The Hot Plasma in the Galactic Center with

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 k. T=5— 8 ke. V. 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 ~3 x 1053 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 (Koyama+07) Sgr B Sgr A He-like Fe Ka H-like Fe Ka Count/s/ke. V X-ray line map with Suzaku Neutral Fe Ka Sgr C 10 -2 Sgr D 1 E 1740. 7 -2842 G 359. 1 -0. 5 Green: He-like S (2. 45 ke. V) Blue : Neutral Fe (6. 40 ke. V) Red : He-like Fe (6. 68 ke. V) 1 deg ~150 pc 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 ke. V) line emission from hot plasma is Blue: 6. 4 -ke. V clouds (fluorescence line from neutral irons, X-ray reflection) Green: Supernova remnants + diffuse emission (~107 K plasma) Red: the hot plasma (~108 K plasma) Ni Ka 5 Energy (ke. V) 10 Origin of the hot plasma: ØTruly diffuse (e. g. Koyama+96) ØIntegration of unresolved X-ray point sources ØChandra (Muno+04; flux > 10 -15 erg/s/cm 2) 10 -3 => cannot explain only 10 % of the total flux ØRevnivtsev+06 suggest that integration of >10 -17 erg/s/cm 2 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. 1 deg 10 -8 Energy (ke. V) 8 He-like Fe Dl (deg) 0. 62± 0. 03 Point source 0. 11± 0. 07 The difference suggests that the hot plasma cannot be explained only by the integration of undetected X-ray point sources. Physical parameters of the hot plasma 0 1 2 Distance from the GC (deg) Summary 1 Comparison between the He-like Fe line (Suzaku) and the X-ray point sources (Chandra, Muno+06). Fitting with an exponential function, Point sources (2— 8 ke. V) × 0. 1 Plasma density He-like Fe Line intensity ratio between the He- and H-like irons distributes over 0. 2 – 0. 6, corresponding plasma temperature of k. T=5— 8 ke. V. The hot plasma with uniform temperature extends over the GC region (l=-2~+2 deg). Integration of point sources 10 -7 Density (cm-3) H-like Fe 10 -6 He-like Fe (line intensity) Distance from the GC (deg) Line intensity ratio H-like Fe Photons/s/cm 2/arcmin 2 Profile of the line intensity from He- and Hlike 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. Photons/s/cm 2/arcmin 2 He-like Fe The same distribution Diffuse emission Comparison with Point Sources Distribution of the hot plasma He-like Fe Chandra (Muno+04) Count/s/ke. V A 1742 -284 Fe Kb The GC spectrum with Suzaku suggests that the Galactic center diffuse X-ray emission (GCDX) consists of (Red) hot plasma (k. T~6. 5 ke. V) , (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. We derived physical parameters of the hot plasma, Temperature (k. T) 5~8 ke. V Electron density (ne ) 0. 2~0. 005 cm-3 Total emission measure 1. 4 x 1059 cm-3 Total thermal energy (E) 3 x 1053 erg Total mass (M) 8 x 103 M◎ Calculated from the distribution of the iron line (the hot plasma) intensity. The Galactic gravitational potential (~e. V) cannot bind the 6. 6 -ke. V hot plasma. Escape time scale from the GC: tsc ~ [Size]/[Sound velocity] ~ [300 pc]/[2 x 108 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. 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 ke. V. 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, S 255 Muno et al. 2004, Ap. J, 613, 326 Muno et al. 2006, Ap. JS, 165, 173 Revnivtsev et al. 2006, Astro-ph/0611952