1. Diffuse Galactic X-ray Emission & the Galactic Centre
Bob Warwick
University of Leicester

2. Accreting Black-holes in the Nearby Galaxy M101
OPTICAL
X-RAY

3. Why are X-rays Important? A Normal Face-on Galaxy – M101
Identified phases of the Galactic ISM:
Very hot: log T > 7.5 i.e. KT > 3 keV.
Hot: 6 < log T < 7.5, i.e < kT < 3 keV
Coronal: 5 < log T < 6
Warm: log T ~ 4, e.g. WIM, WNM.
Cold: log T e.g. Molecular clouds
Why are X-rays Important?
A Normal Face-on Galaxy – M101
XMM-Newton source-removed EPIC image with GALEX UV contours superimposed
(Warwick et al in prep.)
keV

4. X-ray Emission from the Milky Way
Type of Emitter Number in Summed Lx
Galaxy erg s-1
HMXRB ~3
LMXRB ~30
SNR ~ <1
Low Lx Be Binaries ~ <1
CVs ~ <1
RSCVn ~ <1
Late Type Stars <1
Active Nucleus <0.001
Diffuse Disk/GC ~3
Diffuse Bulge ~20
Diffuse Halo/Corona ~10
Total ~60

5. Haslam et al. 1982
408 MHz
Snowden et al. 1997

6. Chandra Mosaic of the Galactic Centre Region
Wang, Gotthelf & Lang (2002)

7. Topics The Local Bubble, the Galactic Halo & Beyond
Loop 1 & the Galactic Bulge Emission
The Origin of the Hard Galactic Ridge
Hot Plasma in the Galactic Center Region
Fluorescent X-rays from GC Molecular Clouds

8. Topics The Local Bubble, the Galactic Halo & Beyond
Loop 1 & the Galactic Bulge Emission
The Origin of the Hard Galactic Ridge
Hot Plasma in the Galactic Center Region
Fluorescent X-rays from GC Molecular Clouds

9. Distribution of ~ 106 K Plasma in the Local Galaxy
T = K
T = K
Galactic Anti-Centre
Galactic Centre
GALACTIC PLANE
Snowden (2002)

10. Shadowing of the ¼ keV SXRB in Draco
IRAS 100 micron
RAS ¼ keV
Burrows & Mendenhall 1991; Snowden et al. 1991

11. Distribution of ~ 106 K Plasma in the Local Galaxy
T = K
Draco Nebula
T = K
270o
90o
Cygnus Super Bubble
Snowden (2002)

12. Simulated Spectrum of the Galactic Foreground at High Latitude
Local Hot Bubble
Active Galaxies
Galactic Halo
IGM of Local Group ?
WHIM ?
Fang et al, 2005

13. WHIM Absorption Along the Line of Sight to Markarian 421
Nicastro et al. (2005)

14. Fang et al, 2005 Hot gas in a Galaxy Group
Diffuse emission from a WHIM filament
Void in the WHIM structure
Fang et al, 2005

15. XMM-Newton EPIC Instrument
Large Effective Area: ~ 2000 cm2 @ 1 keV
Good Imaging Capability: PSF(FWHM) 6 arcsec
Wide Field of View: ~30 arcmin diameter
Broad Bandpass: keV
Good Spectral Resolution: 120 eV @ 6 keV

16. XMM MIRRORS

17. XMM EPIC CCD CAMERAS
MOS CCDs
pn CCD

18. Measuring the Spectrum of the Diffuse XRB with the EPIC CCDspn
Instrumental fluorescent lines
MOS
Particle continuum
Energy (keV)

19. Simulated Spectra
WHIM FILAMENT

20. Topics The Local Bubble, the Galactic Halo & Beyond
Loop 1 & the Galactic Bulge Emission
The Origin of the Hard Galactic Ridge
Hot Plasma in the Galactic Center Region
Fluorescent X-rays from GC Molecular Clouds

