1. The Zoo Of Neutron Stars
Sergei Popov
(SAI MSU) (

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

3. The old zoo of neutron stars
In 60s the first X-ray sources have been discovered.
They were neutron stars in close binary systems, BUT ...
.... they were «not recognized»....
Now we know hundreds
of X-ray binaries with
neutron stars in the
Milky Way and in other
galaxies.

4. The first detections in binaries
Giacconi, Gursky, Hendel (1962)
About ½ of massive stars are members of close binary systems.
Now we know hundreds of close binary systems with neutron stars.
UHURU was launched on December 12, 1970.
2-20 keV
The first sky survey.
339 sources.

5. Good old classics Crab nebula A binary system Radio pulsars discovery
1967: Jocelyn Bell.

6. 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)

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

8. 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.

9. The old Zoo: young pulsars & old accretors
For years only two main types of NSs have been discussed: radio pulsars and accreting NSs in close binary systems

10. The new zoo of neutron stars
During last ~10-15 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)

11. 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)

12. CCOs in SNRs
Age Distance
J Cas A –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 large (>~100 msec) initial spin periods and low magnetic fields: 1E in PKS /52 and PSR J in Kesteven 79 [see Halpern et al. arxiv: ]

13. Magnetars dE/dt > dErot/dt
By definition: The energy of the magnetic field is released
P-Pdot
“Direct” measurements of the field (spectral lines)
Magnetic fields 1014–1015 G

14. 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:

15. Historical notes 05 March 1979. The ”Konus” experiment & Co.
Venera-11,12
Events in the LMC.
SGR
Fluence: about 10-3 erg/cm2
Mazets et al. 1979
N49 – supernova
remnant in the
Large Magellanic
cloud
(G.Vedrenne
et al. 1979)

16. Soft Gamma Repeaters: main properties
Saturation of detectors
Energetic “Giant Flares” (GFs, L ≈ erg/s) detected from 3 (4?) sources
No evidence for a binary companion, association with a SNR at least in one case
Persistent X-ray emitters, L ≈ erg/s
Pulsations discovered both in GFs tails and persistent emission, P ≈ s
Huge spindown rates,
Ṗ ≈ –10-11 ss-1

17. Main types of activity of SGRs
Weak bursts. L<1042 erg/s
Intermediate. L~1042–1043 erg/s
Giant. L<1045 erg/s
Hyperflares. L>1046 erg/s
(from Woods, Thompson 2004)

18. Extragalactic SGRs Burst in M31 [D. Frederiks et al. astro-ph/0609544]
It was suggested long ago (Mazets et al. 1982)
that present-day detectors could alredy detect giant flares from extragalactic magnetars.
However, all searches in, for example, BATSE databse did not provide clear candidates (Lazzati et al. 2005, Popov & Stern 2006, etc.).
Finally, recently several good candidates have been proposed by different groups
(Mazets et al., Frederiks et al., Golenetskii et al.,
Ofek et al, Crider ...., see arxiv: and references therein, for example).
Burst in M31
[D. Frederiks et al. astro-ph/ ]

19. 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

20. 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

21. SGRs and AXPs

22. Are SGRs and AXPs brothers?
Bursts of AXPs (from 6 now)
Spectral properties
Quiescent periods of SGRs ( since 1983)
Gavriil et al. 2002

23. Magnetic field estimates
Spin down
Long spin periods
Energy to support bursts
Field to confine a fireball (tails)
Duration of spikes (alfven waves)
Direct measurements of magnetic field (cyclotron lines)
Ibrahim et al. 2002
Gavriil et al. (2002, 2004)

24. Transient radio emission from AXP
ROSAT and XMM images. The X-ray outburst happened in 2003.
AXP has spin period 5.54 s
Radio emission was detected from XTE J during its active state.
Clear pulsations have been detected.
Large radio luminosity.
Strong polarization.
Precise Pdot measurement. Important for limting models, better distance and coordinates determination etc.
(Camilo et al. astro-ph/ )

25. Transient radiopulsar
PSR J
P=0.326 sec
B= G
However, no radio emission detected.
Due to beaming?
Among all rotation powered PSRs it has the largest Edot. Smallest spindown age (884 yrs).
The pulsar increased
its luminosity in X-rays.
Increase of pulsed X-ray flux.
Magnetar-like X-ray bursts (RXTE).
Timing noise.
See additional info about this pulsar at the web-site ,

26. Twisted Magnetospheres – I
The magnetic field inside a magnetar is “wound up”
The presence of a toroidal component induces a rotation of the surface layers
The crust tensile strength resists
A gradual (quasi-plastic ?) deformation of the crust
The external field twists up
(Thompson, Lyutikov & Kulkarni 2002)
(by R. Turolla)
(Mereghetti arXiv: )
(Thompson & Duncan 2001)

27. Generation of the magnetic field or fossil field?
The mechanism of the magnetic
field generation is still unknown.
α-Ω dynamo (Duncan,Thompson)
α2 dynamo (Bonanno et al.)
or their combination
In any case, initial rotation of a
protoNS is the critical parameter.
There are reasons to suspect that the magnetic fields of magnetars are not due to any kind of dynamo mechanism, but just due to flux conservation:
Study of SNRs with magnetars (Vink and Kuiper 2006).
2. There are few examples of massive stars with field strong enough to produce magnetars (Ferrario and Wickramasinghe 2006)

28. What is special about magnetars?
Link with massive stars
There are reasons to suspect that magnetars are connected to massive stars
(astro-ph/ ).
Link to binary stars
There is a hypothesis that magnetars are formed in close binary systems
(astro-ph/ ).
AXP in Westerlund 1 most probably has a very massive progenitor >40 Msolar.
The question is still on the list.

