Optical analysis of an activity outburst in comet C/1995 O1 (Hale-Bopp) and its connection to an X-ray outburst

We present a detailed analysis of an outburst of activity in Comet C/1995 O1 (Hale-Bopp), which coincided in time with an increase in X-ray luminosity of the comet. The outburst produced a cloud of material expanding through the coma and is visible in images obtained with a continuum filter and a CN filter. The evolution of its intensity in both the dust and the CN could be well fitted by a Maxwellian function with two parameters (integrated enhancement and average radius). From this an average radial expansion velocity of 200±10 m/s for the dust and 850±40 m/s for the CN (phase ≈ 19◦) could be derived. We estimate that during the outburst the dust production increased by a factor of > 7 and the CN production by a factor of < 4 relative to the quiescent level. Assuming that the size distribution and albedo of the dust particles released during the outburst remains the same as on “quiescent” times and that the variations in CN are representative for all gas production rates in Hale-Bopp, the outburst led to temporarily increased production rates that were about a factor of 2 higher in dust than in gas. The luminosity of the soft X-ray emission observed in Hale-Bopp by the BeppoSAX satellite on September 10–11, 1996, was at least a factor of 3.4 greater than that reported from EUVE observations on September 14–19, 1996. This correlation indicates that the outburst observed in the optical may have triggered the increased X-ray emission on September 10–11, 1996.