E. Fürst

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 Eelsberg 100-m telescope with X{ray data from the ROSAT all{sky survey of this area. Including available survey data of the infrared, H i and CO emission, we investigate a number of high latitude features, which are physically related to one of the Cygnus OB associations. These OB associations, however, are located along the local arm at dierent distances. Our results support the view that the Cygnus superbubble is not a physical unity, but results from a projection of unrelated X{ray emitting features at dierent distances blown out from the local arm seen along the line of sight.

35 cm observations of a sample of large supernova remnants

We present radio maps of ten large-diameter supernova remnants observed at 35 cm wavelength with the Eelsberg 100-m telescope. The angular resolution is 14: 5. The sources are G126.2+1.6, G127.1+0.5, HB3, HB9, S147, IC 443, Cygnus Loop, W63 and HB21. For each object we give an integrated flux density and improved spectra when necessary. We also present a map of G213.0 0.6, which we tentatively identify as a new large supernova remnant with a very low surface brightness, apparently interacting with the Hii region S284.

A Sino-German λ6 cm polarization survey of the Galactic plane - II. The region from 129° to 230° longitude

Context. Linearly polarized Galactic synchrotron emission provides valuable information about the properties of the Galactic magnetic field and the interstellar magneto-ionic medium, when Faraday rotation a long the line of sight is properly taken into account. Aims. We aim to survey the Galactic plane atλ6 cm including linear polarization. At such a short wavelength Faraday rotation effects are in general small and the Galactic magnetic field properties can be prob ed to larger distances than at long wavelengths. Methods. The Urumqi 25-m telescope is used for a sensitive λ6 cm survey in total and polarized intensities. WMAP K-band (22.8 GHz) polarization data are used to restore the absolute zero-level of the Urumqi U and Q maps by extrapolation. Results. Total intensity and polarization maps are presented for a Galactic plane reg ion of 129 ◦ ≤ l ≤ 230 ◦ and|b| ≤ 5 ◦ in the anti-centre with an angular resolution of 9. 5 and an average sensitivity of 0.6 mK and 0.4 mK TB in total and polarized intensity, respectively. We briefly discuss the properties of some extended Fara day Screens detected in theλ6 cm polarization maps. Conclusions. The Sino-Germanλ6 cm polarization survey provides new information about the properties of the magnetic ISM. The survey also adds valuable information for discrete Galactic objects and is in particular suited to detect extended Faraday Screens with large rotation measures hosting strong regular magnetic fields.

Radio spectral properties and the magnetic field of the SNR S147

Context. S147 is a large faint shell-type supernova remnant (SNR) known for its remarkable spectral break at cm-wavelength, which is an important physical property to characterize SNR evolution. However, the spectral break is based on radio observations with limited precision. Aims. New sensitive observations at high frequencies are required for a detailed study of the spectral properties and the magnetic field structure of S147. Methods. We conducted new radio continuum and polarization observations of S147 at λ11 cm and at λ6 cm with the Effelsberg 100-m telescope and the Urumqi 25-m telescope, respectively. We combined these new data with published lower-frequency data from the Effelsberg 100-m telescope, and with very high-frequency data from WMAP to investigate the spectral turnover and polarization properties of S147. Results. S147 consists of numerous filaments embedded in diffuse emission. We found that the integrated flux densities of S147 are 34.8 ± 4. 0J y atλ11 cm and 15.4 ± 3. 0J y atλ6 cm. These new measurements confirm the known spectral turnover at ∼1.5 GHz, which can be entirely attributed to the diffuse emission component. The spectral index above the turnover is α = −1.35 ± 0.20 (S ∼ ν α ). The filamentary emission component has a constant spectral index over the entire wavelength range up to 40.7 GHz of α = −0.35 ± 0.15. The weak polarized emission of S147 is at the same level as the ambient diffuse Galactic polarization. The rotation measure of the eastern filamentary shell is about −70 rad m −2 . Conclusions. The filamentary and diffuse emission components of S147 have different physical properties, which make S147 outstanding among shell type SNRs. We attribute the weak polarization of S147 at λ11 cm and at λ6 cm to a section of the S147 shell showing a tangetial magnetic field direction.

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 α = −0.42 ± 0.06 (S ∼ ν α ), 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 ∆α = 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 α = −0. 4a ndα = −0.6 towards northern and southern parts of the object, respectively.

