Almog Yalinewich - Pulsar Coffee 12.6.20

 

Plan of the Talk:

 

  • Previous Observations
  • Recent Observations
  • Implications for magnetar models
    • Interior models
    • Exterior models

 

Previous Observations

SGR 1806-20

Mini EMP from SGR 1806-20

on 21:30:26.5 UT, Dec 27, 2004

10^{46} \, \rm erg

10% of the magnetic energy

SGR 1806-20 - Afterglow

Recent Observations

Transient

Radio Component

400-800 MHz band

two 5ms bursts separated by 30ms pause

\rm{DM} =332.81 \, \rm pc\, cm^{−3}

8 second delay after x ray

Fluence: 6 MJy ms

X Ray Component

X Ray Component 2

Fluence 6.8e−7 erg /cm^2

Energy 8e38 erg

Peak photon energy 70 keV

\eta = \frac{E_r}{E_x} = 10^{-5}

Magnetars are terribly inefficient at producing FRBs

Luminosity 5e40 erg/s

SGR 1935-20

Mature magnetar originally detected in X ray by swift

P \approx 3.2 \, \rm s
\dot{P} \approx 1.43 \cdot 10^{-11}
P/2\dot{P} \approx 3600 \, \rm y
B \approx 2.2 \cdot 10^{14} \, \rm G
L_X \approx 1.7 \cdot 10^{34} \rm erg/s

SNR G57.2+0.8

Distance 6.6kpc

Age 1.6e4

Precision 10%

Comparison to other Magnetar Flares

Suppression of Compton Scattering in Strong Magnetic Fields

m \frac{d v}{d t} = q E + q \frac{v}{c} \times B

E oscillating, B static, both mutually orthogonal

|v| \approx \frac{q E}{m \omega_B}
|a| \approx \frac{q E \omega_E}{m \omega_B}
L \propto a^2
\sigma \approx \sigma_0 \left(\omega_E/\omega_B\right)^2

Magnetic Eddington Limit

\frac{L_m}{L_e} \approx \frac{F_m}{F_e} \approx \left(\frac{\omega_B}{\omega_E}\right)^2
\omega_E \approx \frac{k T}{\hbar} \approx \frac{k}{\hbar} \left(\frac{F_m}{\Sigma}\right)^{1/2}
\frac{L_m}{L_e} \approx 2 \left(\frac{B}{10^{12} \, \rm G}\right)^{4/3} \left(\frac{g}{2 \cdot 10^{14} \, \rm cm/s^2}\right)^{-1/3}

Paczynski 1992, Hamada & Kanno 1974

Implications for Models

Occurance Rates

Is the radio transient part of the population of previous FRBs?

Lifetime

E_{mag} \approx 3 \cdot 10^{49} \left(\frac{B}{10^{16} \, \rm G}\right)^2 \, \rm erg

Energy budget

Time averaged radio luminosity

E_{rad} \approx 5 \cdot 10^{34} \rm \, erg/s

Lifetime

\tau \approx \frac{E_{mag}}{\dot{E}_{rad}/\eta} \approx 200 \left(\frac{B}{10^{16} \, \rm G}\right)^2 \left(\frac{\eta}{10^{-5}}\right) \rm \, y

No galactic magnetar is as potent as cosmic FRB sources

 

Exotic formation channel? (SLSNe, AIC)

Event Rate

Prospect for Extragalactic Detection

Energy Distribution

\lambda \left(>E\right) \propto \left(E/E_{min}\right)^{-\gamma}

Theoretical Models

Low Twist Model

Why is it important that the twist is low?

Wadiasingh & Timokhin 2019, Thompson et al 2001

\rho_{\rm burst}>\rho_{\rm twist}

otherwise burst is masked

Transient Features

Time changing linear polarisation angle

Simultaneous x ray and radio

Blackbody x ray spectrum

Comparable energy in X rays and radio

Other Magnetospheric Models have similar Issues

curvature radiation

Outflow interaction with the magnetosphere

Spindown models

Similar X -ray and radio energies

changes in period?

Synchrotron Maser Blast Wave

Coherent Emission

Stimulated Emission

Antenna emission

Synchronisation

Chu 2004

Cyclotron Maser in Relativistic Shock waves

Precursor wave

Suppression of Low Frequencies

Relativistic cyclotron frequency

The reason such low frequencies were never observed is that they are up - scattered by induced Compton

X-Ray Emission from Shocks

Lyubarksi 2014,  Metzger et al 2019, Margalit et al 2019

Incoherent synchrotron

Magnetar Environment

r_s \approx \sqrt{L_{sd}/4\pi pc} \approx 10^{15} \, \rm cm

Where exactly does the shock occur?

Lyubarksi 2014

Metzger et al 2019

At the nebula - remnant interface

Lower radio to X-ray luminosity ratio compared to FRB200428

Collision with previously ejected material

can be made to fit X-ray to luminosity ratio

Model Postdictions

Conclusion

Association of SGR1935-20 with other FRBs is inconclusive

 

Magnetar models where the emissions happens inside the magnetosphere produce a radio to X-ray luminosity ratio that is too high

 

Shock wave at the nebula - remnant boundary produce a ratio that is too small

 

Internal shocks can reproduce this ratio and also the peak X-ray photon energy

questions?

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