1. Suzaku observations of two Galactic black hole candidates XTE J and MAXI J triggered by MAXI
Kazutaka Yamaoka
(Aoyama Gakuin University),
On behalf of the MAXI and Suzaku team

2. Outline Coordinated MAXI and Suzaku observations
Suzaku observations of XTE J
with MAXI results
Please also see Nakahira et al. P-1 (MAXI) and Koyama et al. P-2 (Suzaku)
Very preliminary results from
Suzaku observations of MAXI J
Summary

3. Coordinated MAXI and Suzaku observations
High sensitive all-sky X-ray survery with Wide-band and high-sensitive X-ray observations with Suzaku
Very powerful collaboration for studying X-ray transients.
　e.x. Discovery of a new MAXI source  Identify the nature of the source with Suzaku
Suzaku ToO Observations by MAXI team have been approved since AO5.
4 Suzaku ToO observations triggered by MAXI team so far
Source
Category
Obs. Date
Exposure
Related information V
X-ray binary pulsar
Feb 16, 2010
32 ksec
XTE J
Black hole candidate
Feb 24-25, 2010
40 ksec
Also proposed from the US side
GX 304-1
Aug. 13, 2010
23 ksec
Discovery of cyclotron features (Yamamoto et al .P-13)
MAXI J
Sep 29, 30, Oct. 1-2, 2010 (3 times)
16, 24, 31 ksec

4. BHC XTE J
Discovered by the RXTE/PCA Galactic-Center scan observations
(Markwardt et al. 2009)
MAXI confirms this new transient and monitor the entire outburst.
(Nakahira et al PASJ, Nakahira et al. P-1 )
Identified as a black hole candidate by RXTE.
Displayed Hard –to-soft, and Soft-to-hard
transitions. Bipolar plasma
ejection events, i.e. jets,
were detected.
The distance, the black
hole mass, and the
inclination angle are
still unknown.
XTEJ

5. Suzaku observation of XTE J1752-223
Details of observations
ObservationDate　 :58:00
　　　　　　　　 – :27:24 (UT)
Total exposure 41 ksec
ＸＩＳ Exposure 0.5 ksec (XIS 1),
　　　　　　　　　　　 6.1 ksec (XIS 0,3)
Observation direction HXD nominal
ＸＩＳ mode
Full window 0.1s burst option (XIS 1) 　　
　 1/4 window 0.3s burst option (XIS 0.3)　
Suzaku observed
“High/Soft state”
Low/hard　　　　
High/Soft

6. The Suzaku/XIS light curve
During the obs.,
the XIS intensity and spectral shape do not change significantly.
Produce the XIS spectra by averaging
over the whole observation.
XIS count rate : keV
Hardness ratio:　2-10 keV/0.5-2 keV
About 1 day

7. Suzaku wide-band spectra
XIS1
Detected up to ~ 50 keV with HXD/PIN.
The HXD/GSO could detect no significant signals above 50 keV.
HXD/PIN
XIS0+3
HXD/GSO
Detection llimit
Energy　(keV)

8. Spectral modeling of wide-band spectra
Modeling with the Multi-Color Disk model (Mitsuda et al. 1984) plus a power-law (χ2 /dof = 508/339)
XIS1
XIS0+3
Power law
Γ=2.34+/-0.07
MCD model
Tin=0.53+/-0.01 keV
Rin(cos i)1/2 /(D/10 kpc)
= /-2.0 km
νFν spectra
HXD/PIN
Power law
MCD

9. Results from RXTE and MAXI observations
RXTE and MAXI monitoring observations show that the innermost radii are almost constant at 110~130 km, which is independent of X-ray flux. This value is almost consistent with Suzaku measured one.
 Can estimate the black hole mass
Innermost temp.
Tin (keV)
Innermost radius Rin
Photon index Γ
Flux keV

10. Estimation of the black hole mass
Suzaku measured innermost radius:
　　　Rin(cosi)1/2 /(D/10 kpc) =117.9±2.0 (km)
rin=ξκ2Rin (Kubota et al. 1998)
κ=1.7：Spectral hardening factor (Shimura & Takahara 1995)
ξ=0.412: boundary condition near the inner edge of the disk
　　 = 198.5±3.4
　　　　　　x (D/10 kpc) x (cosi /cos 60°)-1/2 　（km)
If we assume a Schwartzchild black hole, the innermost stable circular orbit (ISCO): 3Rs=6GM/c2=8.86 (M/M◎) km
 BH mass : M = 22.4±0.4 　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　 　　　　　　 x (D/10 kpc) x (cosi /cos 60°)-1/2 (M◎) Precise determination of a distance and an inclination angle will be desired in a future.

11. BHC MAXI J
The Swift/BAT discovered a new source as GRB A
on Sep. 25, 2010 (Mangano et al. GCN #11296).
The MAXI/GSC independently found a new X-ray source as MAXI J (Negoro et al. Atel #2873).
RXTE follow-up observations reveal
it as a black hole candidate.
(Kalamkar et al. Atel # 2881)
Many multi-wavelength
observations were performed due to
the Swift/BAT GRB trigger and its
source location well above the Galactic plane.
Sep. 24
Sep. 25
MAXI J

12. Suzaku observations of MAXI J1659-152
Details of the three observations
Observation Dates　
Sep. 29, 30, Oct. 1-2, 2010
XIS0/HXD exposure
1.6 k / 16.3 ksec
15.0 k / 23.5 ksec
4.9 k / 30.7 ksec
Observation direction HXD nominal
ＸＩＳ mode
¼ window with no burst option (Sep. 29, 30)
0.3s burst option (Oct 1-2) 　
Suzaku observed a rare “intermediate state” in the rising phase.
High/Soft
MAXI/GSC Hardness-Intensity diagram
Low/hard　　　　

13. Preliminary results of Suzaku data
The XIS+PIN spectra are explained by the disk blackbody plus power law with an exponential cutoff.
QPO features at about 3 Hz are detected in the HXD/PIN data for all the three observations.
Cut-off
LF QPO
The intermediate observations with Suzaku might reveal a disk-corona-jet geometry around the BH during the state transition.

14. Summary MAXI and Suzaku coordinated observations since AO5
Four sources so far:
V 、XTEJ 、GX304-1, and MAXI J
Suzaku observation of XTE J
High/Soft state 　
The 1-50 keV spectra are explained by MCD model plus power law.
Suzaku and RXTE observation suggests a constancy of innermost radius at 120~130 km
 Estimation of the black hole mass
　 /-0.4 M◎ for i=60°, D=10 kpc
Further examination of the “ disk-line feature”
Suzaku observation of MAXI J
Intermediate state in the rising phase.
keV spectra are explained by MCD model plus cutoff power law.
The QPO features are present in the HXD/PIN power spectrum.

15. Presence of a disk line？
Reis et al. (2010) suggested a presence of a disk line using the same Suzaku data.
 They fitted the continuum using the , , keV data.
We can reproduce the same feature with the same procedures, but
using all the energy bands,
we can see a reflection feature instead.
Suzaku
RXTE/PCA

16. Pile-up effects
PHA Ratio to the spectra in the Outer regions(90``<r<120``)
For bright sources, the XIS spectra were affected by pile-up effects。
In the central region, the spectra get harder.
Need to exclude
at least the
region with
r<60``
r<30’’
30’’<r<60’’
60’’<r<90’’

17. MAXI light curve of V
Suzaku observation

18. XIS spectra of V0332+53 The spectrum is rather hard photon index ~1
NH= (-0.17,+021)x1022 cm α= 1.07(-0.09, +0.10) Flux 2-10 keV 6.4x10-12 erg/cm2/s  ~0.3 mCrab (Crab:2.2x10-8)
χ2/dof = 320/325