Volume 613, May 2018
|Number of page(s)||11|
|Published online||30 May 2018|
NGC 4051: Black hole mass and photon index-mass accretion rate correlation
LAPTh, Université Savoie-Mont-Blanc, CNRS,
2 Lomonosov Moscow State University/Sternberg Astronomical Institute, Universitetsky Prospect 13, Moscow 119992, Russia
3 George Mason University, College of Science, 4400 University Drive, Fairfax, VA 22030, USA
4 Dipartimento di Fisica, Università di Ferrara, Via Saragat 1, 44122 Ferrara, Italy
Accepted: 28 January 2018
We present a discovery of the correlation between the X-ray spectral (photon) index and mass accretion rate observed in an active galactic nucleus, NGC 4051. We analyzed spectral transition episodes observed in NGC 4051 using XMM-Newton, Suzaku and RXTE. We applied a scaling technique for a black hole (BH) mass evaluation which uses a correlation between the photon index and normalization of the seed (disk) component, which is proportional to a mass accretion rate. We developed an analytical model that shows the spectral (photon) index of the BH emergent spectrum undergoes an evolution from lower to higher values depending on a mass accretion rate in the accretion disk. We considered Cygnus X-1 and GRO J1550–564 as reference sources for which distances, inclination angles and the BH masses are evaluated by dynamical measurements. Application of the scaling technique for the photon index−mass accretion rate correlation provides an estimate of the black hole mass in NGC 4051 to be more than 6 × 105 solar masses.
Key words: accretion, accretion disks / black hole physics / radiation mechanisms: non-thermal / stars: black holes
© ESO 2018
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