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DOE OSTI · 2583012

An Optically Discovered Outburst from XTE J1859+226

Bellm, Eric (ORCID:0000000180185348)·Wang, Yuankun (ORCID:0000000155380395)·van Roestel, Jan (ORCID:0000000226262872)·Phillipson, Rebecca (ORCID:0000000168917091)·Coughlin, Michael (ORCID:0000000282622924)·Tomsick, John (ORCID:0000000155069855)·Groom, Steven (ORCID:0000000156683507)·Healy, Brian (ORCID:0000000277187884)·Purdum, Josiah (ORCID:0000000312273738)·Rusholme, Ben (ORCID:0000000176484142)·Sollerman, Jesper (ORCID:0000000315466615)·Bealo, Peter·Lora, Stefano·Muyllaert, Eddy·Peretto, Ivo·Schwendeman, Erik
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Abstract

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 full outburst of 320 days in 1999, and the observed peak luminosity was 2 orders of magnitude lower. Its peak bolometric luminosity was only 2 × 10 35 erg s −1 , implying an Eddington fraction of about 3 × 10 −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 light curve. These observations highlight the potential of optical and infrared synoptic surveys to discover low-luminosity activity from X-ray transients.

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Bellm, Eric (ORCID:0000000180185348), Wang, Yuankun (ORCID:0000000155380395), van Roestel, Jan (ORCID:0000000226262872), Phillipson, Rebecca (ORCID:0000000168917091), Coughlin, Michael (ORCID:0000000282622924), Tomsick, John (ORCID:0000000155069855), Groom, Steven (ORCID:0000000156683507), Healy, Brian (ORCID:0000000277187884), Purdum, Josiah (ORCID:0000000312273738), Rusholme, Ben (ORCID:0000000176484142), Sollerman, Jesper (ORCID:0000000315466615), Bealo, Peter, Lora, Stefano, Muyllaert, Eddy, Peretto, Ivo, Schwendeman, Erik. 2023-10-01. An Optically Discovered Outburst from XTE J1859+226. https://doi.org/10.3847/1538-4357%2Facf37c

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