Upper limit for circumstellar gas around the type Ia SN 2000cx F. Patat, S. Benetti, S. Justham, P. A. Mazzali, L. Pasquini, E. Cappellaro, M. Della Valle, Ph. Podsiadlowski, M. Turatto, A. Gal-Yam and J. D. Simon A&A, 474 3 (2007) 931-936 Published online: 23 October 2007 DOI: 10.1051/0004-6361:20078393