Is the Cygnus Loop two supernova remnants?

The Cygnus Loop is classified as a middle-aged supernova remnant (SNR) located below the Galactic equator (l=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.Comment: 4 pages, 2 figures, Astron. Astrophys., accepte

Radio emission from the Cygnus Loop and its spectral characteristics

We present a new sensitive 2675 MHz radio continuum map of the Cygnus Loop, which is used in conjunction with 408 MHz, 863 MHz and 1420 MHz maps from both the Effelsberg 100-m telescope and the DRAO Synthesis Telescope for a spectral analysis. Between 408 MHz and 2675 MHz we find an overall integrated spectral index of $\rm \alpha = -0.42 \pm 0.06$ ($S \sim \nu^{\alpha}$), close to previous results. There is no indication of a spectral break in the integrated spectrum. Spatially highly varying and rather strong spectral curvature was previously reported, but is not confirmed on the basis of new, higher sensitivity observations. We found spectral variations across the Cygnus Loop reaching up to $\Delta\alpha = 0.2$ from a TT-plot analysis. The flattest spectra are seen towards enhanced emission areas. Spectral index maps produced between different frequency pairs, as well as all four maps, revealed that there are at least three flat spectrum regions. In regions interior to the high emission filaments, we have detected at least two spectral components across the whole object with $\alpha=-0.4$ and $\alpha=-0.6$ towards northern and southern parts of the object, respectively.Comment: 22 pages, 13 figures in jpeg format, accepted for publication in Astrophysics & Astronom

The Cygnus superbubble revisited

The Orion local spiral arm is seen tangential towards the Cygnus region. Intense radio emission with quite a complex morphology is observed, which appears to be surrounded by strong soft X-ray emission. This remarkable X-ray structure is known as the Cygnus superbubble. We compare a recent 1.4 GHz radio continuum and polarization map from the Effelsberg 100-m telescope with X-ray data from the ROSAT all-sky survey of this area. Including available survey data of the infrared, H

A catalogue of Galactic supernova remnants from the Canadian Galactic plane survey

We present a new catalogue containing all known Galactic supernova remnants observed in phase I and II of the Canadian Galactic Plane Survey (65\degr \leq \ell \leq 175\degr, -5\degr \leq b \leq +7\degr). Stokes I images at 1420 MHz of 34 SNRs and at 408 MHz of 36 SNRs are displayed. From these 1\arcmin and 3\arcmin-resolution data (respectively) we determine accurate centre positions and angular dimensions. The flux densities at 1420 and 408 MHz are integrated and combined with values from the literature to define more accurate radio spectra. The CGPS polarization data at 1420 MHz were examined and significant linear polarization from 18 SNRs is found, with a modest signal from 6 others.

A 1.4 GHz radio continuum and polarization survey at medium Galactic latitudes

We present the first section of a radio continuum and polarization survey at medium Galactic latitudes carried out with the Effelsberg 100-m telescope at 1.4 GHz. Four large fields have been observed, which all together cover an area of about $1100~\Box$. The rms-sensitivity is about 15 mK TB (about 7 mJy/beam area) in total intensity and is limited by confusion. A sensitivity of 8 mK TB is obtained in linear polarization. The angular resolution of the observations is 9 l35. The maps in total intensity and linear polarization have been absolutely calibrated by low resolution data where ava ilable. Significant linear polarization is seen in all the maps. In general, the intensity fluctuations measured in linear polarization are not correlated with total intensity structures. Areas of high polarization of some degrees extent are seen, again with no apparent corresponding total intensity feature. Modulation of polarized background emission by spatially varying Faraday rotation seems the most likely explanation. Quite unexpected is the detection of filamentary and ring-like depolarization structures in the direction of the anticentre region, whose extents are up to about $3^\circ$