LetX/Fq be a smooth, geometrically connected, quasi projective scheme. Let Ebe a semisimple over convergent F-isocrystal on X. Suppose that irreducible summands Ei of E have rank 2, determinant ̄Qp (−1), and infinite monodromy at∞. Suppose further that for each closed point x of X, the characteristic polynomial of E at x is in Q[t]⊂Qp[t]. Then there exists a non-trivial open set U⊂X such that E|U comes from a family of abelian varieties on U. As an application, let L1 be an irreducible lisse ̄Ql sheaf on X that has rank 2, determinant ̄Ql(−1), and infinite monodromy at∞. Then all crystalline companions to L1 exist (as predicted by Deligne’s crystalline companions conjecture) if and only if there exists a non-trivial open set U⊂X and an abelian scheme πU: AU→U such that L1|U is a summand of R1(πU)∗ ̄Ql.