Diffusion Ionised Gas in the Directions of the Supernova Remnant Kes 79 and Pulsar B1849+00

Abstract

Based on the spatial correlation between the distributions of diffuse ionized gas (DIG) and the HII regions in the Galaxy and using observations of the Galactic background in the H166α line found in literature, we investigated the strong inhomogeneity of the DIG in the direction of longitude 33.5° near the Galaxy plane, where objects located at close angular distances from each other have very different observable parameters due to the DIG effect. We argued the absence of a spectrum cut-off at a frequency of 30.9 MHz for the supernova remnant Kes 79 (G33.6+0.1) by the presence of an insignificant amount of ionized gas between the SNR and the observer. The large value of the pulse broadening of the pulsar B1849+00 (τpsr = 0.86 s at 1 GHz) located at an angular distance of 10 $$' $$ from the center of the Kes 79 is explained by two factors. Firstly, the HII region (G33.46+0.06) is located in the direction of the pulsar with an emission measure of about 2900 pc/cm6, which contributes less than 32% to the dispersion measure of the pulsar and provides about 50% of the pulsar pulse broadening, despite the fact that the emission measure of ionized gas located between the observer and the pulsar, is ≈6150 pc/cm6. Secondly, the largest contribution to the broadening of its pulses comes from an ionized gas located approximately halfway between the pulsar and the observer, which is consistent with the scattering theory. The supernova remnant Kes 79, which is closer to the observer than the pulsar B1849+00, does not significantly affect the radiation scattering from the pulsar and the compact extragalactic source B1849+005. The distance to the pulsar B1849+00 was found to be in the range from 9.8 to 11.5 kpc.