Analytical Model of ROSAT X-RAY Image of Comet Hyakutake

We derive coma properties from the ROSAT X-ray image (Lisse et al. IAUC-6373). We use spherically symmetric ionic distribution which has smooth turnover around 20,000km and extending upto about 60,000km from the comet nucleus (Huebner, W.F. and P.T. Giguere, 1980, Astrophysical Journal, v. 238, p. 753). Simple exponential law for (solar) photon or charged particle attenuation through this matter is assumed. The crescent shape of the X-ray intensity could be clearly reproduced (See figures of isointensity contours kept at tifrc3.tifr.res.in, user=comet, password=HAYAKUTAKE, see also in http://www.tifr.res.in:80/~chakraba/) provided the X-ray attenuation length is not much larger that 1.5e+5km (scal1.gif). Larger attenuation lengths tend to remove crescent shape. Either fluorescence or charged particle scattering can be the basic cause. In photonic interactions the intensity should go up with distance as 1/r**2, but in charged particle interaction the intensity should roughly go up as 1/r**1.5 but keeping the same basic shape. We invite observers to closely monitor the photon counts as the sun-comet distance changes.

We also think that modulation of intensity in 10,000s (roughly three hours) could be obtained by random evaporation of grains at a distance of 30,000km from the nucleus. Each such event can contribute random variation of a distance of about 5-10 thousand kilometers which possibly makes the X-ray image blobby.

S.K. Chakrabarti, K.S. Krishnaswamy (TIFR, Bombay)

Attenuation length: 1.5e+4 Km

84K

Attenuation length: 1.5e+5 Km

60K

Attenuation length: 1.5e+6 Km

57K

Attenuation length: 1.5e+7 Km

68K

Please feel free to mail /suggestions/comments to chakraba@tifrc2.tifr.res.in

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