List of Figures

Watch/download Movie Figure 1: (mpeg-Movie; 14976 KB)
Movie Soft X-rays (red), hard X-rays (blue) and gamma-rays (purple) observed by the RHESSI satellite are overlaid on an optical Hα image. The movie starts in white light zooming into an active region. The color then changes to the Hα line of hydrogen, emitted in the chromosphere. Its brightening indicates the start of the flare. Visualization by RHESSI scientists.
View Image Figure 2:
A schematic profile of the flare intensity at several wavelengths. The various phases indicated at the top vary greatly in duration. In a large event, the preflare phase typically lasts a few minutes, the impulsive phase 3 to 10 minutes, the flash phase 5 to 20 minutes, and the decay one to several hours (from Benz, 2002).
Watch/download Movie Figure 3: (mov-Movie; 15436 KB)
Movie Flare observed in the Fe xii line at 195 Å (sensitive to 1.5 MK plasma) by the TRACE satellite. Note the different phases, starting with irregular brightnings in the impulsive phase. The luminosity peaks when a sheet-like structures appears above the initial brightening. The diffuse emission at this time is attributed to the presence of the Fe xxiv (192 Å) line within the TRACE passband, emitted by a plasma of 20 MK. The flare proceeds into a long decay phase with post-flare loops growing in height.
Watch/download Movie Figure 4: (mpg-Movie; 15763 KB)
Movie Zoom into an active region where a large flare took place on April 21, 2002. The movie starts in white light observed by the SOHO/MDI instrument, adds the coronal images observed by the SOHO/LASCO coronagraph, then changes to extreme ultraviolet observed by SOHO/EIT and later by the TRACE satellite, and later the RHESSI observations of the flare in soft X-rays (red) and hard X-rays (blue). The focus then goes to the associated coronal mass ejection observed by the coronagraph. The movie ends in a storm of streaks produced by energetic flare particles (mostly protons), hitting the detectors on the Solar and Heliospheric Observatory (SOHO) in space. Visualization by RHESSI scientists.
Watch/download Movie Figure 5: (gif-Movie; 4562 KB)
Movie Left: White light image of a sunspot taken with SOT on board the Hinode satellite. The resolution is 2”. Visualization by Hinode scientists. Right: Vector magnetogram showing in red the direction of the magnetic field and its strength (length of the bar). The movie shows the evolution in the photospheric fields that has led to an X class flare in the lower part of the active region. Courtesy of NAOJ/NINS.
View Image Figure 6:
Map of the line-of-sight magnetic field strength measured in a photospheric line by the MSFC magnetograph. Solid curves denote positive field, dashed curves the negative field, and the dotted curve the neutral line. Circles indicate where the transverse field deviates between 70 ∘ and 80∘ from the potential field (perpendicular to the neutral line), and filled squares indicate deviations ∘ > 80. A large flare (X3 class) occurred several hours later at the location of the largest shear (from Hagyard et al., 1990).
View Image Figure 7:
Typical X-ray spectrum of flare observed by the RHESSI satellite. The soft part is fitted with a thermal component (green) having a temperature of 16.7 MK, and the high-energy part with a power law having two breaks at 12 keV (possibly due to the acceleration process if real) and at 50 keV, of which the origin is unknown (Grigis and Benz, 2004).
Watch/download Movie Figure 8: (mpg-Movie; 1895 KB)
Movie Hard X-ray footpoints (with error bars) observed with the RHESSI satellite during the flare of November 9, 2002. Simultaneous footpoints are connected by a line colored sequentially with time. The footpoint information is overlaid on a SOHO/EIT image at 195 Å, indicating enhanced density in the corona. The movie shows two simultaneous footpoints connected by a vertical half-circle. The flux at each footpoint is indicated by the size of the purple circle at logarithmic scale (from Grigis and Benz, 2005a), courtesy of Paolo Grigis.
