Observational evidences for multi-component magnetic field structure in solar flares

Abstract

Two solar flares of 25 July 1981 and 5 November 2004 of importance 2N and M4.1/1B, respectively, were investigated using observational data obtained with the Echelle spectrograph of the Kyiv University Astronomical Observatory. Stokes I and V profiles of the FeI lines 5233, 5247.1, 5250.2, 5250.6, 5576.1 and of CrI 5247.6 Å have been analyzed. We found several evidences for the existence of spatially unresolved magnetic field structures with kG strengths. In particular, the values of the measured average longitudinal field B depend on the Lande factors g of the lines: in general, B increases with increasing factor g. Analogously, the observed line ratio B (5250.2)/B (5247.1) is increasing with increasing distance λ from the line center. The observed Stokes V profiles show some deviations from that of an assumed homogeneous field, presented by the Stokes I gradient, dI /dλ. A comparison with the non-split line FeI 5576.1 Å shows that some of these deviations are real and indicate the presence of subtelescopic magnetic elements with discrete field strengths of several kG. The lines with large Lande factors have considerable broadenings of the Stokes I profiles, indicating a strong background magnetic field of mixed polarity. On the basis of all these data we conclude that a four-component magnetic field structure is a possible explanation. The field strengths are about ±1.05 kG in the background field, and 1.3-1.5, 3.9-4.0, and 7.4-7.8 kG at level of middle photosphere (h ≈ 300 km) in the spatially unresolved, small-scale magnetic elements.

Small-scale magnetic field diagnostics in solar flares using bisectors of I±V profiles

“…Similar peaks were observed by Lozitsky (1980 in non-flare regions, and Lozitsky and Staude (2008) in two flares. In X17.2/4B superflare of 28 October 2003, Lozitsky (2009a) observed in FeI 5233 a very strong effect in the splitting of bisectors of I ± V profiles (local maximum) which was placed on 160-200 mÅ 0 -approximately in the same position, as the second peak in Figs.…”

“…Generally, two approaches are used to evaluate unresolved magnetic field based on Zeeman effect: a classical 'line-ratio' method of comparing splitting of several spectral lines with different magnetic sensitivity (e.g., Howard and Stenflo, 1972;Lozitsky and Staude, 2008) and a method of comparing Zeeman splitting of different parts of spectral lines (e.g., Stenflo, 1973;Lozitsky, 1980;Harvey, 2012). Several attempts been have made to determine the field strength in unresolved magnetic elements in solar flares, as well as their temporal evolution.…”

Comparison of the magnetic fields in active prominences measured from the He I D3 and Hα lines

“…Since the shape of the bisectors resembles the Latin letter V , this feature was previously called the V effect. A twocomponent magnetic field structure (Lozitsky 2003;Lozitsky and Staude 2008), when a narrower profile with a large splitting is superimposed on a wider profile with a small splitting, is probably responsible for this effect. A larger splitting then appears in the overall picture where the intensity contributions only from the narrow component are present in the spectrum.…”

“…Several methods for the measurements of local subtelescopic fields have been suggested for photospheric magnetic fields: the line ratio method and its modifications (Stenflo 1973;Lozitska and Lozitskij 1994;Lozitsky et al 2000), an analysis of the dependence of the relative measured strength on the magnetic sensitivity factor gλ 2 (Lozitskij 1980), and a study of the dependences of the splitting of the I ± V profile bisectors Δλ В on the ratio Δλ/gλ 2 , where Δλ is the distance from the line center (Lozitsky and Staude 2008). However, all these methods require using several spectral lines with close formation depths and temperature sensitivities but with different Lande factors.…”

Simultaneous Magnetic Field Measurements in Sunspots Using Spectral Lines With Different Lande Factors

“…In spectra of powerful solar flares this line has sometimes appreciable splitting of narrow emissive peaks at its core that correspond to magnetic field strength of about several tens kG (see, e.g., Lozitsky, 2011Lozitsky, , 2015.…”