1. Space Cowboys Odissey: Beyond the Gould Belt
Sergei Popov
(SAI MSU)

2. Neutron stars
Superdence matter, strong gravity and superstrong magnetic fields
Cooling
Accretion
Magnetospheric activity

3. Good old classics The pulsar in the Crab nebula A binary system
For years two main types of NSs have been discussed: radio pulsars and accreting NSs in close binary systems
The pulsar in the Crab nebula
A binary system

4. 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.
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)

5. Compact central X-ray sources in supernova remnants
Cas A
RCW 103
Puppis A
No pulsations, small emitting area
6.7 hour period
(de Luca et al. 2006)
Vkick=1500 km/s (Winkler, Petre 2006)

6. CCOs in SNRs Age Distance J232327.9+584843 Cas A 0.32 3.3–3.7
J − G266.1− – –2
J − Pup A – –3.3
J − G – –3.9
J Kes ~ ~10
J − G347.3−0.5 ~ ~6
[Pavlov, Sanwal, Teter: astro-ph/ , de Luca: arxiv: ]
For two sources there are strong indications for small initial spin periods and low magnetic fields: 1E in PKS /52 and PSR J in Kesteven 79 [see Halpern et al. arxiv: ]

7. Magnetars dE/dt > dErot/dt
By definition: The energy of the magnetic field is released
P-Pdot
Direct measurements of the field (Ibrahim et al.)
Magnetic fields 1014–1015 G

8. SGRs: periods and giant flares
P, s
Giant flares
8.0
6.4
7.5
5.2
5 March 1979
27 Aug 1998
27 Dec 2004
18 June 1998
(?)
5.7
See the review in
Woods, Thompson
astro-ph/
and Mereghetti
arXiv:

9. 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

10. Known AXPs Sources Periods, s CXO 010043-7211 8.0 4U 0142+61 8.7
6.4 1E
2.0
CXOU J
10.6
1RXS J
11.0
XTE J
5.5 1E
11.8
AX J
7.0 1E

11. 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. ( )
found a PSR at high frequency.

12. 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 s
Period derivative measured in 3 sources:
B ~ G, age ~ Myr
RRAT J detected in the X-rays, spectrum soft and thermal,
kT ~ 120 eV (Reynolds et al 2006)

13. 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, who’s progenitor was a runaway (or, less probably, hypervelocity) star.

14. 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

15. Pulsating ICoNS Quite large pulsed fractions Skewed lightcurves
RX J (Haberl et al 2004)
Quite large pulsed fractions
Skewed lightcurves
Harder spectrum at pulse minimum
Phase-dependent absorption features

16. 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/
See the book by Lipunov (1987, 1992)

17. Magnetorotational evolution of radio pulsars
Spin-down.
Rotational energy is released.
The exact mechanism is
still unknown.

18. 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.

19. Population of close-by young NSs
Magnificent seven
Geminga and 3EG J
Four radio pulsars with thermal emission (B ; B ; B ; B )
Seven older radio pulsars, without detected thermal emission.
Where are the rest?
UNCATCHABLES

20. 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/ and Physics Uspekhi 2007 N11)

21. Why PS is necessary? No direct experiments computer experiments
Long evolutionary time scales
Selection effects. We see just a top of an iceberg.
Expensive projects for which it is necessary to make predictions

22. 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 future observational projects: satellites, telescopes, etc.

23. Log N – Log S Log of the number of sources
-3/2 sphere:
number ~ r3
flux ~ r-2
-1 disc:
number ~ r2
calculations
Log of the number of sources
brighter than the given flux
Log of flux (or number counts)

24. Population synthesis: ingredients
Birth rate of NSs
Initial spatial distribution
Spatial velocity (kick)
Mass spectrum
Thermal evolution
Interstellar absorption
Detector properties

25. Population synthesis – I.
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 Belt

26. 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
A&A 482, 617 (2008)

27. 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

28. 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.
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

29. 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 – Rbelt = 300 pc

30. 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/

31. 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/
The new spectrum looks more “natural”.
But the effect is ....

32. 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

33. Population synthesis – II. recent improvements
3. Spatial distribution of ISM (NH)
instead of :
NH inside 1 kpc
(see astro-ph/ for details)
now :
Modification of the old one
Hakkila

34. 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.

