Distance of PSR B0458+46 indicated by <i>FAST</i> H <scp>i</scp> absorption observations
W. C. Jing, J. L. Han, Tao Hong, Chen Wang, X. Y. Gao, Legan Hou, D. J. Zhou, J. Xu, Z. L. Yang
Abstract
ABSTRACT The pulsar B0458+46 was previously believed to have a distance of about 1.3 kpc and to be associated with a nearby supernova remnant, SNR HB9 (G160.9+2.6). We observe the neutral hydrogen (H i) absorption spectrum of PSR B0458+46 by using the Five-hundred-meter Aperture Spherical radio Telescope (FAST), and detect two absorption lines at radial velocities of VLSR = −7.7 and −28.1 km s−1. Based on the Galactic rotation curve with a modification factor correcting for the systematic stream in the Galactic anticentre region, we derive the kinematic distance of the farther absorption cloud, which is found to be located $2.7^{+0.9}_{-0.8}$ kpc away, just beyond the Perseus Arm. We also obtain a direct distance estimation of the farther absorption cloud as being $2.3_{-0.7}^{+1.1}$ kpc, based on a comparison of the velocity with the H i emission in the Perseus and Outer Arms that was well-defined by recently measured parallax tracers. As a result, we conclude that PSR B0458+46 should be located beyond the Perseus Arm, with a lower limit for the distance at 2.7 kpc, and therefore not associated with SNR HB9. The doubled distance indicates a deficiency of thermal electrons in the immediate outer Galaxy, with a much less density than current models predict. Additionally, we detect a new high-velocity H i cloud in the direction of this pulsar.