Radio continuum observations of Comet C/1999 S4 (LINEAR) before, during, and after break-up of its nucleus

We observed radio continuum emission from Comet C/1999 S4 before, during, and after break-up of its nucleus. The detections before break-up indicate a photometric diameter of 4.7 km, from which we estimate that the nuclear diameter was about 0.9 km. We derive a dust production rate of ~ 9*E⁴ g s^-1, corresponding to 0.03 g s^-1 per square meter of the nuclear surface area, which is comparable to the values found for comets 1P/Halley and C/1995 O1 (Hale-Bopp). The implied gas-to-dust mass production ratio was between 2 and 5. The high daily erosion rate and the continuous fragmentation over months, as derived from water production rates, could not be confirmed. The low radio emission of the fragments directly after the break-up and their low cometary activity may be explained by their low surface temperatures. The published optical and most radio data support that the main nuclear decay started July 23, 2000. Our upper limits on the flux density obtained after the nuclear disintegration put an upper bound on the particulate dust mass released during that event. A scenario in which most of the nucleus disintegrated into many big boulders and part of it into a dust cloud is consistent with our observations.