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(Reference retrieved automatically from Web of Science through information on FAPESP grant and its corresponding number as mentioned in the publication by the authors.)

A solar burst with a spectral component observed only above 100 GHz during an M class flare

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Author(s):
Cristiani, G. [1] ; de Castro, C. G. Gimenez [2] ; Mandrini, C. H. [1] ; Machado, M. E. [3] ; de Benedetto e Silva, I. [2] ; Kaufmann, P. [2, 4] ; Rovira, M. G. [1]
Total Authors: 7
Affiliation:
[1] Univ Buenos Aires, CONICET, Inst Astron & Fis Espacio, RA-1428 Buenos Aires, DF - Argentina
[2] Escola Engn, Ctr Radio Astron & Astrofis Mackenzie, BR-01302907 Sao Paulo - Brazil
[3] Comis Nacl Actividades Espaciales, RA-1063 Buenos Aires, DF - Argentina
[4] Univ Estadual Campinas, Ctr Componentes Semicondutores, Campinas - Brazil
Total Affiliations: 4
Document type: Journal article
Source: Astronomy & Astrophysics; v. 492, n. 1, p. 215-222, DEC 2008.
Web of Science Citations: 17
Abstract

Context. Since the installation of submillimeter solar radio telescopes, a new spectral burst component was discovered at frequencies above 100 GHz, creating the THz burst category. In all the reported cases, the events were X-class flares and the THz component was increasing. Aims. We report for the first time an M class flare that shows a different submillimeter radio spectral component from the microwave classical burst. Two successive bursts of 2 min duration and separated by 2 min occurred in active region NOAA 10226, starting around 13: 15 UT and having an M 6.8 maximum intensity in soft X-rays. Methods. Submillimeter flux density measured by the Solar Submillimeter Telescope (SST) is used, in addition to microwave total Sun patrol telescope observations. Images with H alpha filters, from the H alpha Solar Telescope for Argentina (HASTA), and extreme UV observations, from the Extreme-ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SoHO), are used to characterize the flaring region. An extensive analysis of the magnetic topology evolution is derived from the Michelson Doppler Imager (SoHO, MDI) magnetograms and used to constrain the solution space of the possible emission mechanisms. Results. The submillimeter component is only observed at 212 GHz. We have upper limits for the emission at 89.4 and 405 GHz, which are less than the observed flux density at 212 GHz. The analysis of the magnetic topology reveals a very compact and complex system of arches that reconnects at low heights, while from the soft X-ray observations we deduce that the flaring area is dense (n similar to 10(12) cm(-3)). The reconnected arches are anchored in regions with magnetic field intensity differing by an order of magnitude. Accordingly, we conclude that the microwave emission comes from mildly relativistic electrons spiraling down along the reconnected loops. A very small portion of the accelerated electrons can reach the footpoint with the stronger magnetic field (2000 G) and produce synchrotron emission, which is observed at submillimeter frequencies. Conclusions. The finding of a submillimeter burst component in a medium-size flare indicates that the phenomenon is more universal than shown until now. The multiwavelength analysis reveals that neither positron synchrotron nor free-free emission could produce the submillimeter component, which is explained here by synchrotron of accelerated electrons in a rather complex and compact magnetic configuration. (AU)

FAPESP's process: 99/06126-7 - Applications for the sub-milimeter Solar Telescope (SST)
Grantee:Pierre Kaufmann
Support type: Research Projects - Thematic Grants