Letter to the Editor

Mass of the active galactic nucleus black hole XMMUJ134736.6+173403

¹ Institute of Physics, Research Centre for Computational Physics and Data Processing, Research Centre for Theoretical Physics and Astrophysics, Faculty of Philosophy & Science, Silesian University in Opava, Bezručovo nám. 13, 74601 Opava, Czech Republic
e-mail: katka.g@seznam.cz
² Astronomical Institute, Boční II 1401/2a, 14131 Praha 4-Spořilov, Czech Republic

Received: 4 December 2018
Accepted: 9 January 2019

Abstract

A recent study of the X-ray source XMMUJ134736.6+173403 has revealed a strong quasi-periodic modulation in the X-ray flux. The observation of two quasiperiodic oscillations (QPOs) that occur on a daily timescale and exhibit a 3:1 frequency ratio strongly supports the evidence for the presence of an active galactic nucleus black hole (AGN BH). Assuming an orbital origin of QPOs, we calculated the upper and lower limit on AGN BH mass M and found M ≈ 10⁷ − 10⁹ M_⊙. When we compare this to mass estimates of other sources, XMMUJ134736.6+173403 appears to be the most massive source with commensurable QPO frequencies, and its mass represents the current observational upper limit on AGN BH mass based on QPO observations. We note that it will be crucial for the falsification of particular resonance models of QPOs whether only a single QPO with a frequency that completes the harmonic sequence 3 : 2 : 1 is found in this source, or if a new different pair of QPOs with frequencies in the 3 : 2 ratio is found. The former case would agree with the prediction of the 3 : 2 epicyclic resonance model and BH mass M ≈ (5a² + 8a + 8)×10⁷ M_⊙, where a is a dimensionless BH spin.