Isolated neutron stars: population synthesis and cooling curves

Sergei Popov

(Sternberg Astronomical Institute)Co-authors: D. Blaschke, H.Grigorian, B. Posselt, R. Turolla, …

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Plan of the talk

Intro. Close-by NSs Population synthesis Solar vicinity. Stars Spatial distribution Mass spectrum Two tests of cooling Brightness constraint Sensitivity of two tests Mass constraint Application to hybrid stars New results and future plans Age-Distance diagram Final conclusions

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Isolated neutron stars population: in the Galaxy and at the backyard

INSs appear in many flavours Radio pulsars AXPs SGRs CCOs RINSs RRATs

Local population of young NSs is different (selection)

Radio pulsarsGeminga+RINSs

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Close-by radioquiet NSs

Discovery: Walter et al. (1996)

Proper motion and distance: Kaplan et al.

No pulsations Thermal spectrum Later on: six brothers

RX J1856.5-3754

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Magnificent Seven

Name Period, s

RX 1856 -

RX 0720 8.39

RBS 1223 10.31

RBS 1556 -

RX 0806 11.37

RX 0420 3.45

RBS 1774 9.44

Radioquiet (?)Close-byThermal emissionLong periods

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Population of close-by young NSs

Magnificent seven Geminga and 3EG J1853+5918 Four radio pulsars with thermal emission

(B0833-45; B0656+14; B1055-52; B1929+10) Seven older radio pulsars, without detected

thermal emission.

It is useful to study these stars using the population synthesis technique

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Population synthesis: ingredients

Birth rate of NSs Initial spatial distribution Spatial velocity (kick) Mass spectrum Thermal evolution Interstellar absorption Detector properties

A brief review on populationsynthesis in astrophysics canbe found in astro-ph/0411792

To build an artificial model

of a population of some astrophysical sources and

to compare the results ofcalculations with observations.

Task:

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Gould Belt : 20 NS Myr-1

Gal. Disk (3kpc) : 250 NS Myr-1

Arzoumanian et al. 2002

ROSAT

• Cooling curves by• Blaschke et al. • Mass spectrum

18°Gould BeltGould Belt

Population synthesis – I.

© Bettina Posselt

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Solar vicinity

Solar neighborhood is not a typical region of our Galaxy

Gould Belt R=300-500 pc Age: 30-50 Myrs 20-30 SN per Myr (Grenier 2000) The Local Bubble Up to six SN in a few Myrs

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The Gould Belt

Poppel (1997) R=300 – 500 pc Age 30-50 Myrs Center at 150 pc from

the Sun Inclined respect to the

galactic plane at 20 degrees

2/3 massive stars in 600 pc belong to the Belt

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Distribution of open clusters

(Piskunov et al. astro-ph/0508575)

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Surface density of open clusters

(Piskunov et al.)

T1: log t <7.9T2: 7.9< log t < 8.3T3: 8.3< log t < 8.6T4: log t >8.6

All clusters

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Spatial distribution of close-by open clusters in 3D

(Piskunov et al.)

Grey contours show projected densitydistribution of young(log T<7.9) clusters.

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Clusters and absorption

(Piskunov et al.)

Triangles – Gould Belt clusters.

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Initial spatial distribution

A very simple model for PS-I: The Gould Belt as a flat inclined disc pluscontribution from the galactic disc up to 3 kpc.

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Some results of PS-I.:Spatial distribution

(Popov et al. 2005 Ap&SS 299, 117)

More than ½ are in+/- 12 degrees from the galactic plane.

19% outside +/- 30o

12% outside +/- 40o

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Mass spectrum of NSs

Mass spectrum of local young NSs can be different from the general one (in the Galaxy)

Hipparcos data on near-by massive stars

Progenitor vs NS mass: Timmes et al. (1996); Woosley et al. (2002)

astro-ph/0305599(masses of secondary objects in NS+NS)

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Woosley et al. 2002

Progenitor mass vs. NS mass

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Woosley et al. 2002

Core mass vs. initial mass

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Two tests

Age – Temperature

&

Log N – Log S

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Standard test: temperature vs. age

Kaminker et al. (2001)

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Uncertainties in temperature

(Pons et al. astro-ph/0107404)

• Atmospheres (composition)• Magnetic field• Non-thermal contributions to the spectrum• Distance• Interstellar absorption• Temperature distribution

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Luminosity and age uncertainties

Page, Geppertastro-ph/0508056

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Log N – Log S

Log of flux (or number counts)

Lo

g o

f th

e n

um

ber

of

sou

rces

bri

gh

ter

than

th

e g

iven

flu

x

-3/2 sphere: number ~ r3

flux ~ r-2

-1 disc: number ~ r2

flux ~ r-2

calculations

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Log N – Log S as an additional test

Standard test: Age – Temperature Sensitive to ages <105 years Uncertain age and temperature Non-uniform sample

Log N – Log S Sensitive to ages >105 years (when applied to close-by NSs) Definite N (number) and S (flux) Uniform sample

Two test are perfect together!!!astro-ph/0411618

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List of models (Blaschke et al. 2004)

Model I. Yes C A Model II. No D B Model III. Yes C B Model IV. No C B Model V. Yes D B Model VI. No E B Model VII. Yes C B’ Model VIII.Yes C B’’ Model IX. No C A

Blaschke et al. used 16 sets of cooling curves.

