9:10-9:50 F. Ozel (Invited): Neutron Star Masses and Radii

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Transcript 9:10-9:50 F. Ozel (Invited): Neutron Star Masses and Radii

Neutron Stars: Insights into their Formation, Evolution & Structure from their Masses and Radii Supernovae and Gamma Ray Bursts in University of Arizona In collaboration with T. Guver, M. Baubock, L. Camarota, P. Wroblewski, A. Santos Villarreal; G. Baym, D. Psaltis, R. Narayan, J. McClintock

Neutron Star Masses

 Understand stellar evolution & supernova explosions  Find maximum neutron star mass  Dense Matter EoS  GR tests  GW signals

Neutron Star Masses

Rely on pulsars/neutron stars in binaries Group by Data Quality: Number of measurements, type of errors Source type: Double NS, Recycled NS, NS with High Mass Companion Total of 6 pairs of double neutron stars (12) and 9 NS+WD systems with precisely measured masses 31 more neutron stars with reasonably well determined masses

NS Mass Measurements

Özel et al. 2012 Current Record Holders: M= 1.97

±0.04 M  Demorest et al. 2010 M= 2.01

±0.04 M  Antoniadis et al. 2013

NS Mass Distributions

Özel et al. 2012

NS Mass Distributions

I. Lifetime of accretion/recycling shifts the mean 0.2 M  up II. There is no evidence for the effect of the maximum mass on the distribution III. Double Neutron Star mass distribution is peculiarly narrow

Why is the DNS distribution so narrow?

Black Hole Masses

Determine velocity amplitude K, orbital period P, mass function f + Varying levels of




) =


2 3

P orb



= ( (


1 sin


) 3


1 +


2 ) 2 data on inclination and mass ratio Time (HJD-2,450,600+) 4U 1543-47 from Orosz et al. 1998

Masses of Stellar Black Holes Özel, Psaltis, Narayan, & McClintock 2010

Parameters of the Distribution • Cutoff mass ≥ 5 M  • Fast decay at high mass end • Not dominated by a particular group of sources Özel et al. 2010 See also Bailyn et al. 1998 Farr et al. 2011

Neutron Stars and Black Holes Özel et al. 2012

Failed Supernovae?

PROGENITOR MASS < 15 M  Successful SNe No fallback NS remnant ~16-25 M  > 25 M  Failed SNe Direct collapse Significant pre-SN mass loss Eject H envelope BH Mass = He core mass Kochanek 2013 Woosley & Heger 2012 Lovegrove & Woosley 2013

NS Radii – What is the Appeal?

The Physics of Cold Ultradense Matter NS/BHs division Supernova mechanism GRB durations Gravitational waves Image credit: Chandra X-ray Observatory

EoS Mass-Radius Relation ρ Ö zel & Psaltis 2009, PRD, 80,103003 Read et al. 2009, PRD The pressure at three fiducial densities capture the characteristics of all equations of state This reduces ~infinite parameter problem to 3 parameters

Mass-Radius Measurement to EoS: a formal inversion  Data simulated using the FPS EoS ≥ 3 Radius measurements achieve a faithful recovery of the EoS Ö zel & Psaltis 2009, PRD

Measuring Neutron Star Radii Complications: 1. The radius and mass measurements are coupled 2. Need sources where we see the neutron star surface, the whole neutron star surface, and nothing but the neutron star surface

Low Mass X-ray Binaries

Two windows onto the neutron star surface during periods of quiescence and bursts Modified Julian Date - 50000 • Low magnetic fields (B<10 9 G) • Expectation for uniform emission from surface

Radii from Quiescent LMXBs in Globular Clusters Five Chandra observations of U24 in NGC 6397 Guillot et al. 2011 Heinke et al. 2006; Webb & Barret 2007; Guillot et al. 2011

Evolution of Thermonuclear Bursts

Constant, Reproducible Apparent Radii 4U 1728-34 Level of systematic uncertainty < 5% in apparent radii

Two Other Measurements: Distances and Eddington Limit

F grav F rad Time (s)

Measuring the Eddington Limit 4U 1820-30 Guver, Wroblewski, Camarota, & Ozel 2010, ApJ

Pinning Down NS Radii Globular cluster source EXO 1745-248 Özel et al. 2009, ApJ, 693, 1775

Current Radius Measurements Remarkable agreement in radii between different spectroscopic measurements R ~ 9-12 km

Majority of the 10 radii smaller than vanilla nuclear EoS AP4 predictions

Can already constrain the neutron star EoS

The Pressure of Cold Ultradense Matter Özel, Baym, & Guver 2010, PRD, 82, 101301

Conclusions • Nuclear EoS that fit low-density data too stiff at high densities • Indication for new degrees of freedom in NS matter • NS-BH mass gap and narrow DNS distribution point to new aspects of supernova mechanism

Additional Slides

The Future a NASA Explorer an ESA M3 mission

Is the low-mass gap due to a selection effect?

Transient black holes Follow-up criterion: 1 Crab in outburst If L ~ M, could lead to a low-mass gap

But it is not a selection effect… Brighter sources are nearby ones

Persistent Sources • Bowen emission line blend technique, @ 4640 A • Applied mostly to neutron star binaries, which are persistent (Steeghs & Casares 2002)

Steeghs & Casares 2002

Persistent Sources • Bowen emission line blend technique • Applied so far to neutron star binaries, which are persistent • Can help address if sample of transients introduces a selection effect

Highest Mass Neutron Star Measurement of the Shapiro delay in PSR J1614-2230 with the GBT Demorest et al. 2010

Highest Mass Neutron Star M= 1.97

± 0.04 M 

SAX J1748.9-2021

GR Effects at Moderate Spins Baubock et al. 2012

Neutron Star Surface Emission • • • Low magnetic fields Plane parallel atmospheres Radiative equilibrium • • Non-coherent scattering Possible heavy elements from Madej et al. 2004 Majczyna et al 2005 Ozel et al. 2009 Suleimanov et al. 2011

Effects of Pile-up on X7 spectrum

Analysis of the Burst Spectra 4U 1636-536 26 d.o.f.

1712 spectra Spectra are well-described by Comptonized atmosphere models

Is There A Stiff EoS in 4U 1724-

Redshift Measurement

M/R from spectral lines:

E = E 0 ( 1 2M R ) Cottam et al. 2003, Nature These lines do not come from the stellar surface Lin, Ozel, Chakrabarty, Psaltis 2010, ApJ