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Astron. Astrophys. 317, 212-222 (1997)

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The HI environment of filled-centre supernova remnants

I. G 74.9+1.2

B.J. Wallace 1, T.L. Landecker 2, A.R. Taylor 1 and S. Pineault 3

1 Department of Physics and Astronomy, The University of Calgary, 2500 University Drive N.W., Calgary AB, T2N 1N4, Canada
2 Dominion Radio Astrophysical Observatory, National Research Council of Canada, Box 248 Penticton B.C., V2A 6K3, Canada
3 Département de Physique et Observatoire du Mont Mégantic, Université Laval, Ste-Foy, PQ, G1K 7P4, Canada

Received 23 November 1995 / Accepted 17 February 1996

Abstract

We present the results of an investigation into the HI environment of the filled-centre supernova remnant (SNR) G 74.9+1.2 (CTB87). We confirm earlier results that G 74.9+1.2 lies within the boundaries of an expanding bubble in the HI distribution at the systemic velocity of the SNR. This bubble is defined by a partial HI shell which opens away from the Galactic plane. The north-west portion of G 74.9+1.2 lies adjacent to the inner boundary of the HI shell. The morphology of the HI boundary and the north-west edge of the SNR are similar, suggesting that the HI shell has impeded the expansion of the SNR in this direction. This result, together with the absence of a steep-spectrum synchrotron shell, rules out the presence of an invisible halo of fast moving ejecta, suggesting that the original supernova explosion did not have enough energy to form such a halo. We find that the observed morphology of G 74.9+1.2 can be explained if the kinetic energy of the nebula is comparable to that found in the Crab Nebula. This is roughly a factor of 30 less than the energy found in a shell SNR. This in turn suggests that the progenitors of filled-centre SNRs (and certainly G 74.9+1.2) may be inherently different from those of shell-type SNRs.

Key words: supernovae: general — ISM: bubbles — ISM: individual objects G 74.9+1.2 — ISM: supernova remnants — radio continuum: ISM — radio lines: ISM

Send offprint requests to: T.L. Landecker

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