Magnetic and emission from magnetars

Andrei Beloborodov Columbia University Magnetars

• strong and evolving B • large variations in emission and spindown

• internal + external heating

• energy budget E ~ t L ~ 1047 −1048 erg Building up magnetic stresses

Hall drift

Goldreich Reisenegger (1992)

ambipolar diffusion

Observed quasi-thermal surface emission

Kaminker et al. (2009)

heating in the outer crust is required with E! ~ 1036 −1037 erg/s Crustal motions and internal heating

• No cracks

• No slippage except along magnetic flux surfaces

• Collapse of ideal crystal? (Chugunov, Horowitz 2010) • Plastic flow (motion of dislocations) heating q! = σ s!

is conducted toward the core and surface (Kaminker et al. 2009; Jose Pons) • QPOs (externally triggered) External (magnetospheric) dissipation Sun

Recorded in extreme ultraviolet from NASA’s Transition Region and Coronal Explorer satellite.

Sun: convective motions twist the anchored to the surface

Dissipated/radiated : L = I Φ vacuum: I = 0 force-free: Φ = 0

Voltage regulated by e+- discharge Φ ~ 109−10V

surface : !ω ~ 3kT ~ 1 keV

B 2 Landau energy: !ωB = mec BQ

3 4 resonant scattering: γω ≈ ωB when γ ~ 10 −10 (σ res ≈ πreλ) 2 + − scattered photon: E ~ γωB ~ γ ω → e + e Magnetosphere

Twisted c j = ∇ × B ≠ 0, j || B force free 4π (cf. solar corona)

Filled with plasma

Dynamic -- Changing (spindown)

-- Changing pulse profiles

-- Bursts Flares δt ~ 0.1-0.3 s

Starquake?

Excitation of Alfven waves on field lines with length > cδt

Reconnection in the magnetosphere?

(Thomspon, Duncan 1996) Twisted magnetospheres and flares

Parfrey et al. 2013 Twist energy

W = W0 for untwisted dipole

Loss of magnetic equilibrium and reconnection

Parfrey et al. (2013)

SGR 1900+14 Observed “anti-glitch” in SGR ……

“anti-glitch”

Woods et al. (1999) Anti-glitch in 1E 2259+586

Archibald et al. (2013) Transient magnetars Crustal cooling? Lyubarsky et al. (2001)

Decay of magnetospheric activity? Beloborodov (2009)

Gotthelf, Halpern (2007) Untwisting magnetosphere XTE J1810-197

Untwisting magnetosphere

time units: µ t = 0 cRΦ

−1 tev ≈ 0.4 Φ10 B14 A12 yr ∂ψ ∂Φ = c ∂t ∂f

(hot spot area) Hard X-ray emission

AXP 4U 0142+61

Den Hartog et al. (2008) AXP 4U 0142+61

Den Hartog et al. (2008) Magnetospheric plasma

discharge: e+, e− injection, 36 −1 L± ~ IΦ ~ 10 erg s

the star emits thermal radiation, L ~ 1035 erg s−1

radiation controls the e± flow Relativistic e+- outflow

B γ ≈ 100 BQ

Beloborodov (2013) [mec] pair creation

B γ ≈ 100 BQ + h e− νsc

γ >> 10 keV γ ∼ 1 Lann ~ 0.1L keV

γ >> 10 e+ − hνsc

B B γ ≈ 100 , radiative zone: B < Q ≈ 1013 G BQ 4 Spectrum radiated by the decelerating outflow

Spectrum variation with inclination Observational test: phase resolved spectra Possible radio emission mechanism

Radiative drag tends to “lock” >> 1 particle velocity β

Electric current (two-fluid outflow model)

Dynamic equation

Two streams with different β => instability

Beloborodov (2013) Summary

Internal dissipation:

no cracks, plastic flow of the crust

(=> externally triggered QPOs)

External dissipation:

(a) Flares: reconnection (+ Alfven wave cascade)

(b) Persistent emission: e+- discharge => hard X-rays “radiative locking” => radio