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					 Fine temporal and spatial
structure of the microwave
     emission sources
from the SSRT and NoRH
        observations
  Altyntsev A. T., Kuznetsov A.A., Meshalkina N.S.


      Institute of Solar-Terrestrial Physics, Irkutsk, Russia
    The great advantage of radio observations is the study
            of the shortest events in solar activity
     The bursts with fine temporal and spectral structure, SSP
     (with duration < 1 s), are of particular interest as they are
     directly connected with the processes of energy release at
     small temporal and spatial scales. Second, they can be used as
     a probe sources to study propagation effect in the low corona.
     The main goal: to verify emission mechanisms using observations
     with high temporal, spatial, and spectral resolution

     First observation with 1D resolution (Owens Valley):
     Gary D.E., Hurford G.J., Flees D.J. ApJ., 369, 255-259, 1991

•    20 ms, 2.8 GHz, beamwidth 28
•    location: overlying a large sunspot, polarization up to 80%
•    electron-cyclotron maser mechanism?
•    the same 1D-location of different pulse sources (within 1)
Ten years' anniversary of the first publications
         NoRH team: 50 ms, 17 GHz, 10 (2D)
    Takano T., the Nobeyama Radioheliograph Group
           8th Int. Symp. on Solar Terrestrial
              Physics, PD1-048, 36, 1994
                         Results:
     Size < 2, location - footpoints of the flare loop

         SSRT team: 56 ms, 5.7 GHz, 15 (1D):
        Altyntsev A.T. et al. A&A, 1995, 303, 249
                         Results:
      Height of the source - up to 35 thousand km,
                apparent size - up to 40,
      plasma emission, scattering in the low corona
Altyntsev A.T., Nakajima H., Takano T., Rudenko G.V.
       Solar Physics, v. 195, Issue 2, p. 401-420 (2000)
Altyntsev A.T., Grechnev V.V., Nakajima H., et al.
       Proc. of Nobeyama Symp. 1998, p. 283


Simultanious observations of the subsecond structures in hard X-
rays (BATSE), at 17 GHz (NoRH) and 5.7 GHz (SSRT).
Two types of the subsecond brightenings:
•Events with the pulse-to-pulse correlation:
Gyrosynchrotron emission generated by directly precipitating
electrons (100-200 keV) from tiny regions close to footpoints.
•Events with the poor correlation:
Coherent plasma emission seems more credible explanation.
                                         Spectral and spatial observations(SSRT, NAOC)

                  August 21, 2002/SSRT/Flux Intensity and Polarization                            Siberian Solar Radio Telescope / North-South / Intensity
                                                                                                                                                                      21 August 2002
                                                                                                                                                                        (04:02:45.5)
                                                                                                                               Burst
                                                                                                                                                             Left: Time profiles from


                                                                         Size, arc min
                                                                                                                                                             SSRT - I & V, interval 6
                                              Intensity (R+L)                                                                                                sec, 14 ms data from NS
                                                                                                                                                             interferometer.
                                                                                                                   Spikes                                    Right:
Arbitrary units




                                                                                                                                                             Top: series of SSRT scans.
                                                                                                     Solar Radio Spectrometer / 5.2-7.6 GHz / Intensity
                                                                                                                                                             The scan length is 240.
                                                                                                                                                             Maximum brightness -
                                                                                                                                                             white.
                                                                                 Frequency, GHz




                                                                                                                                                             Bottom: dynamic spectrum
                                                                                                                                                             (5.2-7.6 GHz) from the
                                                                                                                           SSRT frequency band
                                            Polarization (R-L)                                                                                               Huairou station (NAOC,
                                                                                                                                                             China) corresponding to this
                                                                                                                                                             event. Dashed horizontal
            04:02:45.5             04:02:48.5           04:02:51.5                                                       Time, UT                            lines mark SSRT frequency
                                    Time, UT
                                                                                                                                                             band.
                                     30 March 2001
a: dynamic spectrum in intensity,
b: RCP & LCP time profiles from the spectropolarimeter,
c, d: RCP & LCP time profiles at two frequencies recorded with SSRT simultaneously.




