Scientific achievements. Galaxy
2024
Nature of the Emission Spectrum of NGC 7793 P13: Evidence for Accretion from the Wind of a Donor Star
Based on the results of calculations of non-LTE models of extended atmospheres for the ultraluminous X-ray pulsar NGC 7793 P13 (a system consisting of a neutron star and, presumably, a B9 Ia supergiant), it is shown that most of the observed features of the optical spectrum of the source are naturally reproduced within the framework of a spherically symmetric model of the donor star atmosphere with a mass loss rate in the wind Ṁ ≈ 6 × 10−6 M⊙ yr−1. This value is in good agreement with the estimate of the mass loss rate in the wind of the P13 donor calculated by El Mellah et al. (2019) based on the observed X-ray luminosity of the system for the case of accretion from the wind. Thus, the first reliable evidence for the implementation of such an accretion mechanism in ultraluminous X-ray sources with a neutron star is obtained. The high mass loss rate relative to the standard values for the supergiant B9 Ia can be explained by the high rotation velocity of the star. The mechanism of radiation-field modification in the extended atmosphere model has been implemented and successfully applied for the first time in the problem of modeling the optical spectrum of an ultra-luminous X-ray source, which made it possible to take into account the irradiation of the relatively cold donor wind matter by X-ray radiation from the accretion disk and, as a result, to obtain the observed emission intensity of He II 4686 and improve the agreement between the model and observed neutral helium line profiles. The problem of preserving the wind of a donor star under conditions of irradiation by a powerful X-ray source is considered: it is shown that it can be solved at a qualitative level if, instead of an isotropic source, a source with moderate collimation of X-ray radiation is considered.
Authors:
Vinokurov A. S.*, Kostenkov A. E., Solovyeva Yu. N., together with Atapin K. E. (SAI MSU)
Published:
Vinokurov A. S., Kostenkov A. E., Atapin K. E., Solovyeva Yu. N. “Nature of the Emission Spectrum of NGC 7793 P13: Modeling the Atmosphere of the Donor Star”, Astrophysical Bulletin, Volume 79, Issue 3, pp. 399-413, DOI: 10.1134/S1990341324600558