21. Distribution of ~106 K Plasma in the Local ISM
T = K
T = K
Galactic Centre
Galactic Anti-Centre
Snowden (2002)

22. ROSAT ALL-SKY SURVEY - ¾ keV IMAGE

23. Soft X-ray Spectra of the North Polar Spur
Willingale et al. (2003)

24. Willingale et al. (2003)

25. ROSAT ALL-SKY SURVEY - ¾ keV IMAGE
Ophiuchus Dark Cloud

26. X-ray Shadowing in the Ophiuchus Molecular Cloud
Image: X-ray keV
Contours: IRAS 100 micron
Energy (keV)
EPIC PN SPECTRUM: ON/OFF CLOUD
Mendes et al. (2005) reported in Breitschwerdt et al. (2005)

27. ROSAT ALL-SKY SURVEY - ¾ keV IMAGE

28. EPIC MOS SPECTRA FOR THE GALACTIC BULGE REGION
0.0,0.0
0.5,-2.6
1.1,-3.8
0.4,-5.4
0.5,-8.0
0.0,-11.9
345,+12
345,+24

29. Topics The Local Bubble, the Galactic Halo & Beyond
Loop 1 & the Galactic Bulge Emission
The Origin of the Hard Galactic Ridge
Hot Plasma in the Galactic Center Region
Fluorescent X-rays from GC Molecular Clouds

30. The Galactic X-ray Ridge
Identified as a significant Galactic feature by HEAO1 (Worrall et al. 1982)
Narrow ridge evident in EXOSAT Galactic Plane Scan (Warwick et al. 1985)
Extensively studied in Ginga & ASCA Surveys (Yamauchi & Koyama 1993; Sugizaki et al. 2001)
6. 7 keV line
Excellent Tracer
Galactic
Center

31. Spectrum of the Galactic Ridge
Emission lines from highly ionized Si, S, and Fe  multi-temperature plasma models
ORIGIN OF THE HARD COMPONENT?
Luminosity of 1.4 x 10^38 erg/s
Energy Density ~10 eV/cm^3
Too hot to originate in SN activity
Unbound to Galactic Disk
Possible approaches to various aspects of the problem:
Magnetic reconnection & confinement
Quasi-thermal plasma
LECRe – non-thermal contribution
LECR ions & charge exchange
See Tanaka (2002)
ASCA GIS
6.7 keV iron line
kT ~ 10 keV
Cosmic X-ray
Background
Cool component
kT ~0.8 keV
Kaneda et al. (1997)

32. Is the Hard X-ray Galactic Ridge due to
Truly diffuse emission?
The superposition of point sources?
Ebisawa et al (2005)
Point source contribution

33. Is the Hard X-ray Galactic Ridge due to
Truly diffuse emission?
The superposition of point sources?
Ebisawa et al. (2003,2005)

34. XGPS-I Survey after Point Source Removal
keV
2-6 keV

35. XGPS-I Survey after Point Source Removal
2-6 keV G G G
G =Kes 69
Radio 20 cm

36. Variation of the 2-6 keV surface brightness of the Galactic X-ray Ridge with (l,b)
Galactic Longitude
-0.5o
0.0o
+0.5o
Galactic Latitude

37. The 6. 7 keV iron line – the key diagnostic. ASCA GIS: 6. 61+/-0
The 6.7 keV iron line – the key diagnostic? ASCA GIS: /-0.02 keV (Kaneda et al. 1997)  nei plasma or a blend of thermal emission with 6.4 keV iron fluorescence from LECRe excitation of cold gas ASCA SIS: Blend of 6.70 keV (He-like) & 6.96 keV (H-like) lines (Tanaka 2002)  ~ collisional equilibrium thermal plasma at ~ 8 keV  very similar spectrum to that seen in Galactic Centre! Chandra: /-0.14 keV (Ebisawa et al. 2005)  consistent with ASCA GIS result!

