X-ray emissions from comets detected in the Rontgen x-ray satellite all- sky survey

Science

Volumn 277, Issue 5332, 1997, Pages 1625-1630

  Dennerl, Konrad ^a   Englhauser, Jakob ^a   Trümper, Joachim ^a  

^a NONE

Author keywords

[No Author keywords available]

Indexed keywords

ARTICLE; ASTRONOMY; OPTICS; PHOTON; PRIORITY JOURNAL; X RAY ANALYSIS;

EID: 0030845982     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.277.5332.1625     Document Type: Article

References (47)

1. C. M. Lisse et al., Science 274, 205 (1996).
2. J. Trümper, Adv. Space Res. 2 (no. 4), 241 (1983).
3. W. Voges, in Proceedings of Satellite Symposium 3: Space Sciences with Particular Emphasis on High-Energy Astrophysics, from the "International Space Year" Conference, Munich, Germany, 30 March to 4 April 1992 (ESA ISY-3, 1992), p. 9.
4. W. Voges et al., in preparation.
5. S. L. Snowden et al., Astrophys. J. 454, 643 (1995).
6. E. Pfeffermann et al., Proc. SPIE 733, 519 (1986).
7. B. Aschenbach, H. Bräuninger, G. Kettenring, Adv. Space Res. 2, 251 (1983).
8. Catalogue of Cometary Orbits (Central Bureau for Astronomical Telegrams/Minor Planet Center, Smithsonian Astrophysical Observatory, Cambridge, MA, ed. 11, 1996).
9. K. Dennerl, J. Englhauser, J. Trümper, IAU Circular 6404 (1996); IAU Circular 6413 (1996); IAU Circular 6472 (1996).
10. K. Dennerl, J. Englhauser, J. Trümper, IAU Circular 6404 (1996); IAU Circular 6413 (1996); IAU Circular 6472 (1996).
11. K. Dennerl, J. Englhauser, J. Trümper, IAU Circular 6404 (1996); IAU Circular 6413 (1996); IAU Circular 6472 (1996).
12. h ≤ 2 AU are 43P (Wolf-Harrington), 98P/ 1991 D1 (Takamizawa), and 124P/1991 F1 (Mrkos). At the time of the observation, they were as faint as 13.5, 16.0, and 18.0 mag, respectively. These comets are not detectable in the RASS, although a marginal signal from 43P may be present. In the obs. no. 1 through 4, the comets C/1990 K1 (Levy) and C/ 1990 N1 (Tsuchiya-Kiuchi) have also been detected in the 90-to 206-eV band with the Wide-Field Camera on ROSAT [ J. P. Pye, R. G. West, K. Dennerl, IAU Circular 6486 (1996)].
13. h ≤ 2 AU are 43P (Wolf-Harrington), 98P/ 1991 D1 (Takamizawa), and 124P/1991 F1 (Mrkos). At the time of the observation, they were as faint as 13.5, 16.0, and 18.0 mag, respectively. These comets are not detectable in the RASS, although a marginal signal from 43P may be present. In the obs. no. 1 through 4, the comets C/1990 K1 (Levy) and C/ 1990 N1 (Tsuchiya-Kiuchi) have also been detected in the 90-to 206-eV band with the Wide-Field Camera on ROSAT [ J. P. Pye, R. G. West, K. Dennerl, IAU Circular 6486 (1996)].
14. h ≤ 2 AU are 43P (Wolf-Harrington), 98P/ 1991 D1 (Takamizawa), and 124P/1991 F1 (Mrkos). At the time of the observation, they were as faint as 13.5, 16.0, and 18.0 mag, respectively. These comets are not detectable in the RASS, although a marginal signal from 43P may be present. In the obs. no. 1 through 4, the comets C/1990 K1 (Levy) and C/ 1990 N1 (Tsuchiya-Kiuchi) have also been detected in the 90-to 206-eV band with the Wide-Field Camera on ROSAT [ J. P. Pye, R. G. West, K. Dennerl, IAU Circular 6486 (1996)].
15. The emission may extend further out, but the x-ray surface brightness becomes so low that a detailed model of temporal variations of the PSPC background is essential for a determination of the full extent. During the survey, occasional increases in the overall soft x-ray background with a typical duration of up to 8 hours were detected. These "long-term enhancements" [M. Freyberg, thesis, Ludwig-Maximilians-Universitat, München, Germany (1994)] are a well-established, but unexplained phenomena. In view of the x-ray detections of comets, it is not unlikely that the solar wind interacts with the upper atmosphere of Earth in a similar way as it does with the coma of a comet, causing the sunward side of the geocorona to glow in x-rays. From the low ROSAT orbit, this glow would appear as a temporally variable soft component in the diffuse x-ray emission, as observed [M. Freyberg, K. Dennerl, J. Trümper, in preparation].
