Is the Cygnus Loop two supernova remnants?

Abstract

Abstract. The Cygnus Loop is classified as a middle-aged supernova remnant (SNR) located below the Galactic equator ( = 74• , b = −8.• 6) and 770 pc away from us. Its large size and little confusion with Galactic emission makes it an ideal test ground for evolutionary and structural theories of SNRs. New radio continuum mapping of the Cygnus Loop at 2695 MHz with the Effelsberg 100-m telescope provides indications that the Cygnus Loop consists of two separate SNRs. Combining this result with data from the literature we argue that a secondary SNR exists in the south with a recently detected neutron star close to its center. Two interacting SNRs seem to be the best explanation to account for the Cygnus Loop observations at all wavelengths.

Radio emission from the Cygnus Loop and its spectral characteristics

“…There are strong evidences that the northern remnant and the most prominent filament at the upper part of this remnant are aligned with the large-scale local magnetic field in this region (Uyanıker et al 2002). The two brightest partial shells, NGC 6960 and NGC 6992, may be formed due to magnetic compression.…”

“…This seems irrelevant for the Cygnus Loop as indicated by the flux density at 22 MHz (Roger et al 1999), matching the high-frequency power law. Excessive thermal material should also significantly enhance rotation measure (RM) values; such RMs, however, are not observed (Uyanıker et al 2002, the mean value of the rotation measure is about −20 rad m −2 ). At a distance of 440 pc (Blair et al 1999), the linear size of the Cygnus Loop complex would be about 25 pc.…”

“…5 we analyze and discuss the results of the spectral analysis along with a brief theoretical background on that issue, and compare our results with previous investigations. Haslam et al (1982), b) Reich & Reich (1988), c) Reich et al (2003), d) Uyanıker et al (1998), e) Uyanıker et al (1999), f) Uyanıker et al (2002). Landecker et al (2000).…”

“…Although the Cygnus Loop is often considered as a typical shell-type supernova remnant (SNR) of medium age, its morphology deviates largely from a spherical shell. From a recent analysis of the Cygnus Loop region using sensitive 2675 MHz continuum and polarization data in conjunction with optical, X-ray and infrared data, Uyanıker et al (2002) concluded that the Cygnus Loop consists of two supernova remnants rather than being a single SNR shaped by strong inhomogeneities in the interstellar medium. The significantly polarized "break-out" region towards the south originates from one supernova remnant, which is separate but interacting with the X-ray bright big northern shell.…”

Radio and X-ray study of two multi-shell supernova remnants: Kes 79 and G352.7-0.1

“…The multi-shell morphology can also result from the proper motion of the precursor Carrera del Investigador Científico of CONICET, Argentina. massive star that may cause the star to explode far from the geometric center of its wind bubble, as proposed by Gvaramadze (2006). Alternative scenarios can be the existence of multiple shocks after the encounter of the blast wave with a density jump in the surrounding medium, or from simple projection effects either from three-dimensional structures of the same SNR or from multiple SNRs along the line of sight (as proposed by Uyanıker et al 2002, to explain the morphology of Cygnus Loop). In any case, the detailed observational study of multi-shell SNRs provides insight into evolutionary and structural theories of SNRs.…”