Nathalie Degenaar University of Michigan Xray observations Interior properties Thermal evolution Quiescence Nolittle accretion Neutron star visible Accretion outburst Rapid accretion ID: 493939
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Slide1
Peeking into the crust of a neutron starNathalie Degenaar University of Michigan
X-ray observations
Interior properties
Thermal evolutionSlide2
Quiescence
No/little accretion
Neutron star visible
Accretion outburst
Rapid accretion
Bright X-rays from disk
Transient X-ray binariesSlide3
The neutron star crust10 kmImage courtesy of Ed Brown
Composition: Atomic nuclei electrons, neutrons
Structure?
T
hermal propertiesSlide4
The effect of accretion10 km1 km
10 m
c
m
~2
MeV/nucleon
Compression nuclear reactions crust heated
Haensel
&
Zdunik
2008Slide5
After accretion stops10 km1 km
10 m
c
m
~
2
MeV/nucleon
Thermal conduction
crust cools down
Rutledge+ 2001Slide6
Can we detect cooling of a heated crust?Monitor temperature afterlong accretion outburstsSlide7
Crust cooling: observations
XTE J1701-462 1.5 yr
, ~1038 erg/sEXO 0748-676
25 yr, ~1036
erg/sKS 1731-26012.5 yr
, ~1037 erg/s
MXB 1659-292.5 yr, ~5x10
36 erg/s
Time
since accretion stopped (days)
Neutron star temperature (
eV
)
Wijnands+01;Cackett+06;Degenaar+10;Fridriksson+11Slide8
Crust cooling: what we can learn
Time
since accretion stopped (days)
Neutron star temperature (
eV
)
Magnitude+distribution
of heat sources
Nuclear reactions + last outburstSlide9
Crust cooling: what we can learn
Time
since accretion stopped (days)
Neutron star temperature (
eV
)
Magnitude+distribution
of heat sources
Thermal conductivity
Nuclear reactions + last outburst
Properties of the crustSlide10
Crust cooling: what we can learn
Time
since accretion stopped (days)
Neutron star temperature (
eV
)
Magnitude+distribution
of heat sources
Thermal conductivity
Core temperature
Nuclear reactions + last outburst
Properties of the crust
Composition of the coreSlide11
Crust cooling: modelingHigh thermal conductivity Organized ion lattice
Brown&Cumming’09
Different structureSlide12
Crust cooling: 4
sources
Time
since accretion stopped (days)
Neutron star temperature (
eV
)
Can we build a census of crust?Observe + model more sources
Practical issue:
Rare
opportunitySlide13
Can we observe this for “normal” transients with shorter outbursts?Slide14
Time since 2009 July 1 (
days)
MAXI intensity (counts/s/cm
2
)
Globular cluster
Terzan
5
Quiescence:
B
efore outburst
Quiescence:
After outburst
Outburst
IGR
J17480-2446
Test case
10-week accretion outburst
2010 October-December
11-Hz pulsar: relatively strong magnetic fieldSlide15
Terzan 5
Thermal evolution: crust cooling?
Outburst:
2010 Oct – Dec
Degenaar+2011Degenaar+ in prep.Slide16
Thermal evolution: crust cooling?
Outburst:2010 Oct – Dec
Cooling curve with standard heat:no match
Degenaar+2011
Degenaar+ in prep.Slide17
Outburst:2010 Oct – DecCooling curve with standard heat:no matchCooling curve with extra heat:much better!
Thermal evolution: crust cooling?
Degenaar+2011
Degenaar+ in prep.Slide18
Thermal evolution: crust cooling!
Quite high:
Current models
2 MeV/nucleon
Can be crust cooling, but:
s
ubstantial heating at shallow depth required
Outburst:2010 Oct – Dec
Cooling
curve
with standard heat:
no match
Cooling curve
with extra heat:
much better!Degenaar+2011Degenaar+ in prep.Slide19
Work in progress…
Cooling is ongoing
Continue observingModel full curve
How much heat?Is it realistic?Slide20
Crust cooling observable after short outburstMore source available for study
Heating at shallow depth requiredCould be large, what can it be?
Nuclear reactions, magnetic field, other?Slide21
Neutron stars in transient X-ray binaries:Crust temporarily heated during accretionCrust cooling observable in quiescence Gives insight into crust propertiesLatest results: Crust cooling after short accretion outburstsAdditional heating in outer layers of the crustTo take away