2014MNRAS.438.1813L

We analyse radio and X-ray observations of the supernova remnant (SNR) G18.1-0.1 and the overlapping and surrounding Hii regions. The Hi absorption spectra yield a new distance of 5.6kpc to G18.1-0.1 and confirm previous distance estimates for the surrounding Hii regions. All of the Hii regions are significantly closer (d = 2.9 to 4.1kpc) than SNR G18.1-0.1, so we conclude that they are not physically associated. Chandra archival X-ray observations of G18.1-0.1 show extended shell-type X-ray emission from the SNR. The X-ray spectrum is used to determine that the SNR is in the Sedov adiabatic expansion phase. G18.1-0.1 is ≃ 8.9pc radius, middle-aged (5 kyr), expanding in normal density interstellar medium ( ≃ 0.6/cm3) and has a low explosion energy ( ≃ 2.5x10⁵⁰ erg).