New THz Solar Radio Astronomy

PIERRE KAUFMANN, JEAN PIERRE RAULIN, GUILLERMO GIMIENEZ DE CASTRO, HUGO LEVATO, ADOLFO MARUN, PABLO PEREYRA

Delhi

Conferencia; XXVIIIth URSI General Assembly, Delphi, October 23-29, 2005; 2005

URSI - International Union of Radio Science

New striking aspects of solar activity have been found from observations at frequencies above 100 GHz, provided by the solar submillimeter-wave telescope (SST) at El Leoncito in the Argentina Andes. The SST utilizes a radome-enclosed 1.5-m Cassegrain reflector, operating simultaneously with four 212 GHz and two 405 GHz total power radiometers with 5ms time resolution. Partial overlapping of antenna beams at 212 GHz allow the spatial determination of burst transients as well as estimates of burst source upper limit sizes. Most probable attenuations at El Leoncito are of 0.2 and 0.9 Nepers, at 212 and 405 GHz respectively, along 310 days a year. A new solar burst spectral component has been discovered, exhibiting an intense impulsive bulk emission peaking somewhere in the THz range. It appears along with, but is separated from the well-known microwave emission spectral component. Rapid subsecond submm-w pulsating bursts are associated to all events observed, sometimes without any detectable bulk emission component. Their onset times correlate well with the launch times of coronal mass ejections. However, there are distinctions on the rapid structures also found in the THz burst component. The findings of THz solar activity impose severe constraints to existing models and present new challenges for interpretation of physical processes at the origin of the flaring phenomena, suggesting the acceleration of high energy electrons (> 10 MeV). Observations in this unexplored range are essential. We report current THz developments at El Leoncito with the upgrade of the SST radiometers to increase the sensitivity by a factor of about 10. Uncooled bolometers are being developed to used at the SST focal plane at 670 and 850 GHz. New far-IR camera for the 10-μ (30 THz) solar observations is being installed. Solar THz spatial experiments are being considered in the 2-10 THz range for the next cycle maximum.