Black hole spin measurements based on a thin disc model with finite thickness – I. An example study of MCG−06-30-15. Issue 3 (19th May 2022)

• Record Type: Journal Article
• Authors: Jiang, Jiachen; Abdikamalov, Askar B; Bambi, Cosimo; Reynolds, Christopher S
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 514:Issue 3(2022)
• Page Start: 3246
• Page End: 3259
• Publication Date: 2022-05-19
• Subjects: accretion, accretion discs -- black hole physics -- galaxies: Seyfert -- X-rays: galaxies; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stac1369
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: We present a re-analysis of the XMM–Newton and NuSTAR observing campaigns for the well-studied, X-ray-bright AGN MCG−06-30-15. In particular, we consider a disc model with finite thickness. By fitting the disc reflection spectra in the data, we obtain a black hole spin of 0.87–0.99 (90 per cent confidence range) after taking the thickness of the disc into consideration. Spectral models with a grid of mass accretion rate from 0 to $30{{\, \rm per\, cent}}\, \dot{M}_{\rm Edd}$ are calculated for MCG−06-30-15. This result is obtained by considering a free disc reflection fraction parameter f refl and is consistent with previous measurements based on razor-thin disc models. Besides, an isotropic, point-like geometry, i.e. the 'lamppost' geometry, is assumed for the corona in our model. We find that such a geometry overestimates f refl in the data. Therefore, thin disc models with consistent 'lamppost' values of f refl provide a worse fit than ones with a free f refl parameter. We discuss possible reasons for the discrepancy between the observed and theoretical values of f refl at the end of the paper. Modifications for the over-simplified lamppost model might be needed when the thickness of the thin disc is considered in future work.