Transcript Document

Formation and evolution
of magnetars
Sergei Popov
(SAI MSU)
J.A. Pons, J.A. Miralles,
P.A. Boldin, B. Posselt,
MNRAS (2009) arXiv: 0910.2190
A.Bogomazov,
M. Prokhorov
Astronomy Reports (2009) arXiv: 0905.3238
MNRAS (2006) astro-ph/0505406
Good old classics
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
Diversity of young neutron stars
Young isolated neutron stars
can appear in many flavors:
o Radio pulsars
o Compact central X-ray sources
in supernova remnants.
o Anomalous X-ray pulsars
o Soft gamma repeaters
o The Magnificent Seven
o Unidentified gamma-ray sources
o Transient radio sources (RRATs)
o Calvera ….
Compact central X-ray sources in
supernova remnants
Cas A
RCW 103
CCOs in SNRs
J232327.9+584843
J085201.4−461753
J082157.5−430017
J121000.8−522628
J185238.6+004020
J171328.4−394955
Age
Cas A
0.32
G266.1−1.2 1–3
Pup A
1–3
G296.5+10.0 3–20
Kes 79
~9
G347.3−0.5 ~10
Distance
3.3–3.7
1–2
1.6–3.3
1.3–3.9
~10
~6
[Pavlov, Sanwal, Teter: astro-ph/0311526,
de Luca: arxiv:0712.2209]
For two sources there are strong indications for
large (>~100 msec) initial spin periods and
low magnetic fields:
1E 1207.4-5209 in PKS 1209-51/52 and
PSR J1852+0040 in Kesteven 79
[see Halpern et al. arxiv:0705.0978]
Magnetars
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dE/dt > dErot/dt
By definition: The energy of the magnetic field is released
Magnetic fields 1014–1015 G
Magnetic field estimates
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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
Known magnetars
SGRs
 0526-66
 1627-41
 1806-20
 1900+14
 0501+4516 – Aug.2008!
 1801-23 (?)
 0501+4516 (?)
(СТВ 109)
AXPs
 CXO 010043.1-72
 4U 0142+61
 1E 1048.1-5937
 CXO J1647-45
 1 RXS J170849-40
 XTE J1810-197
 1E 1841-045
 AX J1845-0258
 1E 2259+586
 1E 1547.0-5408
Catalogue: http://www.physics.mcgill.ca/~pulsar/magnetar/main.html
Extragalactic SGRs
It was suggested long ago (Mazets et al. 1982)
that present-day detectors could already detect
giant flares from extragalactic magnetars.
However, all searches in, for example,
BATSE database did not provide god candidates
(Lazzati et al. 2006, 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:0712.1502 and
references therein, for example).
Burst from M31
[D. Frederiks et al. astro-ph/0609544]
Magnificent Seven
Name
RX 1856
RX 0720
RBS 1223
RBS 1556
RX 0806
RX 0420
RBS 1774
Period, s
7.05
8.39
10.31
6.88?
11.37
3.45
9.44
Radioquiet
Close-by
Thermal emission
Absorption features
Long periods
RRATs
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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 7 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)
M7 and other NSs
Evolutionary links of M7
with other NSs are not
clear, yet.
M7-like NSs can be
numerous.
They can be descendants
of magnetars.
Can be related to RRATs.
Or, can be a different
population.
Some reviews on isolated neutron stars
• NS basics:
• SGRs & AXPs:
• CCOs:
• Quark stars:
• The Magnificent Seven:
• RRATs:
• Cooling of NSs:
• NS structure
• EoS
• NS atmospheres
• NS magnetic fields
physics/0503245
astro-ph/0405262
astro-ph/0406133
arXiv:0804.0250
astro-ph/0311526
arxiv:0712.2209
arxiv:0809.4228
astro-ph/0609066
arxiv:0801.1143
arXiv:0908.3813
arXiv: 0906.1621
astro-ph/0402143
arXiv:0705.2708
astro-ph/0612440
arxiv: 0808.1279
astro-ph/0206025
arxiv:0711.3650
arxiv:0802.2227
Read the OVERVIEW in the book by Haensel, Yakovlev, Potekhin
Too many NSs???
[Keane, Kramer 2008, arXiv: 0810.1512]
It seems, that the total birth rate is larger than the rate of CCSN.
e- - capture SN cannot save the situation, as they are <~20%.
Note, that the authors do not include CCOs.
So, some estimates are wrong, or some sources evolve into another.
See also astro-ph/0603258.
Transient radiopulsar
PSR J1846-0258 However,
no radio emission
P=0.326 sec
detected.
B=5 1013 G
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
http://hera.ph1.uni-koeln.de/~heintzma/SNR/SNR1_IV.htm
0802.1242, 0802.1704
Magnetars, field decay, heating
Magnetic fields of NSs are expected to decay
due to decay of currents which support them
Pdot
A model based on field-dependent decay of the magnetic moment of NSs
can provide an evolutionary link between different populations (Pons et al.).
