A New Determination of the Distance to Kepler’s Supernova Remnant

Abstract

Using the Very Large Array, H I observations of Kepler's supernova remnant (SN 1604, 3C 358) have been carried out with an angular resolution of approximately 15" and a velocity resolution of 1.3 km s^-1. The distance to this historical supernova remnant (SNR diameter~3') has been controversial, with estimates ranging from a few kiloparsecs to 12 kpc. Based on a weak H I absorption feature at +21.3 km s^-1 seen in the new data, a lower limit of 4.8+/-1.4 kpc can be derived. No prominent interstellar H I features are detected near Kepler's SNR, indicating that the evolution of the remnant has been influenced by the circumstellar medium, while the interstellar medium seems to have had negligible effect on the expansion process. At a velocity of +21.3 km s^-1, emission from an H I cloud to the east of the SNR is detected, which may be physically associated with the remnant of SN 1604, based on morphological considerations. An upper limit of 6.4 kpc to the distance can be derived based on the lack of H I absorption at a velocity of +50 km s^-1, where extended H I emission is detected.