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}
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?
\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
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
Incoherent synchrotron
Magnetar Environment
r_s \approx \sqrt{L_{sd}/4\pi pc} \approx 10^{15} \, \rm cm
Where exactly does the shock occur?
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?
FRBs and Magnetars
By almog yalinewich
