The Distances of SNRs Kes 69 and G21.5-0.9 from HI and 13CO Spectra

TL;DR

This study refines the distance estimates of supernova remnants Kes 69 and G21.5-0.9 using HI and $^{13}$CO spectra, revealing their association with specific features and a pulsar, thus improving understanding of their properties.

Contribution

The paper provides new, more accurate kinematic distances for Kes 69 and G21.5-0.9 based on HI and $^{13}$CO spectral analysis, and links Kes 69 to an OH maser and G21.5-0.9 to a pulsar.

Findings

Kes 69 distance revised to ~5.5 kpc from 11.2 kpc

G21.5-0.9 distance refined to ~4.8 kpc

Kes 69 associated with a 1720 MHz OH maser

Abstract

We obtain new HI and $^{13}$CO images around Supernova Remnants (SNR) Kes 69 and G21.5-0.9. By comparing HI spectra with $^{13}$CO emission spectra, we significantly revise the kinematic distance for Kes 69 to $\sim$ 5.5 kpc, which was 11.2 kpc, and refine the kinematic distance for G21.5-0.9 to ~4.8 kpc. For Kes 69, the highest velocity of absorption is ~86 km/s and a prominent HI emission feature at ~ 112 km/s has no respective absorption. These new results suggest that Kes 69 is associated with a newly detected extended 1720 MHz OH maser at velocity of ~85 km/s that originates from within the bright southern radio shell of Kes 69. For G21.5-0.9, the highest velocity of absorption is ~67 km/s. The HI absorption spectra of the nearby bright source PMN J1832-1035 and of Kes 69 show a common absorption feature at velocity of ~69 km/s, which is not seen for G21.5-0.9. The resulting velocity of ~68 km/s gives the best distance estimate of ~4.8 kpc for G21.5-0.9 and associated young pulsar J1833-1034.