DECAMETER RADIO EMISSION OF THE SUN: RECENT OBSERVATIONS

DECAMETER RADIO EMISSION OF THE SUN: RECENT OBSERVATIONS V. N. Melnik *,H.O.Rucker, A. A. Konovlenko, V. V. Dorovskyy, E. P. Abrnin, nd A. Leccheux Abstrct We present n overview of the recent results in solr observtions obtined t decmeter rdio wves using the rdio telescope UTR-2. Due to up-to-dte recording fcilities some newly discovered phenomen in the frequency rnge - 30 MHz re given: fst type III bursts, fine time structures in norml type III bursts, solr S-bursts, type IV bursts with zebr-like fine structures, third hrmonic in type II bursts nd bursts in bsorption of different time scle. Newly discovered properties of well known bursts such s type III bursts, type IIIb bursts, type II bursts nd drift pirs were obtined too. Introduction The use of the new spectrometer (continuous bndwidth of 2 MHz, high frequency nd time resolution of 2 khz nd ms respectively) on the rdio telescope UTR-2 (Ukrinin T-shped Rdio telescope - second modifiction) (frequency bnd 30 MHz, bemwidth nd sensitivity 5 Jy) llows us to strongly extend the fesibility of the studies of the solr decmeter rdio emission. In 0 the first decmeter type II burst ws recorded. The drift rte of decmeter type II bursts rnge from 30 khz/s to 70 khz/s. The usul type II bursts re found to hve fine structures in the form of short (durtions bout of s) components with drift rte 0.5 3 MHz/s. Type II bursts with herringbone structures with wve-like bckground were observed too. For the first time fine time structures in usul type III bursts were observed. They consist of sub-bursts hving drift rtes tht cn be lrger or smller thn tht of the prent type III bursts. Decmeter S-bursts were lso observed. Observtionl chrcteristics of drift pirs t 8 30 MHz were nlyzed too. * Institute of Rdio Astronomy, Ukrinin Acdemy of Sciences, Chervonoprporn 4, 602, Khrkiv, Ukrine Spce Reserch Institute, Austrin Acdemy of Sciences, Schmiedlstrsse 6, A-8042 Grz, Austri LESIA, Observtoire de Pris, UMR CNRS 89, 9295 Meudon, Frnce 343

344 V. N. Melnik et l. 8 July 02 Flux in SFU 00 0 :44: :44: :44:30 :44:40 :44:50 Flux, W/(m Hz) 2 - -2 - b July 02 Frequency.2 MHz :44: :44: :44:30 :44:40 :44:50 :45:00 Figure : ) Type III-like burst (:44:30) during type III bursts storm; b) time profiles of type III-like burst nd usul type III bursts. 7 August 02 Flux in SFU -7 7 August 02 Frequency 2.50 MHz 00 0 Flux, W/(m Hz) 2-8 -9 - :05:00 :05:50 :06:40 :07:30-2 b :05: :05:40 :06:00 :06: :06:40 Figure 2: ) Powerful type III burst during storm of type III bursts; b) time profile of powerful type III burst. In this pper we briefly present some recent results (fter PRE VI) obtined in the study of spordic rdio solr emissions. During this time fst type III burst (type III-like bursts), decmeter type IV bursts nd their fine structures in form of fiber bursts nd zebrptterns were reveled. Fine frequency structures of type IIIb bursts were considered. Decmeter spikes nd S-bursts s well s powerful type III bursts were nlyzed too. 2 Type III-like Bursts In the frequency bnd 30MHzweobservedforthefirsttimefsttypeIII-likebursts [Melnik et l., 08] (Fig. ). More thn 00 such bursts were recorded in the yers 02-06. Their drift rtes ( 30 MHz/s) were sometimes higher thn those of the usul type III bursts (2 4 MHz/s) in the decmeter rnge. These bursts lst 2s nd re shorter thn usul type III bursts (Fig.b). Type III-like bursts re wek bursts, in most cses their flux density is not exceeding 0 sfu. Their interesting property is relted to the fct tht they re observed in dys when the ssocited ctive region is ner the centrl meridin. Therefore the beming of the rdio emission of type III-like bursts is bout -30. Their usul high frequency drift rte cn be relted to the group velocity of electromgnetic wves ner the emission source tht is similr to the speed of

