X-RAY-ABSORPTION BY IONIZED OXYGEN IN ASCA SPECTRA OF THE INFRARED QUASAR IRAS-13349+2438

We present evidence for X-ray absorption by ionized oxygen in ASCA spe ctra of the prototype infrared quasar IRAS 13349+2438, This powerful ( L-bol greater than or similar to 2 x 10(46) erg s(-1)) quasar was stud ied in detail with ROSAT, and the combination of the X-ray data and op tical/near-infrared spectropolarimetry strongly suggested the presence of a dusty ionized ('warm') absorber along the line of sight to the c entral X-ray source, The ASCA spectra, in contrast to an earlier claim , show evidence for ionized oxygen edges, and the presence of such edg es appears to provide the most physically plausible interpretation of the data. Thus, the ASCA spectra support the dusty warm absorber hypot hesis. The ASCA data also allow the physical properties of the warm ab sorber to be constrained far better than before, A one-zone warm absor ber model indicates the ionized column to be in the range (2-6) x 10(2 1) cm(-2), and it gives an ionization parameter of xi = 31(-12)(+12) e rg cm s(-1). The dusty warm absorber appears to have a density of less than or similar to 3 x 10(8) cm(-3), and it is probably located outsi de the broad-line region. The dust in the warm absorber cm does not ap pear to have been heavily sputtered or destroyed via other means. Base d on the ASCA fitting, we suggest that ultraviolet absorption lines fr om the warm absorber may be detectable and discuss how they can be use d to further constrain the warm absorber properties, We compare and co ntrast the X-ray properties of IRAS 13349+2438 with those of broad abs orption line quasars, We comment on the steep > 2 keV continuum of IRA S 13349+2438 and examine the relevance to some models of radiative Fe II formation.