Space%20Cowboys%20Odissey:%20Beyond%20the%20Gould%20Belt

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Space Cowboys OdisseyBeyond the Gould Belt

• Sergei Popov
• (SAI MSU)

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Neutron stars
Superdence matter, strong gravity and superstrong
magnetic fields
Magnetospheric activity
Cooling
Accretion
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Good old classics
For years two main types of NSs have been
discussedradio pulsars and accreting NSs in
close binary systems
The pulsar in the Crab nebula
A binary system
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The new zoo of neutron stars

• During last gt10 years
• it became clear that neutron stars
• can be born very different.
• In particular, absolutely
• non-similar to the Crab pulsar.
• Compact central X-ray sources
• in supernova remnants.
• Anomalous X-ray pulsars
• Soft gamma repeaters
• The Magnificent Seven
• Unidentified EGRET sources
• Transient radio sources (RRATs)
• Calvera .

All together these NSs have total birth rate
higher than normal radio pulsars(see discussion
in Popov et al. 2006, Keane, Kramer 2008)
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Compact central X-ray sources in supernova
remnants
Cas A
RCW 103
Puppis A
6.7 hour period (de Luca et al. 2006)
No pulsations, small emitting area
Vkick1500 km/s(Winkler, Petre 2006)
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CCOs in SNRs

Age Distance J232327.9584843 Cas A
0.32 3.33.7 J085201.4-461753
G266.1-1.2 13 12 J082157.5-430017 Pup A
13 1.63.3 J121000.8-522628
G296.510.0 320 1.33.9 J185238.6004020 Kes
79 9 10 J171328.4-394955
G347.3-0.5 10 6 Pavlov, Sanwal,
Teter astro-ph/0311526, de Luca
arxiv0712.2209
For two sources there are strong indications for
small initial spin periods and low magnetic
fields1E 1207.4-5209 in PKS 1209-51/52 andPSR
J18520040 in Kesteven 79 see Halpern et al.
arxiv0705.0978
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Magnetars

• dE/dt gt dErot/dt
• By definition The energy of the magnetic field
  is released
• P-Pdot
• Direct measurements of the field (Ibrahim et al.)

Magnetic fields 10141015 G
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SGRs periods and giant flares

• 0526-66
• 1627-41
• 1806-20
• 190014
• 050145

5.7
See the review in Woods, Thompson astro-ph/0406133
and Mereghetti arXiv 0804.0250
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Anomalous X-ray pulsars
Identified as a separate group in 1995.
(Mereghetti, Stella 1995 Van Paradijs et al.1995)

• Similar periods (5-10 sec)
• Constant spin down
• Absence of optical companions
• Relatively weak luminosity
• Constant luminosity

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Known AXPs
Sources Periods, s
CXO 010043-7211 8.0
4U 014261 8.7
1E 1048.1-5937 6.4
1E 1547.0-5408 2.0
CXOU J164710-4552 10.6
1RXS J170849-40 11.0
XTE J1810-197 5.5
1E 1841-045 11.8
AX J1845-0258 7.0
1E 2259586 7.0
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Unidentified EGRET sources
Grenier (2000), Gehrels et al. (2000)
Unidentified sources are divided into several
groups. One of them has sky distribution similar
to the Gould Belt objects. It is suggested that
GLAST (and, probably, AGILE) Can help to solve
this problem. Actively studied subject (see for
example papers by Harding, Gonthier)
no radio pulsars in 56 EGRET error boxes
(Crawford et al. 2006) However, Keith et al.
(0807.2088) found a PSR at high frequency.
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Discovery of RRATs

• 11 sources detected in the
• Parkes Multibeam survey
• (McLaughlin et al 2006)
• Burst duration 2-30 ms,
• interval 4 min-3 hr
• Periods in the range 0.4-7 s
• Period derivative measured in 3 sources
• B 1012-1014 G, age 0.1-3 Myr
• RRAT J1819-1458 detected in the X-rays, spectrum
  soft and thermal,
• kT 120 eV (Reynolds et al 2006)

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Calvera et al.
Recently, Rutledge et al. reported the discovery
of an enigmatic NS candidated dubbed Calvera. No
radio emission was found. It can be an evolved
(aged) version of Cas A source, but also it can
be a M7-like object, whos progenitor was a
runaway (or, less probably, hypervelocity) star.
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Magnificent Seven
Name Period, s
RX 1856 7.05
RX 0720 8.39
RBS 1223 10.31
RBS 1556 6.88?
RX 0806 11.37
RX 0420 3.45
RBS 1774 9.44
Radioquiet (?) Close-by Thermal
emission Absorption features Long periods
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Pulsating ICoNS

• Quite large pulsed fractions
• Skewed lightcurves
• Harder spectrum at pulse minimum
• Phase-dependent absorption features

