Type III radio bursts observed with LOFAR and Nançay radioheliograph Jasmina Magdalenić 1, C. Marqué 1, A. Kerdraon 2, G. Mann 3, F. Breitling 3, C. Vocks 3, R. Fallows 4, V. Krupar 5, L. Rachmeler 1, I. Dammasch 1, 1 SIDC – Royal Observatory of Belgium, Brussels, Belgium 2 LESIA, Observatoire de Paris, CNRS, UPMC, Meudon, France 3 Leibniz-Institut für Astrophysik Potsdam (AIP), 14482, Potsdam, Germany 4 ASTRON, The Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands 5 Institute of Atmospheric Physics ASCR, Prague, Czech Republic

* motivation continuation of solar radio emission from metric to decametric range is still poorly understood due to the insufficient coverage of high time/frequency resolution imaging and spectral observations. high time/frequency resolution dynamic spectra and imaging observations by LOFAR (LOw Frequency ARray) the Low Band Antenna (LBA) →10−90 MHz the High Band Antenna (HBA) → 110−250 MHz NOT solar dedicated LOFAR Cycle 1 observations:  LBA observations → 10 − 90 MHz  beam-formed data → frequency/time resolution 0.19 MHz & 50 ms  interferometer data → frequency/time resolution MHz & 25 ms LBA

* Overview small group of type III bursts with one stronger type III which extends to decameter frequency range, observed on March 09, close to the limb position of the associated radio sources structured emission indicates we observe type IIIb radio bursts (de la Noë & Boischot, 1972; de la Noë, J., 1974, 1975; Slottje, 1974; Melnik et al., 2011; Zao et al., 2013; Loi et al., 2014) LOFAR LBA ORFEES WIND WAVES STEREO B STEREO A

* type IIIb bursts Slottje, 1974 de la Noë, 1972 Different varieties of the type IIIb bursts are observed, such as type IIIb-III (fundamental- harmonic pairs) and type II-IIIb (fundamental-harmonic pairs).

* LOFAR observations Type III substructures coincide in their characteristics with the fragmentation of the ‘associated continuum’ observed by LOFAR & DAM. Such a continuing structuring was, up to our knowledge, not yet observed.

* Nançay Decametric Array observations Nançay Decametric Array observations (courtesy of A. Lecacheux) confirm fragmentation of the type III and continuum radio emission.

* LOFAR imaging 77 MHz 70 MHz

* ORPHEES & NRH 19:14:10 A B

* Radio event & coronal structures NRH & LOFAR images of the type III bursts overlaid on the SWAP 174 A image. A B

* Associated flare/eruption? LYRA instrument onboard PROBA2 (GOES data gap) show flare with max at about 08:40 UT, seemingly not associated with group of type III bursts. STEREO B does not show presence of a flare. Small emerging flux observed in the possible source region of the electrons generating type III radio burst.

* LASCO No CMEs or flows associated with the event.

* Coronal electron density along the propagation path of type III bursts f  n  similar or larger density gradients than in the generally used coronal density models This result is in a disagreement with Lobzin et al., (2010), who found gently sloping density profiles in the corona, but similar to density profiles obtained using NRH observations by Magdalenić et al., (in preparation). A B f ~ 76 MHz, 2x Saito → density ~ 6 · 10 7 cm -3

* Summary  The small group of type III bursts, with one stronger type III which extends to decameter frequency range was observed on 09 March  The substructures of type III bursts coincide in their characteristics with the fragmentation of the ‘associated continuum’ observed by LOFAR & DAM. Such a continuing structuring was, up to our knowledge, not yet observed.  No associated flare or CME.  NRH observations, combined with SWAP 174 A images indicate propagation along the large close loop system for all type III bursts, with exception of stronger type III observed at about 09:14 UT.  Similar source position of the type III bursts and a fragmented continuum indicated that fragmentation of the radio emission is due to the specific properties of the source region and not due to the density structuring along the propagation path of the radio emission.  The obtained density gradients are similar or larger than in the generally used coronal density models (e.g. Saito, 1970) and significantly larger then the one by Lobzin et al., (2010). LOFAR observation allow a new insight into propagation of the electron beams and extension of inferred coronal electron density profile to bigger heights.   Work to be continued!

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* Radio event & coronal structures NRH & LOFAR images of the type III bursts overlaid on the reconstruction of the magnetic field lines using the PFSS model. WIND WAVES STEREO WAVES B STEREO WAVES A