1. RXTE Spectral Observations of the Galactic Microquasar GRO J1655－40
Koji Saito

2. Microquasars: miniature versions of the quasars
-X-ray binaries with
relativistic jets,
located in our galaxy
BH mass
Microquasars :
stellar size
Quasars :
106-8Msun
Time scale of the
variation ∝ Object size
Light years
Millions of
light years
X-rays

3. State transition in X-rays
Hardness-intensity diagram of GX 339－4 (Belloni 2006)
Energy
Flux
High/Soft
Energy
Flux
power-law
Low/Hard

4. Standard disk model : Multi-color disk (MCD) model
MCD model is expressed as a super-
position of local blackbody at different
radius from the compact object
(Mitsuda et al. 1984, Makishima et al.
1986)
Outer radius (low T) 
Radiation energy from blackbody
≒ released gravitational energy
intensity
Inner radius (high T)
Accretion disk
Black hole
Energy (keV)

5. (low/hard state : power-law, Γ~1.4-1.7)
normalization  Rin
Power law
MCD
cutoff energy : Tin
MCD model
Tin = 1 keV
(low/hard state : power-law, Γ~ )
-high/soft state : MCD model + power-law
MCD + power-law has successfully
explained the observation data of
typical BH binaries e.g.
GS 1124－68 and LMC X-3
…Rin is constant, Ldisk is proportional to Tin4
Comptonization 
power-law shape ?
disk  MCD BH
corona

6. Deviations from the MCD model
Numbers of observation data of black hole binaries were well explained by the picture
of the MCD model. In contrast, another phenomena have been illustrated by recent
observations…
…fluctuating Rin,
Ldisk’s were not proportional
to Tin4
outburst
Tin4
Kubota et al. (2001)

7. RXTE satellite On board detectors ASM (All Sky Monitor) : 1.5—12 keV
PCA (Proportional Counter Array) : 2—60 keV
HEXTE (High Energy X-ray Timing Explorer) : 15—250 keV
Performing long time observations
of one object
suitable for study of the state
transition of the microquasars 7

8. GRO J1655－40 : Observation We proposed ToO observation for
16 months
We proposed ToO
observation for
outburst of GRO
J in 2005
May, ‘96
Sep, ‘97
8 months
Analyzed data
-2005 Feb. 21 ~ Nov. 11
511 data sets
-1996 Mar. 14 ~
1997 Sep. 11
81 data sets
Mar, ‘05
Sep, ‘05

9. Results Fitting energy range PCA : 3~20 keV, HEXTE : 18~200 keV
Spectral modeling
Multi-Color Disk (MCD) model
+ power-law
The observations were classified into
several epochs based on the spectral
characteristics, although their time
boundaries are uncertain and criteria of
determining epochs are not especially
quantitative
Ldisk
Lhard 9

10. hard component decreased, index of the
MCD
power law
~MJD 53450
hard component decreased, index of the
power law could not be well constrained
Epoch 2 : very soft spectra,
could not explained
by the MCD model
Ldisk
Lhard 10

11. The source entered the highly variable
power law
MCD
~ MJD 53500
The source entered the highly variable
period and hard component dramatically
increased
Epoch 3 : parameters fluctuated wildly
hard component was dominant
Ldisk
Lhard 11

12. Values of Rin became constant
MCD
power law
~ MJD 53444
Values of Rin became constant
Epoch 5 : well explained by the MCD model
After this Epoch, the source returned to the
low/hard state
Ldisk
Lhard 12

13. Ldisk-Tin diagram
2005
1996–1997
Similar behavior in Ldisk-Tin relation and almost the same saturation level
were observed in both and 2005 outbursts !
 There is a fixed physical process ?

14. Another types of disk components ?
Luminosity ∝ mass accretion rate
High mass accretion rate
 optically thick advection dominated accretion flow (ADAF)
Standard disk : Qrad >> Qadv
ADAF : Qrad << Qadv
Standard disk
The radius dependence of the temperature :
Standard disk :  optically thick ADAF :
(Watarai et al., 2000)
Application of the variable p disk model
Epoch 2 in 2005, Epoch 1 in ’96–’97 (showed very soft spectra)
p = 0.55±0.03
(typical value) 14

15. 1996–1997 2005 Hardness – Intensity Diagram
There are quite complicated periods … Jets were observed by Radio
Deviations from standard disk relate jet formation ?
1996–1997
2005

16. Summary Energy spectral fitting with the standard model
GRO J1655－40 passed through the similar changes
of states in both and 2005 outbursts
There are Epochs which clearly couldn’t be explained
by the standard disk model
Suggestion of the presence of the ADAF ?
Ldisk saturated at same luminosity in both outburst
 There is a fixed physical process which suppress
the growth of Ldisk ?
Related to the formation of the jets ? 16

18. The source was initially in the low/hard state (Γ < 2)
power law
MCD
The source was initially in the low/hard
state (Γ < 2)
MJD ~
Γ > 2, soft component appeared
Epoch 1 : hard component was strong
Ldisk
Lhard 18

19. Epoch 4 : similar to Epoch 1
power law
MCD
~ MJD 53517
Fluctuations ceased
Epoch 4 : similar to Epoch 1
Ldisk
Lhard 19

20. Comparison with 1996-1997 outburst
1996–1997
2005
’96–’
Epoch 1
Epoch 1 Epoch 2
Epoch 2 Epoch 3
Epoch 4
Epoch 3 Epoch 5 20

21. Comparison with Other Objects
XTE J1550－564
Kubota et al. (2004)
Very soft spectra 　↓
highly fluctuating state
standard disk

22. 4U 1630—47
Abe et al. (2005)