Swift X-ray telescope observations of the deep impact collision

Comet 9P/Tempel 1 was observed by the Swift X-Ray Telescope (XRT) for a total of 250,024s. Soft X-ray emission, 0.2-1.0 keV, was seen as a diffuse extended halo with an FWHM of 1.03 × 10⁵ km centered on the comet's nucleus. The X-ray light curve indicates that the comet exhibited a prolonged soft X-ray outburst just after impact of the NASA Deep Impact (DI) spacecraft and enhanced X-ray activity lasted for 12 days. The radial brightness distribution and X-ray spectrum are in excellent agreement with a model of X-ray production in which highly charged minor heavy ion species in the solar wind undergo charge exchange reactions with water group or carbon dioxide group molecules in the neutral coma of the comet. Using this model, we derive a simple expression for the X-ray emission and show that the X-ray flare is, in part, due to an increase in solar wind flux at the comet but is largely due to an enhanced molecule production rate. Assuming that the main outgassing constituent was water, the comet produced (2.9 ±0.4) × 10⁸ kg over the 12 day period postimpact. The quiescent water production was expected to inject ∼1.0 × 10⁸ kg into the coma over the same period so the observed X-ray flux indicates that an additional (1.9 ± 0.4) × 10⁸ kg of water or, alternatively, (3.9 ± 0.5) × 10 ⁸ kg of carbon dioxide were liberated by the DI impact.