Magnetars
Ohm and Hall decay
τHall depends on B0: τHall ~ 1/B0
M7
PSRs
Fields decay down to ~2 1013 G
Smaller fields decay
by a factor ~2
P
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).
arxiv:0710.0854 (Aguilera et al.)
Extensive population synthesis
We want to make extensive population synthesis studies
using as many approaches as we can to confront theoretical models
with different observational data
 Log N – Log S for close-by young cooling isolated neutron stars
 Log N – Log L distribution for galactic magnetars
 P-Pdot distribution for normal radio pulsars
We make calculations for seven different fields,
which cover the whole range for young objects.
To compare our results with observations we use
six different models of field distribution.
Cooling curves with decay
Magnetic field distribution is more important
than the mass distribution.
Log N – Log S with heating
Log N – Log S for 7 different
Different magnetic field distributions.
magnetic fields.
1. 3 1012 G
2. 1013 G
3. 3 1013 G
4. 1014 G 5. 3 1014 G
6. 1015 G
7. 3 1015 G
[The code used in Posselt et al. A&A (2008) with modifications]
Fitting Log N – Log S
We try to fit the Log N – Log S
with log-normal magnetic field
distributions, as it is often
done for PSRs.
We cannot select the best one
using only Log N – Log S for
close-by cooling NSs.
We can select a combination
of parameters.
Populations and constraints
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
(the task for eROSITA? MAXI?!).
Such limits can be also re-scaled
to put constraints on the number of
the M7-like NSs and the number of
isolated accretors with decayed field.
Lx> 3 1033 erg s-1
[Muno et al. 2007]
Log N – Log L for magnetars
Magnetic field distributions:
with and without magnetars
(i.e. different magnetic field
distributions are used).
7 values of initial magnetic field,
8 masses of NSs.
SNR 1/30 yrs-1.
“Without magnetars” means
“no NSs with B0>1013 G”.
Non-thermal contribution is not
taken into account.
Justified but total energy losses.
Taking into account periods of
transient activity in young
magnetars improves the picture.
Decay parameters and P-Pdot
τOhm=107 yrs
τHall =102/(B0/1015 G)
τOhm=106 yrs
τHall =103/(B0/1015 G)
τOhm=105 yrs
τHall =103/(B0/1015 G)
Longer time scale for the Hall field decay is favoured.
It is interesting to look at HMXBs to see if it is possible
to derive the effect of field decay and convergence.
Realistic tracks and
observational evidence
Kaplan & van Kerkwijk arXiv: 0909.5218
We plot realistic tracks for NS with
masses 1.4 Msolar.
Initial fields are: 3 1012, 1013, 3 1013,
1014, 3 1014, 1015, 3 1015 G
Color on the track encodes surface temperature.
Tracks start at 103 years, and end at ~3 106 years.
Population synthesis of PSRs
Best model: <log(B0/[G])>= 13.25, σlogB0=0.6, <P0>= 0.25 s, σP0 = 0.1 s
Conclusions-1
There are several different populations of neutron stars
which must be studied together in one framework
Population synthesis calculations are necessary
to confront theoretical models with observations
We use different approaches to study different populations
using the same parameters distribution
In the model with magnetic field decay we focused on
log-normal distributions of initial magnetic fields
We can describe properties of several populations
◊ close-by cooling NSs
◊ magnetars
◊ normal PSRs
with the same log-normal magnetic field distribution
Best model: <log(B0/[G])>= 13.25, σlogB0=0.6, <P0>= 0.25 s, σP0 = 0.1 s
We exclude distributions with >~20% of magnetars
Populations with ~10% of magnetars are favoured
Origin of magnetars:
• We present population synthesis calculations of binary systems.
• Our goal is to estimate the number of neutron stars originated
from progenitors with enhanced rotation, as such compact
objects can be expected to have large magnetic fields,
i.e. they can be magnetars.
A question:
Why do all magnetars are isolated?
• 5-10 % of NSs are expected to be
binary (for moderate and small
kicks)
• All known magnetars (or
candidates) are single objects.
• At the moment from the statistical
point of view it is not a miracle,
however, it’s time to ask this
question.
Two possible explanations
• Large kick velocities
• Particular evolutionary path
Generation of the magnetic field
The mechanism of the magnetic
field generation is still unknown.
Turbulent dynamo
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.
Strong field via flux conservation
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:
1. Study of SNRs with magnetars (Vink and Kuiper 2006).
If there was a rapidly rotating magnetar then a huge
energy release is inevitable. No traces of such energy
injections are found.
