Suzaku Study of X-ray Emission from the Molecular Clouds in the Galactic Center M. Nobukawa, S. G....

Suzaku Study of X-ray Emission from the Molecular Clouds

in the Galactic Center

M. Nobukawa, S. G. Ryu, S. Nakashima,

T. G. Tsuru, K. Koyama (Kyoto Univ.), H. Uchiyama (Univ. Tokyo),

V. Dogiel, C. Dmitry (P.N. Lebedev Institute)and Suzaku GC team

Topics on 6.4 keV Emission

1. 6.4 keV Emission from the Galactic center region

1.1. Detailed X-ray view with Suzaku

1.2. K-shell lines from neutral heavy elements

1.3. Time variability

1.4. 3-D distribution of the 6.4 keV MCs

2. Prospective in the Astro-H era

3. Summary


6.4 keV

6.7 keV

100 pc = 300 lys

Sgr A*

Hot Plasma = Tsuru-san’s talk

Focus in this talk

Bright X-ray binaries with no Fe line

Correlation with Molecular clouds

• Correlation with Giant Molecular Clouds• Ionization of Fe atoms due to external particles (E>7.1 keV, Fe-K edge)　　　→ Fluorescence X-ray （ Neutral Fe line ）　　 -> a high energy phenomenon hides

6.4 keV map

Molecular gas （ CS line ）Tsuboi+99

Origin of the 6.4 keV Emission

X-ray illumination (Koyama+96; Murakami+00)

- pronounce Fe line (EW>1 keV) - deep Fe edge (equivalent to NH > 1024 cm-2)- peak shift to the GC from the MC core

-> illuminated from the GC Luminal irradiating source (Lx ~ 1039 erg/s) larger than LEdd for 1 M◎

=> big flare of Sgr A* had occurred in the past?

2’=5 pc

Gray scale: 6.4 keVContour : MC core (Radio)

Murakami+00

5 Energy (keV) 9

Sgr B2

To GC

Origin of the 6.4 keV Emission

Low-energy Cosmic-ray impact Electron (E= a few 10 keV): (e.g. Yusef-Zadeh+07)

– Correlation with non-thermal radio filaments (synchrotron by GeV e-)

– Heating of MCs / HE gamma-rays Proton (E=a few 10 MeV): (e.g. Dogiel+09)

– Generation by Sgr A*, capturing a star

10 pc

X-ray (contour)Ratio(gray)

Sgr C

Yusef-Zadeh+07

• Need multiple information about the origin• Constraint of an irradiating source

Suzaku observation








3. Summary


• Suzaku found a number of MCs with 6.4 keV line

Sgr B1

Common characteristics 　 hard continuum ：　 G = 1.5—2.5 　 strong 6.4 keV line ：　 EW = 1—2 keV

Papers: 　 Koyama+07 M0.74　 MN+08 Sgr B1　 Koyama+08 Time variability in Sgr B2　 Koyama+09 Time variability in 10 years　 Nakajima+09 Sgr C　 Fukuoka+09 G0.174　 Ryu+09 3-D distribution in Sgr B2　 MN+10 K-shell Lines　 Nakashima+10 M359.07　 MN+11 (submitted) Time variability　 Ryu+ in prep 3-D distribution in Sgr C　 (+ theoretical papers)　 Dogiel+09,11, chrenshov+11(submitted)








3. Summary

Fe=1

Ni

Mn

ArCa

Cr

*solar abundance

Low energy lines are absorbed by ISM


Heavy atoms other than Fe can provide a new constraint.

Typical spectrum　 6.4 keV line ＋ absorbed continuum

X-ray spectrum of the brightest MC

Neutral Fe

He-/H-like ions

Si S Ar

Ca

Fe

Plasma MC component(Lines + Continuum)

Abs.(MC)

Abs.(ISM)

x x

Suzaku 200ks

1.2. K-shell Lines

Heavy elements in neutral state

2 Energy (keV) 5 10

plasma

Linecontinuum

Ar CaMn

Cr

→ K-shell line of neutral atoms

Theoretical (keV)

Measured(keV)

Ar 2.96 2.94±0.02Ca 3.69 3.69±0.02Cr 5.41 5.41±0.04Mn 5.90 5.94±0.03

1.2. K-shell Lines

Also detected ionized Cr / Mn K lines

Origin of neutral lines

MC

Line

Externalparticles

Line: K-shell ionization due to external X-ray, electron, protonContinuum: X-ray ・・・ Thomson Scattering Electron ・・・ Bremsstrahlung Proton ・・・ Inverse Brems.

