Profiled spectral lines of Keplerian rings orbiting in the regular Bardeen black hole spacetimes

TL;DR

This paper investigates how non-linear electrodynamics influences the spectral lines emitted by rings orbiting Bardeen black holes, revealing significant effects on the observed spectra that could aid in testing regular black hole models.

Contribution

It demonstrates the impact of NED on photon motion and spectral line profiles around Bardeen black holes, providing potential observational signatures for regular black hole spacetimes.

Findings

NED causes redshift and profile narrowing of spectral lines.

Spectral flux is substantially suppressed by NED effects.

Line shapes are significantly altered for extended Keplerian disks.

Abstract

Considering the regular Bardeen black hole spacetimes, we test the observational effects of the general relativistic solutions coupled to non-linear electrodynamics (NED) by studying the photon motion in the effective geometry governed by the spacetime geometry and the NED Lagrangian. We focus our attention to the observationally important case of profiled spectral lines generated by rings radiating in a fixed frequency and orbiting the black hole along circular geodesics of the Bardeen spacetime. Such profiled spectral lines are observed in active galactic nuclei and in microquasars, giving sufficient data for the test of regular black holes. We expect that such radiating rings could arise around the Galaxy central supermassive black hole SgrA*, and the related profiled spectral lines could give important additional information to those obtained by direct observations due to the Event Horizon (GRAVITY) Telescope. We demonstrate that the profiled spectral lines of the radiating rings predict strong signatures of the NED effects on the photon motion -- namely the frequency shift to the red edge of the spectrum, and narrowing of the profile, by more than one order in comparison with the case of the profiles generated purely by the spacetime geometry, for all values of the magnetic charge and the inclination angle of the observer. The specific flux is substantially suppressed and for extended Keplerian disks even the shape of the profiled line is significantly modified due to the NED effect.