A Fast Expanding H i Shell in W44: A Preexisting Wind-blown Shell Overtaken by a Supernova Remnant
Abstract
We confirm from higher resolution observations that the previously detected high-velocity H I gas in W44 is an expanding shell associated with the supernova remnant (SNR). The H I shell is expanding at 150 km/s and has a kinetic energy of 8 x 1049 ergs, which is very likely to have been imparted by the supernova (SN) explosion that produced W44. However, the radius of the H I shell RH approximately = 9 pc, which is obtained by extrapolating the high-velocity H I data, is considerably smaller than Rc approximately = 15 pc of the W44 radio continuum shell. It is possible that the uncertainty associated with our extrapolation has led us to significantly underestimate the size of the H I shell. But if RH approximately = Rc approximately 15 pc, then the coexistence of the H I shell, the centrally peaked X-ray emission, and the 2 x 104 yr old pulsar PSR 1853+01 in W44 is very difficult to understand based on available theoretical models. Furthermore, there are optical filaments mainly confined within the H I shell. We therefore propose that the H I and radio continuum shells are physically distinct shells. The double-shell structure may have been produced by an SN explosion inside a preexisting wind bubble. We interpret the inner H I structure as a preexisting wind shell that has been rejuvenated and disrupted by the SN blast wave, and the outer radio continuum structure as an SNR shell composed of newly swept-up ambient medium. The well-separated double-shell structure suggests that the SNR W44 is in 'memory-losing' phase, where the SN shell structure on the evolutionary history of W44.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- April 1995
- DOI:
- 10.1086/175473
- Bibcode:
- 1995ApJ...442..679K
- Keywords:
-
- Gas Expansion;
- Hydrogen Plasma;
- Line Spectra;
- Radio Astronomy;
- Radio Spectra;
- Stellar Mass Ejection;
- Stellar Winds;
- Supernova Remnants;
- Astronomical Spectroscopy;
- Mass Distribution;
- Shock Waves;
- Spectrum Analysis;
- Velocity Distribution;
- Astronomy;
- ISM: INDIVIDUAL ALPHANUMERIC: W44;
- ISM: SUPERNOVA REMNANTS;
- RADIO LINES: ISM