The slope of the low-energy spectrum of prompt gamma-ray burst emission M. Toffano, G. Ghirlanda, L. Nava, G. Ghisellini, M. E. Ravasio and G. Oganesyan A&A, 652 (2021) A123 Published online: 23 August 2021 DOI: 10.1051/0004-6361/202141032