Type III radio bursts observed with LOFAR and Nançay radioheliograph

1. Type III radio bursts observed with LOFAR and Nançayradioheliograph Jasmina Magdalenić1, C. Marqué1, A. Kerdraon2, G. Mann3, F. Breitling3, C. Vocks3, R. Fallows4, V. Krupar5, L. Rachmeler1, I. Dammasch1, 1SIDC – Royal Observatory of Belgium, Brussels, Belgium 2LESIA, Observatoire de Paris, CNRS, UPMC, Meudon, France 3Leibniz-Institut für Astrophysik Potsdam (AIP), 14482, Potsdam, Germany 4ASTRON, The Netherlands Institute for Radio Astronomy, Dwingeloo, The Netherlands 5Institute of Atmospheric Physics ASCR, Prague, Czech Republic

2. * 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 (LOwFrequency 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 0.012 MHz &25 ms LBA

3. * Overview • small group of type III bursts with one stronger type III which extends to decameter frequency range, observed on March 09, 2014. • 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) WIND WAVES STEREO BSTEREO A ORFEES LOFAR LBA

4. *type IIIb bursts 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). Slottje, 1974

5. 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. *LOFAR observations

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

7. *LOFAR imaging 77 MHz 70 MHz

8. *ORPHEES &NRH B A 19:14:10

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

10. *Associated flare/eruption? Small emerging flux observed in the possible source region of the electrons generating type III radio burst. 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.

11. *LASCO No CMEs or flows associated with the event.

12. * Coronal electron density along the propagation path of type III bursts f n AB  similar or larger density gradients than in the generally used coronal density models • f ~76 MHz, 2x Saito → density ~ 6 · 107 cm-3 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 Magdalenićet al., (in preparation).

13. * Summary •  The small group of type III bursts, with one stronger type III which extends to decameter frequency range was observed on 09 March 2014. •  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 Lobzinet 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!

14. THANK YOU FOR YOUR ATTENTION!

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