Unveiling the origin of the optical/UV emission from the Galactic ULX Swift J0243.6+6124 during its 2017-2018 giant outburst
arXiv:2312.08080 · doi:10.1051/0004-6361/202347712
Abstract
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.
Accepted for publication in A&A on 7 December 2023; 16 pages, 12 figures, 2 tables
References in corpus (27)
- Estimating distances from parallaxes. V: Geometric and photogeometric distances to 1.47 billion stars in Gaia Early Data Release 3
- Global optical/infrared - X-ray correlations in X-ray binaries: quantifying disc and jet contributions
- Reprocessing of X-rays in the outer accretion disc of the black hole binary XTE J1817--330
- Giant Outbursts in Be/X-ray Binaries
- Evidence for a jet contribution to the optical/infrared light of neutron star X-ray binaries
- Insight-HXMT discovery of the highest energy CRSF from the first Galactic ultra-luminous X-ray pulsar Swift J0243.6+6124
- Super-Eddington accretion onto the Galactic ultraluminous X-ray pulsar Swift J0243.6+6124
- Interpreting Flux from Broadband Photometry
- On the relationship between circumstellar disc size and X-ray outbursts in Be/X-ray binaries
- Magnetic Field Upper Limits for Jet Formation
- Chandra reveals a possible ultra-fast outflow in the super-Eddington Be/X-ray binary Swift J0243.6+6124
- Insight-HXMT observations of Swift J0243.6+6124 during its 2017-2018 outburst
- Optical counterpart to Swift J0243.6+6124
- A re-establishing jet during an X-ray re-brightening of the Be/X-ray binary Swift J0243.6+6124
- Possible regular phenomena in EXO 2030+375
- The origin of optical emission lines in the soft state of X-ray binary outbursts: the case of MAXI J1820+070
- Long-term evolution of accretion discs in Be/X-ray binaries
- Studying the accretion geometry of EXO 2030+375 at luminosities close to the propeller regime
- Radio monitoring of transient Be/X-ray binaries and the inflow-outflow coupling of strongly-magnetized accreting neutron stars
- ULX pulsar Swift J0243.6+6124 observations with NuSTAR -- dominance of reflected emission in the super-Eddington state
- Exploring the role of X-ray reprocessing and irradiation in the anomalous bright optical outbursts of A0538-66
- Long-term optical and X-ray variability of the Be/X-ray binary H 1145-619: discovery of an on-going retrograde density wave
- First characterization of Swift J1845.7-0037 with NuSTAR
- Multiwavelength observations of Swift J0243.6+6124 from 2017 to 2022
- Timing analysis of Swift J0243.6+6124 with NICER and Fermi/GBM during the decay phase of the 2017-2018 outburst
- Long-term optical variability of the Be/X-ray binary GRO J2058+42
- X-ray spectral-timing variability of 1A 0535+262 during the 2020 giant outburst