The origin of X-ray intra-day variability in HBL PKS 2155–304 W. Hu, J. L. Kang, J. X. Wang, G. C. Xiao and G. W. Ren A&A, 697 (2025) A71 Published online: 12 May 2025 DOI: 10.1051/0004-6361/202453490