October 13, 2006 Chandra Fellow Symposium @ Boston, MA

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Joint Chandra and Suzaku CCD Spectroscopy of Hard X-ray Emission

in the Arches Cluster

Masahiro TsujimotoRikkyo Univ.

October 13, 2006 Chandra Fellow Symposium @ Boston, MA

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Talk Plan

1. Arches Cluster & Galactic Center2. Chandra & Suzaku Observations3. Results & interpretations

a. Discrete source.b. Extended emission.

4. SummaryWang, D. Q. et al. (2006, ApJ)Tsujimoto, M. et al. (2006, PASJ)

October 13, 2006 Chandra Fellow Symposium @ Boston, MA

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One of the three massive young star clusters in GC. (Arches, Quintuplet, GC).

Located at ~25pc (projected dist.) from GC. Total Mass > 7000 Mo; Size ~ 0.5 pc; Stellar

Mass Density ~ 3x105 Mo/pc3. Scale comparable only to NGC3603, W49A,

Westerlund 1 (Our Galaxy) and R136 in 30 Dor. (LMC).

1. Arches Cluster & GC

LaRosa et al. (2000)

VLA 90cm

100pc

GC

GP

Arches

Figer et al. (1999)

HST/NICMOS (B=F110W, G=F160W, R=F205W)

5” (0.2pc)

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Intense & extended 6.4 keV emission in GC.

6.4 keV line = K line of iron at low-ionization stages (hereafter “Fe II”). Presumably in dust.

The cause is unknown for a decade. A 6.4 keV clump associated to AC.

1. Arches Cluster & GC

Purpose: To investigate the hard X-ray emission from AC, and to understand the origin of the 6.4 keV emission.

Koyama et al. (2006)

Suzaku/XIS Arches

GPSgr A East (GC)

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2. Chandra/ACIS Observations

ObsID=945 (t=50ks, =7.1’)2276 (10ks, 4.4’)

4500 (100ks, 1.4’)2284 (10ks, 7.6’)

A1N

A1S

A2

A1

Decl

R.A.

A2

A1N A1S

diffuse

bl

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Suzaku Observatory (July, 2005-) X-ray Imaging-Spectometer: Four CCDs. Lowest

background. X-Ray Telescopes: Large EA (~590cm2 @8keV). HPD~1’.

Suzaku observations: ~100ks. Sept. 23 & 30, 2005. Band-limited smoothed images.

A local excess at AC in all bands. 8-10 keV resemble 6.4 keV image.

2. Suzaku/XIS Observations

10pc

8-10 keV

6.7keV (Fe XXV)

6.4 keV (Fe II)

Sgr A East

Arches

GP

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3. Results & Interpretationsa. Point-like Source

A2

A1N A1S

diffuse

3 bright point sources; All src’s: thermal emission. A2, A1S have 2T (kT~0.8, 6 keV).c.f. A debate among Yusef-Zadeh et al.

(2002); Law & Yusef (2003); Wang et al. (2006) for 1T or 2T.

A1S: NH~2x1023/cm2. Lx (2.0-8.0 keV)~1035 erg/s. The brightest stellar X-ray source in our Galaxy.

Diffuse emission. No thermal features.

A1N

A1SA2

S XV

S XVI

Fe XXV

S XV

S XVI

Fe XXV

S XV

S XVI

diffuse

Fe II

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3. Results & Interpretationsa. Point-like Source

Bright X-ray sources in other wavelength. 3 of the brightest 12 NIR sources with

Minit>100Mo. Wolf-Rayet stars (WN7). Radio (thermal free-free cont.) counterparts (X-

ray brightest = radio brightest). Conversely, for the 12 brightest NIR

sources, 11 are WN7. All are bright in radio. Only 3 are bright in X-ray. Others are fainter by

x100. Additional factor is necessary for luminous

hard X-ray production. Binarity (“X-ray spec. binaries”)?

Figer et al. (2002) Keck/NIRSPEC

He I

He I, B

r

He II

N III

C IV

A1N

A1S

A2

Lang et al. (2001)

VLA (8.5GHz)

A1S

A1N

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3. Results & Interpretationsb. Extended Emission

1. Hard-band XIS spectrum: spatially-unresolved, high S/N, < 12 keV. Thermal features (Ca XIX K, Fe XXV K, K, Ni XXVII K) <- composite of point sources. Non-thermal features (Fe II K, Kneutral. PL~12 keV.)<- diffuse emission.

2. Band-limited images: 6.4 (Fe II), 6.7 (Fe XXV), 8-10 (PL) keV Similarity in 6.4 & 8-10 keV images. -> PL & 6.4/7.1 keV lines (FeII K/K) related in the underlying physics.

Two possibilities for the physical process.1. X-ray photo-ionization (Koyama 1996; Sunyaev 1995)

Fe K shell ionization & fluorescence (line) + Thomson scattering (cont).

2. Particle collision ionization (Wang 2006)Fe K shell ionization & vacancy filling (line) + Bremsstrahlung

(cont.) Two obs. tests: EWK (1.5keV) & PL norm.

(~2x10-4/s/keV@10keV).

PL comp.

Thermal features Non-thermal features

Thermalcont.

Non-thermal

cont.

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1. X-ray photo-electric ionization.(X-rays are from the brightest discrete sources in AC).

Lack of Fe K edge alone is not evidence against photo-ionization. Optically-thin case is justified. NH (diffuse) ~ 6x1022/cm2.

Constraints for the incident photons.1. Flat spectrum: I(E)∝E- (~1).2. Flux:~3x107/(ne/102cm-3) /s/cm2/keV@10keV.

No source is found in the vicinity. X-ray emission in AC is too weak for incident

photons.… Scattered emission < Incident emission @ E>7.11 keV.

3. Results & Interpretationsb. Extended Emission

Fe K

ed

ge (

7.1

1 k

eV

)

Scattered X-rays(diffuse

emission)

Incident X-rays(point sources)

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3. Results & Interpretationsb. Extended Emission

2. Particle Collision Ionization.(Electrons accelerated in colliding stellar winds in AC.)

Accelerated electrons of 10-100 keV. Electrons are “optically-thick” to the medium. (c.f. A

100 keV electron is stopped by a hydrogen column of ~4x1021/cm2).

Energy conversion rate ~ 10-5.

Constraints for injected electrons.1. Number density: N(E)∝E-(+1) (~1).2. Flux: 2x101 erg/s/cm2 (~103 eV/cm3).

Wind-accelerated electrons (protons, heavy ions, too) in AC are insufficient for the incident source.… Electron energy injection rate < Wind kinetic energy

rate.

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3. Results & Interpretations

Low-mass starsHigh-mass stars

X-radiationStellar windsWind collisions

Wang et al. (2006)

Irradiated cloud

Magneti

c field

Time variation?Non-spherical

radiation?Magnetic

turbulance?

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4. Summary Results of a joint Chandra & Suzaku study of

Arches cluster are presented. Three bright point sources.

Thermal emission. Two-temperature plasma. WN7 by NIR spectra. Large mass loss by 8.5 GHz flux. A1S: Brightest stellar X-ray source in our Galaxy.

Binary? Extended emission.

Non-thermal emission. Power-law & 6.4/7.1 keV emission related in underlying

physics. AC is insufficient for ionizing photon/particle source.

“Abnormal” ideas are necessary.Thank you for your attention!