The book of records of the chronicles. Compare Esther 2:23, where the title is given more briefly, as "the book of the chronicles." See also Esther 10:2. The character of the book has been already explained (see comment on Esther 2:23).
They were read. Either because the king could not read himself, or because the sound of a man's voice might (it was thought) induce drowsiness.