PHYS 777
Plasma Physics and Magnetohydrodynamics (MHD)
Instructor: Gregory Fleishman
Radio Emission from acceleration
sites of the solar flares
Yixuan Li
motivation
There are various acceleration models
of solar flares which imply the different
radio spectra and light curves.
 We calculate the radio emission in DSR
(Diffusive Synchrotron Radiation) and
GSR (Gyro-synchrotron Radiation)
models to make them observationally
distinguishable.

Cartoon of a flare model suggesting a global view of
acceleration and evaporation processes.
The acceleration site is located in a low-density cusp from
where electron beams are accelerated in upward and
downward directions.
Diffusive Synchrotron Radiation
The electron is trapped by the turbulence on the flare loop-top.
Derived under isotropic random magnetic field and nonrelativistic particles.
Some properties of the acceleration site
(a)
(b)
(c)
(d)
(e)
the size of the site
;
the electron number density
;
the electron temperature
;
the energy density of the magnetic turbulence
;
the power law index δ changing as arctan function from 7 ∼ 3
the break energy Ebr linearly increased from 50 ∼500KeV
The electron distribution remains a Maxwellian distribution
when energy is smaller than E0 and a nonthermal electron tail
begins to form as power law distribution when energy is larger
than E0 ,here E0=4KT.
Radio Power
The DSR radiation
power in different δ
under three different ν.
The blue curves indicate
larger δ, while the red
ones show smaller δ.
Flux observed on
the Earth
here
The DSR spectra in different
temperatures
Gyro-synchrotron Radiation
Fig. on left. Formation of contracting magnetic
traps in the solar corona during a flare. (a) The
magnetic field configuration: the reconnection
region (RR) is located above the closed magnetic
field loops that rest on the chromospheres (CHR).
(b) The schematic view of a magnetic trap.
The number of electrons in a trap
Bm : the magnetic field strength at the footpoint.
The initial condition
We assume the initial condition as follow:
(a) the magnetic field strength B = 30G;
(b) the minimum energy Emin = 0.01MeV,
the maximum energy Emax = 1MeV;
(c) the thermal electron density
the non-thermal electron density
(d) the source size
.
;
The upper panel:
the spectra in
frequency range
1GHz~100GHz ;
The lower panel:
the spectra in
frequency range
0.1GHz~10GHz
Klein’s
Computation Code
for GSR is used.
The light curves of the emission at some fixed frequencies
Discussion

Synchrotron emission: The
emission comes in narrow pulses at the
cyclotron frequency, beamed along the
direction of motion. The pulses contain
many harmonics.
 Gyro-synchrotron emission: The
lines become broader ,so that they
blend together into a continuum
emission.