Radio properties of the low surface brightness SNR G65.2+5.7

Context. SNR G65.2+5.7 is one of few supernova remnants (SNRs) that have been optically detected. It is exceptionally bright in X-rays and the optical [O III]-line. Its low surface brightness and large diameter ensure that radio observations of SNR G65.2+5.7 are technically difficult and thus have hardly been completed. Aims. Many physical properties of this SNR, such as spectrum and polarization, can only be investigated by radio observations. Methods. The λ1 1 cm and λ6 cm continuum and polarization observations of SNR G65.2+5.7 were completed with the Effelsberg 100-m and the Urumqi 25-m telescopes, respectively, to investigate the integrated spectrum, the spectral index distribution, and the magnetic field properties. Archival λ21 cm data of the Effelsberg 100-m telescope were also used. Results. The integrated flux densities of G65.2+5.7 at λ11 cm and λ6 cm are 21.9 ± 3.1 Jy and 16.8 ± 1.8 Jy, respectively. The power-law spectrum (S ~ v α ) is well fitted by α = -0.58 ± 0.07 from 83 MHz to 4.8 GHz. Spatial spectral variations are small. Along the northern shell, strong depolarizion is observed at both wavelengths. The southern filamentary shell of SNR G65.2+5.7 is polarized by as much as 54% at λ6 cm. There is significant depolarization at λ11 cm and confusion with diffuse polarized Galactic emission. Using equipartition principle, we estimated the magnetic field strength for the southern filamentary shell to be between 20 μG (filling factor 1) and 50 μG (filling factor 0.1). A faint HI shell may be associated with the SNR. Conclusions. Despite its unusually strong X-ray and optical emission and its very low surface brightness, the radio properties of SNR G65.2+5.7 are found to be typical of evolved shell-type SNRs. SNR G65.2+5.7 may be expanding in a pre-blown cavity as indicated by a deficit of HI gas and a possible HI-shell.

Polarization surveys of the galaxy

We report on sensitive 21cm and 11cm polarization surveys of the Galactic plane carried out with the Effelsberg 100-m telescope at arcmin angular resolution and some related work. Highly structured polarized emission is seen along the Galactic plane as well as up to very high Galactic latitudes. These observations reflect Faraday effects in the interstellar medium. Polarized foreground and background components along the line of sight, modified by Faraday rotation and depolarization, add in a complex way. The amplitudes of polarized emission features are highly frequency dependent. Small-scale components decrease in amplitude rapidly with increasing frequency. We stress the need for sensitive absolutely calibrated polarization data. These are essential for baseline setting and a correct interpretation of small-scale structures. Absolutely calibrated data are also needed to estimate the high-frequency polarized background. A recent study of polarized emission observed across the local Taurus-Auriga molecular cloud complexes indicates excessive synchrotron emission within a few hundred parsecs. These results suggest that possibly a large fraction of the Galactic high latitude total intensity and polarized emission is of local origin.

An attempt to identify the extended synchrotron structure associated with the micro-quasar GRS 1915+105

We used the Effelsberg 100 m telescope at 10.45 GHz in an attempt to identify extended synchrotron structures formed by jets of GRS 1915+105. For this distant galactic plane source a few suspect structures were pointed out.

The MPIfR Radio Continuum Surveys and Their WWW Distribution

The observation of an area of 120° × 56° centered on RA=8 h DEC=20° at 408 MHz was the first astronomical use of the MPIfR 100-m telescope (1970) and was designed to compile a complete sky survey using also data from Jodrell Bank and Parkes (Haslam et al., 1982). The observation of the northern sky at 1420 MHz started in 1972 using the Stockert 25-m telescope and was finished in 1976 (Reich and Reich 1986). This survey has been completed to an all sky survey using data from Villa Elisa (Argentina). The two surveys are absolutely calibrated. The angular resolutions are 0.8° and 0.59°, respectively. A number of surveys of the Galactic plane have been made with the 100-m telescope at arc minute angular resolution. Surveys at 2695 MHz (|b| ≤ 5°) (Reich et al. 1990, Furst et al. 1990) and at 1410 MHz (|b| ≤ 4°) (Reich et al. 1990) are public.

Radio Observations of Small Diameter Sources in the Direction of Old Supernova Remnants

Radio observations with high sensitivity have shown that lots of more or less compact structures can be found in the field of extended and old supernova remnants (SNRs). These small diameter sources have been subject to many recent observations. The aim of these studies is to infer a possible physical association of these sources with the SNR shell. The interest in this link is based on various aspects, instabilities of shocked interstellar matter, star formation, etc.