1. Suzaku, XMM-Newton and Chandra Observations of the Central Region of M 31 Hiromitsu Takahashi (Hiroshima University, Japan) M. Kokubun, K. Makishima, A. Kong, F. Primini Chandra/Suzaku XMM-Newton ASCA 10 kpc (50’) FOV

2. Diffuse X-ray Emission 5’5’ ACIS-I X-ray Image (~37 ks) Central 6’ (= 1.2 kpc) region Exclude point sources (> 1x10 36 erg/s) Diffuse emission is clearly detected. - Study whether diffuse emission has similar/different properties between in M31 and our Galaxy (cool/hot/non-thermal emission). - Reveal origins of the diffuse emission in normal spiral galaxies.

3. - XIS+XRT : CCD (0.2-12 keV;  E~120 eV @ 6 keV) - HXD : Si-PIN diode (10-70 keV) GSO scintillator (50-600 keV) Hard X-ray Detector (HXD) X-Ray Telescope (XRT) X-ray Imaging Spectrometer (XIS) X-ray Imaging Spectrometer (XIS) Length : ~6.5 m, Weight : ~1700 kg Low Earth orbit Suzaku Satellite Broad band + Low/stable background Powerful for diffuse analysis No imaging capability FOV=30’x30’ (FWHM) } Background for diffuse emission (normalized by effective area/FOV) (Katayama et al.)

4. Suzaku Observation - Date : 2007/Jan/15 th -17 th - Exposure : 100 ksec 5’5’ Cal src ( 55 Fe) XIS and HXD-PIN Spectra Source signal is clearly detected in - 0.4-10 keV (XIS: < 6’) - 10-70 keV (HXD-PIN: 30’x30’) XIS Image (HPD~1’) - Spectra are accumulated without excluding any point source. Central 6’ (= 1.2 kpc) region

5. Spectral Analysis (< 4 keV) 0.6 keV : Lx~1.2x10 38 erg/s 0.3 keV : 1.6x10 38 0.1 keV : 0.4x10 38 Assembly of SNRs ? Coronae of normal stars ? Assembly of Hot Bubbles ? Power-law + Gaussians - Many lines (O, Fe, Ne, Mg, Si, S, Ar) are clearly detected. - Diffuse emission consists of multi temperatures (0.6, 0.3, 0.1 keV). Consistent with previous XMM and Chandra results (HT+2001, 2004). LMXB + 3 MEKAL Origin of each plasma

6. Emission (after excluding bright sources) shows signature of He-like Fe-K line. There may be hot diffuse emission with temperature of several keV. Spectral Analysis (5-7 keV) Power-law + Gaussian (  =0 keV: fixed) XMM (130 ksec) Suzaku (100 ksec) Exclude sources (>1x10 36 erg/s)(> 2x10 36 erg/s) Chandra (37 ksec) Include all the point sources 5 6 7 (keV) 5 6 7 5 6 7 - 6.7 keV line flux (10 -5 photons/s/cm 2 /degrees 2 ) : ~5 (< 10) 6.7 keV

7. Emission (after excluding bright sources) shows signature of He-like Fe-K line. There may be hot diffuse emission with temperature of several keV. Spectral Analysis (5-7 keV) Power-law + Gaussian (  =0 keV: fixed) XMM (130 ksec) Suzaku (100 ksec) Exclude sources (>1x10 36 erg/s)(> 2x10 36 erg/s) Chandra (37 ksec) Include all the point sources 5 6 7 (keV) 5 6 7 5 6 7 - 6.7 keV line flux (10 -5 photons/s/cm 2 /degrees 2 ) : ~5 (< 10) Diffuse emssion in our Galaxy Center : ~500 (Koyama+ 2007) Ridge (l=20 degree) : ~30 (Ebisawa+ submitted) { Suzaku view of our Galactic center 6.4, 6.7, 6.9 keV 6 8(keV)10 (Koyama+ 2007) x 1/50 x 1/3 6.7 keV

8. Spectral Analysis (5-7 keV) Power-law + Gaussian (  =0 keV: fixed) XMM (130 ksec) Suzaku (100 ksec) Exclude sources (>1x10 36 erg/s)(> 2x10 36 erg/s) Chandra (37 ksec) Include all the point sources 5 6 7 (keV) 5 6 7 5 6 7 Emission (after excluding bright sources) shows signature of He-like Fe-K line. There may be hot diffuse emission with temperature of several keV. - 6.7 keV line flux (10 -5 photons/s/cm 2 /degrees 2 ) : ~5 (< 10) Diffuse emssion in our Galaxy Center : ~500 (Koyama+ 2007) Ridge (l=20 degree) : ~30 (Ebisawa+ submitted) Flux of Fe-K line in M31 is at least 3 times fainter. x 1/50 x 1/3 { 6.7 keV

9. Discussion (5-7 keV) Assembly of faint point sources (CVs…), which requires… Fainter flux of Fe-K line in M31 means… (compared with our Galaxy) Truly diffuse emission, which depends on … (M31 vs. Milky Way) - Hot plasma has 1/3 lower abundance ? 1/3 less volume ? ~1 keV lower temperature (emissivity of Fe-K) ? - Origin of hot plasma Lower abundance, since the number of point sources in M31 may be similar (even larger) compared with our Galaxy. - SN rate (Gas mass) ? : 1 vs. 2 (/century) - Rotation curve ? : 260 vs. 220 (km/s) - Scale of Galaxy ? : 20 vs. 10 (kpc) - Central BH mass ? : 40 vs. 3 (10 6 M solar ) - Past activity of central BH ? : ??? M31<MW (likely) M31>MW (unlikely) It is the key to accurately determine physical parameters of hot plasma. : unlikely ? : connected with lower ISM density ?

10. Spectral Analysis (> 10 keV) - Thermal emission cannot represent the observed flux > 20 keV. - Power-law (non-thermal) component is needed. Non-thermal diffuse emission maybe additionally exist in M31. - Power-law (  ~2.0) Lx (20-70 keV) ~ 6x10 38 erg/s @30’x30’(6 kpc x 6 kpc) BB (LMXB) + Power-law (Non thermal) + CXB Some fraction should be come from compact objects in low/hard state. Typical Lx : BHBs : 10 37 erg/s NSs : 10 36 erg/s ~60/600 sources are needed, to explain the total flux. The number is too high ??? We have an approved INTEGRAL proposal of M31 (400 ksec), to confirm this result above 10 keV.

11. Conclusion - We have analyzed Suzaku, XMM-Newton and Chandra observations of the central region of M31, to study the diffuse emission. - Below 4 keV, there are many emission lines, and spectra are well represented with 3 plasma components (0.6, 0.3, 0.1 keV). The origins may connect with SNRs, normal stars, and hot bubbles. - In 5-7 keV, there is a possibility to exist a weak He-like Fe-K line, of which flux is at least 3 times fainter than that in our Galaxy. Accurate determination of the physical properties is the key to reveal the origin of the hot plasma. - Above 10 keV, non-thermal emission is discovered up to 70 keV. The bright Lx (6x10 38 erg/s) may require some diffuse emission, in addition to that from compact objects. (HT+ 2001, 2004)