Broad iron lines from accretion disks K. Iwasawa University 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 Tanaka et al 1995

Other examples of broad iron emission Seyfert nucleus IRAS Galactic black hole binary XTE J Iwasawa et al 2003 Miniutti et al 2003

XMM-Newton observations of MCG 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 MCG / 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 component In MCG 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 ASCA 1994ASCA 1997 Iwasawa et al 1996Iwasawa et al 1999

Excess emission above a fitted absorbed power-law continuum

Line-Flux correlations from the observations

Line-Flux correlations from a simulation for the 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 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 Miniutti Institute of Astronomy - Cambridge In collaboration with Andy Fabian and with Russell Goyder, and Anthony Lasenby

Summary of MCG 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 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 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 Shih et al 02 - Fabian & Vaughan 03 – Vaughan & Fabian 03 (submitted) Reynolds et al 03 (submitted)

A light bending model in the Kerr BH spacetime Primary 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 corotating ring-like source GM et al 03, MNRAS, 344, L22 – GM & Fabian 03, astro-ph/ (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 increases The 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 = 6  = 3 = 3 h s = 1 r g h s = 20 r g

PLC Fe line PLC and Fe line variability induced by light bending The Fe line varies with much smaller amplitude hshs Small h = low PLC flux Large 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 hshs

Regime III: large source height and anti-correlationRegime II: intermediate source height and constant Fe lineRegime I: small source height and correlation IIIIII Fe line – PLC correlation

III

IIIII

I II

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

XTE J during outburst Fe line flux keV PLC flux Rossi et al 03 GM & Fabian 03 I/II III IIIIII ?

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 states 2. 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 states 2. 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 states 4. The hard spectrum is more and more reflection dominated as the PLC flux drops Thank you