38. The X-ray Spectrum of the Galactic X-ray Ridge measured by XMM-Newton
Equivalent width of 6.4 keV Fe fluorescence line < 50 eV
6.7 keV iron line
Raw
Background
Background-subtracted
Preliminary Only

39. Topics The Local Bubble, the Galactic Halo & Beyond
Loop 1 & the Galactic Bulge Emission
The Origin of the Hard Galactic Ridge
Hot Plasma in the Galactic Center Region
Fluorescent X-rays from GC Molecular Clouds

40. XMM-NEWTON GALACTIC CENTRE SURVEYS
WIDE-FIELD SURVEY
Anne Decourchelle Saclay
Bob Warwick Leicester
Masaaki Sakano Leicester
Peter Predehl MPE
Delphine Porquet MPE
SGR A* MONITORING
Andrea Goldwurm Saclay
et al
~ 250 ks
~ 400 ks

41. Sgr A - Radio Arc Region 0.5-1.4 keV X-ray 0.0o -0.2o 0.2o -0.2o
Galactic Latitude
-0.2o
Galactic Longitude

42. Sgr A - Radio Arc Region 2-4.5 keV X-ray 0.0o -0.2o 0.2o -0.2o
Arches Cluster
Sgr A*
0.0o
-0.2o
0.2o 1E
Galactic Latitude
Sgr A East SNR
-0.2o
Galactic Longitude

43. Sgr A - Radio Arc Region 4.5-6 keV X-ray 0.0o -0.2o 0.2o -0.2o
Arches Cluster
Sgr A East SNR
Sgr A*
0.0o
-0.2o
0.2o 1E
Galactic Latitude
NT X-ray Threads
-0.2o
Galactic Longitude

44. Sgr A - Radio Arc Region 6-9 keV X-ray 0.0o -0.2o 0.2o -0.2o Sgr A*
Transient
0.0o
-0.2o
0.2o
Transient
Galactic Latitude
NT X-ray Threads G
Transient
-0.2o
Galactic Longitude

45. 2-6 keV band
2.4 keV S line
6.7 keV Fe line
6.4 keV Fe line

46. Spectral Extraction Region 4.5- 6 keV Continuum
Celestial Coordinates

47. 7-10 keV Thermal and/or Non-Thermal
X-ray Spectrum from the Annular Region around Sgr A
Si XIII
S XV
7-10 keV Thermal and/or Non-Thermal
Ar XVII
Ca XIX Fe
1-3 keV Thermal
Al & Si Fluorescence Lines

48. Fe-line Spectrum from the Annular Region around Sgr A
6.4 keV keV keV
Fe XXV
Fe Neutral
Fe XXVI
Intrinsic width of Fe 6.7 keV line 27 +/- 13 eV

49. Fe K S XV Fe XXV 8 keV thermal 1 keV thermal
Non-thermal bremmstrahlung plus 6.4 keV iron fluorescence from LECRe + molecular gas

50. a x b x c x 4.5-6 keV Continuum 6.4 keV Iron Line 2.4 keV Sulphur Line

51. a = 1.8 (Z~3 ; LECRe component)
b = (Z ~1 ; 1 keV plasma)
c = 3.7 (Z=1 ; 8 keV plasma)

52. Distribution of 6.7 keV line as a tracer of the hard “thermal” component
Corrected for 6.7 keV line emission originating in the softer ~ 1 keV plasma
Surface brightness versus radius
Emissivity ~ r -1.3

53. The GC Bipolar Lobes observed by Chandra Credit: Mark Morris
Galactic plane
Apparently thermal outflow from SgrA*
6’ = 15 pc
Chandra smoothed, point-source removed keV image.
Credit: Mark Morris

54. +b
6’ = 15 pc
Ratio: soft (2– 4.7 keV) / hard (4.7 – 8 keV) emission (most point sources removed)

55. Locations of point sources (Muno et al.)

56. Hot Diffuse Gas in the Galactic Centre
Two temperature components:
keV  attributable to supernovae & the GC outflow
~8.0 keV  implied energy if diffuse and unbounded ~1040 erg s-1
Latter due to sources?
A population of 2 x 10^5 CV-like sources with Lx ~ 10^31 erg/s at the Galactic Centre would do the trick!
(Muno et al. 2004)
Then how about trying the same trick for the Galactic Ridge!

