Detection of a Noble Gas Molecular Ion, 36ArH+, in the Crab Nebula
Ivison, R. J.; Olofsson, G.; Krause, O.; Gomez, H. L.; Barlow, M. J.; Cernicharo, J.; Swinyard, B. M.; Matsuura, M.; Lim, T. L.; Polehampton, E. T.; Owen, P. J.; Miller, S.
United Kingdom, Spain, Germany, Sweden, Canada
Abstract
Noble gas molecules have not hitherto been detected in space. From spectra obtained with the Herschel Space Observatory, we report the detection of emission in the 617.5- and 1234.6-gigahertz J = 1-0 and 2-1 rotational lines of 36ArH+ at several positions in the Crab Nebula, a supernova remnant known to contain both molecular hydrogen and regions of enhanced ionized argon emission. Argon-36 is believed to have originated from explosive nucleosynthesis in massive stars during core-collapse supernova events. Its detection in the Crab Nebula, the product of such a supernova event, confirms this expectation. The likely excitation mechanism for the observed 36ArH+ emission lines is electron collisions in partially ionized regions with electron densities of a few hundred per centimeter cubed.