Electronic Telegram No. 5709 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network (223393) 2003 SD_106 M. Skrutskie, University of Virginia and International Occultation Timing Association (IOTA), reports the discovery of an apparent satellite of minor planet (223393) based on an occultation of the star HIP 19615 (which has catalogued Gaia magnitudes G = 8.57 and R = 8.02, and a diameter of 0".00017 derived from the Gaia FLAME measurement) on 2026 Mar. 12.175 UT. The magnitude of (223393) was 21.0 (which was 12.4 magnitudes fainter than the target star). Skrutskie observed from Nederland, CO, USA using a 40-cm telescope (+ Apollo-M MAX Pro USB3.0 Mono Cooled camera with GPS linked timing running at a cadence of 0.02 s). The recording, with a limiting magnitude of approximately G = 12.6, showed two consecutive occultations of durations 0.10 and 0.08 s, separated by 3.0 s, corresponding to chord lengths of 2.4 and 1.9 km at the minor planet, with the distance between the chords corresponding to 70.6 km. Using UCAC4 558-009184 (Gaia magnitudes G = 11.4 and R = 10.6) as a reference star, the flux was measured to drop to magnitude G = 10.6 and R = 10.2 during the first occultation, and to magnitude G = 10.3 and R = 9.8 during the second occultation. The depths of these drops exclude a double star as an explanation for the light curve. The NEOWISE-catalogued diameter of this main-belt asteroid is 3.8 +/- 0.4 km. Fresnel modeling that includes the effect of the star's diameter indicates that the largest body size to replicate the longer chord has a diameter no greater than 4.2 km. The smallest body size to replicate the shorter chord is 1.5 x 1.0 km with an equivalent diameter of 1.25 km. If a body the size of the NEOWISE diameter is split into two bodies of equal volume and density, their diameters would be 3.0 km (being 79 percent of the NEOWISE diameter). Accordingly, the diameter of the larger body is in the range 3.0-4.2 km (3.6 +/- 0.6 km), and the diameter of the smaller body is in the range 1.25-3.0 km (2.1 +/- 0.9 km). As the lengths of both chords are significantly less than the diameter of the bodies if they are of equal size, it is not possible to associate the larger body of this system with either chord. The separation of the two bodies was 0".0321 in p.a. 267 +/- 1.5 degrees (with a 180-degree ambiguity), with a sky-plane separation of 72.8 km. The sky-plane configuration diagram is posted at the website URL http://www.cbat.eps.harvard.edu/iau/cbet/005700/CBET5709_Fig1.png and shows the observed occultation chord. Three representative models of the system used to model the light curve, and the observed light curve with a superimposed modeled light curve, is posted at the following website URL: http://www.cbat.eps.harvard.edu/iau/cbet/005700/CBET5709_Fig2.png. The upper model has one body at the maximum size of 3.8 km and the other at the minimum size of 1.5 x 1.0 km; the middle model has the two bodies with equal diameters of 3.0 km; and the lower model has the two bodies in reverse juxtaposition with the smaller body at the minimum size of 1.75 x 1.2 km for that light drop. D. Herald and D. Gault, Trans-Tasman Occultation Alliance; and C. Weber, European Section of the IOTA aided in the analysis. The reader is also referred to the end notes on CBET 5679. NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2026 CBAT 2026 June 29 (CBET 5709) Daniel W. E. Green