Dead Stars Do Tell Tales: Chandra Observations of Dense Stellar Systems

1. Dead Stars Do Tell Tales:Chandra Observations of Dense Stellar Systems Michael Muno (UCLA/Hubble Fellow)

3. What Are We Looking For? Black hole and neutron star X-ray binaries. Lx= 1030 to 1039 erg s-1. Accreting white dwarfs (intermediate polars). Lx= 1029 to 1033 erg s-1. WR 124; HST/WFPC Wolf-Rayet and OB stars in colliding-wind binaries. Lx= 1029 to 1034 erg s-1. Pulsars. Lx= 1029 to 1038 erg s-1.

4. N E The Era Before Chandra The central 300 pc of the Galaxy ( 30 pc

5. N E Chandra Observations of Dense Stellar Systems The central 300 pc of the Galaxy: 30 x 12 ks exposures Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

6. N E Chandra Observations of Dense Stellar Systems Sgr A complex BH LMXB LMXB pulsar The central 300 pc of the Galaxy: 30 x 12 ks exposures Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

7. N E Chandra Observations of Dense Stellar Systems Sgr A complex Sgr B GMCs Sgr C GMC The central 300 pc of the Galaxy: 30 x 12 ks exposures Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

8. N E Chandra Observations of Dense Stellar Systems Foreground star cluster Arches & Quintuplet Sgr A complex Foreground star cluster The central 300 pc of the Galaxy: 30 x 12 ks exposures Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

9. N E X-ray Observations of Accreting Black Holes and Neutron Stars The central 300 pc of the Galaxy: 30 x 12 ks exposures Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

10. N E 5 pc 1 Msec over 7 yr Baganoff et al. (2003); Muno et al. (2003a, ApJ, 589, 225)

11. N E 5 pc Iron Fluorescence Sgr A East SNR Sgr A* Outflow from Sgr A* 1 Msec over 7 yr Baganoff et al. (2003); Muno et al. (2003a, ApJ, 589, 225)

12. N E 0.5 pc

13. N E 0.5 pc Pulsar? Sgr A* Small star cluster IRS 13 LMXB

14. The Population of X-ray Sources • What are the X-ray sources? • How do dense stellar environments affect the population of close binaries? • What are the masses of stars that form black holes and neutron stars? The central 300 pc of the Galaxy: Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

15. The Surprises • X-ray transients are concentrated in the central parsec of the Galaxy. • There is an X-ray pulsar in the star cluster Westerlund 1.

16. The Population of X-ray Sources Full survey: 1% of the Galactic stellar mass Deep survey: 0.1% of the Galactic stellar mass The central 300 pc of the Galaxy: Wang, Gotthelf, & Lang 2002; NASA/UMass 30 pc

17. Galactic Center X-ray Sources • Shallow survey: • Lx>5x1032 erg s-1 • 549 foreground sources • 1352 Galactic center sources • <130 background AGN • Deep Sgr A* field: • LX>1031 erg s-1 • 200 foreground sources • 2287 Galactic center sources • <40 background AGN Sgr A*

18. X-ray Sources Trace the Stellar Population In the central 20 pc, the surface density of X-ray sources falls off as R-1, just like the stellar population in the infrared. (Muno et al. 2003a, 2006)

19. Spectra of the Point Sources Color = (H-L/H+L). L = 3.3-4.7 keV H = 4.7-8.0 keV keV Muno et al. (2004b, ApJ, 613, 1179)

20. Spectra of the Point Sources mCV HMXB pulsar WR/O LMXB CV Muno et al. (2004b, ApJ, 613, 1179)

21. Most X-ray Sources are Magnetic CVs • The spectra of the point sources are consistent with those of mCVs. • Seven sources exhibit periodic flux modulations, as expected from mCVs. • 104 CVs are expected in the field, and about 10% of CVs are magnetic, so 1000 should be observed. Muno et al. (2003c) Ruiter et al. (2006)

22. High Mass X-ray Binaries • Pfahl, Rappaport, & Podsiadlowski (2002) predict on order 100 HXMBs. • These will have infrared counterparts with K<17. • IR observations indicate up to 10% of sources (i.e., <100) could be HMXBs (e.g., Laycock et al. 2005). 1” Diffraction-limited Keck Image (K band).

