The supernova remnant G78.2+2.1: New optical and X-ray observations

Abstract

New optical and X-ray observations of the supernova remnant (SNR) G78.2+2.1 are presented. CCD Hα observations with a Fabry-Perot interferometer attached to the 125-cm reflector at the Crimean Station of the Sternberg Astronomical Institute are used to obtain the radial-velocity field toward the SNR and in its vicinity. The brightness distribution and X-ray spectrum of the SNR are obtained from archival ROSAT and ASCA X-ray data. The X-ray image of G78.2+2.1 exhibits a shell structure (Δ R/R ≃0.3) and is generally similar to its radio image; a comparison with the radio map at ν=1.4 GHz constructed from archival VLA data reveals the coincidence of features on scales of several arcminutes at the eastern boundary of G78.2+2.1. Weak X-ray emission (an outer shell or a halo of size ≃2°) has been identified for the first time far outside G78.2+2.1. The X-ray emission from G78.2+2.1 is shown to characterize a young adiabatic SNR [ M X-ray ≃ 100 M ⊙ , V s ≃10 3 km s −1 , t ≃(5–6)×10 3 years], which probably expands inside the cavity swept up by the progenitor's stellar wind. Searches for the corresponding radio structure are required to elucidate the nature of the outer X-ray shell or halo.