For (11.5.8) see Babister (1967, §3.7) with
modified convergence conditions. For (11.5.9) deform the
integration path in (11.5.8) into a loop and use
(11.2.2).
For further integral representations see
Babister (1967, §§3.3, 3.14),
Erdélyi et al. (1954a, §§5.17, 15.3), Magnus et al. (1966, p. 114),
Oberhettinger (1972), Oberhettinger (1974, §2.7),
Oberhettinger and Badii (1973, §2.14), and
Watson (1944, pp. 330, 374, and 426).