2. There are few examples of massive stars with field
strong enough to produce a magnetars due to flux
conservation (Ferrario and Wickramasinghe 2006)
Still, these suggestions can be criticized (Spruit arXiv: 0711.3650)
What is special about magnetars?
Link with massive stars
There are reasons to suspect
that magnetars are connected
to massive stars
(astro-ph/0611589).
Link to binary stars
There is a hypothesis that
magnetars are formed in close
binary systems
(astro-ph/0505406,
0905.3238).
The question is still on the list.
AXP in Westerlund 1
most probably has
a very massive progenitor
>40 Msolar.
Progenitor mass for a SGR
0910.4859
The first calculations
An optimistic scenario
We present population synthesis calculations of binary systems
using optimistic assumptions about spinning up of stellar cores
and further evolution of their rotation rate.
We use the “Scenario Machine” code.
Developed in SAI (Moscow) since 1983
by Lipunov, Postnov, Prokhorov et al.
(http://xray.sai.msu.ru/~mystery/articles/review/ +arXiv: 0704.1387)
We run the population synthesis of binaries
to estimate the fraction of NS progenitors
with enhanced rotation.
MNRAS vol. 367, p. 732 (2006)
The model
Among all possible evolutionary paths that result in
formation of NSs we select those that lead to angular
momentum increase of progenitors.
• Coalescence prior to a NS formation.
• Roche lobe overflow by a primary without a common envelope.
• Roche lobe overflow by a primary with a common envelope.
• Roche lobe overflow by a secondary without a common envelope.
• Roche lobe overflow by a secondary with a common envelope.
Results of calculations
Results for the optimistic scenario
• With an inclusion of single stars (with the total
number equal to the total number of binaries) the fraction
of ``magnetars'‘ is ~8-14%.
• Most of these NSs are isolated due to coalescences of
components prior to NS formation, or due to a system
disruption after a SN explosion.
• The fraction of ``magnetars'' in survived binaries is about
1% or lower.
• The most numerous companions of ``magnetars'' are BHs.
Problems and questions
In these calculations we assume that since a star obtained additional
angular momentum, then it is effectively transferred to the core,
and it doesn’t loose in afterwards.
This is too optimistic.
There are three processes (Hirschi et al. 2004, 2005)
• convection,
• shear diffusion,
• meridional circulation
which result in slowing down the core rotation.
Let us consider more conservative scenarios.
GRBs and magnetars
It is important to remember that a similar problem –
necessity of rapid core rotation –
is in explanation of GRB progenitors.
We hypothesize that a similar channel is operating
in binary systems to produce rapidly rotating pre-SN.
If then a BH is born – we have a GRB.
If a NS – we have a magnetars.
The fraction of magnetars among NSs is similar
to the fraction of GRBs among BH-forming SNae.
Astronomy Reports vol. 53, p. 325 (2009)
Model assumptions
Here we consider only tidal synchronization on late stages
(end of helium burning, or carbon burning).
I.e. a core gets additional momentum not long before the collapse.
This is possible only in very narrow systems (Porb<~10 days).
We used two laws for stellar wind
A. Standard wind
C. Enhanced wind for massive stars
(classification following arXiv: 0704.1387)
Different kicks and mass loss
(1) isotropic kick,
type A wind scenario;
(2) isotropic kick,
type C wind scenario;
(3) Kick along the spin axis,
type A wind scenario;
(4) Kick along the spin axis,
type C wind scenario
We can fit the fraction of isolated
magnetars playing with kick distribution.
But these assumptions seem to be
artificial.
Single maxwellian
distribution
Companions
Most of companions are
-main-sequence stars (49%) and
-black holes (46%).
The remaining 5% are roughly
equally divided among:
-white dwarfs (2%),
-Wolf–Rayet stars (1%),
-stars filling their Roche lobes (0.7%),
-helium stars filling their Roche lobes
(the BB stage),
-hot white dwarfs (0.7%),
-neutron stars (0.6%).
Conclusions for the pessimistic
scenario
• We made population synthesis of binary stars to explore
the evolution and products of stars with enhanced rotation
• In the optimistic scenario we easily explain the fraction of
magnetars an the fact that they are isolated
• In a more conservative scenario we need large kicks to explain
the fact that all known magnetars are isolated
• Without detailed data about spatial velocities of magnetars
it is difficult to make conclusions
• Still, it is possible that the channel for magnetar formation is
the same as for GRB-progenitors formation, most probably
in close binary systems
Final conclusions
• It is possible to explain all main types
of neutron stars using one smooth
(log-gaussian) initial magnetic field
distribution in the framework of
decaying fields
• Explaining the origin of magnetars
it is necessary to take into account that
all known AXP, SGRs, …,etc. are isolated
• In the studied models of magnetar origin
from binary companions with enhanced
rotation it is difficult to explain the data
without additional assumptions about kick