A Neutron Star with a Massive Progenitor in

the Star Cluster Westerlund 1

Michael Muno (UCLA/Hubble Fellow)

J. S. Clark (Open U) R. de Grijs (U Sheffield)

P. Crowther (U Sheffield) S. Dougherty (DAO)

I. Negueruela (Alicante) D. Pooley (Berkeley)

S. McMillan (Drexel) S. Portegies Zwart (Amsterdam)

C. Law (Northwestern) F. Yusef-Zadeh (Northwestern)

M. Morris (UCLA)

Were do Neutron Stars and Black Holes Come From?

M > 20 Msun

8 < M < 20 Msun

M < 8 Msun

Mass

From “Stellar Evolution: A Journey with Chandra”

9 25 40 100 140 260Initial Mass (Solar Masses)

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The Mapping Between Initial Masses and Compact Remnants.

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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.(e.g., Westerlund 1987, Clark et al. 2005)

1 pc

VRI from 2.2m MPG/ESO+WFI Clark et al. (2005)

VRI from 2.2m MPG/ESO+WFI Clark et al. (2005)

A Galactic Super Star Cluster?

• 150 stars with M>35 Msun

• Mass: 105 Msun

• Extent: ~6 pc across• Distance: 5 kpc• Age: 4 +/- 1 MyrThe cluster is coeval, and

old enough to have produced supernovae.

Est. rate: 1 per 10,000 years!

1 pc

Chandra Observations

VRI from 2.2m MPG/ESO+WFI

Clark et al. (2005)

Chandra ACIS1 pc

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.

Chandra Observations

VRI from 2.2m MPG/ESO+WFI

Clark et al. (2005)

Chandra ACIS1 pc

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!

pulsar

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.

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)

Other Neutron Stars with >30 Msun Progenitors

• 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).

1E 1048.1-5937 SGR 1806-20

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Which Stars Form Black Holes?

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Which Stars Form Black Holes?

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Wd 1Cyg X-1

GX 301-2

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).