  We report an unusual regime of emittance self-compensation in an electron
bunch generated in blow-out mode by a radio-frequency photocathode gun.
Simulations clearly show an initial growth and a subsequent self-compensation
of projected emittance in a divergent electron bunch originating from the
effects of: (i) strong space-charge forces of mirror charges on the cathode,
(ii) an energy chirp in the bunch and (iii) substantial re-shaping of the
electron bunch. Furthermore, we show analytically and numerically how a complex
interplay between these effects leads to emittance self-compensation in free
space -- the effect that is normally observed only in a focusing magnetic
field.