57. Topics The Local Bubble, the Galactic Halo & Beyond
Loop 1 & the Galactic Bulge Emission
The Origin of the Hard Galactic Ridge
Hot Plasma in the Galactic Center Region
Fluorescent X-rays from GC Molecular Clouds

58. ASCA
Sgr C
Fe K - Neutral Gas
Koyama et al. (1996)

59. An X-ray echo of the past activity of Sgr A* ?
X-RAY REFLECTION NEBULAE
An X-ray echo of the past activity of Sgr A* ?
Churazov, Gilfanov & Sunyaev 1999
Fluorescence of giant molecular clouds illuminated by a flare on Sgr A* producing LX~1039 erg/s, for t > ~10 yrs, ~300 yrs ago.
(Sunyaev et al. 1993, Koyama et al. 1996, Murakami et al. 2001, Revnivtsev et al )

60. X-ray Reflection From Cold Near-Neutral Matter
Fe K line
dense neutral clouds
X-rays
6.4 keV line
Reflection models predict:
Neutral Fe Kalpha Line Eq. Width ~ 150 eV (wrt direct continuum)
Neutral Fe Kalpha Line Eq. Width > 1 keV (Z = 1) (wrt reflected continuum)
Significant iron-K edge on reflected continuum, NFe ~ 2 x 1019 Fe cm-3

61. Alternative Model: Excitation by Cosmic-ray Electrons
Cosmic-ray electrons E ~ 10 keV – 1 GeV have significant cross-section for interaction with K-shell electrons (Valinia et al. 2000; Yusef-Zadeh et al. 2002)
Such cosmic rays maybe produced in young, massive stellar clusters (Yusef-Zadeh 2003)
Radio data establish a large population of GeV electrons in the inner 300 pc. Fe
Models predict:
Neutral Fe Kalpha Line Eq. Width ~ keV (Z = 1)
Significantly smaller iron-K edge on non-thermal bremsstrahlung cont.
Tatischeff 2005

62. Sgr B2 Giant Molecular Cloud
F line = 5.6 x 10-5 photon/cm2/s
E.W. = 2.2 keV
NFe = 3.4 x 1019 Fe cm-2
6.4 keV line
Chandra Observations – Murakami et al. (2001)

63. 6.4 keV Fe fluorescence line
Sgr A - Radio Arc Region
Radio & 90 cm
90 cm
0.0o
-0.2o
0.2o
Galactic Latitude
6.4 keV Fe fluorescence line
-0.2o
Galactic Longitude

64. 6.4 keV Fe fluorescence line
Sgr A - Radio Arc Region
CS (J=1-0) km/s
0.0o
-0.2o
0.2o
6.4 keV Fe line
Galactic Latitude
6.4 keV Fe fluorescence line
-0.2o
Galactic Longitude

65. Correlation of the 4.5-6 keV X-ray continuum and the 6.4 keV line flux
4.5-6 keV Continuum
Correlation of the keV X-ray continuum and the 6.4 keV line flux
thermal non-thermal
6.4 keV Fe Line

66. X-ray Spectrum of G0.13-0.13 Cloud
S = -0.3 (not constrained)
NH = 1.7 x 1023 H cm-3
Z = 2.9 pn
MOS 1/2
Power-Law + Gaussian Line Model:
Photon Index ~ 1.9
NH = 2.3 x 1023 H cm-2
Fline = 2.4 x 10-5 photon/cm2/s
E.W. = 1.45 keV
NFe < 1 x 1019 Fe cm-2

67. Correspondence of X-ray 6
Correspondence of X-ray 6.4 keV line with Molecular Gas measured in SiO J = 1-0
15-20 km/s
20-25 km/s
25-30 km/s
30-35 km/s
35-40 km/s
40-45 km/s
45-50 km/s
6.4 keV line
Handa et al. (2005)

68. Distribution of 6.4 keV Iron Fluorescence near the Galactic Centre
90 light years
Arches Cluster

69. Arches Cluster 2-6 keV CS J = 2 –1 20 – 40 km/s 0.0o +0.1o
Iron 6.7 keV line (black)
Iron 6.4 keV line (blue)

70. Some Interesting Unresolved Questions Relating to Diffuse Galactic X-ray Emission
What is the origin of the Galactic X-ray halo and does the emission extend into the IGM of the Local Group and beyond?
Can we determine the X-ray properties and nature of the extended Galactic Bulge against the confusion of LOOP 1?
What is the origin of the Galactic X-ray Ridge?
Is the bright central concentration of hard “thermal” emission seen at the Galactic Centre really due to a diffuse component?
Is the iron-line fluorescence seen throughout the Galactic Centre Region excited by photon illumination or cosmic ray electrons?