Optical behavior of GRB 061121 around its X-Ray shallow decay phaseT. Uehara, M. Uemura, A. Arai, R. Yamazaki, K. S. Kawabata, M. Ohno, Y. Fukazawa, T. Ohsugi, M. Yoshida, S. Sato and M. KinoA&A, 526 (2011) A92DOI: https://doi.org/10.1051/0004-6361/201015911