23. Sources with Radio Counterparts G. Bower; Muno et al. (2006) • Found two X-ray sources with radio and IR matches. • One is a known massive, young star in an HII region. 8.4 GHz

24. HMXBs or Colliding Winds? A. Burgasser; Muno et al. (2006) Paschen He I Br g • IR spectra reveal lines from H and He characteristic of winds from stars with T >15,000 K, often classified as B[e], Of, and LBV stars (also, Mikles et al. 2006). • These are only bright in X-rays when in binaries. IRTF/SPEX. R~130

25. Low-Mass X-ray Binaries One Solar Radius Location of Compact Object Image from binsim, by Rob Hynes • Belczynski & Taam (2004) predict hundreds of LMXBs with low mass transfer rates. • The disks will be unstable, producing outbursts with LX>1036 erg s-1. • About 5 per year should be in outburst.

26. Sgr A* 5 pc Searching for X-ray Binaries • We identified accreting black holes and neutron stars by looking for sources that: • varied by at least a factor of 10, and • had peak luminosities >1034 erg s-1. • We found 7 transients in 5 years of data. Muno et al. (2005)

27. Sgr A* 5 pc Searching for X-ray Binaries Neutron Star LMXB GRS 1741.9-2858 • We identified accreting black holes and neutron stars by looking for sources that: • varied by at least a factor of 10, and • had peak luminosities >1034 erg s-1. • We found 7 transients in 5 years of data. Muno et al. (2005)

28. Conclusions • The population of X-ray sources at the Galactic center is dominated by magnetic CVs, with small populations of X-ray binaries and WR/O stars. • X-ray transients are concentrated in the central parsec of the Galaxy. • There is an X-ray pulsar in the star cluster Westerlund 1.

29. An Overabundance of Transients in the Central Parsec • Four lie within 1 pc of Sgr A*. The enclosed stellar mass is 2 106 Mo. • Three lie between 1-25 pc of Sgr A*. The enclosed stellar mass is >3 107 Mo. • Transients are over-abundant by >20x in the inner parsec! Muno et al. (2005) 1 pc

30. 1 pc 47 Tuc LMXBs Are Also Concentrated in Globular Clusters Keel et al. Grindlay et al. 2001; Pooley et al. 2003 Optical: 1.5 m telescope in Chile X-ray: Chandra In globular clusters, LMXBs are over-abundant by a factor of 100 per unit stellar mass.

31. Dynamical Friction • Lighter objects tend to collect in the wakes of heavier ones. • As a result, the heavier object is slowed down. • The heavier object loses energy, and falls deeper into the gravitational potential.

32. 1 pc Dynamically Forming LMXBs Grindlay et al. 2001; Pooley et al. 2003 47 Tuc simulation by E. Pfahl In globular clusters, LMXBs are over-abundant by a factor of 100 per unit stellar mass.

33. 1 pc 47 Tuc Dynamically Forming LMXBs • rc = 6 104 Mo pc-3 • s = 12 km s-1 • rc = 7 106 Mo pc-3 • s = 70 km s-1

34. Dynamically Forming LMXBs • 104 black holes have dynamically settled into the central pc (Morris 1993, Miralda-Escudé & Gould 2000). • Pfahl & Loeb (in prep.) estimate that these form LMXBs via binary-single interactions at a rate of 10-6 yr -1. • Over the dynamical time scale of 1 Gyr, 103 LMXBs could form. simulation by E. Pfahl; Muno et al. (2005)

35. Sgr A* Young HMXBs • Several dozen massive stars formed among 104 stars 7 Myr ago. • Up to 300 black holes may have already formed. • At most 10% of these could be in HMXBs, or on order 30 systems. 1 pc Muno et al. (2005) Infrared laser guide-star image courtesy W.M. Keck Observatory.

36. Conclusions • The population of X-ray sources at the Galactic center is dominated by CVs, with small populations of X-ray binaries and WR/O stars. • X-ray transients in the central parsec of the Galaxy formed through three-body interactions from a population of ~10,000 black holes. • The discovery of an X-ray pulsar in the star cluster Westerlund 1.

37. The Unusual Stellar Population in the Central Parsec Pulsar? Sgr A* IRS 13 Sgr A* IRS 13 1 pc (plus diffuse X-rays) Infrared laser guide-star image (Keck Observatory; Ghez et al. 2005).

