Linear strands of powers of certain binomial edge ideals

We provide a closed formula for the graded Betti numbers in the linear strands of all powers of binomial edge ideals $J_G$ arising from closed graphs $G$ that do not have the complete graph $K_4$ as an induced subgraph. We show that these agree with the corresponding Betti numbers for the powers of the lexicographic initial ideal of $J_G$, thereby confirming a conjecture of Ene--Rinaldo--Terai in a special case.