CRTS-II discovery of an outburst of BH transient Swift J1357.2-0933

ATel #10297; A. J. Drake, S. G. Djorgovski, A. A. Mahabal, M. J. Graham (Caltech); D. Stern (JPL); M. Catelan (PUC Chile); E. Christensen, S. M. Larson (LPL/UA).
on 20 Apr 2017; 23:16 UT
Credential Certification: Andrew J. Drake (

Subjects: Optical, Binary, Transient

Referred to by ATel #: 10314

On 2017-04-20.33 UT CRTS-II detected an optical outburst of short period black hole transient (BHT) candidate Swift J1357.2-0933 (Krimm et al. 2011, ATel#3138; Rau et al. 2011, ATel#3140; Sanchez et al. 2015, MNRAS, 454, 2199). From four observations taken with the Catalina Schmidt telescope plus 19 sq. deg. camera, the source was measured as having V_CSS=16.7+/-0.1. The quiescent brightness is V_CSS~21.

The 2011 outburst of Swift J1357.2-0933 was independently detected by CRTS as transient CSS110208:135717-093238, and was spectroscopically determined to have a featureless blue continuum (Drake et al. 2011, ATel#3343; Drake et al. 2014, MNRAS, 441, 1186). At that time Swift J1357.2-0933 was measured to peak at V_CSS~16.2, with the outburst lasting >170 days.

Additional information regarding Swift J1357.2-0933 is given in the catalog of stellar-mass black holes in X-ray binaries, BlackCAT (, Corral-Santana et al. 2016, A&A, 587, 61).

Optical and spectroscopic follow-up are requested.
All CRTS-II and CRTS discoveries are publicly available via the CRTS home page (