Broad iron lines from accretion disks

K. IwasawaUniversity of Cambridge

Accreting black hole systems

Most energy dissipates at inner radii of the accretion disk

In the accretion disk + corona model

An X-ray source illuminates the disk to give rise reflection

The most prominent spectral feature is Fe K line

Effects of strong gravity

Because of the proximity to a black hole, relativistic effects are important

Doppler shift

Gravitational redshift

ASCA observation of MCG-6-30-15

Tanaka et al 1995

Other examples of broad iron emission

Seyfert nucleus

IRAS 18325-5926

Galactic black hole binary

XTE J1650-500

Iwasawa et al 2003

Miniutti et al 2003

XMM-Newton observations of MCG-6-30-15

Vaughan & Fabian 2003 MNRAS submitted

See also Wilms et al 2002; Fabian et al 2002; Vaughan et al 2002; Fabian & Vaughan 2002; Ballantyne et al 2003; Reynolds et al 2003

Overall spectral shape of MCG-6-30-15

MCG-6-30-15

/ 3C273

Fluxed spectrum

Fe K line profile after correcting for warm absorption (modelled by Turner et al 2003 based on RGS data analysis)

RMS variability spectra for the 2001 data

Whole observation

Neighbouring bins

(See also Matsumoto et al 2003)

Spectral changes seen in 10 flux slices

Spectrum of the variable component

Difference spectrum: (High flux)-(Low flux)

Presence of a stable componentIn MCG-6-30-15

Offset

Spectrum of the constant component fraction

Variable power-law

Stable reflection-dominated component

Schematic picture of the two-component model

Variability of Fe K line in MCG-6-30-15

ASCA 1994 ASCA 1997

Iwasawa et al 1996 Iwasawa et al 1999

Excess emission above a fitted absorbed power-law continuum

Line-Flux correlations from the 2000 + 2001 observations

Line-Flux correlations from a simulation for the 2000+2001 data

Comparison between real-data and simulations

Simulation for the 2000 observation

Line-Flux correlations from the 2000 observation

Simulation-Realdata comparison for the 2000 observation

Rapid variation of the line core during the 2000 observation

See also M Cappi’s poster

Simulation-Realdata comparison for the 2nd orbit of the 2001 observation (high-flux state)

Summary of the Fe K line properties in MCG-6-30-15

• Presence of red wing appears to be robust• Spectral variability can be explained by the

two-component model: variable power-law + (semi)-stable reflection dominated emission.

• There are occasional variability. • The line emission is most likely to originate

from the relativistic region close to a black hole.

Broad Fe lines from Accretion Disks

Giovanni MiniuttiInstitute of Astronomy - Cambridge

In collaboration with Andy Fabian and with

Russell Goyder, and Anthony Lasenby

Summary of MCG-6-30-15 observations:

A broad Fe line is present in all flux states

Fe line red wing suggests a rotating Kerr black hole

1. The broad Fe line

Fabian et al 02

Tanaka et al ’95 – Iwasawa et al ’96 - Guainazzi et al ’99 – Wilms et al 01 – Fabian et al 02 …

Summary of MCG-6-30-15 observations:

A broad Fe line is present in all flux states

Fe line red wing suggests a rotating Kerr black hole

1. The broad Fe line

A steep emissivity profile is implied ( > 3 ) possibly in the form of a broken power-law

The emissivity suggests the presence of a centrally concentrated primary source of hard X-rays

Tanaka et al ’95 – Iwasawa et al ’96 - Guainazzi et al ’99 – Wilms et al 01 – Fabian et al 02 …

Summary of MCG-6-30-15 observations:

The Fe line generally appears to be

The Fe line-continuum correlation is puzzling

2. The variability properties (> 10ks)

1. Fe line almost constant in “normal” flux states while the continuum varies by a factor 3-4

broader in low flux states narrower in high flux states

2. Fe line is correlated with continuum in low flux states

Iwasawa et al ’96 – Iwasawa et al ’99 – Wilms et al 01 – Lee at al 02 ...

Shih et al 02 - Fabian & Vaughan 03 – Vaughan & Fabian 03 (submitted)

Reynolds et al 03 (submitted)

A light bending model in the Kerr BH spacetimePrimary source of X-

rays• isotropic emission• position specified by h

Photons lost into the BH

RDC reaches the disc and then the observer

PLC reaches the observer

The source is linked to the disc

The orbital timescale << 10ks

corotatingring-like source

GM et al 03, MNRAS, 344, L22 – GM & Fabian 03, astro-ph/0309064 (submitted)

The variability of the PLC is induced by light bending

The variability is due to changes in the height of the primary source at constant intrinsic luminosity

(i.e. at constant mass accretion rate)

1. If the height of the source is small

most of the emitted photons are bent towards the disc and only a small fraction can escape at infinit so that the observed PLC is small (low flux states)

2. if the height is increased

light bending is less effective and more photons are able to reach infinity so that the observed PLC

increasesThe main idea is thus that changes in the height of

the source induce the observed variability via gravitational light bending

PLC

Disk

Disk + lost photons

Primary source emission: where do photons land ?

the PLC drops as the source height (x-axis) gets smaller

averaged (ring-like) non averaged (point-like) present X-ray missions future X-ray missions

Disk emissivity

We present results for averaged emissivity

Emissivity dependence on the primary source height (decreasing clockwise)

The emissivity has the form of a broken power law

steeper in the inner disk region and flatter in the outer

Flat profile at large heights and steep at low heights

= 6

= 3

hs = 1 rg

hs = 20 rg

PLC

Fe line

PLC and Fe line variability induced by light bending

The Fe line varies with much smaller amplitude

hs

Small h = low PLC fluxLarge h = high PLC flux

PLC

Fe line

Fe line EW

The Fe line EW is anti-correlated with the PLC

The Fe line EW tends to constant at very low PLC flux

hs

Regime III: large source height and anti-correlationRegime II: intermediate source height and constant Fe line

Regime I: small source height and correlation

IIIIII

Fe line – PLC correlation

III

II III

I IIIII

Variability timescales

Assuming the primary source is moving with v = 0.1 c and that the BH has a mass of 10 solar

masses the PLC can vary by a factor 4 in about 2ks (or by a factor 20 in 10ks)

7

this may help to explain the extreme variability in some systems (such as e.g IRAS 13224-3809)

most extreme variation is a factor 3-4 in 10ks

XTE J1650-500 during outburstFe lin

e fl

ux

9-100 keV PLC flux

Rossi et al 03

GM & Fabian 03

I/II

III

I II III

?

Conclusions Some predictions of the light bending model

1. The Fe line flux is correlated with the continuum

during low flux states and anti-correlated during high flux states2. The Fe line flux is constant during intermediate

flux states while the continuum varies by a factor 4

correlated

constant

anti-correlated

Conclusions Some predictions of the light bending model

1. The Fe line flux is correlated with the continuum

during low flux states and anti-correlated during high flux states2. The Fe line flux is constant during intermediate

flux states while the continuum varies by a factor 4

3. The Fe line EW is generally anti-correlated with the continuum and almost constant only during

very low flux states4. The hard spectrum is more and more reflection

dominated as the PLC flux drops

Thank you