Iron line spectroscopy of black holes in vector-tensor Galileon modified gravity

Recently, a rotating black hole solution was found in vector-tensor Galileon modified gravity that has some significant differences from the Kerr black hole solution. We study the iron line shape that is part of the reflection spectrum of accretion disks around black holes in this new black hole solution. We simulate and compare the iron lines of this solution with those of the Kerr solution to see if the technique of iron line spectroscopy can be used as a tool to test vector-tensor Galileon modified gravity. Our analysis shows that current x-ray facilities can, in principle, be used to test and place constraints on vector-tensor Galileon modified gravity in the strong-coupling and ultraspinning regimes.