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 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 D distribution of the 6.4 keV MCs 2.Prospective in the Astro-H era 3.Summary

Topics on 6.4 keV Emission 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 D distribution of the 6.4 keV MCs 2.Prospective in the Astro-H era 3.Summary

keV Emission from the Galactic center region 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 N H > cm -2 ) -peak shift to the GC from the MC core -> illuminated from the GC Luminal irradiating source (Lx ~ erg/s) larger than L Edd for 1 M ◎ => big flare of Sgr A* had occurred in the past? 2’=5 pc Gray scale: 6.4 keV Contour : 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

Topics on 6.4 keV Emission 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 D distribution of the 6.4 keV MCs 2.Prospective in the Astro-H era 3.Summary

1.1. Detailed X-ray view with Suzaku Suzaku found a number of MCs with 6.4 keV line Sgr B1 Common characteristics hard continuum ：  = 1.5—2.5 strong 6.4 keV line ： EW = 1—2 keV Papers: Koyama+07 M0.74 MN+08Sgr B1 Koyama+08 Time variability in Sgr B2 Koyama+09Time variability in 10 years Nakajima+09Sgr C Fukuoka+09G0.174 Ryu+093-D distribution in Sgr B2 MN+10K-shell Lines Nakashima+10M MN+11 (submitted)Time variability Ryu+ in prep3-D distribution in Sgr C (+ theoretical papers) Dogiel+09,11, chrenshov+11(submitted)

Topics on 6.4 keV Emission 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 D distribution of the 6.4 keV MCs 2.Prospective in the Astro-H era 3.Summary

Fe=1 Ni Mn Ar Ca Cr *solar abundance Low energy lines are absorbed by ISM 1.2. K-shell lines from neutral heavy elements 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) xx Suzaku 200ks 1.2. K-shell Lines

Heavy elements in neutral state 2 Energy (keV) 5 10 plasma Line continuum Ar Ca Mn Cr → K-shell line of neutral atoms Theoretical (keV) Measured (keV) Ar ±0.02 Ca ±0.02 Cr ±0.04 Mn ± K-shell Lines Also detected ionized Cr / Mn K lines

Origin of neutral lines MC Line External particles Line: K-shell ionization due to external X-ray, electron, proton Continuum: X-ray ・・・ Thomson Scattering Electron ・・・ Bremsstrahlung Proton ・・・ Inverse Brems. Fe Ar SCaCrMn Continuum Different spectra are produced e-e- e-e- Equivalent width = Abundance X-ray origin Electron origin 1.2. K-shell Lines

X-ray model : 1.6 solar electron 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~ K) 100 pc 1—2 Z ◎ Metal abundances

Topics on 6.4 keV Emission 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 D distribution of the 6.4 keV MCs 2.Prospective in the Astro-H era 3.Summary

1.3. Time variability 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 Suzaku 1.3. 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

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 luminosity 1.3. 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~10 39 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=4x10 6 M ◎ 15 pc

Other results of time variability 1.3. Time variability Integral (20—60 keV) (Terrier+10) – Decrease by half in 8 year Consistent 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* XMM (Ponti et al. 2010)

Topics on 6.4 keV Emission 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 D distribution of the 6.4 keV MCs 1.5. Diffuse emission other than MCs 2.Prospective in the Astro-H era 3.Summary

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 D distribution Please see Ryu’s poster #37 Preliminary

Topics on 6.4 keV Emission 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 D distribution of the 6.4 keV MCs 2.Prospective in the Astro-H era 3.Summary

2. Prospective in the Astro-H era Direct measurement of motion / position of MCs – Shift : 50 km/s  E = 1 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 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 D distribution of the 6.4 keV MCs 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