Decmeter Rdio Emission of the Sun: Recent Observtions 345 30 2 My 0 Flux in SFU 00 0 09::00 09::05 09:: 09:: 09:: Figure 3: Type IIIb burst followed by type III burst. 8 July 04 Flux in SFU 00 0 8 2 June 04 Flux in SFU 0 09:35:00 09:35: 09:35:40 09:36:00 09:36: b :45:50 :46:40 :47:30 Figure 4: ) Hrmonic pir of U-, J- bursts; b) splitting U-, J- bursts. fst electrons (see pper by Rutkevych nd Melnik []). 3 Powerful Type III Bursts We nlyzed the chrcteristics of powerful type III bursts with flux density > 9 W/m 2 Hz (Fig. 2) [Melnik et l., b]. The min feture of these bursts is the liner dependence of the drift rte in respect to the frequency. This mens tht in the rdio source region of the coron the plsm density n trend is exponentil (n(r) exp( r/), where is constnt). Another property of these bursts is tht their durtion decreses not so fst s /f, it grees with the reltionship 60f 2/3. 4 Decmeter Type IIIb Bursts The drift rte of these bursts is similr to the one of the usul type III bursts however their durtion is 3-4 times shorter. Type IIIb bursts show fine frequency structure similr to chins of strie. The frequency bndwidth of strie is 50 70 khz [Melnik et

346 V. N. Melnik et l. 29 June 03 Flux in SFU 30 5 09:05:50 09:06:40 09:07:30 09:08: Figure 5: Dog-leg type III burst (9:06:). 3 July 04 Flux in SFU 0 08::00 08:53: 09::40 :00:00 :33: Figure 6: Decmeter type IV burst. l., ], their durtion nd therefore the durtion of type IIIb bursts is bout.2 s (Fig. 3). According to some ides these bursts cn be ssocited with electron bems which propgte through density fluctutions in coron. 5 Inverted Decmeter U- nd J-bursts During yers 03-04 we observed in the frequency rnge 30 MHz more thn 50 inverted U- nd J- bursts [Dorovskyy et l., ] (Fig. 4). Tht confirms the evidence of mgnetic loops up to 2-3 solr rdii in the coron. Hrmonic pirs were seen not only in usul U- nd J- bursts but lso in Jb-bursts. There were some cses of splitting U- nd J- bursts (Fig. 4b) tht indicte rdio emission generted in rcdes of mgnetic loops of different sizes.

Decmeter Rdio Emission of the Sun: Recent Observtions 347 July 05 Flux in SFU 00 0 08:36:40 08:40:00 08:43: 08:46:40 08:50:00 08:53: Figure 7: Fiber bursts in emission nd bsorption. July 04 Flux in SFU 08:3: 08:3:40 08:32:00 08:32: 08:32:40 08:33:00 0 Flux, W/(m Hz) b2-9 - July 04 Frequency.45 MHz 08:3:50 08:32:00 08:32: 08:32: 08:32:30 08:32:40 Figure 8: ) Group of zebr pttern stripes; b) equidistnt stripes in zebr structure. 6 Dog-leg Type III Bursts Sometimes we observed strnge type III bursts which present discontinuity in drift rtes nd in durtion t some frequency (Fig. 5) [Dorovskyy et l., c]. There were more thn 0 of such dog-leg type III bursts during yers 02-06. The jump points re distributed in the rnge 3 2 MHz with mximum t bout 6 MHz. The vlues of the sudden chnge of the frequency drift rte t the jump point my rech lso the fctor. We think tht the cuse of such unusul type III bursts is due to coronl plsm inhomogeneity in density, temperture or both of them. 7 Type IV Bursts During yers 02-06 in the frequency rnge 30 MHz we recorded bout 40 type IV bursts [Melnik, et l., 08b]. The sequence of events which ccompnies type IV bursts is the following: group of powerful type III bursts, phse of bsorptions or lrge-scle burst in bsorption, type II burst nd finlly type IV burst (Fig. 6). The type II burst cn precede the type IV event or cn be simultneous with it. The durtion of type IV bursts

