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Decoding the time-lags in accreting black holes with XMM-Newton

Decoding the time-lags in accreting black holes with XMM-Newton. Phil Uttley Thanks to: P. Cassatella, T. Wilkinson, J. Wilms, K. Pottschmidt, M. Hanke, M. Böck. Cyg X-1. Background: disc variability?.

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Decoding the time-lags in accreting black holes with XMM-Newton

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  1. Decoding the time-lags in accreting black holes with XMM-Newton Phil Uttley Thanks to: P. Cassatella, T. Wilkinson, J. Wilms, K. Pottschmidt, M. Hanke, M. Böck

  2. Cyg X-1 Background: disc variability? 1974: Lightman & Eardley propose disc instability as the origin of X-ray variability in black hole XRBs But subsequent observations don’t seem to support this... mean (time-averaged) spectrum rms variability amplitude rms (time-varying) spectrum GX 339-4 Belloni et al. 2005 spectral hardness Variability generated by hot flow/corona? (Churazov et al. 2001) Done et al. (2007) Decreasing disc, increasing power-law

  3. Hard state disc/corona interaction • Several physical components: cool (kT~0.2 keV) optically thick disc, hot optically thin corona, jets • Corona and disc see each other: reflection • Can study both disc thermal and power-law spectra and variability with XMM-Newton EPIC-pn timing mode

  4. Disc X-ray reverberation • X-rays from the continuum source (corona, jet base?) hit the disc • Some are reflected (iron line and reflection continuum) • The absorbed fraction is thermalised and re-emitted at the local disc temperature ~1% of incident flux ~70% of incident flux ~30% of incident flux

  5. GX 339-4 2004 observation 170 s of ~150 ks 0.5-0.9 keV 3-10 keV Both bands (disc+pl and pl only) show large amplitude strongly correlated variability!

  6. GX 339-4 2004 hard state: Energy-dependent PSDs and frequency-resolved rms spectra 0.5-0.9 keV 3-10 keV slow fast Differences in PSD between hard and soft bands can be explained if variability is intrinsic to the disc and PL is correlated with it (Wilkinson & Uttley 2009)

  7. Does the disc drive the power-law variability? (Uttley et al. 2011) Yes, at least below 1 Hz, reprocessing dominates observed disc variability > 1 Hz

  8. XMM-Newton TOO programme 0.12-0.49 Hz Frequency Range

  9. Variable disc or disc/hot-flow boundary? GX 339-4 2004: 0.034-0.12 Hz Range The sharpness of the change in lag below 2 keV requires that the leading component is almost a pure blackbody and not a blackbody plus a steep Comptonised component blackbody plus steep (Γ=3) power-law leads hard (Γ=1.4) power-law blackbody leads hard (Γ=1.6) power-law It really looks like the ‘standard’ accretion disc!  the corona does not see a lot of the disc

  10. Interpreting the variability: signals and amplifiers Signal: mdot fluctuations in disc Amplifier: X-ray emitting regions * Emission mdot Delay Time Input signal from disc is convolved with the emission vs. delay profile

  11. The effect of the emission profile Emission profiles (transfer functions) and light curves for: Disc BB band Power-law band Slow variations are strong in either band Fast variations are suppressed in the disc band Fast variations are further reduced But reprocessing of power-law can add and dominate short-time-scale lags

  12. A viscous propagation + reverberation model 0.1 Hz 1 Hz 10 Hz Reverberation dominates at the short time-scales where the slow viscous time-scale variations of the disc are washed out

  13. Mapping the disc inner edge The observed soft lags imply Rin<50 RG in this hard state 440 ks on Cyg X-1 coming up in October – watch this space!!!

  14. Disk stability changes • Hard state disks look unstable, soft state disks look stable – where does the change occur? • Obtained 2 TOO observations of GX 339-4 at epochs where the source shows significantly low-frequency Lorentzians at significantly different frequencies than in 2004 • Disk stabilises gradually through hard state? mdot connection? 0.5-0.9 keV 3-10 keV

  15. IR vs XMM-Newton: revealing the disc-jet connection Covariance spectra XMM-Newton vs RXTE XMM-Newton vs IR Covariance spectrum shows disc correlates with jet emission: Disc drives at least some jet variability! Does disc correlate better with jet than harder X-rays?

  16. Summary • Disc accretion fluctuations are driving variability in hard state BHXRBs, certainly on time-scales < 1s • Considering the interplay between the disc mdot variability and emitting regions we infer that it is likely the disc drives variability at even shorter time-scales • The disc seems to stabilise gradually towards the intermediate state • The disc is also driving the jet variations!

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