H Line Polarization in the Major Flare of 2002 July 23. I. Observations and Data Analysis

Firstova, N. M.; Xu, Zhi; Fang, Cheng

doi:10.1086/378188

Cited by 18 publications

(7 citation statements)

References 11 publications

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“…These measurements will provide information on the electron anisotropy. Such studies, together with other measurements (i.e., radio imaging and spectroscopy [White et al 2003] and with optical [Firstova, Xu, & Fang 2003] polarization) will provide further constraints on the processes of energy release and particle acceleration in flares. 1 j) of the 300-500 and 700-1400 keV bands, respectively, dominated by bremsstrahlung emission.…”

Section: Gamma-ray Line Emissionmentioning

confidence: 99%

RHESSI Observations of Particle Acceleration and Energy Release in an Intense Solar Gamma-Ray Line Flare

Lin¹,

Krucker²,

Hurford³

et al. 2003

ApJ

449

187

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We summarize Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) hard X-ray (HXR) and gray imaging and spectroscopy observations of the intense (X4.8) g-ray line flare of 2002 July 23. In the initial rise, a new type of coronal HXR source dominates that has a steep double-power-law X-ray spectrum and no evidence of thermal emission above 10 keV, indicating substantial electron acceleration to tens of keV early in the flare. In the subsequent impulsive phase, three footpoint sources with much flatter double-power-law HXR spectra appear, together with a coronal superhot ( MK) thermal source. The north footpoint and the coronal T ∼ 40 source both move systematically to the north-northeast at speeds up to ∼50 km s Ϫ1 . This footpoint's HXR flux varies approximately with its speed, consistent with magnetic reconnection models, provided the rate of electron acceleration varies with the reconnection rate. The other footpoints show similar temporal variations but do not move systematically, contrary to simple reconnection models. The g-ray line and continuum emissions show that ions and electrons are accelerated to tens of MeV during the impulsive phase. The prompt de-excitation g-ray lines of Fe, Mg, Si, Ne, C, and O-resolved here for the first time-show mass-dependent redshifts of 0.1%-0.8%, implying a downward motion of accelerated protons and a-particles along magnetic field lines that are tilted toward the Earth by ∼40Њ. For the first time, the positron annihilation line is resolved, and the detailed high-resolution measurements are obtained for the neutron-capture line. The first ever solar g-ray line and continuum imaging shows that the source locations for the relativistic electron bremsstrahlung overlap the 50-100 keV HXR sources, implying that electrons of all energies are accelerated in the same region. The centroid of the ion-produced 2.223 MeV neutron-capture line emission, however, is located ∼ away, implying 20 ‫ע‬ 6 that the acceleration and/or propagation of the ions must differ from that of the electrons. Assuming that Coulomb collisions dominate the energetic electron and ion energy losses (thick target), we estimate that a minimum of ∼ ergs is released in accelerated 1∼20 keV electrons during the rise phase, with ∼10 31 ergs in ions above 31 2 # 10 2.5 MeV nucleon Ϫ1 and about the same in electrons above 30 keV released in the impulsive phase. Much more energy could be in accelerated particles if their spectra extend to lower energies.

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Section: Gamma-ray Line Emissionmentioning

confidence: 99%

RHESSI Observations of Particle Acceleration and Energy Release in an Intense Solar Gamma-Ray Line Flare

Lin¹,

Krucker²,

Hurford³

et al. 2003

ApJ

449

187

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“…The H α spectral observations of this flare also revealed the mustaches with a strong line inversion [ Firstova et al , 2003] observed at 0032:00 UT, just after the second maximum in hard X‐rays, in the location of hard X‐ray foot point B according to their slit position. The linear polarization of 3–10% with the plane of polarization parallel to the solar center direction is attributed to impact polarization that clearly indicates the presence of fast electrons propagating into the X‐ray B foot point located in the eastern ribbon where the slit was placed.…”

Section: Description Of the Datamentioning

confidence: 78%

“…There are also other indications for the presence of high‐energy electrons at the location of the source C, in the H α spectral observations of this flare, which revealed the mustaches appearing at 0032 UT just after the maximum in hard X‐ray emission in the location of the foot point C according to a slit position [ Firstova et al , 2003, Figure 1]. The H α line at these locations had a strong line inversion, its linear polarization was about 3–10% with the plane of polarization parallel to the solar center direction.…”