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Evolution of neutron stars. I. rotation
magnetic field
Ejector ? Propeller ? Accretor ? Georotator
1 spin down 2 passage through a molecular
cloud 3 magnetic field decay
astro-ph/0101031
See the book by Lipunov (1987, 1992)
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Magnetorotational evolution of radio pulsars
Spin-down. Rotational energy is released. The
exact mechanism is still unknown.
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Evolution of NSs. II.temperature
(Yakovlev et al. (1999) Physics Uspekhi)
First papers on the thermal evolution appeared
already in early 60s, i.e. before the discovery
of radio pulsars.
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Population of close-by young NSs

• Magnificent seven
• Geminga and 3EG J18535918
• Four radio pulsars with thermal emission
  (B0833-45 B065614 B1055-52 B192910)
• Seven older radio pulsars, without detected
  thermal emission.

Where are the rest?
UNCATCHABLES
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Population synthesis in astrophysics
A population synthesis is a method of a direct
modeling of relatively large populations of
weakly interacting objects with non-trivial
evolution. As a rule, the evolution of the
objects is followed from their birth up to the
present moment.
(see astro-ph/0411792 and Physics Uspekhi 2007
N11)
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Why PS is necessary?

1. No direct experiments computer
   experiments
2. Long evolutionary time scales
3. Selection effects. We see just a top of an
   iceberg.
4. Expensive projects for which it is necessary to
   make predictions

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Tasks

• To test and/or to determine initial and
  evolutionary parameters.
• To do it one has to compare calculated and
  observed popualtions.
• This task is related to the main pecularity
  of astronomy we cannot make direct experiments
  under controlled conditions.
• To predict properties of unobserved populations.
• Population synthesis is actively use to
  define programms for futureobservational
  projects satellites, telescopes, etc.

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Log N Log S
Log of the number of sources brighter than the
given flux
Log of flux (or number counts)
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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

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Population synthesis I.
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New version of the code

• Recently we finished an advanced version of the
  code.
• Spatial distribution
• Interstellar distribution
• Interstellar absorption
• Response matrix
• Mass spectrum
• B. Posselt, S. Popov, F. Haberl, R. Neuhauser, J.
  Truemper, R. Turolla
• AA 482, 617 (2008)

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The Gould Belt

• Poppel (1997)
• R300 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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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 inOB associations. For stars lt500 pc we
eventry to take into accountif they belong to
OB assoc.with known age.
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
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Effects of the new spatial distribution on Log N
Log S
There are no significanteffects on the Log N
Log Sdistribution due to moreclumpy initial
distributionof NSs. But, as well see
below,the effect is strong forsky distribution.
Solid new initial XYZ Dashed Rbelt 500
pc Dotted Rbelt 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)

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 thedotted mass spectrum
are treated following astro-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
... Effect is negligible
We also introducednew abundances, andcalculated
count ratemore 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

Hakkila
Modification of the old one
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Effects of the new ISM distribution
Again, the effect is not very significant
forLog N Log S, butit is strong for thesky
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
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.
Motch et al. 2006
De Zeeuw et al. 1999
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50 000 tracks, new ISM model
Candidates
Agueros
Chieregato
radiopulsars
Magn. 7
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Age and distance distributions
1 lt cts/s lt 10
0.1 lt cts/s lt 1
0.01 lt cts/s lt 0.1
Age
New cands.
Distance
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Different models age distributions
Bars with vertical linesold model for Rbelt500
pc White bars new initial dist Black bars
new ISM (analyt.) andnew initial
distribution Diagonal linesnew ISM (Hakkila)
andnew 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 gt0.1 cts/s. Most of new candidates should
be at fluxes 0.01lt f lt 0.1 cts/s. So, they are
expected to be young NSs (ltfew 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., pcCyg OB7     84      96     -5    
9       600-700Cep OB2     96     108    -1  
12       700Cep OB3    108    113     1    
7       700-900Cam OB1   130    153    -3    
8       800-900
90
L110
130
10
0
-10
(ads.gsfc.nasa.gov/mw/)
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Gamma-ray selected sources
Recently 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.
However, Keith et al. (0807.2088) found a PSR at
high frequencyin one of EGRET error boxes.
We are wainting for results fromGLAST-Fermi.
Gamma-ray selected INSs.
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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 et al. 1996looked
for radio pulsars as companionsof runaway stars.
It is reasonable to look for M7-likecompanions
around young OB stars.
Optical star
bh
(for BHs done in astro-ph/0511224)
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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 (lt1012 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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M 7 and CCOs
Both CCOs and M7 seem to be the hottest at
their ages (103 and 106 yrs). However, the
former cannot evolve to become the latter ones!

• Accreted envelopes (presented in CCOs,
  absent in the M7)
• Heating by decaying magnetic field in the
  case of the M7

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Accreted envelopes, B or heating?
(Yakovlev Pethick 2004)
It is necessary to make population synthesis
studies to test all these possibilities.

