The almost unexplored frequency window from submillimeter to mid-infrared (mid-IR) may bring new clues about the particle acceleration and transport processes and the atmospheric thermal response ...during solar flares. Because of its technical complexity and the special atmospheric environment needed, observations at these frequencies are very sparse. The High Altitude THz Solar Photometer (HATS) is a full-Sun ground-based telescope designed to observe the continuum from the submillimeter to the mid-IR. It has a 457-mm spherical mirror with the sensor in its primary focus. The sensor is a Golay cell with high sensitivity in a very wide frequency range. The telescope has a polar mount, and a custom-built data acquisition system based on a 32 ksamples per second, 24 bits (72 dB dynamic range), 8 channels analog-to-digital board. Changing only the composition of the low- and band-pass filters in front of the Golay cell, the telescope can be setup to detect very different frequency bands; making the instrument very versatile. In this article we describe the telescope characteristics and its development status. Moreover, we give estimates of the expected fluxes during flares.
The search for the still unrevealed spectral shape of the mysterious THz solar flare emissions is one of the current most challenging research issues. The concept, fabrication and performance of a ...double THz photometer system, named SOLAR-T, is presented. Its innovative optical setup allows observations of the full solar disk and the detection of small burst transients at the same time. The detecting system was constructed to observe solar flare THz emissions on board of stratospheric balloons. The system has been integrated to data acquisition and telemetry modules for this application. SOLAR-T uses two Golay cell detectors preceded by low-pass filters made of rough surface primary mirrors and membranes, 3 and 7 THz band-pass filters, and choppers. Its photometers can detect small solar bursts (tens of solar flux units) with sub second time resolution. Tests have been conducted to confirm the entire system performance, on ambient and low pressure and temperature conditions. An artificial Sun setup was developed to simulate performance on actual observations. The experiment is planned to be on board of two long-duration stratospheric balloon flights over Antarctica and Russia in 2014–2016.
Solar observations in the mid-infrared 8 – 14 μm band continuum were carried out with cadence of 5 frames per second, in December 2007. Rapid small heated sources, with a typical duration of the ...order of seconds, were found on the bright plage-like areas around sunspots, in association with relatively weak GOES soft X-ray bursts. This work presents the analysis of fast mid-infrared flashes detected during a GOES B2.0-class event on 10 December 2007, beginning at about 10:40 UT. Rapid brightness temperature enhancements of 0.5 to 2.0 K were detected at the Earth by a microbolometer array, using a telescope with 10.5 cm diameter aperture producing a diffraction-limited photometric beam of 25 arc sec. The minimum detectable temperature change was of 0.1 K. The corresponding fluxes are 30 – 130 solar flux units. At the solar surface the estimated rapid brightenings represented a temperature enhancement of 50 – 150 K.
A new solar burst emission spectral component has been found showing sub-THz fluxes increasing with frequency, spectrally separated from the well known microwave component bringing serious ...constraints for the interpretation. The THz spectral component might be the evidence of synchrotron emission from high energy electrons peaking somewhere in the far IR range. The knowledge of THz continuum spectral shape is therefore essential to investigate the nature of the emission mechanisms involved. Sub-THz solar flare flux data are available from observations carried out at El Leoncito high altitude observatory, at two atmosphere transmission windows (0.2 and 0.4 THz). We describe the results from developments addressed to the construction of solar flare radiometers at two frequencies to operate outside the terrestrial atmosphere (i.e. at 3 and 7 THz). The system has been planned as part of the SOLAR-T mission on a stratosphere long-duration balloon flight over Russia sometime in 2013-2016.
Radio and optical observations of the evolution of flare-associated phenomena have shown an initial and rapid burst at 0.4 THz only followed subsequently by a localized chromospheric heating ...producing an H{alpha} brightening with later heating of the whole active region. A major instability occurred several minutes later producing one impulsive burst at microwaves only, associated with an M2.0 GOES X-ray flare that exhibited the main H{alpha} brightening at the same site as the first flash.The possible association between long-enduring time profiles at soft X-rays, microwaves, H{alpha}, and sub-THz wavelengths is discussed. In the decay phase, the H{alpha} movie shows a disrupting magnetic arch structure ejecting dark, presumably chromospheric, material upward. The time sequence of events suggests genuine interdependent and possibly non-thermal instabilities triggering phenomena, with concurrent active region plasma heating and material ejection.
Solar observations at sub-THz frequencies detected a new flare spectral component peaking in the THz range, simultaneously with 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 THz photometer system was developed to observe outside the terrestrial atmosphere on stratospheric balloons or satellites, or at exceptionally transparent ground stations. The telescope was designed to observe the whole solar disk detecting small relative changes in input temperature caused by flares at localized positions. A Golay cell detector is preceded by low-pass filters to suppress visible and near IR radiation, a band-pass filter, and a chopper. A prototype was assembled to demonstrate the new concept and the system performance. It can detect temperature variations smaller than 1 K for data sampled at a rate of 10/s, smoothed for intervals larger than 4 s. For a 76 mm aperture, this corresponds to small solar burst intensities at THz frequencies. A system with 3 and 7 THz photometers is being built for solar flare observations on board of stratospheric balloon missions.
Radio and optical observations of the evolution of flare-associated phenomena have shown an initial and rapid burst at 0.4 THz only followed subsequently by a localized chromospheric heating ...producing an H{\alpha} brightening with later heating of the whole active region. A major instability occurred several minutes later producing one impulsive burst at microwaves only, associated with an M2.0 GOES X-ray flare that exhibited the main H{\alpha} brightening at the same site as the first flash. The possible association between long-enduring time profiles at soft X-rays, microwaves, H{\alpha} and sub-THz wavelengths is discussed. In the decay phase the H{\alpha} movie shows a disrupting magnetic arch structure ejecting dark, presumably chromospheric, material upwards. The time sequence of events suggests genuine interdependent and possibly non-thermal instabilities triggering phenomena, with concurrent active region plasma heating and material ejection.
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