Section: Observed Magnetic Field Variationsmentioning

confidence: 99%

Toward magnetic field dissipation during the 23 July 2002 solar flare measured with Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

et al. 2005

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[1] We analyze the SOHO/MDI high-cadence magnetic field variations that occurred in a bipolar area around the apparent neutral line (ANL) prior to and during the 2B/X4.8 flare on 23 July 2002 and their association with the hard X-ray (HXR) and H a emission observed with RHESSI and BBSO. Magnetic field changes started 6 min prior to the hard X-ray emission onset in 0.3-2 MeV band or 7 min in the 12-25 keV band and finished 20 min later. Before the flare, there are nine preexisting sources of a strong magnetic field of the positive and negative polarities, and six new magnetic sources associated with the hard X-ray foot points emerged 2 min before the flare maximum: two negative and four positive ones. The difference magnetograms show a steady movement with a speed of 250 km/s of the magnetic field changes toward the northeast, or a 'negative magnetic field discharge' associated with the magnetic energy release in this flare. The magnetic field changes in the whole flaring area are irreversible, showing an increase of the magnetic flux from 6.7 Â 10 21 Mx up to 7.9 Â 10 21 Mx lasting for 6 min and returning after to noise fluctuations about the new magnitude. There is an irreversible increase by À120 G of an absolute magnitude of the negative magnetic field component. The rate of magnetic field changes deduced from the total area around the ANL and from the areas of the hard X-ray foot point with the irreversible changes is about 3.1 Â 10 18 Mx/s, and the average Poynting flux is (5-20) Â 10 11 erg/cm 2 /s. The LOS fraction of a magnetic energy released for the whole flare duration is estimated as $(2.3-10) Â 10 31 erg. The possible scenarios of particle acceleration in this flare are proposed based on HXR and g-ray emission.

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“…According to various authors, Hα and Hβ lines are linearly polarized in solar flares (Hénoux & Semel 1981;Metcalf et al 1992Metcalf et al , 1994Vogt & Hénoux 1996Firstova et al 1997Firstova et al , 2003Firstova et al , 2005Vogt et al 2001;Firstova & Kashapova 2002;Hénoux & Karlický 2003;Hanaoka 2003;Xu et al 2005). On the other hand, Bianda et al (2005), using the ZIMPOL instrument, and Hanaoka (2005) did not find any linear polarization signature in solar flares above a sensitivity level of 0.1%.…”

Section: Introductionmentioning

confidence: 96%

Flare line impact polarization

Hénoux¹,

Karlický²

2013

A&A

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Context. The impact polarization of optical chromospheric lines in solar flares is still being debated. For this reason, additional observations and improved flare atmosphere models are needed still. Aims. The polarization-free telescope THEMIS used in multiline 2 MulTiRaies (MTR) mode allows accurate simultaneous linear polarization measurements in various spectral lines. Methods. In the 2001 June 15 flare, Hα, Hβ, and Mg D2 lines linear impact polarization was reported as present in THEMIS 2 MTR observations. In this paper, THEMIS data analysis was extended to the Na D2 line. Sets of I ± U and I ± Q flare Stokes S 2D-spectra were corrected from dark-current, spectral-line curvature and from transmission differences. Then, we derived the linear polarization degree P and polarization orientation angle α 2D-spectra. No change in relative positioning could be found that would reduce the Stokes parameters U and Q values. No V and I crosstalks could explain our results either. Results. The Na D2 line is linearly polarized with a polarization degree exceeding 5% at some locations. The polarization was found to be radial at outer ribbons edges, and tangential at their inner edges. This orientation change may be due to differences in electron distribution functions on the opposite borders of flare chromospheric ribbons. Electron beams propagating along magnetic field lines, together with return currents, could explain both radial and tangential polarization. At the inner ribbon edges, intensity profile-width enlargements and blueshifts in polarization profiles are observed. This suggests chromospheric evaporation.

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H Line Polarization in the Major Flare of 2002 July 23. I. Observations and Data Analysis

Cited by 18 publications

References 11 publications

RHESSI Observations of Particle Acceleration and Energy Release in an Intense Solar Gamma-Ray Line Flare

RHESSI Observations of Particle Acceleration and Energy Release in an Intense Solar Gamma-Ray Line Flare

Toward magnetic field dissipation during the 23 July 2002 solar flare measured with Solar and Heliospheric Observatory/Michelson Doppler Imager (SOHO/MDI) and Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI)

Flare line impact polarization

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