Source : Webster's Revised Unabridged Dictionary (1913)

Indignantly \In*dig"nant*ly\, adv.
   In an indignant manner.

Source : WordNet®

indignantly
     adv : in an indignant manner; "Miss Burney protested indignantly,
           her long thin nose turning pink with mortification at
           this irreverent piece of mimicry"