Constraints on the inner mass profiles of lensing galaxies from missing odd images

Most gravitational lens systems consist of two or four observable images. T he absence of detectable odd images allows us to place a lower limit on the power-law slope of the inner mass profile of lensing galaxies. Using a sam ple of six two-image radio-loud lens systems and assuming a singular power- law surface density (Sigma proportional to r(-beta)) for the inner several kiloparsecs of the mass distribution, we find that there is less than a 10% probability that the data are consistent with profile slopes beta < 0.80. Furthermore, individual mass modeling yields <beta> > 0.85 for B0739+366 an d beta > 0.91 for B1030+074. Modeling central black holes as additional poi nt masses changes the constraints in these systems to beta > 0.84 and beta > 0.83, respectively. The inner mass profiles of lensing galaxies are there fore not much shallower than isothermal.