We compute equations for the families of elliptic curves 9-congruent to a given elliptic curve. We use these to find infinitely many non-trivial pairs of 9-congruent elliptic curves over ℚ, i.e. pairs of non-isogenous elliptic curves over ℚ whose 9-torsion subgroups are isomorphic as Galois modules.
@article{bwmeta1.element.bwnjournal-article-doi-10_4064-aa171-4-5, author = {Tom Fisher}, title = {On families of 9-congruent elliptic curves}, journal = {Acta Arithmetica}, volume = {168}, year = {2015}, pages = {371-387}, zbl = {06526954}, language = {en}, url = {http://dml.mathdoc.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa171-4-5} }
Tom Fisher. On families of 9-congruent elliptic curves. Acta Arithmetica, Tome 168 (2015) pp. 371-387. http://gdmltest.u-ga.fr/item/bwmeta1.element.bwnjournal-article-doi-10_4064-aa171-4-5/