Short-term nongravitational effect due to activity in comet Hale-Boppʹs nucleus

Can activity of cometʹs nucleus, such as jets, cause observable short-term nongravitational effect? We have analysed the data on several nuclear events of Comet Hale-Bopp during late February-early April, 1997 and found the observed position deviated markedly from the position calculated according to the ephemeris after the observing error and the offset of the nucleus mass-center from the cometʹs light-center have been allowed for. Thus, nuclear activity can indeed cause observable short-term nongravitational effect. Possible short-term variation of sun-comet distance due to the effect is estimated and the relation between the effect and the relevant activity is discussed.