ray pulsar (AXP) 1E 2259+586 by analysing 21-cm H I-line and (CO)-C-12-line spectra of CTB 109, H II 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 H I column density large enough to produce H I self-absorption (HISA) and H I 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 +/- 0.8 kpc. The new distance still leads to a normal explosion energy for CTB 109/AXP 1E 2259+586.