ULX accretion state

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ULX accretion state
Roberto Soria (MSSL)
Thanks to (in random order) K. Wu (MSSL), Z
Kuncic (Sydney), D Swartz (MSFC), A Goncalves
(Paris-M), R Mushotzky, T Strohmayer (GSFC), G
Fabbiano (CfA), P Kaaret (Ohio)
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Summary
ULXs look like Galactic BHs in the very high state
Basic ingredient of ULX spectra a disk
transition at R gt 10 RISCO?
Disk optically thick corona
OR JUST
scattering-dominated standard disk?
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Most ULXs have simple X-ray spectra
Lx
soft excess
Power-law G 2
break
1
5
10
0.3
E (keV)
4
Most ULXs have simple X-ray spectra
Lx
To
slope
3 spectral parameters
(sometimes) 1 timing parameter (QPO
frequency 0.020.1 Hz)
X-ray luminosity 1040 erg/s
T1
1
5
10
0.3
E (keV)
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NGC5408 X-1 (Lx 1E40 erg/s)
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NGC5408 X-1 (Lx 1E40 erg/s)
Break at 5 keV
kT 0.15 keV
Power law (G 2.6)
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X-ray time-variability
QPOs at 20 mHz
Low-frequency QPOs like in the very high state
But with a frequency 20100 times lower
NGC5408 X1 Strohmayer et al. 07
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Stellar-mass BHs
ULXs
Tin 1 keV
Tin 0.2 keV
Rin 50 km
Rin 5000 km
?
nQPO 5 Hz
nQPO 0.05 Hz
Intermediate-mass BHs? M 1000 Msun?
Only if we assume that we are directly observing
a standard opt-thick disk near RISCO
Most likely NOT THE CASE
Fitted (large) disk radii and (low)
temperatures may be from R gtgt innermost stable
orbit
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ULX Galactic BH connection?
(Soria 2007)
Feng Kaaret 2006, 2007
NGC1313 X1
XTE1550
NGC1313 X2
Sobczak et al 2000 Done Kubota 2004, 2006
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Ldisk
(erg/s)
ULXs may have a persistently super-Edd accretion
rate
1041
1040
ULXs
Ldisk LEdd
1039
High/soft
1038
Very high
ultraluminous
1037
Tin
0.2
0.1
1
2
(keV)
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Receding inner disk in the galactic BH XTE1550
Receding disk
RISCO
Spectral hardening
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Receding inner disk in ULXs (Soria 2007)
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Ultraluminous
Very high (SPL)
High/soft (TD)
Low/hard
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Phenomenological model
10
90
Rc
Rc
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Physical interpretation?
10
90
Rc
Rc
16
Rc
Rc spherization radius? Ldisk (RgtRc)
LEdd Outflows launched at R Rc
(Poutanen et al 06 Begelman, King Pringle 07)
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Optically-thick, warm corona?
Te
To
Compton up-scattering medium completely covering
the inner disk
Te few keV
Done Kubota 06 Goad et al 06 Dewangan et al
06 Stobbart et al 06 Tim Robertss talk
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Optically-thick corona 3 parameters ? good fit
Lx
T0
f(t)
Te
Disk temperature at RRc Electron temperature in
the corona Optical depth nesesH a few
1
5
10
0.3
E (keV)
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Optically-thick corona or standard disk?
Te
T0
nesesH a few
ne 1017 cm-3
A very dense corona!
Same density predicted for a scattering-dominated
standard disk (Shakura Sunyaev 73)
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Disk optically-thick corona
OR MORE SIMPLY
Standard scattering-dominated disk?
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Shakura-Sunyaev standard model
When the disk is optically-thick at all radii
disk-blackbody spectrum
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Shakura-Sunyaev standard model
For
Radiation pressure gt gas pressure at small R
For
at small radii
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Shakura-Sunyaev standard model
Inner disk is dominated by radiation pressure
scattering opacity gt free-free opacity
is (moderately) optically thin
radiates less efficiently than bb
T must increase to radiate the same power
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T must increase to radiate the same power
This effect can be approximated by an increasing
hardening factor (Shimura Takahara 1995)
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fin 10
f
fout 1
R
t gtgt1
t lt1
Integrate over 2pRdR.
Multicolour disk spectrum with variable
hardening factor
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fin 6
Integrated spectrum looks like ULX spectra
fout 1
Slope df/dR
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Integrated spectrum looks like ULX spectra
(Shimura Takahara 1995)
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Thick/thin transition occurs at
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L0
Observational test
Opt thick disk
Opt-thin inner region
T0
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Conclusions I
Low disk temperature, large fitting radius, low
QPO frequency
BH mass 1000 Msun
Transition from cooler outer disk to
hotter/Comptonized inner region, at accretion
rates gt Eddington
Transition radius Rc 5000 km T(Rc) 0.2 keV
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Conclusions II
What is this transition?
Spherization radius? (outflows at R lt Rc)
Standard disk ? slim disk?
Standard disk ? optically-thick corona?
Optically-thick disk ? optically thin(ner),
scattering-dominated
disk
when Prad gt Pgas,
Consistent with MBH 50 100 Msun
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A finis si. Mersi che i leve scota.