SwiftX‐Ray Telescope Observations of theDeep ImpactCollision

Abstract

Comet9P/Tempel1wasobservedbytheSwiftX-RayTelescope(XRT)foratotalof 250,024s.SoftX-rayemission, 0.2Y1.0keV,wasseenasadiffuseextendedhalowithanFWHMof1:03 ;10 5 kmcenteredonthecomet’snucleus.The X-raylightcurveindicatesthatthecometexhibitedaprolongedsoftX-rayoutburstjustafterimpactoftheNASADeep Impact (DI) spacecraft and enhanced X-ray activity lasted for 12 days. The radial brightness distribution and X-ray spectrumareinexcellentagreementwithamodelof X-rayproductioninwhichhighlychargedminorheavyionspecies inthesolar windundergochargeexchangereactions withwatergrouporcarbondioxidegroup moleculesintheneutral comaof thecomet.Usingthismodel,wederiveasimpleexpressionfortheX-rayemissionandshowthattheX-rayflare 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) ;10 8 kg over the 12 day period postimpact. The quiescent water production was expected to inject � 1:0 ;10 8 kg into the coma over the same period so the observed X-ray flux indicates that an additional (1:9 � 0:4) ;10 8 kg of water or, alternatively, (3:9 � 0:5) ; 10 8 kg of carbon dioxide were liberated by the DI impact. Subject headingg comets: general — comets: individual (9P/Tempel 1) Online material: color figures