1. A Slow X-ray Pulsar in the Young, Massive Star Cluster Westerlund 1 M. MunoJ. S. ClarkP. Crowther S. DoughertyR. De GrijsC. Law S. McMillanM. MorrisI. Negueruela D. PooleyS. Portegies Zwart F. Yusef Zadeh 2MASS Atlas Image

2. A Galactic Super Star Cluster Distance: 5kpc Mass: 10 5 M sun Core radius: 0.6 pc Extent: ~6 pc across Core density:~10 6 pc - 3 Age: 4 +/- 1 Myr Supernova rate: 1 every 10,000 years

3. Chandra Observations This is a pulsar! Two exposures: 2005 May, 18 ks 2005 June, 38 ks WR/O star binaries, plus unresolved pre-MS stars

4. Pulsar CXO J164710.2- 455216 Period: 10.6107(1) s Spin-down: <2x10 -10 s s -1 L X = 3x10 33 erg s -1 (not a radio pulsar) Spectrum: kT = 0.6 keV blackbody (not a cooling NS) No IR counterpart, so K>18.5 (M count. < 1M sun ; not an X-ray binary) This pulsar is almost certainly a magnetar.

5. The Pulsar is within Westerlund 1(99.95% conf.) 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 a magnetar 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)

6. The Progenitor to the Pulsar had an Initial Mass of >40 M sun Westerlund 1 contains O6V and O7V stars with initial masses of 35-37 M sun (Clark et al., in prep). Its age is <5 Myr. At this age, only stars more massive than 40 M sun would have under- gone supernovae.

7. Massive Stars and Magnetars The Westerlund 1 pulsar is the third example of a magnetar with a >30 M sun progenitor. –An HI shell has been interpreted as a bubble blown by a 30-40 M sun progenitor to 1E 1048.1- 5397 (Gaensler et al 2005). –SGR 1806-20 is thought to belong to a 50 M sun (e.g., Figer et al. 2005). Note that SGR 1900+15 may belong to a 20 M sun (Vrba et al. 2000).

8. Conclusions Massive stars can lose 95% of their mass either through winds or during supernovae (e.g., Heger et al 2003, Akiyama & Wheeler 2005). Magnetars probably form from rapidly- rotating cores, in stars that evolved too quickly to dissipate their angular momentum (e.g., Duncan & Thomas 1992; Heger et al. 2005).