Wind braking of pulsars and
magnetars
H. Tong ( 仝号 )
Xinjiang Astronomical Observatory, Chinese
Academy of Sciences
Homepage: www.escience.cn/people/tonghao
Collaborators: R. X. Xu, L. Li, F. F. Kou et al.
2015.9
Based on: Tong arXiv:1506.04605
Pulsar
• Pulsar=rotating magnetized neutron star
• Pulsars are good clocks
• Why they are good clocks: (1)radiation;
(2)spin down
Magnetars
Pulsars are slowing down
Tong & Wang (2014)
Generic picture
1.Pulsars have a magnetosphere, where
there is particle acceleration and
subsequent radiation process--> pulse
profile
2.When flowing out, this particle component
will also take away the rotational energy of
the pulsar --> spin down
• Dipole radiation+particle component: wind
braking model (Xu & Qiao 2001; Kou &
Tong 2015)
Wind braking of magnetars
Tong, Xu, Song & Qiao 2013
Citations: 33
Various winds
1. Solar wind
2. Stellar wind: Wolf-Rayet star -->Ib,Ic SNe;
HMXBs (wind accreting NSs)
3. Wind of pulsars and magnetars: detailed
in below
Magnetic dipole braking of pulsars
• Rotating (perpendicular) dipole in vacuum
• Only as crude approximation to the real
case (Goldreich & Julian 1969, Ruderman
& Sutherland 1975)
• It is only a pedagogical model
• The characteristic magnetic field and age
are just very crude estimations
Pulsar magnetosphere
(Goldreich & Julian 1969)
Goldreich-Julian density
Steady state: no Lorentz force
Meaning of GJ density
1. Difference between positive and negative
charges
2. Only valid for a static magnetosphere
3. If actual charge density derivatives from
GJ density: particle acceleration
(polar gap; free flow; outer gap; annular
gap etc)
4. Problem: What's the actual charge
density?
wind braking of normal pulsars
• Pulsars as oblique rotators: magnetic dipole
radiation+particle wind (rotation-powered)
• Effects:
• braking index (Xu & Qiao 2001; Wang+ 2012; Kou & Tong
2015)
• Variable timing (Kou, Ou & Tong 2015)
• timing noise (Lyne+ 2010; Liu+ 2011)
• a rotation-powered PWN
• Exist: intermittent pulsars (Kramer+ 2006; Li+
2014 )
Wind braking of puslars (II)
Rotational energy loss rate:
Vacuum gap model (Ruderman & Sutherland 1975):
Intermittent pulsars B1931+24
(Kramer+ 2006)
The 2nd intermittent pulsar
J1841-0500
Camilo+2012:
More transient pulsars?
The 3rd intermittent pulsar
J1832+0029
Lorimer+2012:
1. Arecibo obs during off state
2. Arecibo obs during on state:
Polarization & emission geometry
(in the future)
3. Spontaneous X-ray obs:
Negative at present
The 4th intermittent pulsar
J1839+15
Surnis+2012 (GMRT):
More transient pulsars?
Summary of observations: off time
1. B1931+24: 30d
2. J1841-0500: 580d
3. J1832+0029: 650d/850d
4. J1839+15: 278d
A continuous distribution of “off-time”?
from nulling to RRATs to intermittent pulsars
Summary of observations: spindown ratio
1. B1931+24: nudot_on/nudot_off=1.5
2. J1841-0500: 2.5
3. J1832+0029: 1.8
4. J1839+15:
Theoretically:
the spindown ratio depends on the magnetic inclination angle,
which may be tested by future Arecibo & FAST observations
& different braking index predictions (Li et al. 2014)
Wind braking model for the spin down behavior of intermittent pulsars
Li et al. 2014
Improving the wind braking
model


Inconsistencies in the original wind
braking model
Improvements (Kou & Tong 2015):
1. Particle density (consistent with inclination
angle observations)
2. Pulsar death (long term evolution)
Evolution of pulsars on the P-Pdot diagram (for the Crab pulsar)
Kou & Tong 2015
Marshall et al. (2015)
Increase of spin down rate by 36%
<--due to a stronger particle wind
Varying particle wind result in a varying spin down rate
Kou, Ou & Tong 2015
Magnetars



Magnetars=AXPs/SGRs
Magnetars are always variable
Variable timing behavior of several
sources: SGR 1806-20,
radio-loud magnetar (PSR J1622-4950),
1E 1048.1-5937
Restless magnetars SGR 1806-20:
Woods et al. (2007)
bursts
A period of enhanced
spindown
Restless magnetars
PSR J1622-4950 (Levin et al. 2012)
Repeated delayed torque variations in 1E 1048
Archibald et al. (2015)
Wing braking of magnetars
(Tong+ 2013)
• In summary
• Magnetism-powered particle wind
• When Lp >> Edot, a much lower magnetic
field (plus higher order effects, magnetar
case)
1.
2.
3.
4.
My previous works: pulsar
timing
small inclination angle--> higher B for SGR 0418+5729
(2012)
Decreasing wind luminosity-->decreasing Pdot of Swift
J1822 (2013)
Stronger particle wind during the observational interval->net spindown (i.e. anti-glitch, 2014)
Geometry for the spindown of the Galactic center magnetar
(2015)
Anti-glitch of magnetar
1E 2259+586

Archibald+ (2013), Nature
14 days interval
Anti-glitch
Anti-glitch in the wind braking scenario
(Tong 2014)
1.Due to an enhanced particle wind
2.Anti-glitch always accompanied by
radiative events
3.No anti-glitch, but a period of enhanced
spindown

Future anti-gltich without radiative event
or a very small timescale can rule out the
wind braking model
Unification in the wind braking
model


Wind braking of pulsars and magnetars
Unified explanations of Crab braking
index, variable timing of B0540 & J1846,
intermittent pulsar, and anti-glitch in
magnetars, variable timing of magnetars
etc
Discussions


More works in the wind braking model
Fundamental questions:
(1) Trigger of magnetospheric activities:
glitch? (as happened in J1846 and
magnetars)
(2) Trigger of intermittent pulsar on and off,
magnetar transient radio etc: fallback disk
(as in swinging pulsars)?
(3) Relationship between observations
different wavelength etc: positive
correlation or negative correlation?
Conclusions: Wind braking of pulsars and
magnetars
• Magnetic dipole braking:
perpendicular rotator in vacuum; must be wrong;
correct to the 1st order approximation (1969); only a
pedagogical model
1. Wind braking of pulsars:
2nd order effect (braking index, noise); 1st order effect
seen in intermittent pulsars (2006), variable timing
(2015)
2. Wind braking of magnetars:
Pdot variation during the persistent state (several
times); Pdot variation during the outburst (up to 100
times)

Correlations between the timing and radiative events
(for both magnetars and normal pulsars; big
telescopes are needed for this process)