A New Distance to the Supernova Remnant DA 530 Based on HI Absorption of Polarized Emission

TL;DR

This paper introduces a new method using polarized HI absorption to accurately determine the distance to the supernova remnant DA 530, providing insights into its size and position in the galaxy.

Contribution

It presents a novel data processing technique for polarized HI absorption measurements and applies it to estimate the distance to DA 530.

Findings

Minimum distance to DA 530 is 4.4 kpc.

The SNR's diameter is approximately 34 pc.

The method can be applied to other SNRs for distance estimation.

Abstract

Supernova remnants (SNRs) are significant contributors of matter and energy to the interstellar medium. Understanding the impact and the mechanism of this contribution requires knowledge of the physical size, energy, and expansion rate of individual SNRs, which can only come if reliable distances can be obtained. We aim to determine the distance to the SNR DA 530 (G93.3+6.9), an object of low surface brightness. To achieve this, we used the Dominion Radio Astrophysical Observatory Synthesis Telescope and the National Radio Astronomy Observatory Very Large Array to observe the absorption by intervening HI of the polarized emission from DA 530. Significant absorption was detected at velocities $-28$ and -67 km/s (relative to the local standard of rest), corresponding to distances of 4.4 and 8.3 kpc, respectively. Based on the radio and X-ray characteristics of DA 530, we conclude that the minimum distance is 4.4$^{+0.4}_{-0.2}$ kpc. At this minimum distance, the diameter of the SNR is 34$^{+4}_{-1}$ pc, and the elevation above the Galactic plane is 537$^{+40}_{-32}$ pc. The $-67$ km/s absorption likely occurs in gas whose velocity is not determined by Galactic rotation. We present a new data processing method for combining Stokes $Q$ and $U$ observations of the emission from an SNR into a single HI absorption spectrum, which avoids the difficulties of the noise-bias subtraction required for the calculation of polarized intensity. The polarized absorption technique can be applied to determine distances to many more SNRs.