ETD system

Electronic theses and dissertations repository


Tesi etd-05062015-183055

Thesis type
Tesi di laurea magistrale
Panchromatic study of the impulsive phase of solar flares
Corso di studi
relatore Prof. Shore, Steven Neil
Parole chiave
  • sun magnetic field
  • sun corona
  • gamma ray
  • Magnetohydrodynamics
  • magnetic reconnection
  • acceleration of particles
  • astroparticles physics
  • tecniques of imaging spectroscopy
  • x-ray
  • flares
  • Sun
Data inizio appello
Riassunto analitico
My thesis presents a panchromatic study of a set of X-class solar flares that occurred on 2013 May 13th - 15th, using multi-band integrated and polarized radio data from Nobeyama Radio Polarimeter (NoRP) and three satellites: Solar Dynamics Observatory (SDO) for ultraviolet (UV), extreme ultraviolet (EUV) line spectra and the photospheric magnetic field; the GBM instrument on board of the Fermi Gamma-ray Space Telescope and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) for the broad band observations of the x-ray emission.

The analysis of time series in radio and x-ray shows that, in general, the same temporal substructures found in the x-ray thick-target bremsstrahlung emission are also present in the gyro-synchrotron radio emission and that x-ray emission leads the radio one. The interpretation of this effect is that: i) the same particles (i.e. electrons) that are responsible for the x-ray emission are also responsible for the radio emission; ii) X-rays radiation provide the time reference for the emission; the delay of the radio emission is used to derive physical properties of the environment in which the particles are moving (index of refraction of the plasma, structures that constrain the movement of the particles). The radio emission shows a sort of particular ``delay curve'' which has not been described in the literature previously and has been interpreted in this work as the effect of the refraction index of the material that lies along the line of sight, or as the fact that the streaming particles
encounter different magnetic field strength in different location of the loop, causing a change in the gyrosynchrotron frequency.

The the analysis of the combined spatially resolved data in x-ray and EUV confirm that Soft x-ray emission (3 - 50 keV) comes mainly from the looptop and Hard x-ray emission comes mainly from the footpoints. The flare initiation event observed by Masuda et al. (1995) has been resolved in the May 13th. The event was, by chance, a ``flare on the limb'' with soft x-ray emission at different energies coming from different locations near the looptop (the more energetic it is, the higher in the atmosphere it is emitted).

I developed new IDL-based tools for the analysis of the data. For example: i) using spatially resolved data, computes the lightcurve of each resolved element of the visible surface of the Sun, following the rotation of the Sun during the observation; ii) displays a lightcurve (no matter the energy range) and let us instantly compare what is happening on the surface of the Sun (up to five different bands of emission) simply by selecting a point in time on the lightcurve. These tools uncovered another effect which has not been previously reported in the literature: the lightcurve in EUV emission coming exclusively from the loop arms shows a sort of periodic repetition of the footpoint pattern of emission, with a delay compatible with the period of the Magnetoacoustic slow mode of loop oscillation.

Additionally, using the same procedures, I spatially decomposed the lightcurve from the lowest observable layer of the solar atmosphere, where it is supposed that the particle (which are accelerated in the corona) deposit all their kinetic energy. This kind of decomposition locates the emission region of the substructures present on the lightcurve (i.e. single peaks that constitute the whole lightcurve) and provide information about the accelerated particles and the environment in which the process is taking place (i.e. spectrum of accelerated particle for each peak, density of the environment, strength of the magnetic field).

As a by-product of the thesis work, I also made corrections to some procedures included in the standard SolarSoft package. This package is used in solar physics to analyze the data coming from instruments designed to observe the Sun. In particular, the procedures corrected are related to the quality enhancement from Level 1.0 to Level 1.5 of the data from SDO\AIA, which is a crucial point for the analysis performed in this work. These procedures are now public and are included in the SolarSoft package.