Optical monitoring of extragalactic sources for linking the ICRF and the future Gaia celestial reference frame - I. Variability of ICRF sourcesF. Taris, A. Andrei, A. Klotz, F. Vachier, R. Côte, S. Bouquillon, J. Souchay, S. Lambert, S. Anton, G. Bourda and D. CowardA&A, 552 (2013) A98DOI: https://doi.org/10.1051/0004-6361/201219686