• Related to e-capture SN?
• low-mass objects
• low kicks
• 10 of all NSs

However, small emitting area remains
unexplained.Accretion???
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M7 and RRATs
Similar periods and Pdots In one case similar
thermal properties Similar birth rate?
(arXiv 0710.2056)
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M7 and RRATs pro et contra
Based on similarities between M7 and RRATs it was
proposed that they can bedifferent
manifestations of the same type of INSs
(astro-ph/0603258).To verify it a very deep
search for radio emission (including RRAT-like
bursts)was peformed on GBT (Kondratiev et
al.).In addition, objects have been observed
with GMRT (B.C.Joshi, M. Burgay et al.). In both
studies only upper limits were derived. Still,
the zero result can be just due to unfavorable
orientations(at long periods NSs have very
narrow beams).It is necessary to increase
statistics.
(Kondratiev et al, in press, see also arXiv
0710.1648)
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M7 and high-B PSRs
Strong limits on radio emission from the M7are
established (Kondratiev et al. 2008
0710.1648). However, observationally it is still
possible thatthe M7 are just misaligned high-B
PSRs.
Are there any other considerations to verify a
link between thesetwo popualtions of NSs?
In most of population synthesis studies of
PSRsthe magnetic field distribution is described
as agaussian, so that high-B PSRs appear to be
notvery numerous.On the other hand, population
synthesis of thelocal population of young NSs
demonstrate thatthe M7 are as numerous as
normal-B PSRs.
So, for standard assumptionsit is much more
probable, thathigh-B PSRs and the M7 are not
related.
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Magnetars, field decay, heating
A model based on field-dependent decay of the
magnetic moment of NSscan provide an
evolutionary link between different populations
(Pons et al.).
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Magnetic field decay
Magnetic fields of NSs are expected to decay due
to decay of currents which support them.
Crustal field of core field? It is easy to decay
in the crust. In the core the filed is in the
formof superconducting vortices. They can decay
only when they aremoved into the crust (during
spin-down). Still, in most of models strong
fields decay.
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Period evolution with field decay
An evolutionary track of a NS isvery different
in the case of decaying magnetic field. The
most important feature isslow-down of
spin-down. Finally, a NS can nearly freezeat
some value of spin period. Several episodes of
relativelyrapid field decay can happen. Number
of isolated accretors can be both decreased or
increasedin different models of field decay. But
in any case their average periods become shorter
and temperatures lower.
astro-ph/9707318
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Magnetic field decay vs. thermal evolution
Magnetic field decay can be an important source
of NS heating.
Heat is carried by electrons. It is easier to
transport heat along field lines. So, poles are
hotter. (for light elements envelope
thesituation can be different).
Ohm and Hall decay
arxiv0710.0854 (Aguilera et al.)
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Joule heating for everybody?
It is important to understandthe role of heating
by thefield decay for different typesof INS.
In the model by Pons et al.the effect is more
importantfor NSs with larger initial B. Note,
that the characteristicage estimates (P/2
Pdot)are different in the case ofdecaying
field!
arXiv 0710.4914 (Aguilera et al.)
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Magnetic field vs. temperature
The line marks balancebetween heating due to the
field decay and cooling.It is expected by the
authors(Pons et al.) that a NSevolves downwards
till itreaches the line, then theevolution
proceeds along the line. Selection effects
are notwell studied here.A kind of
populationsynthesis modeling iswelcomed.
Teff Bd1/2
(astro-ph/0607583)
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Log N Log S with heating

• Log N Log S for 4 different magnetic fields.
• No heating (lt1013 G) 3. 1014 G
• 5 1013 G 4. 2 1014 G

Different magnetic field distributions.
Popov, Pons, work in progress the code used
in Posselt et al. AA (2008) with modifications
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Log N Log L
Two magnetic field distributionswith and
without magnetars(i.e. different magnetic
fielddistributions are used). 6 values of inital
magnetic field, 8 masses of NSs. SNR 1/30
yrs-1. Without magnetars meansno NSs with
B0gt1013 G.
Popov, Pons, work in progress
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Populations ....
Birthrate of magnetars is uncertain due to
discovery of transient sources. Just from
standard SGR statistics it is just 10, then,
for example,the M7 cannot be aged magnetars
with decayed fields, but if there are many
transient AXPs and SGRs then the situation is
different. Limits, like the one by Muno et al.,
on the number of AXPs from asearch for
periodicity are very important and have to be
improved(a task for eROSITA?).
Lxgt 3 1033 erg s-1
Muno et al. 2007
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Resume on the pop. synthesis of INSs

• 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
  0.01ltcts/slt0.1 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 M7.
• New ways to find candidates can be discussed.
• The M7 can be related to RRATs (and even
  magnetars), but CCOs are different.
• If the magnetic field decay is important or not
  is still unclear for the M7.
• Still, it is possible to explain the local
  population of NSs with field decay.

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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.