Profiled spectral lines generated by Keplerian discs orbiting in the Bardeen and Ayòn-Beato–Garcìa spacetimes

Abstract

Shape and frequency-shift maps of direct and indirect images of Keplerian discs orbiting in Bardeen and Ayòn-Beato–Garcìa (ABG) black hole and no-horizon spacetimes are determined. Then profiles of spectral lines generated in the innermost parts of the Keplerian discs in the Bardeen and ABG spacetimes are constructed. The frequency-shift maps and profiled spectral lines are compared to those generated in the field of Schwarzschild black holes and possible observationally relevant signatures of the regular black hole and no-horizon spacetimes are discussed. We demonstrate that differences relative to the Schwarzschild spacetimes are for the no-horizon spacetimes much more profound in comparison to the regular black hole spacetimes and increase with increasing charge parameter of the spacetime. The differences are greater for small and large inclination angles than for intermediate ones. For the no-horizon spacetimes, the differences enable us to distinguish the Bardeen and ABG spacetime, if inclination angle to the distant observer is known. We also show that contribution of the so-called ghost images to the profiled lines increases with increasing charge parameter of the spacetimes.