Context :

Aims : We present an analysis of simultaneous X-Ray and UV observations of comet C/2007 N3 ( Lulin ) taken on three days between January 2009 and March 2009 using the Swift observatory .

Methods : For our X-ray observations , we used basic transforms to account for the movement of the comet to allow the combination of all available data to produce an exposure-corrected image .
We fit a simple model to the extracted spectrum and measured an X-ray flux of 4.3 \pm 1.3 \times 10 ^ { -13 } \mathrm { ergs } \mathrm { cm } ^ { -2 } \mathrm { s } ^ { -1 } in the 0.3 to 1 keV band .
In the UV , we acquired large-aperture photometry and used a coma model to derive water production rates given assumptions regarding the distribution of water and its dissociation into OH molecules about the comet ’ s nucleus .

Results : We compare and discuss the X-ray and UV morphology of the comet .
We show that the peak of the cometary X-ray emission is offset sunward of the UV peak emission , assumed to be the nucleus , by approximately 35,000 km .
The offset observed , the shape of X-ray emission and the decrease of the X-ray emission comet-side of the peak , suggested that the comet was indeed collisionally thick to charge exchange , as expected from our measurements of the comet ’ s water production rate ( 6–8 \times 10 ^ { 28 } \mathrm { mol . } \mathrm { s } ^ { -1 } ) .
The X-ray spectrum is consistent with solar wind charge exchange emission , and the comet most likely interacted with a solar wind depleted of very highly ionised oxygen .
We show that the measured X-ray lightcurve can be very well explained by variations in the comet ’ s gas production rates , the observing geometry and variations in the solar wind flux .

Conclusions :