Observing neutron stars: constrain the physics of nuclear - PowerPoint PPT Presentation

Observing neutron stars: constrain the physics of nuclear interactions at high densities Chris Done, Hiroki Yoneda (ISAS/JAXA) + Hitomi LMXRB WG

Different regimes Collisions, hot, Watts 2016 time dependent NS stars cool stable – long timescale processes like electron capture reach equilibrium, neutron rich matter Repulsive 2 & 3 ρ/ρ0 1 6 body interactions – 3 nucleon these are the Many body problem! forces forces

Different regimes Nuclear Hamiltonian Lattimer 2012 experimentally constrained for symmetic matter – parametric expansion u= ρ/ρ sat and proton fraction +S(Sv,L)(1-2x) 2 Not going to be valid at high u and low x (Ozel 2016). Need fully relativistic QCD (Thomas)

Different regimes But just classic particle physics not enough (even fully relativistic QCD) Superfluidity? Pairing Get insights from BEC(!) but need full theory (Ohashi) +rotation = vortices?(Nitta) Large scale structures inside NS? How do these change the EoS??

Equation of state Watts 2016 Maximum mass set by behaviour at 5-8 ρ sat Strange nucleons Lattimer & Prakash 2005 quark/hyper Radius 1-2 ρ sat ons Lattimer & Prakash 2001 Non-nucleonic phases (hyperons) do not carry nuclear repulsive forces so reduce pressure - max mass and radii decrease

Neutron stars – non interacting Densest observable objects – much higher than can be produced in experiments, best constrains on interactions M&R - Hyperons? Is there a transition to quark material? pulsars central compact objects in SNR

Neutron stars - mass Can only measure mass in binary NS Still clean if not interacting. If one is a pulsar then it’s a clock in orbit – get binary parameters to high accuracy

The Equation of State Compilation of EOS from Lattimer & Prakash 2001 • NS constrain EoS of dense matter • Masses of NS from PSR1614 orbits of pulsars round companion. standard • 2M � (3 objects) NS mass constrains NS EoS • (majority ~1.4M � due to formation) • Need radius as well to determine the EoS

Measure radius in NS - 1 • Look at something we understand – thermal emission • Pulsars – X-ray hotspot at pole (thermal - understand emission pattern, unlike pulsar beam. But geometry. dim)

Measure radius in NS - 2 • Look at something we understand – thermal emission • Neutron star surface - L=A σ T 4 (but emission depends on surface abundances and B field. dim) Geppert et al 2006

Interacting systems - BRIGHT High mass XRB & low mass XRB High/low: mass second star low mass = Roche lobe overflow High mass = strong winds B < 10 9 G, fast spin B>10 12 G, mid-slow spin

R in accretion powered NS? • Same ideas as isolated NS • Model thermal radiation from surface – LMXB (no B field) • 8-12km Ozel 2013 • 11-15km Kajeva et al 2016 • Models – abundances, geometry

R in accretion powered NS? • Same ideas as isolated NS • Model thermal pole cap light curves in accretion powered pulsars • 5-20km Ozel 2013 • Models! geometry

How can we do better? Suleimanov et al. 2011 • Accurate (statistically) and unambiguous (systematics, models) • Atomic lines! If there was an obvious line then measure redshift and get M/R • Model atmospheres partially ionised Fe if T<1.5x10 7 K

How can we do better? Rauch et al 2008 • Accurate (statistically) and unambiguous (systematics) • Atomic lines! If there was an obvious line then measure redshift and get M/R <1% • Model atmospheres partially ionised Fe if T<1.5 x10 7 K

What we need to see these lines • Metals on surface • They sink! Accretion • Need to 0.5-1.5 keV surface • Accretion! • Low B: Zeeman � ∆ E=12B 9 eV • HMXRB have 10 12 G!! • Low rotation: 10km radius. � ∆ E=1600 ( ν spin /600 Hz) eV • LMXB 185-650Hz

Interacting systems - BRIGHT High mass XRB & low mass XRB High/low: mass second star low mass = Roche lobe overflow High mass = strong winds B < 10 9 G, fast spin B>10 12 G, mid-slow spin

Spectra of accretion flow: disc • Differential Keplerian rotation • Friction: gravity → heat • Thermal emission: L = A σ T 4 • Temperature increases Log ν f( ν) inwards until minimum radius R lso (a * ) For a * =0 and L ~ L Edd T max is 2 keV (2x10 7 K) 1.4M � Log ν • Ld=1/2 Lgravity other half as KE of rotation – emit as BL

Disc and boundary layer: LMXB Disc Ld~LEdd Boundary layer Ls=Ld, T=2.5keV Disc Ld Boundary layer Ls=Ld, T=2.5keV neutron star surface 0.5- 1.5keV

Accretion geometry - LMXB

Nature of accretion flow • Accretion flow like in BHB – hard/soft transition • Alternative solution of accretion flow equations - geometrically thick, hot flow at low L - thin cool disc Neutron star Black hole

Accretion geometry changes!! • Accretion flow like in BHB – hard/soft transition • Alternative solution of accretion flow equations - geometrically thick, hot flow at low L Neutron star Black hole

Changing accretion geometry LMXB Sakurai et al 2014 We can see neutron star surface at mid and low L

Find face on system and look for narrow line • Ser X-1 • Binary orbit ~10 o Cornelisse et al 2012 – NS spin still gives narrow line • Luminosity is mid range • NEED GOOD DATA!! • Combination of high spectral resolution to see narrow line and good sensitivity – high s/n. and ability to handle very bright sources

Current data from Ser X-1 Yoneda et al 2016 • Suzaku: good sensitivity – high s/n, but not good resolution

Current data from Ser X-1 Yoneda et al 2016 • Chandra: moderate sensitivity and moderate resolution • No features seen in energy band. But what would we predict?

Current data from Ser X-1 • Chandra: moderate sensitivity and moderate resolution • No features seen in energy band. But what would we predict? Yoneda et al 2016

Current data from Ser X-1 • Suzaku: good sensitivity – high s/n, but not good resolution • Add in the surface emission for different temperature surfaces • Do surface redshift and residual spin in los. • And simulate through the chandra response... Yoneda et al 2016

Depends on surface temperature • Predict 1eV EW for 0.7 keV – can’t see this • 10eV EW for 1keV – RULED OUT Yoneda et al 2016 • Need high resolution • With better sensitivity • Hitomi…. • Recovery mission? • ESA Athena 2028!

Summary • We should be able to see narrow lines from the surface from mid-low mass accretion rate NS in LMLXRB if seen face on! • Gets unambiguous, high accuracy M/R measurement • Need high resolution, high sensitivity detector able to look at bright sources • Hitomi… (recovery mission? ESA Athena satellite) • Maybe 5-10% limits next year from thermal pole cap lightcurve models in pulsars in NASA NICER • Gravitation waves from merging NS-NS systems?? • Astrophysics is a bit messy – but so is theory!