EUVE Search for X-rays from Comets Encke, Mueller (C/1993 A1), Borrelly, and Postperihelion Hale–Bopp
✍ Scribed by Vladimir A. Krasnopolsky; Michael J. Mumma; Mark J. Abbott
- Publisher
- Elsevier Science
- Year
- 2000
- Tongue
- English
- Weight
- 174 KB
- Volume
- 146
- Category
- Article
- ISSN
- 0019-1035
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✦ Synopsis
Our observation of postperihelion Hale-Bopp on November 17-23, 1997, revealed the comet soft X-ray luminosity of (3.7 ± 1.2) × 10 24 photons s -1 in an aperture of 6 × 10 5 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) × 10 23 photons s -1 for the aperture of ρ = 7 × 10 4 km. Upper limits of 2.7 × 10 23 and 1.4 × 10 24 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 × 10 5 and 4.1 × 10 5 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 r 3/2 Q gas dependence having the efficiency of (6.4 ± 0.9) × 10 -5 AU 3/2 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 longterm 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.