Synoptic source surface map computed for r = 2.5 R_⊙ using photospheric measurements for Carrington rotation 2123. The location of the flare on May 17th, 2012, is indicated with a triangle. The central meridian at the time of the flare is indicated with a star. The Parker spiral connecting footpoints for each observer, assuming a solar wind speed of 400 km s⁻¹, are shown with squares, numbered as 1: Earth, 2: MSL, 3: STA, 4: STB, 5: MES. Purple regions indicate outward-pointing magnetic fields, orange regions inward-pointing magnetic fields, and the boundary line is shown as a solid black curve. The heliographic equatorial plane is shown as a solid white line. Contour values are given in microtesla. A fit for a simple wavy current sheet is shown as a black dashed curve, and the boundary of the injection region used in particle transport simulations is shown with a black rectangle. Potential field data is provided by the Wilcox Solar Observatory.