16. The emission may extend further out, but the x-ray surface brightness becomes so low that a detailed model of temporal variations of the PSPC background is essential for a determination of the full extent. During the survey, occasional increases in the overall soft x-ray background with a typical duration of up to 8 hours were detected. These "long-term enhancements" [M. Freyberg, thesis, Ludwig-Maximilians-Universitat, München, Germany (1994)] are a well-established, but unexplained phenomena. In view of the x-ray detections of comets, it is not unlikely that the solar wind interacts with the upper atmosphere of Earth in a similar way as it does with the coma of a comet, causing the sunward side of the geocorona to glow in x-rays. From the low ROSAT orbit, this glow would appear as a temporally variable soft component in the diffuse x-ray emission, as observed [M. Freyberg, K. Dennerl, J. Trümper, in preparation].
17. x = 8′ (Table 2), this aperture is so small that background inhomogeneities are negligible, while it is large enough to provide a useful signal to noise ratio: for a gaussian profile, it would contain exactly half of the emission. We used this aperture definition for the determination of the x-ray luminosities and for spectral studies.
18. K. Dennerl, J. Englhauser, J. Trümper, C. Lisse, IAU Circular 6495 (1996).
19. J. C. Raymond and B. W. Smith, Astrophys. J. Suppl. Ser. 35, 419 (1977).
20. 2 = 2.37 for 6 degrees of freedom). The mean value is = 0.23 ± 0.04 keV.
21. R. M. Häberli, T. I. Gombosi, D. L. De Zeeuw, M. R. Combi, K. G. Powell, Science 276, 939 (1997).
22. T. E. Cravens, Geophys. Res. Lett. 24.1, 105 (1997).
23. -23.
24. R. Wegmann, H. U. Schmidt, C. M. Lisse, K. Dennerl, J. Englhauser, in preparation.
25. C. Lisse et al., IAU Circular 6433 (1996).
26. 2 - 1.
27. E. Lamla, in Landolt-Bömstein, H. H. Voigt, Ed., Group VI, Vol. I, 5.2.6.0.3 (Springer Verlag, Berlin, 1965), p. 317.
28. Afp is defined as the product of the dust albedo A, the filling factor f of the dust within the aperture, and the projected radius p of the aperture; it provides an aperture-independent measure of the dust production for a comet with a canonical spatial distribution of dust.
29. C. Arpigny et al., Atlas of Cometary Spectra (Kluwer, Dordrecht, Netherlands, 1997).
30. M. F. A'Hearn, R. L. Millis, D. G. Schleicher, D. J. Osip, P. v. Birch, Icarus 118, 223 (1995).
31. D. Schleicher et al., IAU Circular 6372 (1996).
32. x by binning the photons into 30″ by 30″ pixels and smoothing the images with a gaussian filter with σ = 2′.
33. -1 adopted by Cravens for obs. no. 8 referred to a measurement on March 24.5 UT, when Q was systematically higher than during the ROSAT observations from March 26.5 to 28.4 (26).
34. x as the peak surface flux observed at φ = 0°.
35. We note that "resolved" in this context is different from the usual definition, which compares the observed brightness distribution with the point spread function of the imaging device.
36. c) and σ are not unreasonable (37). Because the peak surface fluxes are also close to the value expected for the chosen solar wind parameters, all assumptions are self-consistent.
37. N. C. Wickramasinghe and F. Hoyle, Astrophys. Space Sci. 239, 121 (1996).
38. W. H. Ip and V. Chow, Icarus, in press.
39. R. Bingham, J. M. Dawson, V. D. Shapiro, D. A. Mendis, B. J. Kellet, Science 275, 49 (1997).
40. T. G. Northrop, C. M. Lisse, M. J. Mumma, M. D. Desch, Icarus 127, 246 (1997).
41. J. Brandt, C. Lisse, Y. Yi, Bull. Am. Astron. Soc. 189, 25.05 (1996).
42. c decreases by less than 10% [for example, H. L. F. Houpis and D. A. Mendis, Moon Planets 25, 95 (1995)].
43. H. U. Zimmermann et al., EXSAS User's Guide, MPE Report 257 (ROSAT Scientific Data Center, Garching, Germany, ed. 4, October, 1994).
44. The International Comet Quarterly, D. Green, C. Morris, S. Nakano, Eds. (Smithsonian Astrophysical Observatory, Cambridge, MA, 1989-91), vols. 11-13.
45. h.
46. H. Kosai, IAU Circular 5157 (1991).
47. We thank C. Lisse, B. Aschenbach, F. Favata, M. Freyberg, W.-H. Ip, K. Jockers, E. Rieger, H.-U. Schmidt, S. Snowden, R. Treumann, and R. Wegmann for interesting and stimulating discussions. We are grateful to P. Camilleri for supplying the optical image of comet C/1990 K1. The ROSAT project is supported by the German Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF/DARA) and the Max-Planck-Gesellschaft.