Computer Science
Scientific paper
Jul 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000icar..146..152k&link_type=abstract
Icarus, Volume 146, Issue 1, pp. 152-160 (2000).
Computer Science
18
Scientific paper
Our observation of postperihelion Hale-Bopp on November 17-23, 1997, revealed the comet soft X-ray luminosity of (3.7+/-1.2)×1024 photons s-1 in an aperture of 6×105 km and in the EUVE range of 97-165 eV. We also analyzed observations of three comets from the EUVE archive. The X-ray luminosity of Comet Borrelly on November 20-22, 1994, was (7.5+/-0.6)×1023 photons s-1 for the aperture of ρ=7×104 km. Upper limits of 2.7×1023 and 1.4×1024 photons s-1 were obtained for Comets Encke and Mueller (C/1993 A1) on November 30, 1993, and June 9-11, 1994, for ρ=1.7×105 and 4.1×105 km, respectively. This work has doubled the number of comet observations in our EUVE database. Soft X-ray emissions have been detected in five of the eight observations. The measured X-ray luminocities are consistent with a r3/2 Qgas dependence having the efficiency of (6.4+/-0.9)×10-5 AU3/2 and therefore favors a gas-related mechanism. The only viable candidate is the charge transfer mechanism. Using our X-ray luminosities as functions of aperture and assuming the presentation of the charge transfer spectrum by thermal bremsstrahlung or the power law, it is possible to make careful comparison of X-ray observations made with different instruments. While both our pre- and postperihelion observations of Hale-Bopp demonstrate a regular behavior of X-rays from that comet, the outburst detected with the BeppoSAX and the nondetection with the ROSAT look puzzling. We suggest that the long-term EUVE observations reflect a mean X-ray emission while the comparatively short BeppoSAX and ROSAT observations of Comet Hale-Bopp could coincide with a maximum and a minimum in the heavy ion flux, respectively.
Abbott Mark J.
Krasnopolsky Vladimir A.
Mumma Michael J.
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