38. Sgr A* What Affects on the X-ray Population? • The gravitational potential of the supermassive black hole? • The recent burst of star formation? • 22 Wolf-Rayet stars. • ~60 main sequence and supergiant OB stars. • A handful of red supergiants. 1 pc Infrared laser guide-star image (Keck Observatory; Ghez et al. 2005). e.g., Genzel et al. 2003, Paumard et al. 2005

39. The Unusual Stellar Population in Westerlund 1 • Main sequence 06 stars. • Over 25 Wolf-Rayet stars. • Over 80 OB supergiants • One confirmed LBV. • Several red supergiants. • Five yellow hypergiants. 1 pc (e.g., Westerlund 1987, Clark et al. 2005) VRI from 2.2m MPG/ESO+WFI Clark et al. (2005)

40. A Galactic Super Star Cluster • 150 stars with M>35 Msun • Mass: 105 Msun • Extent: ~6 pc across • Distance: 5 kpc • Age: 4 +/- 1 Myr The cluster is coeval, and old enough to have produced supernovae 1 pc VRI from 2.2m MPG/ESO+WFI Clark et al. (2005)

41. Chandra Observations 1 pc VRI from 2.2m MPG/ESO+WFI Clark et al. (2005) Chandra ACIS We see diffuse X-rays from the cluster wind and unresolved pre-main-sequence stars, stellar emission from colliding wind binaries, and black holes.

42. Chandra Observations pulsar 1 pc VRI from 2.2m MPG/ESO+WFI Clark et al. (2005) Chandra ACIS We see diffuse X-rays from the cluster wind and unresolved pre-main-sequence stars, stellar emission from colliding wind binaries, and a pulsar!

43. Pulsar CXO J164710.2-455216 • Period: 10.6107(1) s • Spin-down: <2x10-10 s s-1 • LX = 3x1033 erg s-1 (not a radio pulsar) • Spectrum: kT = 0.6 keV blackbody (not a cooling NS) • No IR counterpart, so K>18.5 (Mcount. < 1Msun; not an X-ray binary) This pulsar is almost certainly a magnetar.

44. A Massive Progenitor pulsar 1 pc VRI from 2.2m MPG/ESO+WFI Clark et al. (2005) Chandra ACIS With 35 Msun stars still on the main sequence, only stars with initial masses >40 Msun could have exploded.

45. Other Neutron Stars with >30 Msun Progenitors 1E 1048.1-5937 SGR 1806-20 • A HI shell around 1E 1048.1-5937 was interpreted as the wind-blown bubble from a 30-40 Msun progenitor (Gaensler et al. 2005) • SGR 1806-20 is the member of a star cluster ~3 Myr old, and so had a ~50 Msun progenitor (Figer et al. 2005).

46. WhichStars Form Black Holes? solar White Dwarf Metallicity Heger et al. 2003 metal-free 9 25 40 100 140 260 Initial Mass (Solar Masses)

47. WhichStars Form Black Holes? Wd 1 solar White Dwarf Metallicity Heger et al. 2003 metal-free 9 25 40 100 140 260 Initial Mass (Solar Masses)

48. Massive Progenitors to Neutron Stars • These pulsars show that massive stars can lose 95% of their mass: • Through winds (e.g., Heger et al 2003), • Via binary mass transfer (Wellstein & Langer 1999), • Or during supernovae (Akiyama & Wheeler 2005). • As magnetars, B-fields appear important: • Massive stars could produce rapidly-rotating cores (e.g., Duncan & Thomas 1992; Heger et al. 2005). • Or magnetars could form from highly-magnetic progenitors (e.g., Ferrario & Wickramasinghe 2005).

49. Conclusions • The population of X-ray sources at the Galactic center is dominated by CVs, with small populations of X-ray binaries and WR/O stars. • X-ray transients in the central parsec of the Galaxy formed through three-body interactions from a population of ~10,000 black holes. • The discovery of an X-ray pulsar in the star cluster Westerlund 1 implies that the progenitor to the neutron star had an initial mass of >40 Msun.

50. What’s Next: • How many high mass X-ray binaries are in the Galactic center? How about pulsars? • Multi-wavelength survey, including deeper Chandra observations. • Which stars form black holes? • Chandra observations of clusters being discovered using 2MASS and Spitzer/ GLIMPSE.