Solar U - and J - bursts at the decameter wavelengths

1. SolarU- andJ- burstsat the decameterwavelengths V. V. Dorovskyy 1, V. N. Melnik 1, A. A. Konovalenko 1, H.О. Rucker2, E. P. Abranin1, A. Lecacheux3 1. Institute of Radio Astronomy,Kharkov, Ukraine. 2. Space Research Institute, Graz, Austria. 3. Paris Observatory, Meudon, France.

2. The HISTORY • 1958 - U-burstswere firstly observedat the meter wavelengths(Maxwell A., Swarup G. Harvard Observatory Station) • 1971 – U-burstswere registered at 0.7 – 5MHz (Stone R. G., Fainberg J., RAE-1) • 1974– U-burstswere registered at decameter wavelengths (Stewart R. T., Culgoora radio telescope) • 1984 – one more U-burstsobservation at 20-70 MHz (Leblanc Y., Hoyos M., NDA) • 1991 – the highest known frequency of U-bursts observations - 1.4 GHz (Aschwanden M. J. et al., VLA).

3. The HISTORY in pictures А. О. Benz et al. 1979 Leblanc, Y., Hoyos, M, 1984

4. C O R O N A ++ -- ++ SUN

5. U-bursts are much more rare events, than ordinary Type III bursts. Most oftenU- andJ- burstsare observed at 20-200MHz. Kuperus, et al. 1967

6. Instruments All observations were carried out with the Northern branch of the Radio Telescope UTR-2 Effective area ~ 50 000 m2 Antenna beam 1ox15o Frequency band 10 – 30 MHz Dynamic range covered with calibration 42 dB

7. July 2, 2004 July 8, 2004 Frequency, MHz 10:05:50 10:06:40 10:07:30 10:08:20 Time, UT Time, UT Observations During 2003-2004 about 50 U- andJ- bursts were registered Only 7 of them had well developed descending branch.

8. Number of bursts Turning Frequency, MHz Distributionof U- andJ- burstson turning frequencies 90% of all registeredU-burstshadturning frequencies below 24 MHz.

9. June 26, 2004 Groups of J-bursts Turning Frequency Drift (TFD) = -2кHz/s , that correspondsto Vlin=60km/s t2-t1=90 s t3-t2=70 s

10. Active regions on June 26 2004 NOAA 10635 и NOAA 10637

11. 1

12. The lift velocities of the loop structures fromSOHOdata – around 40кm/s, In frames of Newkirk corona model such velocity results inTFD -1кHz/s At the same timethe accompanying СМЕ moved much faster -about 300кm/s

13. August 15, 2004 Flux, s.f.u. Frequency, MHz Time, UT Harmonicstructure of U- andJ- bursts Harmonic structure of the U- J- burstswas observed many times. The ration of the F- and H-component frequencies in average was less than 2 Harmonic pairJ-Jb on the background of the storm

14. Flux, s.f.u. F component Frequency, MHz H component Time, UT Average harmonic ratio equals 1.8 (on the base of 6 pairs analysis) Isolated harmonic pairJ-Jb Durationsof Н-componentsequal 6-13swith average value of 9,3 s Durationsof F-componentsequal 1.5-3.8swith average value of 3 s

15. Flux, s.f.u. Frequency, MHz Time, UT UnusualU- andJ- bursts Caroubalos, C., et al. 1973 «Split» U-burst Drift rate at high frequencies-3 МHz/s Duration 8.2 s. Turning frequencies are – 18 МHzand 23 MHz

16. Flux, s.f.u. Frequency, MHz Time, UT UnusualU- andJ- bursts «Nested» U-bursts

17. C O R O N A ++ -- SUN

18. Simulation

19. Simulation t1=0, t2=10.4 s, t3=20.4 s, t4=32.4 s : t2-t1=10.4 s, t3-t2=10 s, t4-t3=12 s f1= 30 МHz (h = 1,7 R), f2= 17 МHz (h = 2,25 R), f3= 14 МHz (h = 2,5 R). The loop radius – 0.8R, source velocity – 0.18 с.

20. Simulation results 3 2 4 Frequency, MHz 1 Time, UT

21. We should markthat real loop may differfrom shown above due to at least two reasons : • The times of the source travel along the segments2-3and3-4are different (10s и 12saccordingly), what may be the result of either the loop asymmetryor the source deceleration at the top of the loop. • The loops, which were registered by theLASCO-С2 coronagraph and which are presumably connected with the discussed U-bursts, havetransverse dimensionabout 0.8 –1 R◉, whereas the model estimation of this dimension from the dynamic spectrum of the discussed U-burst gives the value of 1,2R◉. One of this discrepancy reasons could be the loop ellipticity. For the burstof June 2, 2004 to get the transverse loop dimension of 0.8R◉ the ellipse axes ratioshould be 1.5.

22. CONCLUSION • Observations of the U-burstswith turning frequencies 10-30МHzprove the existence of the magnetic loops with heights of 2–3 Solar radii. • The harmonic structure of U- and J- bursts was found.It was shown that average harmonic ration in harmonic pairs was 1,8. Также впервые обнаружены пары Jb – Jbursts pairs were firstly registered, which are analogous to well-known IIIb – IIIpairs. • Groups of J - burstswith unusualTFD – 1 – 2 кHz/sthatcorrespondsto linear velocities 40 – 60 кm/sandis very close to values obtained from optical observations.No stable relation was found between the absolute drift rates of the ascending and descending branch of the U-burst at fixed frequency.

23. REFERENCES - Caroubalos, C., Couturier, P. and Prokakis, T. A U-Like radio bursts observed with high space-time resolution. Astron. Astrophys. 1973,vol.23, pp. 131-138. -Kuperus, М., Tandberg-Hanssen, Е. The Nature of Quiescent Solar Prominences. Solar Physics, 1967, Vol.2, pp.39-48 -Benz, A. O., Urbarz, H. W. and Zlobec, P. The evolution of polarization in Type U solar radio bursts. Astron. Astrophys. 1979, vol. 79, pp. 216-222. -Leblanc, Y. and Hoyos, M. Storms of U-bursts and the stability of coronal loops. Astron. Astrophys., 1985, Vol. 143, pp.365-373 -Maxwell, A., Swarup, G. A new spectral characteristic in solar radio emission. Nature, 1958, Vol. 181, pp. 36 -Stone, R.G., Fainberg, J. A U-Type solar radio bursts originating in the outer corona. Solar Physics, 1971.vol.20,pp.106-111. -Stewart, R. T. Harmonic ratios of inverted-U Type III bursts. Solar Physics, 1974, Vol.39, pp.451-458. -Aschwanden, M.J., Bastian, T.S., Benz, A.O. and Brosius, J.W. Decimetric solar type-U bursts: VLA and PHOENIX observations. The Astrophys. J., 1992.vol.391, pp.380-392.