Transcript Document

Extensive population
synthesis studies of
isolated neutron stars
with magnetic field decay
Sergei Popov
(SAI MSU)
J.A. Pons, J.A. Miralles,
P.A. Boldin, B. Posselt
Tarusa, May 2009
The old Zoo: young pulsars & old accretors
Diversity of young neutron stars
Young isolated neutron stars
can appear in many flavours:
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 ….
Compact central X-ray sources in
supernova remnants
Cas A
Problem: small emitting area
RCW 103
6.7 hour period
(de Luca et al. 2006)
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
Spectral lines claims
All claims were done for RXTE observations (there are few other candidates).
All detections were done during bursts.
1E 1048.1-5937 Gavriil et al. (2002, 2004) 4U 0142+61 Gavriil et al. (2007)
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
http://www.physics.mcgill.ca/~pulsar/magnetar/main.html
The newest SGR
The most recent SGR candidate
was discovered in Aug. 2008
(GCN 8112 Holland et al.)
It is named SGR 0501+4516.
Several recurrent bursts have been
detected by several experiments
(see, for example, GCN 8132 by
Golenetskii et al.).
Spin period 5.769 sec.
Optical and IR counterparts.
SWIFT
P=5.7620690(1) s
Pdot=7.4(1)E-12 s/s
Pdotdot=-4.3(1.1)E-19 s/s^2
Israel et al. ATel #1837 (11 Nov)
QPOs after giant flares
A kind of quasi
periodic oscillations
have been found
in tail of two events
(aug. 1998, dec. 2004).
They are supposed
to be torsional
oscillations of NSs,
however, it is not clear,
yet.
(Israel et al. 2005 astro-ph/0505255,
Watts and Strohmayer 2005 astro-ph/0608463)
See a recent review in aXiv: 0710.2475
Extragalactic SGRs
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. 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]
Transient radio emission from AXP
ROSAT and XMM images
an X-ray outburst
happened in 2003.
AXP has spin period 5.54 s
Radio emission was detected from XTE J1810-197
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/0605429)
Another AXP detected in radio
1E 1547.0-5408
P= 2 sec
SNR G327.24-0.13
Pdot changed significantly on the scale of just
~few months
Rotation and magnetic axis seem to be aligned
Also these AXP demonstrated weak
SGR-like bursts (Rea et al. 2008, GCN 8313)
Radio
[simultaneous]
X-rays
0802.0494 (see also arxiv:0711.3780 )
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
Bursts from the
transient
PSR
Chandra: Oct 2000
June 2006
Gavriil et al. 0802.1704
Mysterious bursts of
SWIFT J195509.6+261406
Optical bursts which is some sense
similar to magnetars weak X-ray bursts.
[Stefanescu et al. arXiv:0809.4043]
See also arXiv: 0809.4231.
Periodicity ~7 sec is suspected.
However, in our opinion, this can be
not a magnetar, but a magnetic WD.
Optic vs. X-ray, longer time scales,
lower energies etc.
[Kaslival et al. arXiv: 0708.0226]
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
The isolated neutron star candidate
2XMM J104608.7-594306
A new INS candidate.
B >26, V >25.5, R >25
(at 2.5σ confidence level)
log(FX/FV) >3.1
kT = 118 +/-15 eV
unabsorbed X-ray flux:
Fx ~1.3 10−12 erg s−1 cm−2
in the 0.1–12 keV band.
At 2.3 kpc (Eta Carina)
the luminosity is
LX ~ 8.2 1032 erg s−1
R∞ ~ 5.7 km
M7-like? Yes!
[Pires & Motch arXiv: 0710.5192 and Pires et al. 0812.4151 ]
Discovery of
radio transients
McLaughlin et al. (2006) discovered a new type of sources– RRATs
(Rotating Radio Transients).
For most of the sources periods about few seconds were discovered.
The result was obtained during the Parkes survey of the Galactic plane.
These sources can be related to The Magnificent seven.
Thermal X-rays were observed from one of the RRATs
(Reynolds et al. 2006). This one seems to me the youngest.
P-Pdot diagram for RRATs
McLaughlin et al. 2006 Nature
Estimates show that there should
be about
400 000
Sources of this type in the Galaxy.
Young or old???
Relatives of the
Magnificent seven?
(astro-ph/0603258)
RRATs. Recent data
X-ray pulses overlaped on
radio data of RRAT J1819-1458.
(arXiv: 0710.2056)
RRATs
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11 sources detected in the Parkes Multibeam survey
(McLaughlin et al 2006)
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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)
Some of sources appeared to be radio pulsars
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.
NS birth rate
[Keane, Kramer 2008, arXiv: 0810.1512]
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.
Are SGRs and AXPs brothers?
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Bursts of AXPs
(from 6 now)
Spectral properties
Quiescent periods of
SGRs (0525-66 since
1983)
Gavriil et al. 2002
Unique AXP bursts?
Bursts from AXP J1810-197. Note a long exponential tail with pulsations.
(Woods et al. 2005)
RRATs
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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 ?
Some RRATs are radio pulsars
New discussion about birth rates in Keane, Kramer arXiv: 0810.1512
Magnetars, field decay, heating
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
M7
PSRs
P
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.
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/9707318
It is important to look at old sources,
but we have only young ….
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:0710.0854 (Aguilera et al.)
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: 0710.4914 (Aguilera et al.)
Magnetic field vs. temperature
The line marks balance
between heating due to
the field decay and cooling.
It is expected that a NS
evolves downwards till it
reaches the line, then the
evolution proceeds along
the line:
1/2
Teff ~ Bd
Selection effects are not
well studied here.
A kind of population
synthesis modeling is
welcomed.
(astro-ph/0607583)
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
Cooling curves: field dependence
Cooling curves: mass dependence
Fields and models
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.
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
2. 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]
Statistical fluctuations
For each model we run
5000 tracks all of which
are applied to 8 masses,
and statistics is collected
alone the track with
time step 10 000 years
till 3 Myrs.
However, it is necessary
to understand the level
of possible fluctuations,
as we have the birth rate
270 NSs in a Myr.
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 inital 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.
Transient magnetars at youth
Young magnetars can be
transient sources.
In the model we use
we cannot take this into
account self-consistently.
We can make a simple test.
Clearly, transient periods
at youth help to have
more bright magnetars.
P-Pdot diagram and field decay
Let us try to see how
PSRs with decaying
magnetic fields evolve
in the P-Pdot plot.
At first we can use
a simple analytical
approximation to the
evolutionary law for
the magnetic field.
τOhm=106 yrs
τHall=104/(B0/1015 G) yrs
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
Using the model by Pons et al.
(arXiv: 0812.3018) 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
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