We use three–integral models to infer the distribution function ( df ) of the boxy E3-E4 galaxy NGC 1600 from surface brightness and line profile data on the minor and major axes .
We assume axisymmetry and that the mass-to-light ratio is constant in the central \sim 1 R _ { e } .
Stars in the resulting gravitational potential move mainly on regular orbits .
We use an approximate third integral K from perturbation theory , and write the df as a sum of basis functions in the three integrals E,L _ { z } and K .
We then fit the projected moments of these basis functions to the kinematic observables and deprojected density , using a non-parametric algorithm .

The deduced dynamical structure is radially anisotropic , with \sigma _ { \theta } / \sigma _ { r } \approx \sigma _ { \phi } / \sigma _ { r } \approx 0.7 on the major axis .
Both on the minor axis and near the centre the velocity distribution is more isotropic ; thus the model is flattened by equatorial radial orbits .
The kinematic data is fit without need for a central black hole ; the central mass determined previously from ground-based data therefore overestimates the actual black hole mass .
The mass-to-light ratio of the stars is M / L _ { V } = 6 h _ { 50 } .

The anisotropy structure of NGC 1600 with a radially anisotropic main body and more nearly isotropic centre is similar to that found recently in NGC 1399 , NGC 2434 , NGC 3379 and NGC 6703 , suggesting that this pattern may be common amongst massive elliptical galaxies .
We discuss a possible merger origin of NGC 1600 in the light of these results .