An Optically Discovered Outburst from XTE J1859+226

October 2023 • 2023ApJ...956...21B

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

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 × 10³⁵ 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 10¹¹ 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.

Links

• SIMBAD http://simbad.u-strasbg.fr/simbo.pl?bibcode=2023ApJ...956...21B
• PDF https://iopscience.iop.org/article/10.3847/1538-4357/acf37c/pdf
• PREPRINT http://arxiv.org/abs/2309.10742
• DATA http://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/biblink.pl?code=2023ApJ...956...21B
• ELECTR https://doi.org/10.3847%2F1538-4357%2Facf37c