348 V. N. Melnik et l. vries from - 2 up to 6-7 hours. All the observed decmeter type IV events show fine structures in form of fiber bursts in emission nd bsorption [Konovlenko et l., 07; Melnik et l., b] with positive nd negtive drift rte (Fig. 7). Fiber drift rtes nd their durtions re close to those of usul type III bursts. In one cse we recorded fine structures in form of zebr pttern (Fig. 8) which ws repeted some times during the whole type IV burst. Ech such group consisted of sequence of equidistnt (up to 40) stripes (Fig 8b) [Melnik et l., 08b]. The time intervl between neighboring stripes ws 2.5 s (Fig. 8b). Type II bursts ssocited with type IV bursts show two or sometimes even three hrmonics (Fig. 9) [Melnik et l., 08b]. 8 Decmeter Spikes Decmeter spikes re short durtion bursts (life time bout s) with bndwidth 50 70 khz [Melnik et l., d] with flux density up to 0 sfu. Spikes re plced choticlly on the dynmic spectrum (Fig. ). We believe tht they re generted by fst electron smll density bems nd tht their source hs not lrge sptil size. The spike durtion is defined by prticle collision time [Melnik et l., d]. This llows to estimte the temperture of the coronl plsm t frequencies 30 MHz. We found [Melnik et l., d], using dt from July 27 to August 2, 02, tht t height 3R s the plsm temperture ws bout 6 K. Moreover it is possible to find the ngle into which fst electrons propgte long open mgnetic field lines. In most cses this ngle is not lrger thn [Melnik et l., d]. 9 S-bursts S-bursts (Fig. b) re the shortest decmeter bursts, their durtion is only 0.3 0.5 s [Melnik et l., c]. They, s type III bursts, drift from high to lower frequency, but their drift rte is 3-4 time smller thn those of usul type III bursts. Most S-bursts hve flux density smller thn 0 sfu. Another interesting property of these bursts is the liner increse of their bndwidth with frequency. It is possible to explin the properties of these bursts nd to find the mgnetic field nd the prmeters of the bckground Lngmuir turbulence in their source in the frme of the genertion model bsed on colescence of Lngmuir wves with fst mgnetosonic wves [Melnik et l., c]. During the pssge of n ctive region on the solr disk in July, 02 the estimted mgnetic field ws 2 G. Conclusion Our observtions of the solr rdio emission in the decmeter rnge during the period 0-06 gve us some importnt results. First of ll it is to mention type IV bursts which were ssocited with CMEs (Coronl Mss Ejection). The obtined dt fill the gp existing between meter nd hectometer rdio emission of the CMEs. The study of these bursts should be helpful in understnding the CME properties nd the peculirities

Decmeter Rdio Emission of the Sun: Recent Observtions 349 4 June 04 Flux in SFU 00 0 07:46:40 07:55:00 08:03: 08::40 Figure 9: Type II bursts with three hrmonics ssocited with type IV burst. 8 August 02 Flux in SFU 0 30 My 0 Flux in SFU 0 09:50: 09:50:40 09:5: 09:5:40 09:52:00 b :4: :4: :4:30 :4:40 :4:50 Figure : ) Decmeter spikes choticlly locted on the dynmic spectrum; b) storm of S- bursts. of the interction of CMEs with the coronl plsm. The nlysis of properties of decmeter spikes, type III-like bursts nd S-bursts showed tht they cn be used s dignostic instrument for obtining some chrcteristics of the coronl plsm (density, temperture, mgnetic field, bckground Lngmuir turbulence) t height 3R s nd some prmeters pertinent to ccelerted electrons (velocity, density, size, etc). Our observtions show tht the fst electron bems responsible for type III bursts cn sometimes hve complex nture tht is mnifested in type III bursts with fine time structure. Moreover we obtined tht the durtion of usul decmeter type III bursts defines the spce size of the relted electrons but not the collision time. There re lso some chrcteristics of spordic decmeter rdio emissions such s fine structures in type II bursts, existence of the third hrmonic in type II bursts, burst in bsorption of different time scle, zebr structures in type IV, fiber bursts with positive frequency drift rtes etc, which wit for interprettion nd understnding. We re sure tht the recent nd future observtions with the UTR-2 (in the frequency rnge 30 MHz) nd the GURT (Gint Ukrinin Rdio Telescope in construction ner Khrkiv) (in the frequency rnge 70 MHz) will bring new findings in the field of solr rdio emission.

