X-Band VLA observations of comet Hyakutake (C/1996 B2) and implications for nuclear properties

The results of our observations during the close approach of comet C/1996 B2 (Hyakutake) using Very Large Array (VLA) at a wavelength of 3.55 cm (X-band) are presented. The scientific goals were to observe the thermal microwave continuum from the nucleus and constrain the cometʹs nuclear properties. The 12 h track allows 3-σ upper limits to be placed on the emission that are about a factor of four lower than any previous VLA observation of a cometʹs continuum. With the caveat that some assumptions about the microwave emissivity, the temperature, and the thermal conductivity must be made, the effective radius of Hyakutakeʹs nucleus is constrained to be less than 3.0 km, which provides an addition to the sparse body of knowledge on long-period cometary nuclei. Since the observations overlap several of the ROSAT observations of this comet, the strength of the microwave flux is estimated from the X-ray emitting region of the coma to place constraints on possible emission mechanisms.