They were different in three main respects:

1. Absence or presence of pion condensate

2. Different gaps for superfluid protons and neutrons

3. Different Ts-Tin

Pions Crust Gaps

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Model I

Pions. Gaps from Takatsuka & Tamagaki

(2004) Ts-Tin from Blaschke, Grigorian,

Voskresenky (2004)

Can reproduce observed Log N – Log S

(astro-ph/0411618)

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Model II

No Pions Gaps from Yakovlev et al.

(2004), 3P2 neutron gap suppressed by 0.1

Ts-Tin from Tsuruta (1979)

Cannot reproduce observed Log N – Log S

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Model III

Pions Gaps from Yakovlev et al.

(2004), 3P2 neutron gap suppressed by 0.1

Ts-Tin from Blaschke, Grigorian, Voskresenky (2004)

Cannot reproduce observed Log N – Log S

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Model IV

No Pions Gaps from Yakovlev et al.

(2004), 3P2 neutron gap suppressed by 0.1

Ts-Tin from Blaschke, Grigorian, Voskresenky (2004)

Cannot reproduce observed Log N – Log S

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Model V

Pions Gaps from Yakovlev et al.

(2004), 3P2 neutron gap suppressed by 0.1

Ts-Tin from Tsuruta (1979)

Cannot reproduce observed Log N – Log S

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Model VI

No Pions Gaps from Yakovlev et al.

(2004), 3P2 neutron gap suppressed by 0.1

Ts-Tin from Yakovlev et al. (2004)

Cannot reproduce observed Log N – Log S

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Model VII

Pions Gaps from Yakovlev et

al. (2004), 3P2 neutron gap suppressed by 0.1.

1P0 proton gap suppressed by 0.5

Ts-Tin from Blaschke, Grigorian, Voskresenky (2004)

Cannot reproduce observed Log N – Log S

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Model VIII

Pions Gaps from Yakovlev et al.

(2004), 3P2 neutron gap suppressed by 0.1. 1P0

proton gap suppressed by 0.2 and 1P0 neutron gap suppressed by 0.5.

Ts-Tin from Blaschke, Grigorian, Voskresenky (2004)

Can reproduce observed Log N – Log S

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Model IX

No Pions Gaps from Takatsuka &

Tamagaki (2004) Ts-Tin from Blaschke,

Grigorian, Voskresenky (2004)

Can reproduce observed Log N – Log S

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HOORAY!!!!

Log N – Log S can select models!!!!!Only three (or even one!) passed the second test!

…….still………… is it possible just to update the temperature-age test???

May be Log N – Log S is not necessary?Let’s try!!!!

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Brightness constraint

Effects of the crust (envelope)

Fitting the crust it is possible to fulfill the T-t test …

…but not the second test: Log N – Log S !!!

(H. Grigorian astro-ph/0507052)

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Sensitivity of Log N – Log S

Log N – Log S is very sensitive to gaps Log N – Log S is not sensitive to the crust if it is applied to

relatively old objects (>104-5 yrs) Log N – Log S is not very sensitive to presence or

absence of pions

We conclude that the two test complement each other

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Mass constraint

• Mass spectrum has to be taken into account when discussing data on cooling• Rare masses should not be used to explain the cooling data• Most of data points on T-t plot should be explained by masses <1.4 Msun

In particular:• Vela and Geminga should not be very massive

Phys. Rev .C (2006)nucl-th/0512098(published as a JINR preprint)

Cooling curves fromKaminker et al.

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Another attempt to test a set of models. Hybrid stars. Astronomy meets QCD

We studied several models for hybrid stars applying all possible tests: - T-t- Log N – Log S- Brightness constraint- Mass constraint

nucl-th/0512098

We also tried to present examples when a model successfully passesthe Log N – Log S test, but fails to pass the standard T-t test or fails tofulfill the mass constraint.

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Model I

Brightness - OKT-t - OKLog N – Log S - poorMass - NO

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Model II

Brightness - OK

T-t - No

Log N – Log S - OK

Mass - NO

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Model III

Brightness - OK

T-t - poor

Log N – Log S - OK

Mass - NO

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Model IV

Brightness - OK

T-t - OK

Log N – Log S - OK

Mass - OK

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Resume for HySs

One model among four was able to pass all tests.

