  We analyze the free energy of the integrable two dimensional O(4) sigma model
in a magnetic field. We use Volin's method to extract high number (2000) of
perturbative coefficients with very high precision. The factorial growth of
these coefficients are regulated by switching to the Borel transform, where we
perform several asymptotic analysis. High precision data allowed to identify
Stokes constants and alien derivatives with exact expressions. These reveal a
nice resurgence structure which enables to formulate the first few terms of the
ambiguity free trans-series. We check these results against the direct
numerical solution of the exact integral equation and find complete agreement.
