Information on Martyrdom and Ascension of Isaiah from http://www.earlyjewishwritings.com/ascensionisaiah.html

Michael A. Knibb writes: "The Martyrdom of Isaiah is a Jewish work which has come down to us as part of a larger Christian composition known as the Ascension of Isaiah. The Ascension consists of three separate writings: (1) the Martyrdom itself (the basic material in AscenIs 1:1-3:12+5:1-16). (2) An account of a vision seen by Isaiah (AscenIs 3:13-4:22) to which the title the Testament of Hezekiah has sometimes been given. The contents of this Christian writing are summarized below on p. 190. (3) A Christian work known as the Vision of Isaiah (AscenIs 6-11), which describes Isaiah's journey through the seven heavens. While in the seventh heaven he sees the descent to earth, life, death, resurrection an ascension of the Lord. It is this account of Isaiah's journey, or ascension, through the heavens which gives the title to the whole work. Here, however, we are only concerned with the Martyrdom of Isaiah." (Outside the Old Testament, p. 178)

James Charlesworth writes: "The Martyrdom and Ascension of Isaiah, like many pseudepigrapha (especially 1 Enoch) is composite, comprising three separate sections: the Martyrdom of Isaiah (basically chs. 1-5, except for THez); the Testament of Hezekiah (3:13-4:18); and the Vision of Isaiah (chps. 6-11). Some specialists see only two sections, chapters 1-5 and 6-11, but argue for the existence of extraneous material in each section (viz. Flemming and Duensing, no. 920, pp. 642f.; A. Vaillant, no. 943). Two or three of the writings originally may have circulated independently (see Box in Charles' The Ascension of Isaiah, p. vii; M. Philonenko, no. 231, p. 2; contrast C. C. Torrey, Apoc. Lit., esp. pp. 133-35)....