New 6-cm observations of a large sample of radio SNRs
aa r X i v : . [ a s t r o - ph ] J a n New 6-cm observations of a large sampleof radio SNRs
Sebastian Soberski, Eugeniusz Pazderski and Andrzej Kus
Torun Centre for Astronomy, Nicholas Copernicus University,ul.Gagarina 11, 87-100 Torun, Poland
Abstract.
Almost 50 radio SNR objects were selected from Green’s catalogue for continuum andpolarization observations . We present preliminary results of this observational campaign at 4.7 GHzcarried out with Torun 32-metre radio telescope.
Keywords:
SNR: supernova remnant, polarization, radio
PACS:
INTRODUCTION
We present 4.7 GHz polarimetric measurements of a large sample of galactic SNRsobserved using 32-metre radio telescope in Torun. About 50 objects were selected forour studies. Supernova (SN) rates depend on star formation and are therefore related tothe type of galaxy [1]. The SNe rate in Galaxy is expected to be on the level of oneSNe event in the range of 30 to 50 years. Within the last 2000 years only about 8 areidentified. There are several selection effects which make SNR catalogues incomplete.For old SNRs which are expected to be intrinsically fainter than young ones, the fractionof undetected SNRs may be similar or even larger. A SN explosion within very densematerial reduce the lifetime of the SNR largely. Otherwise the SNR must reach a verylarge diameter, when exploding in a hot and thin environment, until it collect enoughmass to become visible. These faint shell-type objects are difficult to identify in theGalactic plane because of the superposition of a large number of emission structuresalong the line of sight. Outside of the Galactic plane confusion by extragalactic sourceslimits the sensitivity of single-dish surveys (needed to identify extended faint objects).
OBSERVATIONSReceiving System
Polarimetric observations were performed with Torun 32-metre radio telescopeequiped with 4.7 GHz receiving system connected to polarimeter. The polarimeterwas tested by observations of 3c286 at various paralactic angles and it shows that theinstrumental polarization is less than 2% [3]. Some details about parameters of thereceiving system are shown in Table 1.
ABLE 1.
Parameters of the receiving sys-tem at 32-metre radio telescope in Torun:
Parametar Value
Frequency center : 4,7 GHzBandwidth : 500 MHzTime of integration per point : 1 secSystem temperature : 22 KRMS noise (typical) : 6 mJy/baTb/S : 0.2 K/JyHPBW : 7.’2
First results
About 70% of 50 seleted galactic radio SNRs were observed. We present four ex-ample maps, three of them shows (Jy) polarization intensity with total power contourssuperimposed (Fig.1,2,3) and one displays (Jy) polarization intensity with polarizationintensity contours superimposed (Fig.4). Description for maps: • SNR G82.2+5.3 (W63) (Fig.1 top-left). SNR short description [4]: size 95x65 ar-cmin, type S, flux density at 1 GHz: 120? Jy, spectral index: 0.5?. Object is locatedin the Cygnus X complex. Spectra indicate SNR filaments at optical wavelengths. • SNR G54.4-0.3 (HC40) (Fig.3 top-right). SNR short description [4]: size 40 ar-cmin, type S, flux density at 1 GHz: 28 Jy, spectral index: 0.5 . This shell is locatedin a complex region. Faint filaments are visible at optical wavelengths. • SNR G39.7-2.0 (W50, SS433) (Fig.2 bottom-left). SNR short description[4]: size120x60 arcmin, type ?, flux density at 1 GHz: 85 Jy, spectral index: 0.7?. Elongatedshell, containing SS433, adjacent to the HII region S74 (radio). Faint filaments atthe edge of the radio emission (optical). Emission from SS433 and two lobes (X-ray). The centre of W50 contains compact source SS433. Estimated distance isabout 3 kpc (association with HI). • SNR G182.4+4.3 (Fig.4 bottom-right). SNR short description [4]: size 50 arcmin,type S, flux density at 1 GHz: 1.2 Jy, spectral index: 0.4 . Incomplete shell.
ACKNOWLEDGMENTS
We are grateful to Prof. Richard Wielebinski and MPIfR in Bonn for many advices andthe polarimeter device. We also would like to thank our colleagues from JagiellonianUniversity Astronomical Observatory who helped us in data reduction and analysisprocess.
REFERENCES
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