Watch/download Movie Figure 9: (mpg-Movie; 9784 KB)
Movie Left: RHESSI flare observations of soft X-rays (red, 8 – 12 keV) and hard X-rays (blue, 20 – 50 keV) overlaid on an Hα background. Note the high-energy footpoints moving on the Hα flare ribbons, which moves apart in the very late phase. Visualization by RHESSI scientists.
View Image Figure 10:
Image of a solar flare in hard X-rays observed by the RHESSI satellite. The curved line indicates the limb of the photosphere. The displayed energy range 12 – 50 keV is dominated by the low energies, where the coronal source (right) prevails. Two footpoints (left) are clearly visible on the disk. The spider like structures are mostly artifacts of image reconstruction (from Battaglia and Benz, 2007).
View Image Figure 11:
Spectra of the three sources shown in Figure 10 as observed by RHESSI at peak time. Left and middle: Spectra of footpoints. A power-law was fitted in energy between the dotted lines. Right: Spectrum of the coronal source. A power-law and a thermal population was fit between the dashed lines (from Battaglia and Benz, 2007).
View Image Figure 12:
The derivation of the soft X-ray flux (observation by the GOES satellite) correlates in 80% of the flares with the hard X-ray flux (observation of the RHESSI satellite). This is an example of what is called the Neupert effect (from Dennis and Zarro, 1993).
View Image Figure 13:
A schematic drawing of the standard flare scenario assuming energy release at high altitudes.
View Image Figure 14:
Averaged density profile along a loop inferred from the separation of X-ray footpoints, moving up the flare loop in a very dense flare. Note the increase in density between the first profile (dashed) and last profile (dotted). The loop fills up in between from the bottom (solid curve) (from Liu et al., 2006).
View Image Figure 15:
RHESSI observations at 6 – 12 keV (red) and 25 – 50 keV (blue) of a coronal flare. The high-energy photons have a non-thermal origin and originate near the loop-top without pronounced footpoints (Veronig and Brown, 2004).
View Image Figure 16:
Left: A schematic drawing of the one-loop flare model. Right: Observation of an apparent X-point behind a Coronal Mass Ejection observed by LASCO/SOHO in white light.
Watch/download Movie Figure 17: (gif-Movie; 265 KB)
Movie Thermal emission and a flare observed with the Nobeyama interferometer at 17 GHz. The event has the classic signatures of an event associated with a coronal mass ejection: motion is seen first in the prominence material, then the flare goes off, leaving long-duration soft-X-ray emitting loops around for several hours. Note that the prominence material is at a temperature of less than 10,000 degrees K (shown at top), whereas the flare loops come from material at 10 MK: both cool and hot material show up at this radio frequency. The left panel shows total intensity, and the right panel shows circularly-polarized radio emission. Polarization is only detected during the early phase of the flare, when very energetic electrons fill up the loop and emit intense synchrotron radiation. Courtesy of Stephen White.
View Image Figure 18:
Spectrogram of type III radio bursts (drifting structures in the upper right) and meter wave type of narrowband spikes (center) (from Benz et al., 1996).
View Image Figure 19:
Reconstructed trajectories of two radio events involving type III bursts and spikes, both of the kind often observed at meter wavelength. Upper right: Positions with error bars observed by the Nancay Radio Heliograph at three frequencies. The symbols represent the observed frequencies: × for 327.0 MHz, □ for 236.6 MHz, and △ for 164.0 MHz. Bottom left: Position of the radio emissions on the Sun. The small square indicates the size of the image presented in the upper right image. Upper left: Projection of the sources on the meridian plane (as seen by an observer West of the source as seen from Earth). Lower right: The radio sources projected on the equatorial plane, showing the view of an observer North of the Sun). In both graphs the trajectories have been 3-dimensionally spline interpolated to outline the trajectory (Paesold et al., 2001).
View Image Figure 20:
RHESSI gamma-ray spectrum from 0.3 to 10 MeV integrated over the duration of the flare of July 23, 2002. The lines show the different components of the model used to fit the spectrum (Lin et al., 2003).