  •   High agreement between the time profiles                    
  •   Mean drift velocity and the standard deviation is 9.6 GHz/s
  •   The band of the instantaneous spectrum varies from 1 to 3%
30 March 2001
 Structure of microwave sources
 (SSRT, NoRH, Yohkoh)

 Altyntsev et al., The 10th European
 Solar Physics Meeting, Prague, 2002,
 p. 761

 Background: top – 5.7 GHz, Stokes I
 (TBmax = 48 MK), bottom: HXR.

 Contours: Stokes V at 5.7 GHz (top)
 and 17 GHz (bottom).
 White lines: I and V scans at 5.7 GHz
 according to the scanning direction of
 the SSRT/NS array: SSP solid,
 background burst dashed.
Density structure of the flare region

       Top: soft X-ray image (AlMg filter)
       Middle: emission measure
       Bottom: time profile of the maximum
       density, assuming the emission depth
       of 5000 km.


       The densest plasma is observed in the
       SSP source, where the value of 1011
       cm-3 is achieved.

       This value corresponds to the
       harmonic plasma emission at 5.7 GHz.
30 March 2001. Subsecond pulse recorded in two interference orders
                                    Top: dynamic spectrum (Stokes I,
                                    NAOC), middle: SSRT time
                                    profiles for LCP (dashed 5.69
                                    GHz, solid 5.78 GHz).
                                    Bottom: positions of the SSP
                                    sources (weighted centers) at the
                                    two SSRT frequencies.

                                    The positions of the SSP sources
                                    were measured using differences
                                    of 1d scans recorded during the
                                    SSP and just before it.

                                    Drift velocity of 8 GHz/s

                                    Velocity of the source
                                    2 · 1010 cm/s
                                    Density gradient
                                    1.6 · 109 cm-3/thousand km
LCP spatial 1D profiles of the SSP at 5.78 and 5.69 GHz

                              Solid: 5.78 GHz,
                              dashed: 5.69 GHz.
                              The lowest scan represents the
                              initial 1D profile of the background
                              burst at 05:13:06.5.

                              Differences of the profiles at
                              consecutive times with the initial
                              one are shown above. All the 1D
                              profiles are normalized to unity.

                              Direct measurements of the SSP
                              spatial and temporal shifting do
                              not contradict the standard model
                              with the electron beam, but the
                              measurement accuracy is
                              insufficient.
Microwave U-type burst         June 2, 2000
                         Altyntsev A.T. et al., A&A 411,
                         263, 2003


                         Top: time profiles of the
                         burst.


                         Middle: extended time
                         profiles for the interval
                         marked by the vertical
                         lines at the top panel.


                         Bottom: NAOC dynamic
                         spectrum.
Microwave U-type burst                  2 June 2000
                         Top: expanded time profiles
                         detected by SSRT EW linear
                         interferometer (5.68 GHz) for RCP
                         & LCP. Vertical lines correspond to
                         the crossing of the different
                         branches.




                         Middle: profiles detected by SSRT
                         NS linear interferometer (5.73 GHz).


                         Bottom: center-of-gravity positions
                         of one-dimensional scans.
                         Displacement of the position of the
                         sources referring to different
                         branches of U-structure do not
                         exceed 3.
30 March 2001
                    • Full width of the U-
                      burst spectrum 0.2 –
                      1.0 GHz
                    • Instantaneous
                      bandwidth 1–5 %
30 March 2001         from mean emission
                      frequency
                    • Drift velocities of the
                      branches 1–10 GHz/s
                    • Interval between the
                      recording of the U-
17 September 2001     structure branches at
                      the SSRT frequency
                      50 – 270 ms
Positions of the background
burst sources
in MDI magnetograms

Contours – background burst
(SSRT, I).
Crosses in the circles – SSP
Shading - MDI magnetogram
Dashed lines – neutral line of
magnetic fields

