HIGH MAGNETIC fiELD NSS
IN BINARY SYSTEMS
Sergei Popov
2201.07507
WHAT DO WE CALL “A MAGNETAR”?
Is it just a neutron star with a strong magnetic field?
Or it is necessary to have dominance of magnetic energy release
in the total energy budget of the source?
Or, we are speaking about the same object, but at different stages of evolution?
DO WE EXPECT MAGNETARS IN BINARIES?
All know Galactic SGRs/AXPs are single sources Field decay might result in absence of older magnetars
McGill on-line catalogue lists ~30 magnetars.
All of them are isolated objects.
However, an existence of a binary companion
(except cases of accretion on a compact object)
hardly can prevent detection of an SGR flare,
and the expected number of NSs in binaries
is not as small as ~3%.
Observations and theoretical
models favour magnetic field
decay.
Evolution is faster for higher
fields due to Hall cascade.
Characteristic time scale for decay of magnetars’ field
is at least less than ~few thousand years.See, however,
2204.09701
2203.14947
WHO IS KILLING MAGNETARS?
To have reasonable number
of magnetars in e.g.
X-ray binaries we need
to terminated field decay
while fields are relatively high,
as typical ages of binaries
are large in comparison
with the decay time scale.
STOP HALL AND
SLOW DOWN OHM!
ORIGIN OF MAGNETARS FIELD
Generated Fossil
Classical dynamo scenario starting from DT in 90s Critisized by Spruit (2008)
DYNAMO MECHANISM CONDITIONS
Rapid initial rotation is necessary
to produce large dipolar fields!
P0~ few msec
This is difficult to achieve due to slowdown of
a stellar core rotation (Heger et al. 2004, Meynet, Maeder 2005).
The same problem appear in GRB scenario.
In several recent studies fallback is used to spin-up the compact object.
Stellar rotation can be enhanced only in binaries.
In binaries there are different possibilities
to gain additional angular momentum
due to mass transfer or tidal interaction.
We need to perform population
synthesis calculations.
A QUESTION:
• 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.
Why do all magnetars are isolated?
Two possible explanations
• Large kick velocities
• Particular evolutionary path
BINARY EVOLUTION CHANNELS.
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.
This is an optimistic scenario, as it is assumed that angular momentum
is not lost in significant amount after it has been gained
(astro-ph/0505406)
OBSERVATIONAL EVIDENCE
0910.4859
There are several cases where
observations favour magnetar birth
in binary systems
ANOTHER CASE
1405.3109
ORIGIN OF MAGNETARS IN BINARIES
The mechanism of the magnetic
field generation is still unknown.
α-Ω dynamo (Duncan,Thompson)
α2 dynamo (Bonanno et al.)
or their combination
If a dynamo mechanism is operating
then it is necessary to have
rapid rotation to produce
large dipolar field.
Three possibilities to spin-up a star during evolution in a binary:
1) Spin-up of a progenitor star in a binary by accretion;
3) Spin-up of a progenitor star via synchronization;
2) Coalescence of binary companions prior to a compact object formation.
Popov,Prokhorov2006
We obtained ~10% of magnetars (i.e., NSs from spun-up progenitors),
but among these NSs only ~1% are in survived binaries.
And, of course, all magnetars formed in NS+NS or NS+WD coalescence are isolated.
MAGNETIC FIELD AMPLIFICATION IN BINARIES
1910.14058
magnetic star τ Sco – result of coalescence
If all of the magnetic flux is conserved
until core collapse of the merger product,
a resulting neutron star of 10 km radius would have
a surface magnetic field strength of about 1016 G.
9 Msun +8 Msun
WHY DO WE NEED MAGNETARS, SOMETIMES?
Large luminosity Spin properties
If an accretion column is formed than the luminosity
can exceed the Eddington (Basko, Sunyaev 1975, 1976).
Large magnetic fields can result in:
- Long spin periods;
- Rapid spin-down;
- Rapid spin-up;
- Accretor/Propeller transitions
even for relatively large accretion rates.
Lipunov
+ FRBs with
long periodicity?
2003.03596
ULTRALUMINOUS X-RAY PULSARS
ULX scheme
Fabrika et al.
2105.10537
Bachettietal.2014
2105.10537
ACCRETING MAGNETARS
1709.10385
Typically magnetic fields of neutron stars in accreting X-ray binaries are estimated with indirect methods.
• Spin-up
• Spin-down
• Equilibrium period
• Accretion model
• …….
FIELD ESTIMATES BASED ON SPIN PROPERTIES
There are many classical and modern approaches to estimate NS’s magnetic field from spin properties.
[See, eg. Chashkina&Popov 2012, Klus et al. 2014, Ho et al. 2014, Shi et al. 2015, Igoshev&Popov2018
and references to classical papers by Ghosh&Lamb, Davidson&Ostriker and many others therein.]
