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C.M. Lisse (STScI), D.J. Christian (STScI/CSC), K. Dennerl (Max-Planck-Institut fur extraterrestrische Physik), F.E. Marshall, R. Mushotzky, R. Petre, S. Snowden (NASA/GSFC), H.A. Weaver (JHU), B. Stroozas (University of California), S. Wolk (Harvard/SAO)
Using the Chandra X-ray Observatory (CXO) and the Extreme Ultraviolet Explorer (EUVE), we have discovered the first direct evidence for x-ray emission from a comet produced by charge exchange between highly ionized solar wind minor ions and and cometary gaseous species in the coma.
Comet C/LINEAR 1999 S4 was observed by CXO on 14 July 2000 UT (pre-breakup, maximum signal) and again on 01 Aug 2000 UT (post-breakup, minimum signal). The EUVE observations spanned from 11 July 2000 UT to 18 July 2000 UT. Pre-breakup, the comet was detected by CXO with a count of 0.3 cps, a total integral flux of 8x10-13 erg/sec/cm2 from 0.2 - 0.7 keV, and a total x-ray luminosity of 6x1014 erg/sec. The EUVE Lexan B count rate at 04:57 July 14 UT was 0.06 cps in 5400 sec, for an equivalent luminosity of 1x1015 erg/sec at 0.16 keV, consistent with the reddish CXO spectrum. The CXO emission morphology was a hemispherical shell some 30 arcsec across, centered between the nucleus and the Sun.
The 14 July CXO spectrum shows the clear signatures of x-ray line emission due to charge exchange between cometary neutrals and solar wind minor ions; these include a strong line at 570 eV due to charge exchange to O+6, detected at greater than 10-sigma. The observed spectrum is most probaby due to a forest of atomic line emission, as the best fit to the preliminary spectrum is the Mewe et al. (MEKAL) plasma spectrum using solar elemental abundances with enhanced oxygen, carbon, and nitrogen abundances, and a plasma temperature of 0.17 keV.
We present preliminary imaging, spectroscopy, and light curve, and modeling results from our CXO and EUVE observations.
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