Fine temporal and spatial structure of the microwave

emission sourcesfrom 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 studyof 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)

21 August 2002 (04:02:45.5)

Left: Time profiles from SSRT - I & V, interval 6 sec, 14 ms data from NS interferometer.

Right:

Top: series of SSRT scans. The scan length is 240. Maximum brightness - white.

Bottom: dynamic spectrum (5.2-7.6 GHz) from the Huairou station (NAOC, China) corresponding to this event. Dashed horizontal lines mark SSRT frequency band.

Intensity (R+L)

Polarization (R-L)

August 21, 2002/SSRT/Flux Intensity and Polarization Siberian Solar Radio Telescope / North-South / Intensity

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30 March 2001a: 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%

  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.

30 March 2001

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/sDensity 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, 2000Altyntsev 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 burstTop: 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.

2 June 2000

• Full width of the U-burst spectrum 0.2 – 1.0 GHz

• Instantaneous bandwidth 1–5 % from mean emission frequency

• Drift velocities of the branches 1–10 GHz/s

• Interval between the recording of the U-structure branches at the SSRT frequency

50 – 270 ms

30 March 2001

17 September 2001

30 March 2001

Positions of the background burst sources in MDI magnetograms

Contours – background burst (SSRT, I). Crosses in the circles – SSPShading - MDI magnetogramDashed 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.

Magnetogram (color) and UV emission (contours). Zebra pattern source is situated at the intersection point of EW & NS knife-edge beams. Black: extrapolated magnetic field lines.

• 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 line (thick) are close. The height of this point is about 14 thousand km above the 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 1.1107 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 modeMeshalkina et al., Sol.Phys. 221, 85, 2004

18 events were chosen with polarization > 30%, located -60 to +60 from the central meridian.

The sources are often situated at distances < 10 from the photospheric neutral line (apparently, at tops of magnetic loops). In other events (bottom, black) subsecond pulses correspond, as a rule, to the o-mode.

RCP LCP LCP RCP

N S N S 10 10 9 6 5 3

Х О Х О BURST SSP

Fast mode observations (SSRT, NoRH)

NoRHAbout 10% of flares had fine fine time structures shorter than 1 secNakajima H., Grechnev V.V.The Yohkoh 8th Symp., 1999

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

Common time intervals: 28 eventsPulse-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!