1. Equilibrium.
A) disc accretion B) wind accretion
2. Spin-up. 3. Spin-down.
Many more equations exist to estimate magnetic fields using spin and its derivatives (e.g. Shi et al. 2015).
Typically, only dipolar component can be estimated.
E.g., 4U 0114+65, 4U 2206+54, SXP 1062, Swift J0451 were proposed as accreting magnetars.
SETTLING ACCRETION HELPS AGAINST MAGNETARS
Shakuraetal.1302.0500
~10
Postnov,Shakuraetal.1307.3032
Typically, for wind-accreting systems
long spin periods lead to
high magnetic field estimates
(e.g., Klus et al. 2014): However, for the settling accretion model
which is valid for low accretions rates
the field estimate is much lower:
FIELD DECAY IN HMXBSChashkina,Popov(2012)
It is possible to use HMXBs to test models of field decay
on time scale >1 Myr (Chashkina, Popov 2012).
We use observations of Be/X-ray binaries in SMC
to derive magnetic field estimates,
and compare them with prediction of the Pons et al. model.
SXP 1062
A peculiar source was discovered in SMC.
Be/Xray binary, P=1062 sec.
A SNR is found. Age ~104 yrs.
(1110.6404; 1112.0491)
Typically, it can take ~1 Myr for a NS
with B~1012 G to start accretion.
SXP 1062
A crucial thing for studying
magneto-rotational evolution
is to have an independent age estimate.
In the case of HMXBs an interesting source
with known age is SXP1062
(H´enault-Brunet et al. 2012, Haberl et al. 2012).
B0=
4 1014, 1014,
7 1013, 4 1013,
1013 G
arXiv:1112.2507
We were able to reproduce
properties of SXP 1062 assuming
a magnetic field decay.
I.e., initially the NS was a magnetar
but now it has s standard
magnetic field.
The crucial element of this model is
the new accretion model by
Shakura et al. (2013).
BURSTS FROM LS I +61 303
Torresetal.1109.5008
Another burst was detected by Swift
in 2012 (Burrows et al. 2012).
Spin period 0.27 s (2203.09423)
LS I 62 303 - the only example of
a magnetar-like activity in a binary system.
Low luminosity (2 1037 erg/s) can point
towards relative low field (<1014G)
LS 5039 can be another magnetar
in a gamma-ray binary
if pulsations and the Pdot value
are confirmed (Yoneda et al. 2009.02075).
No bursts, but system similar to LS I +61 303.
HOW TO MAKE AN ACCRETING MAGNETAR?
Igoshev,Popov1709.10385
Three conditions are necessary:
1. Hall attractor;
2. Rapid cooling of the crust;
3. Low values of Q.
Hall attractor:
Gourgouliatos, Cumming 1311.7004
HALL CASCADE AND ATTRACTOR
Hall cascade can reach the stage of so-called Hall attractor,
where the field decay stalls for some time (Gourgouliatos, Cumming).
The system is trying to relax towards a state of isorotation, with the electron fluid having the
same angular velocity on a poloidal field line.
EVOLUTION OF DIFFERENT COMPONENTS
1311.7004
Hall attractor
mainly consists of
dipole and octupole
INDEPENDENT STUDIES OF THE HALL CASCADE
1501.05149
New calculations support the idea of a kind of stable configuration.
See also 1604.01399
CORE AND CRUST FIELD EVOLUTION
1709.09167
Hall attractor is confirmed.
Q=10
τHall=104yrs (1015 G/B)
τOhm=2 106 yrs/Q
PARAMETERS OF ULX M82 X-2
1709.10385
SEARCHING FOR EVIDENCE. I. CYCLOTRON LINES
Brightmanetal.1803.02376
ULX in M51
If electrons cyclotron – then B~ 6 1011 G.
But the line is too narrow.
If proton cyclotron – then B~ 7 1014 G.
NGC 300 ULX
Electron cyclotron lime: B~1012 G.
Waltonetal.1803.07571
SEARCHING FOR EVIDENCE. II. MAGNETAR ACTIVITY
Konus-Wind
HMHT-insight
Integral
Agile
Fermi
Swift
Continuous monitoring of high energy flares
is going on thanks to many space detectors.
THE FIRST EXAMPLE?
Doroshenkoetal.2101.10834
SGR 0755−2933
One 30 msec burst detected by Swift in 2016
Coincident with a HMXB.
Swift localization
HMXB
See 2302.00027 about the evolution of this system
(UNCERTAIN) CONCLUSIONS
Important for:
- origin of magnetars;
- field evolution;
- accretion physics;
- FRBs.
Perspectives:
Detection of activity – ultimate proof
for REAL magnetars in binaries.
Are there relatively old (few Myrs) NSs
with large fields, but no magnetar-like activity?
Still, we are not sure
if there are magnetars
in binary systems.
Some evidence exists,
but definite proof is lacking.
Also, formation mechanism and
evolution are uncertain.
2201.07507