Fe

Fe

Ar

S

CaCr

Mn

ContinuumDifferent spectra are produced

e-

e-

Equivalent width = Abundance

X-ray origin

Electron origin

1.2. K-shell Lines

X-ray model : 1.6 solarelectron model: 4 solar

Abundance from observed EWs

Abundances

6.4 keV = cold medium (T~10 K)

Sgr A*X-ray origin 　 1.6 Z◎

electron origin 4 Z◎Proton origin < 2 Z◎

6.7 keV = hot plasma (T~107-8 K)

100 pc

1—2 Z◎

Metal abundances








3. Summary


• X-ray flux in the Sgr B2 MCs had decreased by a factor of ~0.5 in 10 years (Inui+09)

1994 (ASCA) 　 2000 (Chanrda) 　 2003 (XMM) 2005 (Suzaku)

Systematic uncertainty remains because of data taken from different satellites.

Suzaku observation of the same position in 2005 / 2009

Observation in 2005/2009 with Suzaku1.3. Time variability

6.4 keV line・ Sgr B2/M0.74 become darkened.・ No change in the surroundings

Hard X-ray・ Sgr B2/M0.74 become darkened.・ No significant change in the surroundings.

Time variability both in 6.4 keV and hard continuum

Coherent decrease between the two MCs

0 0.5 1

0 0.5 1

• MC Size of ~10 lys time scale of variability <10 years ⇔– MCs should be irradiated by X-rays – not by protons (E~10 MeV; v = 0.1 c < light velocity).

• Coherent decrease suggests a single origin for the two MCs.

Illuminating source – required luminosity1.3. Time variability

Lx of illuminating source depends on the distance from the MC Sgr B2 case:

• No such a bright XRB has been observed in the Sgr B2 vicinity.• No XRB with Lx~1039 erg/s has been found even in the GC region.• Possible scenario is a past big flare of Sgr A*, super-massive black hole with M=4x106 M◎

erg/s > 4 x 1037 erg/s (d=15 pc; the closest case)

15 pc

Other results of time variability1.3. Time variability

• Integral (20—60 keV) (Terrier+10)

– Decrease by half in 8 yearConsistent with our result

• XMM (6.4keV) (Ponti+10)

– Super-luminal motion in MCs near Sgr A* (d~5 pc)

• Chandra (2-10keV) (Muno+08)

– MCs near Sgr A*

• These facts also suggest the past X-ray flare of Sgr A*.

2004 2007

2008 2009

XMM (Ponti et al. 2010)







1.5. Diffuse emission other than MCs


3. Summary

1.4. 3-D distribution of the 6.4 keV MCs• In order to investigate the detailed history of the past

activity, we must know positions of MCs relative to the super-massive black hole.

• Measurement of MC position:– MCs absorb a part of plasma emission

MC Distribution and Past history of Sgr A*

• Distribution of the MCs illuminated by X-rays indicate the history of the past Sgr A* activity.

1.4. 3-D distribution

Please see Ryu’s poster #37

Preliminary








3. Summary


• Direct measurement of motion / position of MCs– Shift : 50 km/s <-> DE = 1 [email protected] keV c.f. velocity ~ 200 km/s– Shape of the Compton shoulder -> source direction

• Chemical composition in GC– K-shell lines and absorption edge– Ratio of Comp. shoulder to 6.4 keV line –> Hydorogen density in the MC

Thank you for your attention






2. Prospective in the Astro-H era– History of the past activity of Sgr A*

Measurement of the motion and position of MCs

– Chemical abundances in the GC region

Suzaku Study of X-ray Emission from the Molecular Clouds in the Galactic Center M. Nobukawa, S. G....

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