P. Kaufmann, A. Abrantes, E. C. Bortolucci, E. Correia, J. A. Diniz, G. Fernandez, L. O. T. Fernandes, C. G. Giménez de Castro, R. Godoy, G. Hurford, A. S. Kudaka, M. Lebedev, R. Lin, N. Machado, V. S. Makhmutov, R. Marcon, A. Marun, V. Nicolaev, P. Pereyra, J.-P. Raulin, C. M. da Silva, A. Shih, Y. Stozhkov, J. Swart, A. Timofeevsky, A. Valio, T. Villela, M. B. Zakia
A new solar flare spectral component has been found with intensities increasing for larger sub-THz frequencies,
spectrally separated from the well known microwaves component, bringing challenging constraints for interpretation.
Higher THz frequencies observations are needed to understand the nature of the mechanisms occurring in flares. A twofrequency
THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons
or satellites, or at exceptionally transparent ground stations. 76 mm diameter telescopes were designed to observe the
whole solar disk detecting small relative changes in input temperature caused by flares at localized positions at 3 and 7
THz. Golay cell detectors are preceded by low-pass filters to suppress visible and near IR radiation, band-pass filters,
and choppers. It can detect temperature variations smaller than 1 K with time resolution of a fraction of a second,
corresponding to small burst intensities. The telescopes are being assembled in a thermal controlled box to which a data
conditioning and acquisition unit is coupled. While all observations are stored on board, a telemetry system will forward
solar activity compact data to the ground station. The experiment is planned to fly on board of long-duration
stratospheric balloon flights some time in 2013-2015. One will be coupled to the GRIPS gamma-ray experiment in
cooperation with University of California, Berkeley, USA. One engineering flight will be flown in the USA, and a 2
weeks flight is planned over Antarctica in southern hemisphere summer. Another long duration stratospheric balloon
flight over Russia (one week) is planned in cooperation with the Lebedev Physics Institute, Moscow, in northern
hemisphere summer.
P. Kaufmann, R. Marcon, A. Marun, A. Kudaka, E. Bortolucci, M. Zakia, J. Diniz, M. Cassiano, P. Pereyra, R. Godoy, A. Timofeevsky, V. Nikolaev, A. Pereira Alves da Silva, L. Fernandes
KEYWORDS: Terahertz radiation, Linear filtering, Sensors, Visible radiation, Cameras, Bandpass filters, Black bodies, Solar radiation, Microbolometers, Near infrared
The knowledge of THz continuum spectra is essential to investigate the emission mechanisms by high energy particle
acceleration processes. Technical challenges appear for obtaining selective spectral sensing in the far infrared range to
diagnose radiation produced by solar flare burst emissions measured from space as well as radiation produced by high
energy electrons in laboratory accelerators. Efforts are been carried out intended for the development of solar flare high
cadence radiometers at two THz frequencies to operate outside the terrestrial atmosphere (i.e. at 3 and 7 THz). One
essential requirement is the efficient suppression of radiation in the visible and near infrared. Experimental setups have
been assembled for testing (a) THz transmission of "low-pass" filters: rough surface mirrors; membranes Zitex G110G
and TydexBlack; (b) a fabricated 2.4 THz resonant grid band-pass filter transmission response for polarization and angle
of incidence; (c) radiation response from distinct detectors: adapted commercial microbolometer array using HRFZ-Si
window, pyroelectric module and Golay cell; qualitative detection of solar radiation at a sub-THz frequency has been
tested with a microbolometer array placed at the focus of the 1.5 m reflector for submillimeter waves (SST) at El
Leoncito, Argentina Andes.
The solar submillimeter-wave telescope (SST) is the only one of its kind dedicated to solar continuous observations.
Two radiometers at 0.740 mm (405 GHz), and four at 1.415 mm (212 GHz) are placed in the Cassegrain focal plane of
the 1.5-m dish at El Leoncito high altitude site, San Juan, Argentina. The aperture efficiencies are close to design
predictions: 20% and 35% for 2 and 4 arcminutes beam sizes at 405 and 212 GHz, respectively. The positioner absolute
pointing accuracy is 10 arcseconds. Spectral coverage is complemented by ground-based mid-infrared telescopes
developed for high cadence observations in the continuum 10 micron band (30 THz), using small apertures and room-temperature
microbolometer cameras. Using the system, a new solar burst spectral component was discovered,
exhibiting fluxes increasing for smaller wavelengths, separated from the well known microwave component. Rapid sub-second
pulsations are common for all bursts. The pulsations onset times of appear to be connected to the launch times of
CMEs. Active regions are brighter for shorter submillimeter-waves. Mid-IR bright regions are found closely associated
with calcium plages and magnetic structures near the solar photosphere. Intense and rapid 10 micron brightening was
detected on active centers in association with weak flares. These results raise challenging difficulties for interpretation.
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