ZTF detects an optical brightening of Swift J1357.2-0933

ATel #14539; Eric C. Bellm (UW) on behalf of the Zwicky Transient Facility collaboration
on 11 Apr 2021; 01:00 UT
Credential Certification: Eric Bellm (ecbellm@uw.edu)

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We report discovery of an optical brightening of the black hole candidate Swift J1357.2-0933 (Krimm et al. 2011, ATel #3138) with the Zwicky Transient Facility (ZTF; Bellm et. al 2019, Graham et. al 2019). The last outburst from this source occurred in 2019 (van Velzen et al. 2019, ATel #12796). ZTF detected the object (internally designated ZTF19aanxwrq) with difference imaging at m_g ~ 18.7 on 2021-04-10.38. No source was detected in images taken on 2021-04-07.3 to limiting magnitudes of m_g ~ 19.5, m_r ~ 20.4. Forced photometry at this epoch provides a 4-sigma detection at m_r = 21.1, indicating that the source was near quiescence at this time.

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/ANT2019qwjh2

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. The ZTF forced-photometry service was funded under the Heising-Simons Foundation grant #12540303 (PI: Graham). We acknowledge further support from the NSF under grants AST-1812779 and the Heising-Simons Foundation under grant 2018-0908.