29. ROSAT ROentgen SATellite German satellite
(with participation of US and UK).
Launched 01 June 1990.
The program was successfully ended
on 12 Feb 1999.

30. 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 J

31. 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

32. 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

33. The Optical Excess
In the four sources with a confirmed optical counterpart Fopt  5-10 x B(TBB,X)
Fopt  2 ?
Deviations from a Rayleigh-Jeans continuum in RX J0720 (Kaplan et al 2003) and RX J1605 (Motch et al 2005). A non-thermal power law ?
RX J1605 multiwavelength SED
(Motch et al 2005)

34. Period Evolution
RX J : bounds on derived by Zane et al. (2002) and Kaplan et al (2002)
Timing solution by Cropper et al (2004), further improved by Kaplan & Van Kerkwijk (2005):
= 7x10-14 s/s, B = 2x1013 G
RX J : timing solution by Kaplan & Van Kerkwijk (2005a),
= s/s, B = 3x1013 G
Spin-down values of B in agreement with absorption features being proton cyclotron lines
B ~ G

35. Featureless ? No Thanks !
RX J (Haberl et al 2004)
RX J is convincingly featureless (Chandra 500 ks DDT; Drake et al 2002; Burwitz et al 2003)
A broad absorption feature detected in all other ICoNS (Haberl et al 2003, 2004, 2004a; Van Kerkwijk et al 2004; Zane et al 2005)
Eline ~ eV; evidence for two lines with E1 ~ 2E2 in RBS 1223 (Schwope et al 2006)
Proton cyclotron lines ? H/He transitions at high B ?

36. Source Energy (eV) EW Bline (Bsd) (1013 G) Notes RX J1856.5-3754 no ?
270 40
5 (2)
Variable line
RX J
460 33 9
RX J
330 43 7
RX J
300
150
6 (3)
RX J
450 36
1RXS J
700 50 14

37. Long Term Variations in RX J0720.4-3125
A gradual, long term change in the shape of the X-ray spectrum AND the pulse profile (De Vries et al 2004; Vink et al 2004)
Steady increase of TBB and of the absorption feature EW (faster during 2003)
Evidence for a reversal of the evolution in 2005 (Vink et al 2005)
De Vries et al. 2004

39. 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.

40. 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 X-rays, spectrum soft and thermal,
kT ~ 120 eV (Reynolds et al 2006)

41. RRATs
P, B, ages and X-ray properties of RRATs very similar to those of XDINSs
Estimated number of RRATs:
~ 3-5 times that of PSRs
If τRRAT ≈ τPSR,
βRRAT ≈ 3-5 βPSR
βXDINS > 3 βPSR (Popov et al 2006)
Are RRATs far away XDINSs ?

42. RRAT in X-rays
X-ray pulses overlaped on radio data of RRAT J
Thermally emitting NS
kT ~ 120 eV
(Reynolds et al 2006)
(arXiv: )

43. 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.
No radio emission was found.

44. CCO vs. M7. New population?
Gotthelf & Halpern (arXiv: ) recently suggested that 1E and PSR J (in Kes 79) can be prototypes of a different subpopulation of NSs born with low magnetic field (< few 1011 G) and relatively long spin periods (few tenths of a second).
These NSs are relatively hot, and probably not very rare.
Surprisingly, we do not see objects of this type in our vicinity.
In the solar neighbourhood we meet a different class of object.
This can be related to accreted envelopes (see, for example, Kaminker et al. 2006).
Sources in CCOs have them, so they look hotter, but when these envelopes disappear, they are colder than NSs which have no envelopes from the very beginning. So, we do not see such sources among close-by NSs.

45. M7 and CCOs Temperature Age
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. P
Pdot
PSRs M7
B=const
Magnetars
Magnetic fields of NSs are expected to decay
due to decay ofcurrents which support them.

51. 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/

52. 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.)

53. 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.)

54. 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/ )

55. 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]

56. 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]

57. Populations, new candidates ....
Birthrate of magnetars is uncertain due to discovery of transient sources.
Just from “standard” SGR statistics it is only 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 (<540) are very important and have to be improved (a task for eROSITA?).
Lx> erg s-1
[Muno et al. 2007]

58. Conclusions There are several types of sources: CCOs, M7,
SGRs, AXPs, RRATs ...
Significant fraction of all newborn NSs
Unsolved problems:
1. Are there links?
2. Reasons for diversity

59. Dorothea Rockburne

60. Some reviews on isolated neutron stars
NS basics: physics/
astro-ph/
SGRs & AXPs: astro-ph/ arXiv:
CCOs: astro-ph/ arxiv:
Quark stars: arxiv:
The Magnificent Seven: astro-ph/
arxiv:
RRATs: arXiv:
Cooling of NSs: astro-ph/
astro-ph/
NS structure arXiv:
EoS astro-ph/
NS atmospheres astro-ph/
NS magnetic fields arxiv: arxiv: