Abstract
The strong gravitational field of a black hole has distinct effects on the observed profile of a spectral line from an accretion disc near a black hole. The observed profile of the spectral line is broadened and skewed by a fast orbital motion and redshifted by a gravitational field. These effects can help us to constrain the parameters of a system with a black hole, both in active galactic nuclei and in a stellar-mass black hole. Here we explore the fact that an accretion disc emission can be mathematically imagined as a superposition of radiating accretion rings that extend from the inner edge to the outer rim of the disc, with some radially varying emissivity. In our work, we show that a characteristic double-horn profile of several radially confined (relatively narrow) accretion rings or belts could be recognized by the planned instruments onboard future satellites (such as the proposed ESA Large Observatory for X-ray Timing).
Highlights
An observation of spectral lines from the inner regions of an accretion disc around a black hole, both in active galactic nuclei (AGN) [1, 2] and in Galactic black holes [3, 4], gives us information about matter in extreme conditions
It is expected to have peaks of enhanced emissivity occurring at particular radii, e.g. due to localized irradiation by magnetic flares [7, 8]
We address the question whether the emission excesses on top of the standard emission profile can be resolved in observed spectra and used to further constrain the black hole spin to better precision
Summary
An observation of spectral lines from the inner regions of an accretion disc around a black hole, both in active galactic nuclei (AGN) [1, 2] and in Galactic black holes [3, 4], gives us information about matter in extreme conditions. These spectral lines are broadened and skewed by a fast orbital motion and redshifted by a strong gravitational field. Correct modeling of the background is crucial for the success of the measurements, because LOFT does not contain any telescope that could measure the background from the neighborhood of the observed object
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