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arXiv · 2309.10742

An Optically-Discovered Outburst from XTE J1859+226

Eric C. Bellm·Yuankun Wang·Jan van Roestel·Rebecca A. Phillipson·Michael W. Coughlin·John A. Tomsick·Steven L. Groom·Brian Healy·Josiah Purdum·Ben Rusholme·Jesper Sollerman·Peter Bealo·Stefano Lora·Eddy Muyllaert·Ivo Peretto·Erik J. Schwendeman
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Abstract

Using the Zwicky Transient Facility, in 2021 February we identified the first known outburst of the Black Hole X-ray Transient XTE J1859+226 since its discovery in 1999. The outburst was visible at X-ray, UV, and optical wavelengths for less than 20 days, substantially shorter than its 320-day full outburst in 1999, and the observed peak luminosity was two orders of magnitude lower. Its peak bolometric luminosity was only $2\times 10^{35}$ erg s$^{-1}$, implying an Eddington fraction of about $3\times10^{-4}$. The source remained in the hard spectral state throughout the outburst. From optical spectroscopy measurements we estimate an outer disk radius of 10$^{11}$ cm. The low observed X-ray luminosity is not sufficient to irradiate the entire disk, but we observe a surprising exponential decline in the X-ray lightcurve. These observations highlight the potential of optical and infrared (O/IR) synoptic surveys to discover low-luminosity activity from X-ray transients.

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Eric C. Bellm, Yuankun Wang, Jan van Roestel, Rebecca A. Phillipson, Michael W. Coughlin, John A. Tomsick, Steven L. Groom, Brian Healy, Josiah Purdum, Ben Rusholme, Jesper Sollerman, Peter Bealo, Stefano Lora, Eddy Muyllaert, Ivo Peretto, Erik J. Schwendeman. 2023-09-19. An Optically-Discovered Outburst from XTE J1859+226. https://arxiv.org/abs/2309.10742

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