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

ρ/ρ0

6 1

Collisions, hot, time dependent NS stars cool stable – long timescale processes like electron capture reach equilibrium, neutron rich matter Repulsive 2 & 3 body interactions – these are the problem! 3 nucleon forces Many body forces

Watts 2016

Different regimes

Nuclear Hamiltonian experimentally constrained for symmetic matter – parametric expansion u=ρ/ρsat 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)

Lattimer 2012

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

Maximum mass set by behaviour at 5-8ρsat

Lattimer & Prakash 2005

Radius 1-2ρsat

Lattimer & Prakash 2001

Non-nucleonic phases (hyperons) do not carry nuclear repulsive forces so reduce pressure - max mass and radii decrease

nucleons Strange quark/hyper

• ns

Watts 2016

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

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

Neutron stars - mass

• NS constrain EoS of

dense matter

• Masses of NS from
• rbits of pulsars

round companion.

• 2M (3 objects)

constrains NS EoS

• (majority ~1.4M

due to formation)

• Need radius as well

to determine the EoS

The Equation of State

standard NS mass PSR1614

Compilation of EOS from Lattimer & Prakash 2001

• 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 - 1

• Look at something we understand – thermal emission
• Neutron star surface - L=AσT4 (but emission depends on

surface abundances and B field. dim)

Measure radius in NS - 2

Geppert et al 2006

Interacting systems - BRIGHT High mass XRB & low mass XRB

High/low: mass second star High mass = strong winds B>1012G, mid-slow spin low mass = Roche lobe overflow B < 109G, fast 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?

• 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<1.5x107K

Suleimanov et al. 2011

How can we do better?

• 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 x107K

Rauch et al 2008

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=12B9 eV

• HMXRB have 1012G!!
• Low rotation: 10km radius.

∆E=1600 (νspin/600 Hz) eV

• LMXB 185-650Hz

Interacting systems - BRIGHT High mass XRB & low mass XRB

High/low: mass second star High mass = strong winds B>1012G, mid-slow spin low mass = Roche lobe overflow B < 109G, fast spin

• Differential Keplerian

rotation

• Friction: gravity → heat
• Thermal emission:

L = AσT4

• Temperature increases

inwards until minimum radius Rlso(a*) For a*=0 and L~LEdd Tmax is 2 keV (2x107K) 1.4M

• Ld=1/2 Lgravity other half as

KE of rotation – emit as BL

Spectra of accretion flow: disc

Log ν Log ν f(ν)

Disc and boundary layer: LMXB

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

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

We can see neutron star surface at mid and low L

Sakurai et al 2014

Find face on system and look for narrow line

• Ser X-1
• Binary orbit ~10o 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

• Suzaku: good sensitivity

– high s/n, but not good resolution

Yoneda et al 2016

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

• 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
• Need high resolution
• With better sensitivity
• Hitomi….
• Recovery mission?
• ESA Athena 2028!

Yoneda et al 2016

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!