Proper Motion of Cygnus Loop Shock Filaments

Abstract

We determined the shock speed in the Galactic supernova remnant Cygnus Loop, using the proper motion of its optical filaments and the latest estimate of its distance. The proper motion was measured by comparing Hα images of the remnant observed in two epochs: 1993 (Kitt Peak National Observatory) and 2018/2019 (National Astronomical Observatory Rozhen and Astronomical Station Vidojevica). We derived shock speed for 35 locations along different filaments, which is twice as much as in earlier studies of the north-eastern part of the Cygnus Loop. For the first time, we have measured the shock speed of the radiative filaments in this region. Three of the analyzed locations where we measured the proper motion of filaments are radiative, based on their presence in [SII] images from the second epoch. The other filaments are non-radiative. The speed we obtained for the non-radiative filaments is in the range of 240-650 km s-1, with an estimate for the uncertainty of 70 km s-1. These values are mostly in agreement with previous studies. The radiative filaments have lower speeds of 100-160 ± 70 km s-1, which is in agreement with the assumption that they are older in evolutionary terms. This clear distinction between the speed of the two types of filaments proves that [SII] emission can be used for identifying radiative filaments in supernova remnants.