View
43
Download
0
Category
Preview:
DESCRIPTION
Peeking into the crust of a neutron star Nathalie Degenaar University of Michigan. Neutron stars: heating and cooling provide a window into their dense interior. X-ray observations. Interior properties. Thermal evolution. This talk. Endpoints of stellar evolution Mass:1.4 Msun - PowerPoint PPT Presentation
Citation preview
Peeking into the crust of a neutron star
Nathalie DegenaarUniversity of Michigan
Neutron stars: heating and cooling provide a window into their dense interior
This talk
X-ray observations Interior propertiesThermal evolution
Neutron starsEndpoints of stellar
evolution
Mass: 1.4 MsunRadius: ~10 km
Extremely dense objects!
Neutron stars are the densest, directly observable objects in the universe
Gateway to understand the fundamental behavior of matter
Outstanding probes of strong gravity
Motivation
What we know
Atmosphere: ~cm
Crust: ~kmIons, electrons,neutrons
Core: ~10 kmProtons, electrons, neutrons
What we want to know
Crust: ~kmStructure?Gravitational waves
Core: ~10 kmExotic particles?Behavior of ultra-dense matter
Neutron stars in X-ray binaries
Neutron star accreting matter from a companion
X-ray binaries
Neutron star
Neutron stars in transient X-ray
binaries
Quiescence:No/little accretion
Faint X-ray emission
Accretion outburst:Rapid accretion
Bright X-ray emission
X-ray bright Detectable by
many satellites
X-rays fromAccretion disk
Transient outbursts
OutburstQuiescence
Terzan 5
Duration of weeks-months Recur every few
years-decades
Transients in quiescence
OutburstQuiescence
Terzan 5 X-ray faint Detectable by
sensitive satellites
X-rays fromNeutron star
Examine the X-ray spectrum
X-ray energy spectrum
Quiescent X-ray spectra
X-ray image
EXO 0748-676 Components:1) Thermal- < 2 keV - Neutron star
surface- Atmosphere
model
Temperature
1) Thermal emission
EXO 0748-676
2) Non-thermal- > 2-3 keV - Not
understood
2) Non-thermal emission
Components:1) Thermal- < 2 keV - Neutron star
surface- Atmosphere
model temperature
Neutron star thermal emission
Origin thermal emissionAccretion induces nuclear reactions in the crust
1 km
10 m
cm
10 km
Image courtesy of Ed Brown
Origin thermal emissionAccretion sets the temperature of the neutron
star
1 km
10 m
cm
10 km
~1.5 MeV/par
ticle
Image courtesy of Ed Brown
Neutron star coolingGained heat is re-radiated via the surface and core
Surface: Thermal photons
Core: Neutrino emissions
Temperature set by heating/cooling
balance
Neutron star interior isothermal
X-ray emission tracks core temperature
Prior to an accretion outburst
Neutron star crust heated
Surface not observableX-ray emission dominated
by accretion disk
During an accretion outburst
Neutron star crust hotter than core
X-ray emission track crust temperature rather than
core
Just after an accretion outburst
Can we detect cooling of the heated crust?
Time since 1996 January 1 (days)RXT
E A
SM c
ount
rat
e (c
ount
s/s)
Good candidates to try
12.5 yr accretion
ended 2001
2.5 yr accretionended 2001
Long outbursts severely heated crust good targets!
Outburst:Monitoring satellites
Time since 1996 January 1 (days)RXT
E A
SM c
ount
rat
e (c
ount
s/s)
Good candidates to try
12.5 yr accretion
ended 2001
2.5 yr accretionended 2001
Long outbursts severely heated crust good targets!
Quiescence:Sensitive satellites
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
t ~ 4 yr
Wijnands+ ‘01, ‘02, ‘03, ‘04 Cackett+ ‘06, ‘08, ‘10
Quiescent monitoring
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
t ~ 4 yr
Crust cooling!
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
t ~ 4 yr
Crust cooling!
Temperaturecore
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
t ~ 4 yr
Temperature crustCooling
Crust cooling!
Temperaturecore
What have we learned?
Crust cooling is observable! Cooling timescale requires conductive crust Crust has a very organized ion structure
New challenges: Conductive crust problem for other
observationsthat require a high crust temperature
Is there extra heating in the crust that we missed?
Task for observers:
More sources +more observations
Crust cooling: 2 more sources
Better sampling!
1) XTE J1701-462:
Active 1.5 yr Quiescent 2007
2) EXO 0748-676:
Active 24-28 yr Quiescent 2008
Time since accretion stopped (days)
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Crust cooling: 4 sources
Time since accretion stopped (days)
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Similarities: Crust cooling
observable Decay requires
conductive crust
Differences: Cooling time
Can we explain differences?
Observe and model more
sources
Practical issue: Rare opportunities
Crust cooling: 4 sources
Time since accretion stopped (days)
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Observable for more common neutron
stars?
10-week accretion outburst2010 October-December
Time since 2009 July 1 (days)
MAX
I int
ensi
ty (c
ount
s/s/
cm2)
Globular cluster Terzan 5
Quiescence:Chandra
Quiescence:Chandra
OutburstIGR J17480-2446
Test case!
Statistics not great (2 photons / hour)
But: looks thermal
IGR J17480–2446
X-ray spectra before and after
(Outburst: 2010 Oct-Dec)
Clear difference before and after2 months after4 months after1 year before
IGR J17480–2446
X-ray spectra before and after
Crust cooling?
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
(Outburst: 2010 Oct-Dec)
- Initially enhanced, but decreasing
IGR J17480–2446
Thermal evolution: crust cooling?
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
(Outburst: 2010 Oct-Dec)
- Initially enhanced, but decreasing
- Standard heating no match!
Thermal evolution: crust cooling?
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
(Outburst: 2010 Oct-Dec)
- Initially enhanced, but decreasing
- Standard heating no match!- Extra heating match!
Thermal evolution: crust cooling!
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
Quite high: Current models2 MeV/nucleon
Thermal evolution: crust cooling
(Outburst: 2010 Oct-Dec)
- Initially enhanced, but decreasing
- Standard heating no match!- Extra heating match!
More source available for
study!
Neu
tron
sta
r te
mpe
ratu
re (e
V)
Time since accretion stopped (days)
Initial calculations not `fits’ to the data
Observations are ongoing
How much heat do we really
need?
What causes it?
Work in progress…
Theoreticians: Observations of three new sources match with models, can we explain differences? What could be the source of the extra heat
release? nuclear experimentalists?
Observers: Continue monitoring current cooling
neutron stars Stay on the watch for new potential targets
Work to be done
Neutron stars: Matter under extreme conditions Strong gravity probes Try to understand their interior
Neutron stars in X-ray binaries: Crust temporarily heated during accretion Crust cooling observable in quiescence Probe the interior properties of the neutron
star
To take away
Recommended