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1. Spatial distribution of progenitor stars

a) Hipparcos stars up to 400 pc[Age: spectral type & cluster age (OB ass)]

b) Star associations: birth rate ~ Nstar

c) Field stars in the disc up to 3 kpc

Population sythesis – II.recent improvements

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3. Further improvements:

• Mass spectrum • fainter XMM EPIC PN count rates• cooling curves (Grigorian et al. 2005, Popov et al . 2006)

2. Spatial distribution of ISM (NH)

instead of : now :

+ new cross sections & abundances

1kpc

1kpc

Population synthesis – II.recent improvements

(by Bettina Posselt)

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b= +90°

b= -90°

First results First results The new initial distribution of progenitor stars:

For comparison: ROSAT, old ISM distribution, masses etc. as before

GB 500 pc

GB 300 pc

New

Popov et al. 2005

Outlook Outlook Different log N - log S curve for distinct sky regions

Population synthesis for fainter (XMM) sources

Count rate > 0.05 cts/s

OriSco OB

Cep?Per?

PSRs+

Geminga+

M7

PSRs-

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INSs and local surrounding

De Zeeuw et al. 1999 Motch et al. 2006

Massive star population in the Solar vicinity (up to 2 kpc) is dominated by OB associations. Inside 300-400 pc the Gould Belt is mostly important.

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50 000 tracks, new ISM model

AguerosChieregato

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Age and distance distributions

Age

1 < cts/s < 10 0.1 < cts/s < 1 0.01 < cts/s < 0.1

Distance

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Where to search for more cowboys?

We do not expect to find more candidates at fluxes >0.1 cts/s.

Most of new candidates should be at fluxes 0.01< f < 0.1 cts/s.So, they are expected to be young NSs (<few 100 Mys) just outside the Belt.I.e., they should be in nearby OB associations and clusters.

Most probable candidates are Cyg OB7, Cam OB1, Cep OB2 and Cep OB3.Orion region can also be promising.

Name           l-      l+      b-    b+      Dist., pc

Cyg OB7     84      96     -5     9       600-700

Cep OB2     96     108    -1   12       700

Cep OB3    108    113     1     7       700-900

Cam OB1   130    153    -3     8       800-900

0

10

-10

L=110 90130

(ads.gsfc.nasa.gov/mw/)

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Age-distance diagram

(astro-ph/0407370)

Detectability of close-byyoung NSs stronglyDepends on their agesand distance from the Sun.

A toy-model: a localsphere (R=300 pc)and a flat disk.

Rate of NS formationin the sphere is235 Myr-1 kpc-3

(26-27 NS in Myr inthe whole sphere).

Rate in the disc is10 Myr-1 kpc-2

(280 NS in Myr up to3 kpc).

visibility

13 sources

1 source

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More realistic age-dist. diagram

Initial distributionfrom Popov et al. 2005.

Spatial evolution is notfollowed.

For the line of “visibility”(solid line in the middle)I assume the limitingflux 10-12 erg s-1 cm-2 and masses are <1.35(Yakovlev et al. curves).

In 4.3 Myr in 1 kpc around the Sun 200 NSsare expected to be born.

(astro-ph/0407370)

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Realistic age-distance diagram

Realistic initial distribution.

Spatial evolution is takeninto account.

The line of “visibility” isdrawn as the dotted line.

Five curves correspond to1, 4 , 13, 20 and 100 NSs.

At the moment in 1 kpconly about 10% of NSswith ages <4-5 Myrs areobserved.

(astro-ph/0407370)

visibility

100201 134

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Resume

We live in a very interesting region of the Milky Way! Log N – Log S test can include NSs with unknown ages, so additional sources (like the Magnificent Seven) can be used to test cooling curves. Two tests (LogN–LogS and Age-Temperature) are

perfect together. Additional considerations (brightness and mass constraints) have to be taken into account. More detailed PS models are welcomed. Age-distance diagram can be used as an additional tool.

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THAT’S ALL. THANK YOU!

I thank all scientistswith whom I collaborated duringdifferent stagesof work on INSs andhad fruitful discussions:M. Colpi, F. Haberl,V. Lipunov,R. Neuhauser,M. Prokhorov,A. Treves,J. Trumper, ….

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Radio detection

Malofeev et al. (2005) reported detection of 1RXS J1308.6+212708 (RBS 1223) in the low-frequency band (60-110 MHz) with the radio telescope in Pushchino.

In 2006 Malofeev et al. reported radio detectionof another one.

(back)

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NS+NS binaries

Pulsar Pulsar mass Companion mass

B1913+16 1.44 1.39B2127+11C 1.35 1.36B1534+12 1.33 1.35J0737-3039 1.34 1.25J1756-2251 1.40 1.18

(PSR+companion)/2

J1518+4904 1.35J1811-1736 1.30J1829+2456 1.25

(David Nice, talk at Vancouver 2005)

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