  Radiative nucleon-deuteron capture and two- and three-body photo
disintegration of the three-nucleon bound state are described. The description
uses the purely nucleonic charge-dependent CD-Bonn potential and its
coupled-channel extension CD Bonn + $\Delta$. The $\Delta$-isobar excitation
yields an effective three-nucleon force and effective two- and three-nucleon
currents besides other $\Delta$-isobar effects; they are mutually consistent.
Exact solutions of three-particle equations are employed for the initial and
final states of the reactions. The current has one-baryon and two-baryon
contributions and couples nucleonic with $\Delta$-isobar channels.
$\Delta$-isobar effects on the observables are isolated. Shortcomings of the
theoretical description are discussed and their consequence for the calculation
of observables is estimated.
