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Recent Chandra Observations of The Galactic Center. Observations: Large-scale mapping 360 ks (Wang, Gotthelf, & Lang 2002) new 600 ks (Muno et al.) Pointed 100 ks each for Sgr B (Koyama et al.) and Sgr C 50 ks for the Radio Arc (Yusef-Zadeh et al. 2002)

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recent chandra observations of the galactic center
Recent Chandra Observations ofThe Galactic Center


  • Large-scale mapping
    • 360 ks (Wang, Gotthelf, & Lang 2002)
    • new 600 ks (Muno et al.)
  • Pointed
    • 100 ks each for Sgr B (Koyama et al.) and Sgr C
    • 50 ks for the Radio Arc (Yusef-Zadeh et al. 2002)
    • 100 ks for Arches cluster (Wang et al. 2006)
    • ~ 1 Ms for Sgr A (Baganoff et al. )

Qingde Daniel Wang

x ray sources



X-ray Sources

Wang et al. (2002); Muno et al. (2006)

Spatial resolution varies from subarcsecond on axis to a few arcseconds off-axis

discrete x ray sources summary of results
Discrete X-ray sources: Summary of results
  • Discrete sources
    • ~ 1400 from the large-scale survey
    • ~ 2400 in the Sgr A* region alone.
    • LogN-LogS relation is flatter in massive SF regions
  • Nature of the sources
    • Bright ones (Lx > 1036 erg/s): X-ray binaries
    • Intermediate ones (1036 > Lx > 1033): transient LMXBs, colliding wind binaries, and young pulsars
    • Faint ones (1033 > Lx ): active low-mass stars (CVs)

Consistent with existing radio and near-IR IDs or lack of them. Some sources have very hard intrinsic spectra (power law photon index < 1)

diffuse x ray emission spectrum

--- S XV K

---Ar XVII K

---Si XIII K

---Fe (neutral)K

Diffuse X-ray emission: spectrum
diffuse x ray emission summary of results
Diffuse X-ray emission: Summary of results
  • Diffuse X-ray Emission
    • Accounting for ~90% of the emission.
    • Showing strong He-like and H-like K lines from Si, S, Ar, Ca, and Fe  gas at T ~ 1 – 10 keV.
    • Global, but not detailed, correction between 6.4-keV Fe K line and cool dense clouds: reflection of past Sgr A* bursts, low-energy comic rays, and possible NEI plasma.
    • Probably largely due to coronally active binaries and CVs (Revnivtsev et al. 2005).
    • More quantitative modeling is needed!
massive star forming region composite chandra map




Massive star forming region: Composite Chandra map
  • Chandra Intensity:
  • 1-4 keV
  • 4-6 keV
  • 4-9 keV

Wang, Hui, & Lang (2006)

massive star forming region from radio to x ray




Massive star forming region:from radio to X-ray

20 cm (Yusef-Zadeh et al. 84)

MSX 24 m (Price et al. 01)

Chandra 1-9 keV (Wang et al. 06)

arches cluster brightest x ray sources in the core
Arches Cluster: brightest X-ray sources in the core

ACIS-I 1-9 keV

NICMOS image (Figer et al. 99)

arches cluster bright x ray sources in the core
Arches Cluster: bright X-ray sources in the core
  • Remarkably similar thermal spectra
  • Metal abundance = 1.8 (1.6-2.6) solar
  • L(0.3-8 keV)=(0.5-11) x1033 erg/s
  • Late-type WN components
  • Likely to be extreme massive colliding wind binaries.

Combined ACIS-I spectrum

arches cluster 6 7 kev line plume
Arches Cluster: 6.7-keV line plume
  • Elongated and Size ~ 30”
    • Matches the region with an extinction deficit of Av~10 (Stolte et al. 02)
arches cluster the 6 4 kev line emission and a cs cloud

Fe Ka

X-ray or electron

Arches Cluster: the 6.4-keV line emission and a CS cloud
  • Not due to florescence: no spatial correlation with the CS cloud.
  • net too small to be due to a NEI plasma.
  • Likely due to low-energy cosmic-ray electrons interacting with the cloud (vr > 120 km/s).