350 V. N. Melnik et l. References Dorovskyy, V. V., V. N. Melnik, A. A. Konovlenko, H. O. Rucker, E. P. Abrnin, nd A. Leccheux, Solr U- nd J- rdio bursts t the decmeter wves, ASTRO- PHYSICS AND COSMOLOGY AFTER GAMOW, Proc. 4th Gmow Interntionl Conf. AIP Conference Proceedings, 6, 433 439,. Dorovskyy, V. V., V. N. Melnik, A. A. Konovlenko, H. O. Rucker, E. P. Abrnin, nd A. Leccheux, Unusul Type III Bursts t the Decmetre Wvelengths, in Plnetry Rdio Emissions VII, edited by H. O. Rucker, W. S. Kurth, P. Lourn, nd G. Fischer, Austrin Acdemy of Sciences Press, Vienn, this issue, 359 366,. Konovlenko, A. A., A. A. Stnislvsky, E. P. Abrnin, V. V. Dorovskyy, V. N. Melnik, M. L. Kiser, A. Leccheux, nd H. O. Rucker, Absorption in Burst Emission, Solr Phys., 5, 345, 07. Melnik,V.N.,A.A.Konovlenko,H.O.Rucker,B.P.Rutkevych,V.V.Dorovskyy, E.P.Abrnin, A. I. Brzhenko, A. A. Stnislvskyy, nd A. Leccheux, Decmeter Type III-like bursts, Solr Phys., 0, 33, 08. Melnik, V. N., H. O. Rucker, A. A. Konovlenko, V. V. Dorovskyy, E. P. Abrnin, A. I. Brzhenko, B. Thidé, A.A. Stnislvskyy, Solr Type IV Bursts t Frequencies -30 MHz, in Solr Physics Reserch Trends, edited by P. Wng, Nov Science Publishers, New York, 7 3, 08b. Melnik, V. N., H. O. Rucker, A. A. Konovlenko, N. V. Shevchuk, E. P. Abrnin, V. V. Dorovskyy, nd A. Leccheux, Type IIIb bursts nd their fine structure in frequency bnd 8-30 MHz, ASTROPHYSICS AND COSMOLOGY AFTER GAMOW, Proc. 4th Gmow Interntionl Conf. AIP Conference Proceedings, 6, 445 449,. Melnik, V. N., A. A. Konovlenko, A. I. Brzhenko, H. O. Rucker, V. V. Dorovskyy, E. P. Abrnin, A. Leccheux, nd A. S. Lonsky, Bursts in emission nd bsorption s fine structure of Type IV bursts, ASTROPHYSICS AND COSMOLOGY AFTER GAMOW, Proc. 4th Gmow Interntionl Conf. AIP Conference Proceedings, 6, 450 454, b. Melnik, V. N., A. A. Konovlenko, H. O. Rucker, V. V. Dorovskyy, E. P. Abrnin, A. Leccheux, nd A. S. Lonsky, Solr S-bursts t Frequencies of -30 MHz, Solr Phys., 4, 3 7, c. Melnik, V. N., A. A. Konovlenko, H. O. Rucker, A. I. Boiko, V. V. Dorovskyy, E. P. Abrnin, nd A. Leccheux, Observtions of powerful type III bursts in the frequency rnge 30 MHz, Solr Phys., 9, 335,. Melnik, V. N., N. V. Shevchuk, H. O. Rucker, A. A. Konovlenko, E. P. Abrnin, V. V. Dorovskyy, A. Leccheux, Properties of decmeter spikes, Plnetry Rdio Emissions VII, edited by H.Ø. Rucker, W. S. Kurth, P. Lourn, nd G. Fischer, Austrin Acdemy of Sciences Press, Vienn, this issue, 35 358, b. Rutkevych, B. P., nd V. N. Melnik, Numericl Simultion of Propgtion of Type III Electrons Emission, Plnetry Rdio Emissions VII, this issue, 39 398,.