The Hot Plasma in the Galactic Center with Suzaku

1. The Hot Plasma in the Galactic Center with Suzaku Masayoshi Nobukawa, Yoshiaki Hyodo, Katsuji Koyama, Takeshi Tsuru, Hironori Matsumoto (Kyoto Univ.) E-mail: nobukawa@cr.scphys.kyoto-u.ac.jp We have observed the Galactic center X-ray emission (GCDX) using Suzaku/XIS. We examine the highly ionized (He-like and H-like) iron lines from hot plasma of the GCDX along the Galactic longitude (l=-2~+2 deg). The ratio of [H-like]/[He-like] obtained from each place is 0.2—0.6, suggesting the plasma temperature is kT=5—8 keV. The He-like iron line intensity along the Galactic longitude exponentially decreases with the scale height of ~0.62 deg from the GC. On the other hand, distribution of X-ray point sources detected by Chandra is not similar to that of the He-like iron line. It indicates that the hot plasma cannot be explained only by integration of undetected point sources. If the hot plasma is truly diffuse, the plasma density is estimated to be ~0.1 cm-3 around the GC (at l~0 deg) and ~0.005 cm-3 at l~2 deg (300 pc away from the GC). he total thermal energy of the plasma is ~3x1053 erg, corresponding to 300 SN (supernova) explosions. The hot plasma with such high temperature should not be gravitationally bound and escape from the GC in ~105 years. The huge energy might have been injected by multiple (~300) SNe in the past 105 years. The Galactic Center Diffuse Emission Deep observation of the Galactic center with Suzaku Suzaku (Koyama+07) The GC spectrum with Suzaku suggests that the Galactic center diffuse X-ray emission (GCDX) consists of (Red) hot plasma (kT~6.5 keV) , (Blue) neutral lines (Fe Ka, Kb, Ni Ka), (Green) hard tail (G~1.4). Though many components coexist in the GC, He- and H-like Fe Ka lines can purely tell us the nature of the hot plasma. X-ray line map with Suzaku He-like Fe Ka H-like Fe Ka Count/s/keV Neutral Fe Ka Sgr B Sgr A Sgr C Fe Kb 10-2 Ni Ka Sgr D 1E 1740.7-2842 5 Energy (keV) 10 • Origin of the hot plasma: • Truly diffuse (e.g. Koyama+96) • Integration of unresolved X-ray point sources • Chandra (Muno+04; flux > 10-15 erg/s/cm2) • => cannot explain only 10 % of the total flux • Revnivtsev+06 suggest that integration of >10-17 • erg/s/cm2 sources can explain 100 % of the total flux. • However, ~Ms observation is needed. (difficult) • Two or more sources piling up cannot be resolved. • => Comparison between distribution of the hot plasma and that of the point sources. A 1742-284 G 359.1-0.5 Chandra (Muno+04) Green: He-like S (2.45 keV) Blue : Neutral Fe(6.40 keV) Red : He-like Fe (6.68 keV) 1 deg ~150 pc 10-3 Diffuse emission We have observed the Galactic center region for ~2 Ms with Suzaku so far (2005/09—). We can find many diffuse clumps with emission lines in the narrow line map of He-like sulfur neutral iron. However the He-like iron (6.68 keV) line emission from hot plasma is Blue: 6.4-keV clouds (fluorescence line from neutral irons, X-ray reflection) Green: Supernova remnants + diffuse emission (~107 K plasma) Red: the hot plasma (~108K plasma) Count/s/keV Integration of point sources 1 Energy (keV) 8 Comparison with Point Sources Distribution of the hot plasma Comparison between the He-like Fe line (Suzaku) and the X-ray point sources (Chandra, Muno+06). Fitting with an exponential function, He-like Fe (line intensity) He-like Fe 10-6 Photons/s/cm2/arcmin2 1 deg 10-7 Point sources (2—8 keV) ×0.1 Profile of the line intensity from He- and H-like irons along b=0~-0.1 deg (the Galactic plane). The two distributions exponentially decrease from the peak (l=0 deg) and they are similar to each other. 10-8 He-like Fe The difference suggests thatthe hot plasma cannot be explained only by the integration of undetected X-ray point sources. Distance from the GC (deg) Physical parameters of the hot plasma Line intensity ratio The same distribution Photons/s/cm2/arcmin2 We derived physical parameters of the hot plasma, Plasma density H-like Fe H-like Fe Density (cm-3) Temperature (kT) 5~8 keV Electron density (ne ) 0.2~0.005 cm-3 Total emission measure 1.4x1059 cm-3 Total thermal energy (E) 3x1053 erg Total mass (M) 8x103M◎ 0 1 2 Distance from the GC (deg) He-like Fe Calculated from the distribution of the iron line (the hot plasma) intensity. The Galactic gravitational potential (~eV) cannot bind the 6.6-keV hot plasma. Escape time scale from the GC: tsc ~ [Size]/[Sound velocity] ~ [300 pc]/[2x108 cm/s] ~ 105 years If multiple supernovae have injected the huge energy to the hot plasma, E ~ 300 supernovae (SNe) => 1 SN/300 years is necessary. Line intensity ratio between the He- and H-like irons distributes over 0.2 – 0.6, corresponding plasma temperature of kT=5—8 keV. The hot plasma with uniform temperature extends over the GC region (l=-2~+2 deg). Summary We have observed X-ray emission in the Galactic center (GC) regions using Suzaku. We examined the distributions of the He- and H-like Fe line intensities indicating the nature of the GC hot plasma. The line intensity ratio of [H-like]/[He-like] is 0.2—0.6, suggesting that the plasma temperature of 5—8 keV. Comparing the distribution of surface brightness of the iron line emission and that of X-ray point sources, they are likely different. This result will indicate that the GC hot plasma cannot be explained only by integration of X-ray point sources. However, the diffuse plasma cannot be bound by the Galactic gravity, and escape from the GC in ~105 years. 1 SN per 300 years is necessary to inject the huge thermal energy to the plasma. References Koyama et al, 1996, PASJ, 48, 249 Koyama et al. 2007, PASJ, 59, S255 Muno et al. 2004, ApJ, 613, 326 Muno et al. 2006, ApJS, 165, 173 Revnivtsev et al. 2006, Astro-ph/0611952