Abstract
We compute the Picard group of the stack of elliptic curves equipped with a cyclic subgroup of order two, and of the stack of elliptic curves equipped with a cyclic subgroup of order three, over any base scheme on which $6$ is invertible. This generalizes a result of Fulton-Olsson, who computed the Picard group of the stack of elliptic curves (with no level structure) over a~wide variety of base schemes.
Citation
Andrew Niles. "The Picard groups of the stacks $\mathscr{Y}_0(2)$ and $\mathscr{Y}_0(3)$." Funct. Approx. Comment. Math. 55 (1) 105 - 112, September 2016. https://doi.org/10.7169/facm/2016.55.1.7
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