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V.A. Krasnopolsky, M.J. Mumma, M.J. Abbott
We observed soft X-ray emissions from four comets in a range of 70-180 eV using the Extreme Ultraviolet Explorer orbiting observatory. Comet 6P/d'Arrest was observed on 9/4/95 at a heliocentric distance r = 1.42 AU; its X-ray emission was Q_{X} = 1.1 x 10(24) ph/s in an aperture radius rho = 1.2 x 10(5) km and was offset by d <= 3 x 10(4) km from the nucleus. Data for comet Bradfield (C/1995 Q1) are 11/7/95, r = 1.50 AU, Q_{X} <= 3 x 10(23) ph/s for the same aperture. Data for comet Hyakutake (C/1996 B2) are 3/22/96, r = 1.07 AU, Q_{X} = 7.5 x 10(24) ph/s for the same aperture, d = (5.6 +/- 1) x 10(4) km. Data for comet Hale-Bopp (C/1995 O1) are 9/14/96, r = 3.07 AU, Q_{X} = 1.6 x 10(24) ph/s for the same aperture and 8 x 10(24) ph/s for rho = 4 x 10(5) km, d = (2.7 +/- 1.2) x 10(4) km. X-ray spectra and correlations of the soft X-ray emissions with the observed He 584 Angstroms emissions and with gas and dust production rates in the comets are studied to identify processes of X-ray excitation and to determine their relative contributions.
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