The sources of SSP were well
apart (> 7000 km) from the
neutral line of the photospheric
magnetic field. The signs of
polarization were the same for
both branches of the
U-structures.
       So, the usual explanation of the U-structure
encounter difficulties in the cm-microwaves.
       We propose that U-shaped structures are
produced due to an impulsive plasma heating of a part
of flare loop (a few thousand km long). The existing of
local heating areas in the flaring loops is confirmed by
soft X-rays observations (Acton et al. 1992, PASJ, 44,
L71; Feldman et al. et al. 1994, ApJ 421, 843; Doschek
1999, ApJ 527, 426)
       The instantaneous spectrum with a relatively
narrow bandwidth can be formed in this case as the
result of a density distribution pattern in this region.
Sketch of the heating region (a) and
of the spectrum shape dependence
(c) on the density distribution (b).
Model of the plasma density and emission
frequency dynamics in the U-burst source
U-burst
The observed evolution of microwave emission fits
well with the concepts of the response to impulsive
heating of a limited part of the magnetic loop with the
diameter of several tens of kilometers and with the
length of about a few thousand kilometers.

Estimates of the plasma parameters:
Magnetic field: 100 G,
T: up to 12 MK,
Density: 1011 cm-3
Zebra pattern (5 January 2003)
                     Altyntsev et al.,
                     A&A (in press)

                     NAOC dynamic
                     spectrum with zebra-
                     pattern burst.
                     A frequency interval
                     between strips equals
                     0.16 GHz

                     Time profiles from
                     SSRT linear arrays and
                     NAOC
                     spectropolarimeters at
                     the same frequencies.
                                                      • The source of the zebra
                                                      pattern is above the N-polarity
                                                      region. The emission
                                                      corresponds to the x-mode.
                                                      • The source size of the zebra
                                                      pattern does not exceed 10,
                                                      and the sources of different
                                                      stripes of zebra pattern
                                                      coincide.
                                                      • Several magnetic field lines
                                                      are shown. The lines were
                                                      extrapolated from the
                                                      magnetogram using the
                                                      potential approximation. The
                                                      observed zebra pattern source
                                                      and 60 G point of the magnetic
Magnetogram (color) and UV emission
                                                      line (thick) are close. The
(contours). Zebra pattern source is situated at the   height of this point is about 14
intersection point of EW & NS knife-edge beams.       thousand km above the
Black: extrapolated magnetic field lines.             photosphere.
 Zebra pattern

Assuming the frequency interval between adjacent strips of zebra
pattern to be equal to the electron cyclotron frequency in the
source, B  60 G. From soft X-ray data: Te  1.1107 K, Ne  1011
cm-3. Therefore, the emission frequency is close to the double
plasma frequency.

Present explanations of bursts with zebra patterns assume either
simultaneous generation of several cyclotron harmonics, or
generation of different strips in several spatially separated sources.
In our case, the spatial displacement between the sources of
different zebra stripes was not detected.

The most probable emission mechanism is nonlinear coupling
of harmonics of Bernstein waves (with harmonic numbers
about 17-18).
                         Emission wave mode
                                                       Meshalkina et al., Sol.Phys. 221,
                                                       85, 2004
    RCP            LCP                 LCP       RCP
                                                       18 events were chosen with
                                                       polarization > 30%, located
N              S                  N          S
                                                       -60 to +60 from the central
                                                       meridian.

                                                       The sources are often situated
                                                       at distances < 10  from the
                                  10
                                                       photospheric neutral line
          10         9

                             6
                                                       (apparently, at tops of magnetic
           5
                         3                             loops). In other events (bottom,
                     Х   О   Х     О                   black) subsecond pulses
                                                       correspond, as a rule, to the
                   BURST         SSP
                                                       o-mode.
Fast mode observations (SSRT, NoRH)
                  NoRH
                  About 10% of flares had fine fine time
                  structures shorter than 1 sec
                  Nakajima H., Grechnev V.V.
                  The Yohkoh 8th Symp., 1999

                  SSRT (2000-2004)
                  177 events
                  Too late for observation together with the
                  NoRH: 58 events

                  Common time intervals:
                  28 events
                  Pulse-to-pulse correlation:
                  6 events

                      Example:
                 NoRH – corr. plot, SSRT – flux.
                 SSP polarization at 5.7 GHz: 10% (RCP)
We thank Nobeyama Solar Group for
 data, fruitful discussion, assistance,
opportunity to participate this meeting
          and the hospitality !
Thank you!

				
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