CS data: from OVRO+IRAM

arches cluster diffuse x ray emission1
Arches Cluster:Diffuse X-ray emission
  • In the core (r < 0.6 pc)
    • 6.7-keV line
    • Steep intensity decline
    • Probably due to the cluster wind
  • In the outer region
    • 6.4-keV line
    • Flat intensity profile
    • Probably due to the low-energy cosmic-ray electrons --- a result of the collision of the cluster wind with the CS cloud

cluster wind (Rockefeller et al. 05)


Radial intensity profile

arches cluster constraints on the imf
Arches cluster: Constraints on the IMF
  • YSOs (0.3-3 Msun) accounts for 75% of the Orion nebula Lx.
  • Each YSO has Lx ~ 1.2 x1030 erg/s per star (2-8 keV).
  • The observed total diffuse X-ray Lx ~ 2 x1034 erg/s (r < 2.5 pc)  an upper limit of 2x104 YSOs.
  • Miller & Scalo IMF overpredicts YSOs by > 10
  • Power law with Γ~ -0.86 is consistent with the upper limit.

X-ray limit

Miller & Scalo IMF


MF for r < 0.4 pc (Stolte et al. 05)

quintuplet cluster x ray sources
Quintuplet cluster: X-ray sources
  • Dimmer and diverse in spectral propertie
  • Some maybe embedded in dusty winds

Wang et al. (2006)

Law & Yusef-Zadeh (2004)

quintuplet cluster diffuse x ray emission
Quintuplet cluster: Diffuse X-ray emission
  • Very weak (Lx ~ 2 x1033 erg/s)
  • Cluster wind contribution is small
  • Follows approximately the stellar distribution
  • Probably mostly due to ~2x103 YSOs.

cluster wind (Rockefeller et al. 2005)


galactic center inner pc region
Galactic Center: inner pc region


Sgr A*

IRS 13

ACIS-I 1-9 keV

(Wang, Lu, Gotthelf 06; see also Baganoff et al. 03)


(Eisenharer et al. 05)

comparison with other extended x ray emitting features
Comparison with other extended X-ray-emitting features

Sgr A*


IRS 13


The spectra of Sgr A*, IRS 13, and diffuse X-ray emission all show the Fe K line at ~6.6 keV  NEI emission from gas heated recently (net~103 cm-3 yr).

a pwn within 1 ly of sgr a
A PWN within 1 ly of Sgr A*?


Sgr A*

IRS 13

Red: radio (3.6 cm, Roberts & Goss 93)

Green: near-IR (Eisenhauer et al. 05)

Blue: X-ray (4-9 keV)

evidence for the pwn
Evidence for the PWN

Pulsar wind nebula

  • Nonthermal point-like source (putative pulsar)
  • Comet-like shape: ram-pressure confinement
  • Spectral steepening with off-source distance
  • Inverse-Compton scattering of the ambient radiation, a natural explanation of the TeV emission from the GC.

Shock into SN ejecta

  • Does the pulsar origin in the GC cluster?
  • What effect on the GC environment?
  • About 4000 X-ray sources are detected within 0.8x2 deg2 GC region.
  • IDs have been difficult, but will be easier with improved source position accuracy (<1”).
  • Some of the X-ray sources are likely to be young pulsars and extreme colliding wind massive binaries.
  • Bulk of faint sources are due to low-mass old stars.
  • X-ray-inferred Fe abundance is ~ 2 x solar.
  • Limits on # of YSOs indicate top-heavy IMFs of young clusters.
  • Collisions between young clusters and molecular clouds may be important in star formation.

28’x28’ FoV

Red: 0.5-1 keV

Green: 1-2 keV

Blue: 2-4 keV)

NASA/UMass/Z.Li & Q.D.Wang

m31 bulge
M31 Bulge

Red: Mid-IR (Spitzer)

Green: 0.5-2 keV)

Blue: 2-4 keV

Red: 0.5-1 keV

Green: 1-2 keV

Blue: 2-4 keV)

m31 nuclear region
M31 Nuclear Region

10 ly

X-ray images: (NASA/SAO/CXC/M.Garcia et al.)Optical Contours: (NASA/GSFC/T.Brown et al.)