Space Cowboys Odissey:Beyond the Gould BeltSpace Cowboys Odissey:Beyond the Gould BeltSergei Popov, Bettina Posselt(co-authors: F. Haberl, R. Neuhauser, J. Truemper, R. Turolla)

astro-ph/0609275, 0710.1547 and A&A in press

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The new zoo of neutron starsThe new zoo of neutron starsThe new zoo of neutron starsThe new zoo of neutron starsDuring last >10 years it became clear that neutron stars can be born very different.In particular, absolutely non-similar to the Crab pulsar.

o Compact central X-ray sources in supernova remnants.

o Anomalous X-ray pulsars

o Soft gamma repeaters

o The Magnificent Seven

o Unidentified EGRET sources

o Transient radio sources (RRATs) o Calvera ….

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Magnificent SevenMagnificent Seven

Name Period, sRX 1856 7.05RX 0720 8.39RBS 1223 10.31 RBS 1556 6.88?RX 0806 11.37RX 0420 3.45RBS 1774 9.44

Radioquiet (?)Close-byThermal emissionAbsorption featuresLong periods

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Population of close-by young NSsPopulation 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.

Where are the rest?

UNCATCHABLES

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Log N – Log S 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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Population synthesis: ingredientsPopulation 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/0411792and in Physics-Uspekhi (2007).

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. Population synthesis – I.

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The Gould BeltThe 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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1. Spatial distribution of progenitor stars

a) Hipparcos stars up to 500 pc[Age: spectral type & cluster age (OB

ass)]b) 49 OB associations: birth rate ~

Nstar

c) Field stars in the disc up to 3 kpc

Population synthesis – II.recent improvementsPopulation synthesis – II.recent improvements

We use the same normalization for NS formation rate inside 3 kpc: 270 per Myr.

Most of NSs are born inOB associations.

For stars <500 pc we eventry to take into accountif they belong to OB assoc.with known age.

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Effects of the new spatial distribution on Log N – Log SEffects of the new spatial distribution on Log N – Log S

Solid – new initial XYZDashed – Rbelt = 500 pcDotted – Rbelt = 300 pc

There are no significanteffects on the Log N – Log Sdistribution due to moreclumpy initial distributionof NSs.

But, as we’ll see below,the effect is strong forsky distribution.

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Mass spectrum of NSsMass 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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Population synthesis – II.recent improvementsPopulation synthesis – II.recent improvements

2. New cross sections & abundances and new mass spectrum

Low mass progenitors for thedotted mass spectrum are treated followingastro-ph/0409422.

The new spectrum looksmore “natural”.

But the effect is ....

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Effects of the new mass spectrum and abundances on the Log N – Log S

Effects of the new mass spectrum and abundances on the Log N – Log S

Solid – new abundances, old massDotted – old abundances, old massDashed – new abundances, new mass

... Effect is negligible

We also introducednew abundances, andcalculated count ratemore accurately than before. Still,the effect is small.

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3. Spatial distribution of ISM (NH)

instead of :

now :

Population synthesis – II.recent improvementsPopulation synthesis – II.recent improvements

Hakkila

(see astro-ph/0609275 for details)

Modification of the old one

NH inside 1 kpc

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Effects of the new ISM distributionEffects of the new ISM distribution

Dot-dashed and dot-dot-dashed linesRepresent two new models of theISM distribution.

Again, the effect is not very significant forLog N – Log S, butit is strong for thesky distribution(see below).

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b= +90°

b= -90°

Popov et al. 2005

Count rate > 0.05 cts/s

OriSco OB

Cep?Per?

PSRs+

Geminga+

M7

PSRs-

First results: new mapsFirst results: new maps

Clearly several richOB associations startto dominate in thespatial distribution

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INSs and local surroundingINSs 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 model50 000 tracks, new ISM model

AguerosChieregato

Candidates:

radiopulsarsMagn. 7

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Age and distance distributionsAge and distance distributions

Age

1 < cts/s < 100.1 < cts/s < 10.01 < cts/s < 0.1

Distance

New cands.

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Different models: age distributionsDifferent models: age distributions

Bars with vertical lines:old model for Rbelt=500 pc

White bars: new initial dist

Black bars: new ISM (analyt.) andnew initial distribution

Diagonal lines:new ISM (Hakkila) andnew initial distribution

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Different models: distance distr.Different models: distance distr.

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Where to search for more cowboys?Where to search for more cowboys?

We do not expect to find much 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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56 EGRET sources56 EGRET sourcesRecently Crawford et al. (astro-ph/0608225) presented a studyof 56 well-identified EGRET error boxes. The idea was to find radio pulsars. Nothing was found.

Obviously, they can be geminga-like sources, or represent some other subpopulation of cooling NSs.

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OB runaway starsOB runaway starsAnother possibility to find new ICoNSs isto search for (un)bound compact companions of OB runaway stars.More than one hundred OB runaway stars are known in 1 kpc around the Sun (astro-ph/9809227).

Unbounded NSs Bounded NSs

(for BHs done in astro-ph/0511224)

bh

Optical star

Sayer et al. 1996 and Philp et al. 1996looked for radio pulsars as companionsof runaway stars. It is reasonable to look for M7-likecompanions around young OB stars.

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Calvera et al.Calvera et al.Recently, Rutledge et al. reported the discovery of an enigmaticNS candidated dubbed Calvera.

It can be an evolved (aged) version of Cas A source,but also it can be a M7-like object, who’s progenitor was a runaway (or, less probably, hypervelocity) star.

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CCO vs. M7CCO vs. M7Gotthelf and Halpern (2007) presented evidence in favor of hypothesis that among CCOs there is a population of NSs born with long spin periods (few tenths of a second) and small magnetic fields (<1012 G).These sources are hot. The M7 sources are hot, too, but they seemto belong to different populations.This can be explained by accreted envelopes in CCOs (Kaminker et al. 2006).

It is necessary to make a general population synthesis, which would include all types of isolated NSs.

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Resume Resume New more detailed population synthesis model for local population

of isolated NS is made New results provide a hint to search for new coolers. We predict that new objects can be identified at 0.01<cts/s<0.1

behind the Gould Belt in the directions of close-by rich OB associations, in particular Cep OB2.

These objects are expected to be younger and hotter than the Magnificent seven.

New ways to find candidates can be discussed.

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The Magnificent Seven Vs. UncatchablesThe Magnificent Seven Vs. Uncatchables

Born in the Gould Belt.Bright. Middle-aged.Already observed.

Born behind the Belt.Dimmer. Younger.Wanted.

That’s all!

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Radio detectionRadio 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.

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NS+NS binariesNS+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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