Chandra's Close Encounter with the Disintegrating Comets 73P/2006 (Schwassmann-Wachmann 3) Fragment B and C/1999 S4 (LINEAR)

Abstract

On 2006 May 23, we used the ACIS-S instrument on Chandra to study the X-ray emission from the B fragment of comet 73P/2006 (Schwassmann-Wachmann 3) (73P/B). We obtained a total of 20 ks of Chandra observation time of Fragment B, and also investigated contemporaneous Advanced Composition Explorer and Solar and Heliospheric Observatory solar wind physical data. The Chandra data allow us to spatially resolve the detailed structure of the interaction zone between the solar wind and the fragment's coma at a resolution of ~1000 km, and to observe the X-ray emission due to multiple comet-like bodies. We detect a change in the spectral signature with the ratio of the C V/O VII line increasing with increasing collisional opacity as predicted by Bodewits et al. The line fluxes arise from a combination of solar wind speed, the species that populate the wind, and the gas density of the comet. We are able to understand some of the observed X-ray morphology in terms of nongravitational forces that act upon an actively outgassing comet's debris field. We have used the results of the Chandra observations on the highly fragmented 73P/B debris field to reanalyze and interpret the mysterious emission seen from comet C/1999 S4 (LINEAR) on 2000 August 1, after the comet had completely disrupted. We find the physical situations to be similar in both cases, with extended X-ray emission due to multiple, small outgassing bodies in the field of view. Nevertheless, the two comets interacted with completely different solar winds, resulting in distinctly different spectra.