Solar flare X-ray source motion as a response to electron spectral hardening A. M. O’Flannagain, P. T. Gallagher, J. C. Brown, R. O. Milligan and G. D. Holman A&A, 555 (2013) A21 Published online: 20 June 2013 DOI: 10.1051/0004-6361/201220368