854 research outputs found
Evidence of widespread hot plasma in a non-flaring coronal active region from Hinode/XRT
Nanoflares, short and intense heat pulses within spatially unresolved
magnetic strands, are now considered a leading candidate to solve the coronal
heating problem. However, the frequent occurrence of nanoflares requires that
flare-hot plasma be present in the corona at all times. Its detection has
proved elusive until now, in part because the intensities are predicted to be
very faint. Here we report on the analysis of an active region observed with
five filters by Hinode/XRT in November 2006. We have used the filter ratio
method to derive maps of temperature and emission measure both in soft and hard
ratios. These maps are approximate in that the plasma is assumed to be
isothermal along each line-of-sight. Nonetheless, the hardest available ratio
reveals the clear presence of plasma around 10 MK. To obtain more detailed
information about the plasma properties, we have performed Monte Carlo
simulations assuming a variety of non-isothermal emission measure distributions
along the lines-of-sight. We find that the observed filter ratios imply
bi-modal distributions consisting of a strong cool (log T ~ 6.3-6.5) component
and a weaker (few percent) and hotter (6.6 < log T < 7.2) component. The data
are consistent with bi-modal distributions along all lines of sight, i.e.,
throughout the active region. We also find that the isothermal temperature
inferred from a filter ratio depends sensitively on the precise temperature of
the cool component. A slight shift of this component can cause the hot
component to be obscured in a hard ratio measurement. Consequently, temperature
maps made in hard and soft ratios tend to be anti-correlated. We conclude that
this observation supports the presence of widespread nanoflaring activity in
the active region.Comment: 12 figures, accepted for publication on refereed journa
The space physics environment data analysis system (SPEDAS)
With the advent of the Heliophysics/Geospace System Observatory (H/GSO), a complement of multi-spacecraft missions and ground-based observatories to study the space environment, data retrieval, analysis, and visualization of space physics data can be daunting. The Space Physics Environment Data Analysis System (SPEDAS), a grass-roots software development platform (www.spedas.org), is now officially supported by NASA Heliophysics as part of its data environment infrastructure. It serves more than a dozen space missions and ground observatories and can integrate the full complement of past and upcoming space physics missions with minimal resources, following clear, simple, and well-proven guidelines. Free, modular and configurable to the needs of individual missions, it works in both command-line (ideal for experienced users) and Graphical User Interface (GUI) mode (reducing the learning curve for first-time users). Both options have “crib-sheets,” user-command sequences in ASCII format that can facilitate record-and-repeat actions, especially for complex operations and plotting. Crib-sheets enhance scientific interactions, as users can move rapidly and accurately from exchanges of technical information on data processing to efficient discussions regarding data interpretation and science. SPEDAS can readily query and ingest all International Solar Terrestrial Physics (ISTP)-compatible products from the Space Physics Data Facility (SPDF), enabling access to a vast collection of historic and current mission data. The planned incorporation of Heliophysics Application Programmer’s Interface (HAPI) standards will facilitate data ingestion from distributed datasets that adhere to these standards. Although SPEDAS is currently Interactive Data Language (IDL)-based (and interfaces to Java-based tools such as Autoplot), efforts are under-way to expand it further to work with python (first as an interface tool and potentially even receiving an under-the-hood replacement). We review the SPEDAS development history, goals, and current implementation. We explain its “modes of use” with examples geared for users and outline its technical implementation and requirements with software developers in mind. We also describe SPEDAS personnel and software management, interfaces with other organizations, resources and support structure available to the community, and future development plans.Published versio
Where is the chromospheric response to conductive energy input from a hot pre-flare coronal loop?
Before the onset of a flare is observed in hard X-rays there is often a pro- longed pre-flare or pre-heating phase with no detectable hard X-ray emission but pronounced soft X-ray emission suggesting that energy is being released and deposited into the corona and chromosphere already at this stage. This work analyses the temporal evolution of coronal source heating and the chromospheric response during this pre-heating phase to investigate the origin and nature of early energy release and transport during a solar flare. Simultaneous X-ray, EUV, and microwave observations of a well observed flare with a prolonged pre-heating phase are analysed to study the time evolution of the thermal emission and to determine the onset of particle acceleration. During the 20 minutes duration of the pre-heating phase we find no hint of accelerated electrons, neither in hard X-rays nor in microwave emission. However, the total energy budget during the pre-heating phase suggests that energy must be supplied to the flaring loop to sustain the observed temperature and emission measure. Under the assumption of this energy being transported toward the chromosphere via thermal conduc- tion, significant energy deposition at the chromosphere is expected. However, no detectable increase of the emission in the AIA wavelength channels sensitive to chromospheric temperatures is observed. The observations suggest energy release and deposition in the flaring loop before the onset of particle acceleration, yet a model in which energy is conducted to the chromosphere and subsequent heating of the chromosphere is not supported by the observations
Relations between concurrent hard X-ray sources in solar flares
Context: Solar flares release a large fraction of their energy into
non-thermal electrons, but it is not clear where and how. Bremsstrahlung X-rays
are observed from the corona and chromosphere.
Aims: We aim to characterize the acceleration process by the coronal source
and its leakage toward the footpoints in the chromosphere. The relations
between the sources reflect the geometry and constrict the configuration of the
flare.
Methods: We studied solar flares of GOES class larger than M1 with three or
more hard X-ray sources observed simultaneously in the course of the flare. The
events were observed with the X-ray satellite RHESSI from February 2002 until
July 2005. We used imaging spectroscopy methods to determine the spectral
evolution of each source in each event. The images of all of the five events
show two sources visible only at high energies (footpoints) and one source only
visible at low energies (coronal or looptop source, in two cases situated over
the limb).
Results: We find soft-hard-soft behavior in both, coronal source and
footpoints. The coronal source is nearly always softer than the footpoints. The
footpoint spectra differ significantly only in one event out of five.
Conclusions: The observations are consistent with acceleration in the coronal
source and an intricate connection between the corona and chromosphere.Comment: accepted for publication in A&A, 11 pages, 9 figure
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