View Image Figure 21:
Location of the gamma-ray sources observed by the RHESSI satellite on October 28, 2003. The contours at 50%, 70%, and 90% of the peak value show in blue the deuterium recombination line at 2.223 MeV and red the electron bremsstrahlung at 200 – 300 keV. The centroid positions of the bremsstrahlung emission at different times are indicated by plus signs. The FWHM angular resolution is 35”, given at bottom left. The RHESSI data are overlaid on the negative of a TRACE 195 Å image dominated by the emission of Fe xii (Hurford et al., 2006).
Watch/download Movie Figure 22: (mpg-Movie; 1139 KB)
Movie Soft X-ray images observed by Hinode on April 30, 2007. It shows an active region during two hours. Some small flares or microflares occurred; the largest was of class B2.6 (prepared by A. Savcheva).
View Image Figure 23:
Overlays of RHESSI hard X-ray (orange) and white light difference (thick blue) image contours on a white-light image observed by the TRACE satellite. The thin white contours show white light contours as observed by MDI on SOHO; the accuracy of the pointing can be assessed by comparing the white light background observed by MDI and TRACE (Fletcher et al., 2007).
Watch/download Movie Figure 24: (mpg-Movie; 3460 KB)
Movie An overview in Fe xii EUV emission observed by EIT/SOHO, later zooming into the observations by TRACE, both showing thermal coronal emission of a plasma at about 1.5 MK. The 12 – 25 keV hard X-ray emission observed by RHESSI is shown in red and yellow colors (courtesy of Pascal Saint-Hilaire).
View Image Figure 25:
Time profile of nanoflare observed in Fe xi/x, and Fe xii lines at 17.1 nm and 19.5 nm by EIT/SOHO. Top panel: temperature averaged over the area of the event; second panel: the emission measure; third panel: radio flux observed by the VLA at 6 and 3.6 cm wavelength at the location of the 6 cm peak; bottom panel: same at the location of the 3.6 cm peak.
View Image Figure 26:
Top: Light curves in two energy bands (upper curve, 6 – 12 keV ; lower curve, 25 – 50 keV) of the April 15, 2002 flare observed by RHESSI. Bottom: Altitude of the loop-top centroid obtained using the 60% contour for the images in the 6 – 12 (crosses) and 12 – 25 keV (diamonds) bands. The triangles show the altitude of the lower source above the flare loop. The horizontal bars on each point represents the integration time of the corresponding image. The lines show linear fits to the altitudes vs. time for two time ranges and two energy bands (from Sui et al., 2004).
View Image Figure 27:
Flux density at 35 keV and power-law index as determined from RHESSI observations of the non-thermal component of flare hard X-ray emission. Colors mark individual subpeaks. The close correlation demonstrates soft-hard-soft behavior in the smallest details (from Grigis and Benz, 2004).
View Image Figure 28:
Radio spectrogram observed by the Phoenix-2 spectro-polarimeter operated by ETH Zurich. At low frequencies (top of image), the radio emission is dominated by type III bursts and U bursts emitted by escaping electron beams and trapped electron beams. The brightest feature is a type V event, possibly caused by electrons left behind by unstable beams. At high frequencies (bottom of image) the synchrotron emission of mildly relativistic electrons (gyrosynchrotron) dominates, correlating well with hard X-rays. In the middle of the frequency range at about 800 – 2000 MHz, narrowband spikes of the decimetric type can be seen.
Watch/download Movie Figure 29: (mpg-Movie; 2079 KB)
Movie The particle distribution vs. energy in time (blue) as described by Equation (9View Equation). A tail develops out of the thermal distribution (purple). The solution becomes stationary after about one second when acceleration balances particle escape out of the acceleration region. The spectral index resulting from fitting a power-law in the region limited by dashed red lines is also shown (from Grigis and Benz, 2006).