C. E. Woodward, M. S. Kelley, University of Minnesota, and P. Hinz, M. Kenworthy, University of Arizona, Steward Observatory report the discovery of a detached coma feature at a P.A. of ~ 43 deg, 3.4 arcsec (corresponding to 2700 km at a cometocentric distance of 1.10 AU) from the nucleus of comet C/2006 M4 (SWAN) detected in the 10.55 micron narrow-band (FWHM 0.97 micron) images obtained with the 6.5-m MMT telescope (+MIRAC4) and adaptive optics secondary (BLINC) on 2006 November 07.08 UT. Aperture photometry, derived from images obtained through thin cirrus with the AO system locked on the diffuse comet nucleus, in a 3.1 arcsec circular beam yields a 10.55 micron flux of 9.5 +/- 0.5 Jy and 4.1 +/- 0.4 Jy on the nucleus and detached coma feature, respectivley. The detached coma feature is elongated along the same P.A., with a spatial extent of ~3 arcsec by 1.5 arcec. The nucleus was unresolved in the diffraction limited images (FWHM 0.4 arcec), and appears to be embedded in a diffuse coma (FWHM 0.7 arcsec). Further mid-infrared observations are encouraged. (Click on image for larger version.)
