1. Galloway, “Accreting neutron stars and the equation of state” Accreting neutron star spins and the equation of state Duncan Galloway Monash University Deepto Chakrabarty Center for Space Research, MIT Andrew Cumming McGill University, Canada MAD ‘07, November 2007

2. Galloway, “Accreting neutron stars and the equation of state” What is a neutron star made of? Theory predicts in detail the likely structure in outer layers Crust (1-2km) nuclei (mainly 56 Fe) plus neutrons ( 1 S 0 superfluid?) Composition of inner & outer cores (up to 99% of mass) however EXTREMELY uncertain; Hyperons? Pions? Kaons? Quark matter? How can we find out? (Figure courtesy D. Page)

3. Galloway, “Accreting neutron stars and the equation of state” Constraining the equation of state Basically we want a simultaneous mass and radius measurement from a neutron star This can be achieved by Detection of rapidly-rotating neutron stars (in LMXBs or elsewhere) Measurements of the neutron-star radius from the spectrum of thermonuclear (type-I) burst tails Measurement of the Eddington limit from radius-expansion bursts Detecting discrete spectral features from the neutron star surface Measurement of the heat flux from the crust via thermonuclear burst recurrence times & energetics …?

4. Galloway, “Accreting neutron stars and the equation of state” Low-mass X-ray binaries

5. Galloway, “Accreting neutron stars and the equation of state” (Some) present-day instruments RXTE, launched 1995 (NASA) large effective area and very high timing resolution but no imaging capability [2-200 keV] Chandra, launched 1999 (NASA), small effective area but very high spatial and spectral resolution (courtesy transmission gratings) [0.5-10 keV] XMM-Newton, launched 1999 (ESA), moderate effective area, spatial and spectral resolution (reflection gratings) + optical monitor [0.5-10 keV] INTEGRAL, launched 2002 (ESA), primarily gamma-ray instrument but also wide-field X-ray and optical capability [4 keV - 10 MeV]

6. Galloway, “Accreting neutron stars and the equation of state” Constraints via rapid spin Allowed region is to the left of the dashed curves While the robust maximum spin rate is still 716 Hz… …a neutron star spinning at 1122 Hz or faster would rule out many EOSs… So it’s not enough to find neutron stars spinning above the present maximum; we really want to be well above 1000 Hz Given the present limit of 716 Hz, this seems unlikely Lattimer & Prakash 2007

7. Galloway, “Accreting neutron stars and the equation of state” Gravitational wave observatories There are currently ~4 interferometric gravitational wave observatories operational worldwide Candidate sources include binary inspirals, stochastic background and rapidly rotating neutron stars Hotly anticipated first detection of gravitational waves, perhaps within the next decade! http://www.ligo.caltech.edu

8. Galloway, “Accreting neutron stars and the equation of state” Examples of X-ray bursts from RXTE

9. Galloway, “Accreting neutron stars and the equation of state” Constraints from thermonuclear bursts We can measure the radius of the neutron star from the (~blackbody) emission in the burst tail Burst recurrence time depends on the heat flux from the interior -> composition We have lots of good quality (archival) data! (RXTE catalog, MINBAR project)

10. Galloway, “Accreting neutron stars and the equation of state” For more high-energy fun… Monthly High-Energy Astrophysics Teleconference (HEAT); http://users.monash.edu.au/~dgallow/heat email Stephen Ng (ncy@physics.usyd.edu.au) to join the mailing list http://users.monash.edu.au/~dgallow/heatncy@physics.usyd.edu.au High-energy Astrophysics Workshop, Kialoa, NSW, April 20- 22; details TBA http://www.physics.monash.edu.au/research/astronomy research areas & honours/PhD projectshttp://www.physics.monash.edu.au/research/astronomy http://users.monash.edu.au/~dgallow