Relative time delay in a spinning black hole as a diagnostic for no-hair theorem Ramil N. Izmailov, Eduard R. Zhdanov, Arunava Bhadra and Kamal K. Nandi Eur. Phys. J. C, 79 2 (2019) 105 Published online: 01 February 2019 DOI: 10.1140/epjc/s10052-019-6618-6