35. First results: new maps
b= +90°
b= -90°
Popov et al. 2005
Count rate > 0.05 cts/s
Ori
Sco OB
Cep?Per?
PSRs+
Geminga+ M7
PSRs-
Clearly several rich
OB associations start
to dominate in the
spatial distribution

36. INSs and local surrounding
Massive star population in the Solar vicinity (up to 2 kpc)
is dominated by OB associations.
Inside pc the Gould Belt is mostly important.
Motch et al. 2006
De Zeeuw et al. 1999

37. 50 000 tracks, new ISM model Candidates: Agueros Chieregato
radiopulsars
Magn. 7

38. Age and distance distributions
0.01 < cts/s < 0.1
0.1 < cts/s < 1
1 < cts/s < 10
Age
New cands.
Distance

39. 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

40. Different models: distance distr.

41. 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       Cep OB2     96     108    -1   12       700 Cep OB3    108    113     1     7       Cam OB1   130    153    -3     8      
130
L=110 90 10
-10
(ads.gsfc.nasa.gov/mw/)

42. Gamma-ray selected sources
Recently Crawford et al. (astro-ph/ ) 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.
However, Keith et al. ( )
found a PSR at high frequency in one of EGRET error boxes.
We are wainting for results from GLAST-Fermi. Gamma-ray selected INSs.

43. 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/ ).
Unbounded NSs
Bounded NSs
Sayer et al and Philp et al looked for radio pulsars as companions of runaway stars.
It is reasonable to look for M7-like companions around young OB stars.
Optical star bh
(for BHs done in astro-ph/ )

44. 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.

45. 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!
Age
Temperature
CCOs M7
Accreted envelopes (presented in CCOs, absent in the M7)
Heating by decaying magnetic field in the case of the M7

46. 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???

47. M7 and RRATs Similar periods and Pdots
In one case similar thermal properties
Similar birth rate?
(arXiv: )

48. M7 and RRATs: pro et contra
Based on similarities between M7 and RRATs it was proposed that they can be different manifestations of the same type of INSs (astro-ph/ ). 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: )

49. M7 and high-B PSRs
Strong limits on radio emission from the M7 are established (Kondratiev et al. 2008: ).
However, observationally it is still possible that the M7 are just misaligned high-B PSRs.
Are there any other considerations
to verify a link between these two popualtions of NSs?
In most of population synthesis studies of PSRs the magnetic field distribution is described as a gaussian, so that high-B PSRs appear to be not very numerous. On the other hand, population synthesis of the local population of young NSs demonstrate that the M7 are as numerous as normal-B PSRs.
So, for standard assumptions it is much more probable, that high-B PSRs and the M7 are not related.

50. Magnetars, field decay, heating
A model based on field-dependent decay of the magnetic moment of NSs can provide an evolutionary link between different populations (Pons et al.). P
Pdot
PSRs M7
B=const
Magnetars

51. 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 form of superconducting vortices.
They can decay only when they are moved into the crust (during spin-down).
Still, in most of models strong fields decay.

52. Period evolution with field decay
An evolutionary track of a NS is very different in the case of decaying magnetic field.
The most important feature is slow-down of spin-down.
Finally, a NS can nearly freeze at some value of spin period.
Several episodes of relatively rapid field decay can happen.
Number of isolated accretors can be both decreased or increased in different models of field decay.
But in any case their average periods become shorter and temperatures lower.
astro-ph/

53. 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 the situation can be different).
Ohm and Hall decay
arxiv: (Aguilera et al.)

54. Joule heating for everybody?
It is important to understand the role of heating by the field decay for different types of INS.
In the model by Pons et al. the effect is more important for NSs with larger initial B.
Note, that the characteristic age estimates (P/2 Pdot) are different in the case of decaying field!
arXiv: (Aguilera et al.)

55. Magnetic field vs. temperature
The line marks balance between heating due to
the field decay and cooling. It is expected by the authors (Pons et al.) that a NS evolves downwards till it reaches the line, then the evolution proceeds along the line.
Selection effects are not well studied here. A kind of population synthesis modeling is welcomed.
Teff ~ Bd1/2
Pons et al. There is an extra free parameter b. It is the ratio B^2/B_d^2. B - field in the crust due to surrents, B_d – dipole field in the crust.
(astro-ph/ )

56. Log N – Log S with heating
Log N – Log S for 4 different magnetic fields.
No heating (<1013 G) G
G G
Different magnetic field distributions.
[Popov, Pons, work in progress; the code used in Posselt et al. A&A (2008) with modifications]

57. Log N – Log L
Two magnetic field distributions: with and without magnetars (i.e. different magnetic field distributions are used).
6 values of inital magnetic field,
8 masses of NSs.
SNR 1/30 yrs-1.
“Without magnetars” means “no NSs with B0>1013 G”.
[Popov, Pons, work in progress]

58. 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 a search for periodicity are very important and have to be improved (a task for eROSITA?).
Lx> erg s-1
[Muno et al. 2007]

59. 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 0.01<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 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.

60. 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!