1. October 13, 2006Chandra Fellow Symposium @ Boston, MA1 Joint Chandra and Suzaku CCD Spectroscopy of Hard X-ray Emission in the Arches Cluster Masahiro Tsujimoto Rikkyo Univ.

2. October 13, 2006Chandra Fellow Symposium @ Boston, MA 2 Talk Plan 1.Arches Cluster & Galactic Center 2.Chandra & Suzaku Observations 3.Results & interpretations a.Discrete source. b.Extended emission. 4.Summary Wang, D. Q. et al. (2006, ApJ) Tsujimoto, M. et al. (2006, PASJ)

3. October 13, 2006Chandra Fellow Symposium @ Boston, MA 3 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 ~ 3x10 5 Mo/pc 3. 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)

4. October 13, 2006Chandra Fellow Symposium @ Boston, MA 4 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 GP Sgr A East (GC)

5. October 13, 2006Chandra Fellow Symposium @ Boston, MA 5 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 b l

6. October 13, 2006Chandra Fellow Symposium @ Boston, MA 6 Suzaku Observatory (July, 2005-) X-ray Imaging-Spectometer: Four CCDs. Lowest background. X-Ray Telescopes: Large EA (~590cm 2 @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

7. October 13, 2006Chandra Fellow Symposium @ Boston, MA 7 3. Results & Interpretations a. 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: N H ~2x10 23 /cm 2. Lx (2.0-8.0 keV)~10 35 erg/s. The brightest stellar X-ray source in our Galaxy. Diffuse emission. No thermal features. A1N A1S A2 S XV S XVI Fe XXV S XV S XVI Fe XXV S XV S XVI diffuse Fe II

8. October 13, 2006Chandra Fellow Symposium @ Boston, MA 8 3. Results & Interpretations a. Point-like Source Bright X-ray sources in other wavelength. 3 of the brightest 12 NIR sources with M init >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, Br  He IIN III C IV A1N A1S A2 Lang et al. (2001) VLA (8.5GHz) A1S A1N

9. October 13, 2006Chandra Fellow Symposium @ Boston, MA 9 3. Results & Interpretations b. 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 , K  neutral. 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 (Fe II 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: EW K  (1.5keV) & PL norm. (~2x10 -4 /s/keV@10keV). PL comp. Thermal features Non-thermal features Thermal cont. Non- thermal cont.

10. October 13, 2006Chandra Fellow Symposium @ Boston, MA 10 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. N H (diffuse) ~ 6x10 22 /cm 2. Constraints for the incident photons. 1.Flat spectrum: I(E) ∝ E -  (  ~1). 2.Flux:~3x10 7 /(n e /10 2 cm -3 ) /s/cm 2 /keV@10keV. No source is found in the vicinity. X-ray emission in AC is too weak for incident photons. … Scattered emission 7.11 keV. 3. Results & Interpretations b. Extended Emission Fe K edge (7.11 keV) Scattered X-rays (diffuse emission) Incident X-rays (point sources)

11. October 13, 2006Chandra Fellow Symposium @ Boston, MA 11 3. Results & Interpretations b. 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 ~4x10 21 /cm 2 ). Energy conversion rate ~ 10 -5. Constraints for injected electrons. 1.Number density: N(E) ∝ E -(  +1) (  ~1). 2.Flux: 2x10 1 erg/s/cm 2 (~10 3 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.

12. October 13, 2006Chandra Fellow Symposium @ Boston, MA 12 3. Results & Interpretations Low-mass stars High-mass stars X-radiation Stellar winds Wind collisions Wang et al. (2006) Irradiated cloud Magnetic field Time variation? Non-spherical radiation? Magnetic turbulance?

13. October 13, 2006Chandra Fellow Symposium @ Boston, MA 13 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!