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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 UttleyThanks to: P. Cassatella, T. Wilkinson, J. Wilms, K.
Pottschmidt, M. Hanke, M. Böck
Phil UttleyThanks to: P. Cassatella, T. Wilkinson, J. Wilms, K.
Pottschmidt, M. Hanke, M. Böck
Background: disc variability?Background: disc variability?1974: Lightman & Eardley propose disc instability as the origin of X-
ray variability in black hole XRBsBut subsequent observations don’t seem to support this...
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...
rms
vari
abili
ty a
mplit
ud
e
spectral hardness
GX 339-4Belloni et al. 2005
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 interactionHard 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
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
Disc X-ray reverberationDisc X-ray reverberation
~70% of incident flux ~30%
of incident flux
~1% of incident flux
X-rays from the X-rays from the continuum source continuum source (corona, jet base?) hit (corona, jet base?) hit the discthe disc Some are reflected Some are reflected (iron line and reflection (iron line and reflection continuum)continuum) The absorbed fraction The absorbed fraction is thermalised and re-is thermalised and re-emitted at the local disc emitted at the local disc temperaturetemperature
GX 339-4 2004 observation
GX 339-4 2004 observation
0.5-0.9 keV 3-10 keV
170 s of ~150 ks
Both bands (disc+pl and pl only) show large amplitude strongly correlated variability!
GX 339-4 2004 hard state: Energy-dependent PSDs and frequency-resolved
rms spectra
GX 339-4 2004 hard state: Energy-dependent PSDs and frequency-resolved
rms spectra
fast
slow
0.5-0.9 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?
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)
Variable disc or disc/hot-flow boundary?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 339-4 2004: 0.034-0.12 Hz Range
Interpreting the variability: signals and amplifiers
Interpreting the variability: signals and amplifiers
Signal: mdot fluctuations in disc Amplifier: X-ray emitting regions
Delay
Em
issi
on
Time
mdo
t
*Input signal from disc is convolved with the emission vs. delay profile
The effect of the emission profileThe effect of the emission profileEmission 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
A viscous propagation +
reverberation model0.1 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
Mapping the disc inner edge
The observed soft lags imply Rin< 50 RG in this hard stateThe observed soft lags imply Rin< 50 RG in this hard state
440 ks on Cyg X-1 coming up in October – watch this space!!!
Disk stability changesDisk 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
IR vs XMM-Newton: revealing the disc-jet connection
IR vs XMM-Newton: revealing the disc-jet connection
XMM-Newton vs RXTEXMM-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?
SummarySummary 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!
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!