42 research outputs found
The 6 September 2017 X9 super flare observed from submillimeter to mid-IR
Active Region 12673 is the most productive active region of solar cycle 24: in a few days of early September 2017, four Xâclass and 27 Mâclass flares occurred. SOL2017â09â06T12:00, an X9.3 flare also produced a twoâribbon white light emission across the sunspot detected by Solar Dynamics Orbiter/Helioseismic and Magnetic Imager. The flare was observed at 212 and 405 GHz with the arcminuteâsized beams of the Solar Submillimeter Telescope focal array while making a solar map and at 10 ÎŒm, with a 17 arcsec diffractionâlimited infrared camera. Images at 10 ÎŒm revealed that the sunspot gradually increased in brightness while the event proceeded, reaching a temperature similar to quiet Sun values. From the images we derive a lower bound limit of 180âK flare peak excess brightness temperature or 7,000 sfu if we consider a similar size as the white light source. The rising phase of midâIR and white light is similar, although the latter decays faster, and the maximum of the midâIR and white light emission is âŒ200 s delayed from the 15.4âGHz peak occurrence. The submillimeter spectrum has a different origin than that of microwaves from 1 to 15 GHz, although it is not possible to draw a definitive conclusion about its emitting mechanism
A bright impulsive solar burst detected at 30 THz
Ground- and space-based observations of solar flares from radio wavelengths
to gamma-rays have produced considerable insights but raised several unsolved
controversies. The last unexplored wavelength frontier for solar flares is in
the range of submillimeter and infrared wavelengths. Here we report the
detection of an intense impulsive burst at 30 THz using a new imaging system.
The 30 THz emission exhibited remarkable time coincidence with peaks observed
at microwave, mm/submm, visible, EUV and hard X-ray wavelengths. The emission
location coincides with a very weak white-light feature, and is consistent with
heating below the temperature minimum in the atmosphere. However, there are
problems in attributing the heating to accelerated electrons. The peak 30 THz
flux is several times larger than the usual microwave peak near 9 GHz,
attributed to non-thermal electrons in the corona. The 30 THz emission could be
consistent with an optically thick spectrum increasing from low to high
frequencies. It might be part of the same spectral component found at sub-THz
frequencies whose nature remains mysterious. Further observations at these
wavelengths will provide a new window for flare studies.Comment: 9 pages, 11 figures, accepted by Astrophysical Journal, March 23,
201
Comparison of 30 THz impulsive burst time development to microwaves, H-alpha, EUV, and GOES soft X-rays
The recent discovery of impulsive solar burst emission in the 30 THz band is
raising new interpretation challenges. One event associated with a GOES M2
class flare has been observed simultaneously in microwaves, H-alpha, EUV, and
soft X-ray bands. Although these new observations confirm some features found
in the two prior known events, they exhibit time profile structure
discrepancies between 30 THz, microwaves, and hard X-rays (as inferred from the
Neupert effect). These results suggest a more complex relationship between 30
THz emission and radiation produced at other wavelength ranges. The multiple
frequency emissions in the impulsive phase are likely to be produced at a
common flaring site lower in the chromosphere. The 30 THz burst emission may be
either part of a nonthermal radiation mechanism or due to the rapid thermal
response to a beam of high-energy particles bombarding the dense solar
atmosphere.Comment: accepted to Astronomy and Astrophysic
Exponential behavior of a quantum system in a macroscopic medium
An exponential behavior at all times is derived for a solvable dynamical
model in the weak-coupling, macroscopic limit. Some implications for the
quantum measurement problem are discussed, in particular in connection with
dissipation.Comment: 8 pages, report BA-TH/94-17
Macroscopic limit of a solvable dynamical model
The interaction between an ultrarelativistic particle and a linear array made
up of two-level systems (^^ ^^ AgBr" molecules) is studied by making use of
a modified version of the Coleman-Hepp Hamiltonian. Energy-exchange processes
between the particle and the molecules are properly taken into account, and the
evolution of the total system is calculated exactly both when the array is
initially in the ground state and in a thermal state. In the macroscopic limit
(), the system remains solvable and leads to interesting
connections with the Jaynes-Cummings model, that describes the interaction of a
particle with a maser. The visibility of the interference pattern produced by
the two branch waves of the particle is computed, and the conditions under
which the spin array in the limit behaves as a ^^ ^^
detector" are investigated. The behavior of the visibility yields good insights
into the issue of quantum measurements: It is found that, in the
thermodynamical limit, a superselection-rule space appears in the description
of the (macroscopic) apparatus. In general, an initial thermal state of the ^^
^^ detector" provokes a more substantial loss of quantum coherence than an
initial ground state. It is argued that a system decoheres more as the
temperature of the detector increases. The problem of ^^ ^^ imperfect
measurements" is also shortly discussed.Comment: 30 pages, report BA-TH/93-13
Factorization in the model of unstable particles with continuous masses
We study processes with unstable particles in intermediate time-like states.
It is shown that the amplitudes squared of such processes factor exactly in the
framework of the model of unstable particles with continuous masses. Decay
widths and cross sections can then be represented in a universal factorized
form for an arbitrary set of interacting particles. This exact factorization is
caused by specific structure of propagators in the model. We formulate the
factorization method and perform a phenomenological analysis of the
factorization effects. The factorization method considerably simplifies
calculations while leading to compact and reasonable results.Comment: 20 pages, 6 figure
Spectral Trends Of Solar Bursts At Sub-thz Frequencies
Previous sub-THz studies were derived from single-event observations. We here analyze for the first time spectral trends for a larger collection of sub-THz bursts. The collection consists of a set of 16 moderate to small impulsive solar radio bursts observed at 0.2 and 0.4 THz by the Solar Submillimeter-wave Telescope (SST) in 2012 â 2014 at El Leoncito, in the Argentinean Andes. The peak burst spectra included data from new solar patrol radio telescopes (45 and 90 GHz), and were completed with microwave data obtained by the Radio Solar Telescope Network, when available. We critically evaluate errors and uncertainties in sub-THz flux estimates caused by calibration techniques and the corrections for atmospheric transmission, and introduce a new method to obtain a uniform flux scale criterion for all events. The sub-THz bursts were searched during reported GOES soft X-ray events of class C or larger, for periods common to SST observations. Seven out of 16 events exhibit spectral maxima in the range 5 â 40 GHz with fluxes decaying at sub-THz frequencies (three of them associated to GOES class X, and four to class M). Nine out of 16 events exhibited the sub-THz spectral component. In five of these events, the sub-THz emission fluxes increased with a separate frequency from that of the microwave spectral component (two classified as X and three as M), and four events have only been detected at sub-THz frequencies (three classified as M and one as C). The results suggest that the THz component might be present throughout, with the minimum turnover frequency increasing as a function of the energy of the emitting electrons. The peculiar nature of many sub-THz burst events requires further investigations of bursts that are examined from SST observations alone to better understand these phenomena. © 2017, Springer Science+Business Media Dordrecht.292