Unveiling the origin of the optical/UV emission from the Galactic ULX Swift J0243.6+6124 during its 2017-2018 giant outburst
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arXiv
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| Autori principali: | , , , , , , , , , , |
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| Natura: | Preprint |
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2023
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| author | Alfonso-Garzón, J. Eijnden, J. van den Kuin, N. P. M. Fürst, F. Rouco-Escorial, A. Fabregat, J. Reig, P. Mas-Hesse, J. M. Jenke, P. A. Malacaria, C. Wilson-Hodge, C. |
| author_facet | Alfonso-Garzón, J. Eijnden, J. van den Kuin, N. P. M. Fürst, F. Rouco-Escorial, A. Fabregat, J. Reig, P. Mas-Hesse, J. M. Jenke, P. A. Malacaria, C. Wilson-Hodge, C. |
| contents | From late September 2017 to February 2018, the Be X-ray binary (BeXB) Swift J0243.6+6124 underwent an unprecedently bright giant outburst. The reported X-ray luminosities were so high that the system was classified as an Ultraluminous X-ray source (ULX). It was also the first BeXB pulsar showing radio jet emission. The source was not only bright in X-rays and radio, but also in optical and UV wavelenghts. In this paper we aim to understand the origin of the observed optical/UV fluxes simultaneous to the X-ray emission. We studied the optical/UV light curves in comparison with the X-ray fluxes along the outburst, considering the main mechanisms that can explain the optical/UV emission in X-ray binaries. Due to the tight correlation observed between the optical/UV and X-ray light curves, reprocessing of X-rays seems to be the most plausible explanation. We calculated the timescales of the light curves decays and studied the correlation indexes between the optical and X-ray emission. Finally, we built a physical model considering X-ray heating of the surface of the donor star, irradiation of the accretion disk, and emission from a viscously heated accretion disk, in order to reproduce the observed optical/UV SEDs along the outburst. We considered in our model that the Be circumstellar disk was co-planar to the orbit, and then we neglected its irradiation in the current model. As an input of the model, we used as incident X-ray luminosities those calculated from the bolometric X-ray fluxes obtained from the spectral fit of the Swift/XRT and BAT observations. We conclude that reprocessing of X-rays as X-ray heating of the Be star surface and irradiation of the accretion disk are the two main mechanisms that can reproduce the observed optical/UV emission during the 2017-2018 giant outburst of Swift J0243.6+6124. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2312_08080 |
| institution | arXiv |
| publishDate | 2023 |
| record_format | arxiv |
| spellingShingle | Unveiling the origin of the optical/UV emission from the Galactic ULX Swift J0243.6+6124 during its 2017-2018 giant outburst Alfonso-Garzón, J. Eijnden, J. van den Kuin, N. P. M. Fürst, F. Rouco-Escorial, A. Fabregat, J. Reig, P. Mas-Hesse, J. M. Jenke, P. A. Malacaria, C. Wilson-Hodge, C. High Energy Astrophysical Phenomena From late September 2017 to February 2018, the Be X-ray binary (BeXB) Swift J0243.6+6124 underwent an unprecedently bright giant outburst. The reported X-ray luminosities were so high that the system was classified as an Ultraluminous X-ray source (ULX). It was also the first BeXB pulsar showing radio jet emission. The source was not only bright in X-rays and radio, but also in optical and UV wavelenghts. In this paper we aim to understand the origin of the observed optical/UV fluxes simultaneous to the X-ray emission. We studied the optical/UV light curves in comparison with the X-ray fluxes along the outburst, considering the main mechanisms that can explain the optical/UV emission in X-ray binaries. Due to the tight correlation observed between the optical/UV and X-ray light curves, reprocessing of X-rays seems to be the most plausible explanation. We calculated the timescales of the light curves decays and studied the correlation indexes between the optical and X-ray emission. Finally, we built a physical model considering X-ray heating of the surface of the donor star, irradiation of the accretion disk, and emission from a viscously heated accretion disk, in order to reproduce the observed optical/UV SEDs along the outburst. We considered in our model that the Be circumstellar disk was co-planar to the orbit, and then we neglected its irradiation in the current model. As an input of the model, we used as incident X-ray luminosities those calculated from the bolometric X-ray fluxes obtained from the spectral fit of the Swift/XRT and BAT observations. We conclude that reprocessing of X-rays as X-ray heating of the Be star surface and irradiation of the accretion disk are the two main mechanisms that can reproduce the observed optical/UV emission during the 2017-2018 giant outburst of Swift J0243.6+6124. |
| title | Unveiling the origin of the optical/UV emission from the Galactic ULX Swift J0243.6+6124 during its 2017-2018 giant outburst |
| topic | High Energy Astrophysical Phenomena |
| url | https://arxiv.org/abs/2312.08080 |