Suzaku, XMM-Newton and Chandra Observations of the Central Region of M 31

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

2. 5’ Diffuse X-ray Emission ACIS-I X-ray Image (~37 ks) Exclude point sources (> 1x1036 erg/s) Diffuse emission is clearly detected. Central 6’ (= 1.2 kpc) region • 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. Background for diffuse emission (normalized by effective area/FOV) (Katayama et al.) Suzaku Satellite X-Ray Telescope (XRT) Length : ~6.5 m, Weight : ~1700 kg Low Earth orbit Hard X-ray Detector (HXD) X-ray Imaging Spectrometer (XIS) - XIS+XRT : CCD (0.2-12 keV; DE~120 eV @ 6 keV) - HXD : Si-PIN diode (10-70 keV) GSO scintillator (50-600 keV) } No imaging capability FOV=30’x30’ (FWHM) Broad band + Low/stable background Powerful for diffuse analysis

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

5. Spectral Analysis (< 4 keV) Power-law + Gaussians LMXB + 3 MEKAL • 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) . Origin of each plasma 0.6 keV : Lx~1.2x1038 erg/s 0.3 keV : 1.6x1038 0.1 keV : 0.4x1038 Assembly of SNRs ? Coronae of normal stars ? Assembly of Hot Bubbles ?

6. 6 6 6 5 5 5 7 7 7 (keV) (keV) (keV) Spectral Analysis (5-7 keV) Power-law +Gaussian (s=0 keV: fixed) Suzaku(100 ksec) Chandra(37 ksec) XMM(130 ksec) Exclude sources (>1x1036 erg/s) (> 2x1036 erg/s) Include all the point sources 6.7 keV 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/cm2/degrees2) : ~5 (< 10)

7. 6 6 6 5 5 5 7 7 7 (keV) (keV) (keV) x 1/50 Diffuse emssion in our Galaxy { Center : ~500(Koyama+ 2007) Ridge (l=20 degree) : ~30(Ebisawa+ submitted) x 1/3 Suzaku view of our Galactic center 6.4, 6.7, 6.9 keV (Koyama+ 2007) 6 8 10 (keV) Spectral Analysis (5-7 keV) Power-law +Gaussian (s=0 keV: fixed) Suzaku(100 ksec) Chandra(37 ksec) XMM(130 ksec) Exclude sources (>1x1036 erg/s) (> 2x1036 erg/s) Include all the point sources 6.7 keV 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/cm2/degrees2) : ~5 (< 10)

8. 6 6 6 5 5 5 7 7 7 (keV) (keV) (keV) Spectral Analysis (5-7 keV) Power-law +Gaussian (s=0 keV: fixed) Suzaku(100 ksec) Chandra(37 ksec) XMM(130 ksec) Exclude sources (>1x1036 erg/s) (> 2x1036 erg/s) Include all the point sources 6.7 keV 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/cm2/degrees2) : ~5 (< 10) x 1/50 { Diffuse emssion in our Galaxy Center : ~500(Koyama+ 2007) Ridge (l=20 degree) : ~30(Ebisawa+ submitted) x 1/3 Flux of Fe-K line in M31 is at least 3 times fainter.

9. : unlikely ? : connected with lower ISM density ? M31<MW (likely) • -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 (106 Msolar) • - Past activity of central BH ? : ??? M31>MW (unlikely) Discussion (5-7 keV) Fainter flux of Fe-K line in M31 means… (compared with our Galaxy) - Hot plasma has • 1/3 lower abundance ? • 1/3 less volume ? • ~1 keV lower temperature (emissivity of Fe-K) ? - Origin of hot plasma • Assembly of faint point sources (CVs…), which requires… Lower abundance, since the number of point sources in M31 may be similar (even larger) compared with our Galaxy. • Truly diffuseemission, which depends on … (M31 vs. Milky Way) It is the key to accurately determine physical parameters of hot plasma.

10. Spectral Analysis (> 10 keV) BB (LMXB) +Power-law (Non thermal) + CXB - Power-law (G~2.0) Lx (20-70 keV) ~ 6x1038 erg/s @30’x30’(6 kpc x 6 kpc) We have an approved INTEGRAL proposal of M31 (400 ksec), to confirm this result above 10 keV. • Thermal emission cannot represent the observed flux > 20 keV. • Power-law (non-thermal) component is needed. Some fraction should be come from compact objects in low/hard state. ~60/600 sources are needed, to explain the total flux. Typical Lx : BHBs : 1037 erg/s NSs : 1036 erg/s The number is too high ??? Non-thermal diffuse emission maybe additionally exist in M31.

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. (HT+ 2001, 2004) • 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 (6x1038 erg/s) may require some diffuse emission, • in addition to that from compact objects.