Thick radio shell in supernova remnant DA 495 (G 65.7+ 1.2)? |
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| Authors: | T Velusamy R H Becker W M Goss D J Helfand |
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| Institution: | (1) Radio Astronomy Centre, Tata Institute of Fundamental Research, PO Box 8, 643001 Udhagamandalam (Ooty);(2) Institute of Geophysics and Planetary Physics, University of California, Lawrence Livermore National Laboratory, 94550 Livermore, CA, USA;(3) Physics Department, University of California at Davis, 95616 Davis, CA, USA;(4) Institute of Geophysics and Planetary Physics, University of California, Lawrence Livermore National Laboratory, 94550 Livermore, CA, USA;(5) National Radio Astronomy Observatory, PO Box 0, 87801 Socorro, New Mexico, USA;(6) Physics Department, Columbia University, 10027 New York, NY, USA |
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| Abstract: | High resolution (11.7 to 64 arcsec) multifrequency radio observations of DA 495 (G 65.7 +1.2) at 20, 49 and 92 cm wavelengths
with the VLA, WSRT and OSRT are presented. A map of infrared emission in the surrounding region is also presented. Although
the remnant has a minimum near the centre, its brightness distribution does not show limb brightening. Hence it has characteristics
of both shell-type SNRs and Crab-type SNR. Alternatively it has an unusually thick shell with inner and outer radii of 125
and 500 arcsec respectively. The volume emissivity within the shell decreases radially outward. Its integrated flux density
spectrum is characteristic of a shell-type remnant. The role of the reverse shock in the formation of a thick shell is discussed.
The association of the open star cluster NGC6834 with DA 495 is also noted. The parameters of twenty-nine small diameter sources
detected around DA 495 are also presented. The radio source 1949 + 291 is associated with an IRAS source. 1948 + 292 may be
a Crablike pulsar-driven synchrotron nebula. The radio spectrum of the planetary nebula NGC 6842 is optically thick at 49
cm. |
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| Keywords: | supernova remnants DA 495 (G 65 7+ 1 2) interstellar medium |
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