Maximal curves from subcovers of the GK-curve

For every q=n3q=n3 with n   a prime power greater than 2, the GK-curve is an Fq2Fq2-maximal curve that is not Fq2Fq2-covered by the Hermitian curve. In this paper some Galois subcovers of the GK curve are investigated. Infinitely many examples of maximal curves that cannot be Galois covered by the Hermitian curve are obtained. We also describe explicit equations for some families of quotient curves of the GK-curve. In several cases, such curves provide new values in the spectrum of genera of Fq2Fq2-maximal curves.