Suzaku, XMM-Newton and ChandraObservations 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

Diffuse X-ray Emission

5’

ACIS-I X-ray Image (~37 ks)

Central 6’ (= 1.2 kpc) region

Exclude point sources (> 1x1036 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.

- 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)Hard X-ray Detector (HXD)

X-Ray Telescope (XRT)X-Ray Telescope (XRT)

X-ray Imaging Spectrometer (XIS)X-ray Imaging Spectrometer (XIS)

Length : ~6.5 m, Weight : ~1700 kgLow Earth orbit

Suzaku Satellite

Broad band + Low/stable background Powerful for diffuse analysis

No imaging capabilityFOV=30’x30’ (FWHM)}

Background for diffuse emission(normalized by effective area/FOV)

(Katayama et al.)

Suzaku Observation- Date : 2007/Jan/15th -17th

- Exposure : 100 ksec

5’

Cal src(55Fe)

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

Spectral Analysis (< 4 keV)

0.6 keV : Lx~1.2x1038 erg/s0.3 keV : 1.6x1038

0.1 keV : 0.4x1038

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

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 (>1x1036 erg/s) (> 2x1036 erg/s)

Chandra (37 ksec)Include all the point sources

5 6 7(keV)

5 6 7(keV)

5 6 7(keV)

- 6.7 keV line flux (10-5 photons/s/cm2/degrees2) : ~5 (< 10)

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.

Spectral Analysis (5-7 keV)Power-law + Gaussian (=0 keV: fixed)

XMM (130 ksec)Suzaku (100 ksec)Exclude sources (>1x1036 erg/s) (> 2x1036 erg/s)

Chandra (37 ksec)Include all the point sources

5 6 7(keV)

5 6 7(keV)

5 6 7(keV)

- 6.7 keV line flux (10-5 photons/s/cm2/degrees2) : ~5 (< 10)

Diffuse emssionin 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

Spectral Analysis (5-7 keV)Power-law + Gaussian (=0 keV: fixed)

XMM (130 ksec)Suzaku (100 ksec)Exclude sources (>1x1036 erg/s) (> 2x1036 erg/s)

Chandra (37 ksec)Include all the point sources

5 6 7(keV)

5 6 7(keV)

5 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)

Diffuse emssionin 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

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 besimilar (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 (106 Msolar)- 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 ?

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) ~ 6x1038 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 : 1037 erg/s NSs : 1036 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.

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

(HT+ 2001, 2004)