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Space Cowboys Odissey: Beyond the Gould Belt S e r g e i P o p o v, B e t t in a P o s s e lt

(co-authors: F. Haberl, R. Neuhauser, J. Truemper, R. Turolla)

astro-ph/0609275, 0710.1547 and work in progress


The new zoo of neutron stars
During 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 Seven
N R R R R R R R am e P e r io d , s X 1 856 7.05 X 0720 8.39 B S 1 22 3 1 0.31 B S 1 55 6 6.88? X 0806 1 1 .37 X 0420 3.45 B S 1 77 4 9.44

Radioquiet (?) Close-by Thermal emission Absorption features Long periods
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Population of close-by young NSs




M a g n if ic e n t s e v e n G e m in g a a n d 3E G J 1 853+591 8 F o u r r a d io p u ls a r s w it h t h e r m a l e m is s io n ( 0833- 5; B 0656+1 4; B 4 B 1 055- 2; B 1 929+1 0) 5 S e v e n o ld e r r a d io p u ls a r s , w it h o u t d e t e c t e d t h e r m a l e m is s io n . Where are the rest?

UNCATCHABLES
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Log N ­ Log S
Log of the number of sources brighter than the given flux

calculations - 3/ 2 s pher e: num ber ~ r3 flux ~ r-

2

-1 disc: number ~ r2 flux ~ r-

2

Log of flux (or number counts)

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Population synthesis: ingredients


B ir t h r a t e o f N S s I n it ia l s p a t ia l d is t r ib u t io n S p a t ia l v e lo c it y ( ic k ) k M a s s s p e c tru m T h e r m a l e v o lu t io n I n t e r s t e lla r a b s o r p t io n D e t e c t o r p r o p e r t ie s

Task: To build an artificial model of a population of some astrophysical sources and to compare the results of calculations with observations.

A brief review on population synthesis in astrophysics can be found in astro-ph/0411792 and in Physics-Uspekhi (2007).

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Population synthesis ­ I.
G o u l d B e l t : 2 0 N S M y r-1 G a l . D i s k (3 k p c ) : 2 5 0 N S M y r
-1

· C o o ling c urves b y · B las c hke et al. · M as s s p ec trum

R OS AT

18°

G o u ld B e lt

A rzo u m a n ia n et al. 2002
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The Gould Belt




P o p p e l ( 997) 1 R =300 ­ 500 p c A g e 30- 0 M y r s 5 C e n te r a t 1 50 p c f r o m th e S u n I n c lin e d r e s p e c t t o t h e g a la c tic p la n e a t 20 d e g re e s 2/ m a s s iv e s ta r s in 600 3 p c b e lo n g t o t h e B e lt
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Population synthesis ­ II. recent improvements
1. Spatial distribution of progenitor stars
We use the same normalization for NS formation rate inside 3 kpc: 270 per Myr. Most of NSs are born in OB associations. For stars <500 pc we even try to take into account if they belong to OB assoc. with known age.
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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


Effects of the new spatial distribution on Log N ­ Log S
There are no significant effects on the Log N ­ Log S distribution due to more clumpy initial distribution of NSs. But, as we'll see below, the effect is strong for sky distribution.

Solid ­ new initial XYZ Dashed ­ Rbelt = 500 pc Dotted ­ R = 300 pc

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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)


(masses of secondary objects in NS+NS)

astro-ph/0305599
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Population synthesis ­ II. recent improvements
2. New cross sections & abundances and new mass spectrum
Low mass progenitors for the dotted mass spectrum are treated following astro-ph/0409422. The new spectrum looks more "natural". But the effect is ....

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Effects of the new mass spectrum and abundances on the Log N ­ Log S
... Effect is negligible We also introduced new abundances, and calculated count rate more accurately than before. Still, the effect is small.

Solid ­ new abundances, old mass Dotted ­ old abundances, old mass Dashed ­ new abundances, new mass

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Population synthesis ­ II. recent improvements
3. Spatial distribution of ISM (NH) instead of :
NH inside 1 kpc (see astro-ph/0609275 for details)

now :

Modification of the old one

Hakkila

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Effects of the new ISM distribution
Again, the effect is not very significant for Log N ­ Log S, but it is strong for the sky distribution (see below).

Dot-dashed and dot-dot-dashed lines Represent two new models of the ISM distribution.

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First results: new maps
P o p o v et al. 2 0 0 5

Count rate > 0.05 cts/s
b= +90°

Cep?Per? Sco OB Ori

b = -9 0 °

PSRs+ Geminga+ M7 PSRs-

Clearly several rich OB associations start to dominate in the spatial distribution
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INSs and local surrounding
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.

De Zeeuw et al. 1999

Motch et al. 2006

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50 000 tracks, new ISM model

Candidates:
Agueros Chieregato radiopulsars Magn. 7

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Age and distance distributions
0.01 < cts/s < 0.1 0.1 < cts/s < 1 1 < cts/s < 10

Ag e

New cands.

Distance

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Different models: age distributions
Bars with vertical lines: old model for Rbelt=500 pc

White bars: new initial dist Black bars: new ISM (analyt.) and new initial distribution Diagonal lines: new ISM (Hakkila) and new initial distribution
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Different models: distance distr.

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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 ( (ads.gsfc.nasa.gov/mw/) 22

L=110

90 10 0 -10


56 EGRET sources
Recently Crawford et al. (astro-ph/0608225) presented a study of 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 stars
Another possibility to find new ICoNSs is to 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 Sayer et al. 1996 and Philp looked for radio pulsars as of runaway stars. It is reasonable to look for companions around young

et al. 1996 companions M7-like OB stars.
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Optical star

bh

(for BHs done in astro-ph/0511224)


Calvera et al.
Recently, Rutledge et al. reported the discovery of an enigmatic NS 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. M7
Gotthelf 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 seem to 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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Re s um e




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
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The 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 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 detection of another one.

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NS+NS binaries
Pulsar B1913+16 B2127+11C B1534+12 J0737-3039 J1756-2251 Pulsar mass 1.44 1.35 1.33 1.34 1.40 Companion mass 1.39 1.36 1.35 1.25 1.18 (PSR+companion)/2 J1518+4904 J1811-1736 J1829+2456 1.35 1.30 1.25 (David Nice, talk at Vancouver 2005)
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