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A Neutron Star with a Massive Progenitor in the Star Cluster Westerlund 1

A Neutron Star with a Massive Progenitor in the Star Cluster Westerlund 1. Michael Muno (UCLA/Hubble Fellow). Were do Neutron Stars and Black Holes Come From?. M > 20 Msun. Mass. 8 < M < 20 Msun. M < 8 Msun. From “Stellar Evolution: A Journey with Chandra”.

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A Neutron Star with a Massive Progenitor in the Star Cluster Westerlund 1

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  1. A Neutron Star with a Massive Progenitor in the Star Cluster Westerlund 1 Michael Muno (UCLA/Hubble Fellow)

  2. Were do Neutron Stars and Black Holes Come From? M > 20 Msun Mass 8 < M < 20 Msun M < 8 Msun From “Stellar Evolution: A Journey with Chandra”

  3. The Mapping Between Initial Masses and Compact Remnants. solar White Dwarf Metallicity Heger et al. 2003 metal-free 9 25 40 100 140 260 Initial Mass (Solar Masses)

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

  5. 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. Est. rate: 1 per 10,000 years! 1 pc VRI from 2.2m MPG/ESO+WFI Clark et al. (2005)

  6. 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, point-like emission from colliding wind binaries, and black holes.

  7. 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, point-like emission from colliding wind binaries, and a pulsar!

  8. 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.

  9. The Progenitor Was >40 Msun • The Pulsar is in Wd 1 (99.95% confidence) • A search of 300 archival Chandra and XMM fields reveals no new 5-30 s pulsars, so there is a <0.5% chance of finding one in any field (Nechita, Gaensler, Muno, et al. in prep). • The pulsar is well within the cluster, with a <10% chance of being an unrelated X-ray source. Position of pulsar Expected density of interlopers (dashed line, very small number)

  10. 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; also Vrba et al. 2000 for SGR 1900+14).

  11. 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)

  12. WhichStars Form Black Holes? Wd 1 solar Cyg X-1 GX 301-2 White Dwarf Metallicity Heger et al. 2003 metal-free 9 25 40 100 140 260 Initial Mass (Solar Masses)

  13. 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).

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