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The optical spectra of ultraluminous X-ray sources (ULXs) show signs of powerful outflows of matter. These outflows are responsible for the formation of a significant portion of optical and ultraviolet emission in ULXs and can either be stellar winds of the donor stars or optically thick outflows (winds) from the surface of supercritical accretion disks. In the latter scenario the outflows are still expected to be similar to stellar winds of massive stars, which allows one to use the same methods for their study based on a comparison of the observed spectra with those simulated within the framework of non-LTE extended atmosphere models. In this paper, we simulate the optical spectrum of the ultraluminous X-ray pulsar NGC 7793 P13, assuming that its emission part is produced in the wind of the supercritical accretion disk. The estimated mass loss rate is about yr . We consider the positive and negative aspects of the model and also discuss the applicability of the concept of supercritical disk winds to NGC 7793 P13 and to another well-known ultraluminous X-ray pulsar, NGC 300 ULX-1. [ABSTRACT FROM AUTHOR]

We describe a model of spectral energy distribution in supercritical accretion disks (SCAD) based on the conception by Shakura and Sunyaev. We apply this model to five ultra-luminous X-ray sources (ULXs). In this approach, the disk becomes thick at distances to the center less than the spherization radius, and the temperature dependence is T ∝ r. In this region the disk luminosity is L ∼ L $$\ln \left( {{{\dot M} \mathord{\left/ {\vphantom {{\dot M} {\dot M_{Edd} }}} \right. \kern-\nulldelimiterspace} {\dot M_{Edd} }}} \right)$$, and strong wind arises forming a wind funnel above the disk. Outside the spherization radius, the disk is thin and its total luminosity is Eddington, L. The thin disk heats the wind from below. From the inner side of the funnel the wind is heated by the supercritical disk. In this paper we do not consider Comptonization in the inner hot winds which must cover the deep supercritical disk regions. Our model is technically similar to the DISKIR model of Gierlinski et al. The models differ in disk type (standard-supercritical) and irradiation (disk-wind).We propose to distinguish between these two models in the X-ray region of about 0.3-1 keV, where the SCAD model has a flat νF spectrum, and the DISKIR model never has a flat part, as it is based on the standard α-disk. An important difference between the models can be found in their resulting black hole masses. In application to the ULX spectra, the DISKIR model yields black hole masses of a few hundred solar masses, whereas the SCAD model produces stellar-mass (about 10M) black holes. [ABSTRACT FROM AUTHOR]