Recent Chandra Observations ofThe 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)– 100 ks for Arches cluster (Wang et al. 2006) – ~ 1 Ms for Sgr A (Baganoff et al. )

Qingde Daniel Wang

X-ray Sources

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

2o

0.8o

Spatial resolution varies from subarcsecond on axis to a few

arcseconds off-axis

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)

---S

i XII

I K

---

S X

V K

---F

e (n

eutr

al) K

---A

r X

VII

K

Diffuse X-ray emission: spectrum

SXV Line

Fe 6.7-keV line

Fe 6.4-keV Line

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

Arches

Quintuplet GC

Chandra Intensity:

•1-4 keV

•4-6 keV

•4-9 keV

Wang, Hui, & Lang (2006)

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

Quintuplet GC

Arches Cluster: brightest X-ray sources in the core

NICMOS image (Figer et al. 99)ACIS-I 1-9 keV

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: diffuse X-ray emission

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

• 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).

Fe KX-ray or electron

CS data: from OVRO+IRAM

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

Radial intensity profile

cluster wind (Rockefeller et al. 05)

NICMOS

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.

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

Miller & Scalo IMF

PL MF

X-ray limit

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

• 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)

NICMOS

Galactic Center: inner pc region

VLT SINFONI near-IR

(Eisenharer et al. 05)

ACIS-I 1-9 keV

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

Sgr A*IRS 13

PWN?

Comparison with other extended X-ray-emitting features

Sgr A*

IRS 13

PWN

Diffuse

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*?

Red: radio (3.6 cm, Roberts & Goss 93)Green: near-IR (Eisenhauer et al. 05)Blue: X-ray (4-9 keV)

Sgr A*

IRS 13

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?

Conclusions• 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.

M31

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

28’x28’ FoV

Red: 0.5-1 keVGreen: 1-2 keV Blue: 2-4 keV)

M31 Bulge

Red: 0.5-1 keVGreen: 1-2 keV Blue: 2-4 keV)

Red: Mid-IR (Spitzer)Green: 0.5-2 keV)Blue: 2-4 keV

M31 Nuclear Region

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

10 ly