Optical properties of Kerr–Newman spacetime in the presence of plasma Gulmina Zaman Babar, Abdullah Zaman Babar and Farruh Atamurotov Eur. Phys. J. C, 80 8 (2020) 761 Published online: 20 August 2020 DOI: 10.1140/epjc/s10052-020-8346-3