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 Phil Uttley Thanks to: P. Cassatella, T. Wilkinson, J. Wilms, K. Pottschmidt, M. Hanke, M. Böck

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 : 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... rms variability amplitude spectral hardness GX Belloni et al Decreasing disc, increasing power-law Done et al. (2007) Cyg X-1 mean (time- averaged) spectrum rms (time- varying) spectrum Variability generated by hot flow/corona? (Churazov et al. 2001)

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

Disc X-ray reverberation ~70% of incident flux ~30% of incident flux ~1% of incident flux  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

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

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

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

XMM-Newton TOO programme Hz Frequency Range

Variable disc or disc/hot-flow boundary? blackbody plus steep (Γ=3) power-law leads hard (Γ=1.4) power-law blackbody leads hard (Γ=1.6) power-law 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 It really looks like the ‘standard’ accretion disc!  the corona does not see a lot of the disc GX : Hz Range

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

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

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

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

Disk stability changes  Hard state disks look unstable, soft state disks look stable – where does the change occur?  Obtained 2 TOO observations of GX 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? keV 3-10 keV

IR vs XMM-Newton: revealing the disc-jet connection XMM-Newton vs RXTE XMM-Newton vs IR Covariance spectra 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?

Summary G Disc accretion fluctuations are driving variability in hard state BHXRBs, certainly on time-scales < 1s G 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 G The disc seems to stabilise gradually towards the intermediate state G The disc is also driving the jet variations! G Disc accretion fluctuations are driving variability in hard state BHXRBs, certainly on time-scales < 1s G 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 G The disc seems to stabilise gradually towards the intermediate state G The disc is also driving the jet variations!