Untwisting the Tornado: X-Ray Imaging and Spectroscopy of G357.7-0.1
Abstract
We report on the detection of X-ray emission from the unusual Galactic radio source G357.7-0.1 (the ``Tornado''). Observations made with the Chandra X-Ray Observatory demonstrate the presence of up to three sources of X-ray emission from the Tornado: a relatively bright region of dimensions 2'×1' coincident with and interior to the brightest radio emission at the ``head'' of the Tornado, plus two fainter extended regions possibly associated with the Tornado's ``tail.'' No X-ray point sources associated with the Tornado are seen down to a 3 σ luminosity (0.5-10 keV) of 1×1033 ergs s-1, for a distance to the system of 12 kpc. The spectrum of the brightest region of X-rays is consistent with a heavily absorbed (NH~1023 cm-2) thermal plasma of temperature kT~0.6 keV; an absorbed power law can also fit the data but implies an extremely steep photon index. From these data we tentatively conclude that the Tornado is a supernova remnant (SNR), although we are unable to rule out the possibility that the Tornado is powered either by outflows from an X-ray binary or by the relativistic wind of an unseen pulsar. Within the SNR interpretation, the head of the Tornado is a limb-brightened radio shell that contains centrally filled thermal X-rays and that is interacting with a molecular cloud. We therefore propose that the Tornado is a ``mixed morphology'' supernova remnant. The unusual tail component of the Tornado remains unexplained in this interpretation but might result from expansion of the SNR into an elongated progenitor wind bubble.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- September 2003
- DOI:
- 10.1086/378260
- arXiv:
- arXiv:astro-ph/0306050
- Bibcode:
- 2003ApJ...594L..35G
- Keywords:
-
- ISM: Individual: Alphanumeric: G357.7-0.1;
- ISM: Supernova Remnants;
- X-Rays: ISM;
- Astrophysics
- E-Print:
- 4 pages of text, plus one embedded EPS figure. Minor changes following referee's report. ApJ Letters, in press