ZTF detects an optical brightening of XTE J1859+226
ATel #14372; Eric C. Bellm (UW) on behalf of the Zwicky Transient Facility Collaboration
on 6 Feb 2021; 15:41 UT
Credential Certification: Eric Bellm (ecbellm@uw.edu)
Subjects: Optical, Binary, Black Hole
We report discovery of an optical brightening of the black hole LMXB XTE J1859+226 with the Zwicky Transient Facility (ZTF; Bellm et. al 2019, Graham et. al 2019). ZTF detected the object (internally designated ZTF21aagyzqr) at m_r ~18.9 on 2021-02-04.6 in five r-band images taken in twilight. No source was detected in five observations taken 24 hours earlier with limiting magnitudes of m_r ~ 19.5-19.8.
We identified the outburst using a watchlist of known X-ray binaries hosted by the ANTARES alert broker (Matheson et. al 2020). Public data for this object can be retrieved at https://antares.noirlab.edu/loci/ANT2021dn4jk
This optical brightening may presage a later X-ray nova (Russell et. al 2019), although some previous optical re-brightenings of this source have not led to increased X-ray emission (Atel #2845). No X-ray brightening is currently apparent in the Swift-BAT or MAXI one-day lightcurves.
Based on observations obtained with the Samuel Oschin Telescope 48-inch and the 60-inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under Grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW. We acknowledge further support from the NSF under grants AST- 1812779 and the Heising-Simons Foundation under grant 2018-0908.
