Coronal Shock Waves, EUV waves, and Their Relation to CMEs. I. Reconciliation of "EIT waves", Type II Radio Bursts, and Leading Edges of CMEs

We show examples of excitation of coronal waves by flare-related abrupt eruptions of magnetic rope structures. The waves presumably rapidly steepened into shocks and freely propagated afterwards like decelerating blast waves that showed up as Moreton waves and EUV waves. We propose a simple quantitative description for such shock waves to reconcile their observed propagation with drift rates of metric type II bursts and kinematics of leading edges of coronal mass ejections (CMEs). Taking account of different plasma density falloffs for propagation of a wave up and along the solar surface, we demonstrate a close correspondence between drift rates of type II bursts and speeds of EUV waves, Moreton waves, and CMEs observed in a few known events.Comment: 30 pages, 15 figures. Solar Physics, published online. The final publication is available at http://www.springerlink.co

The multifrequency Siberian Radioheliograph

The 10-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the LAN. The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West-East-South subarray of the SSRT. The radioheliograph will be fully constructed in autumn of 2012. We plan to reach the brightness temperature sensitivity about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and polarization measurement accuracy about a few percent. First results with the 10-antenna prototype are presented of observations of solar microwave bursts. The prototype abilities to estimate source size and locations at different frequencies are discussed

Hall effect and magnetic ordering in RB₁₂

The concentration of carriers in LuB₁₂ is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high precision measurements of the Hall RH(T) coefficient which were carried out on single crystals of the rare earth dodecaborides RB₁₂ (R = Ho, Er, Tm, Lu) at temperatures 1.8–300 K. A nature of the antiferromagnetic ordering in RB₁₂ is investigated within the RKKY-like model, which was supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic and antiferromagnetic phases

Coronal Shock Waves, EUV Waves, and Their Relation to CMEs. III. Shock-Associated CME/EUV Wave in an Event with a Two-Component EUV Transient

On 17 January 2010, STEREO-B observed in extreme ultraviolet (EUV) and white light a large-scale dome-shaped expanding coronal transient with perfectly connected off-limb and on-disk signatures. Veronig et al. (2010, ApJL 716, 57) concluded that the dome was formed by a weak shock wave. We have revealed two EUV components, one of which corresponded to this transient. All of its properties found from EUV, white light, and a metric type II burst match expectations for a freely expanding coronal shock wave including correspondence to the fast-mode speed distribution, while the transient sweeping over the solar surface had a speed typical of EUV waves. The shock wave was presumably excited by an abrupt filament eruption. Both a weak shock approximation and a power-law fit match kinematics of the transient near the Sun. Moreover, the power-law fit matches expansion of the CME leading edge up to 24 solar radii. The second, quasi-stationary EUV component near the dimming was presumably associated with a stretched CME structure; no indications of opening magnetic fields have been detected far from the eruption region.Comment: 18 pages, 10 figures. Solar Physics, published online. The final publication is available at http://www.springerlink.co

Eruptions of Magnetic Ropes in Two Homologous Solar Events on 2002 June 1 and 2: a Key to Understanding of an Enigmatic Flare

The goal of this paper is to understand the drivers, configurations, and scenarios of two similar eruptive events, which occurred in the same solar active region 9973 on 2002 June 1 and 2. The June 2 event was previously studied by Sui, Holman, and Dennis (2006, 2008), who concluded that it was challenging for popular flare models. Using multi-spectral data, we analyze a combination of the two events. Each of the events exhibited an evolving cusp-like feature. We have revealed that these apparent ``cusps'' were most likely mimicked by twisted magnetic flux ropes, but unlikely to be related to the inverted Y-like magnetic configuration in the standard flare model. The ropes originated inside a funnel-like magnetic domain whose base was bounded by an EUV ring structure, and the top was associated with a coronal null point. The ropes appear to be the major drivers for the events, but their rise was not triggered by reconnection in the coronal null point. We propose a scenario and a three-dimensional scheme for these events in which the filament eruptions and flares were caused by interaction of the ropes.Comment: 22 pages, 11 figure

Pressure effect on electronic structure and magnetic properties of iron-based high Tс superconductors

Pressure effects on electronic structure and magnetic properties of iron-based superconductors FeSe1−xTex (x ≃ 0, 0.5 and 1.0) and LaFeAsO are investigated. The superconducting transition was observed at TC ≃ 8, 13.6−14.2, and 26 K in FeSe₀.₉₆₃, FeSe₀.₅Te₀.₅, and LaFeAsO₀.₈₅F₀.₁, respectively. The intrinsic magnetic susceptibility χ in the series of FeSe₀.₉₆₃, FeSe₀.₅Te₀.₅ and FeTe is found to increase gradually approximately 10 times as much with Te content. A kink in the low-field dependence of χ(T) was detected at TM ≃ 135 K for LaFeAsO₀.₈₅F₀.₁. The electronic structures and paramagnetic susceptibilities of the studied compounds are calculated ab initio in external magnetic field as a function of atomic volume and structural parameter Z, which specifies the relative height of chalcogen atoms above iron plane. The calculated field-induced magnetic moments and their volume derivatives indicate that these systems are in a close proximity to a quantum critical point. For FeSe and FeTe the calculated paramagnetic susceptibilities reveal a large magnetovolume effect and a drastic sensitivity to parameter Z.Досліджено вплив тиску на електронну структуру та магнітні властивості надпровідників на основі заліза FeSe1−xTex (x ≃ 0, 0.5 та 1.0) й LaFeAsO. Перехід в надпровідний стан в сполуках FeSe₀.₉₆₃, FeSe₀.₅Te₀.₅ й LaFeAsO₀.₈₅F₀.₁ спостерігався відповідно при TC ≃ 8, 13.6−14.2 та 26 K. Визначено, що притаманна сполукам магнітна сприйнятливість χ в ряду FeSe₀.₉₆₃, FeSe₀.₅Te₀.₅ й FeTe поступово збільшується приблизно на порядок величини зі зростанням концентрації телуру. Для сполуки LaFeAsO₀.₈₅F₀.₁ на виміряній в слабкому полі залежності χ(T) виявлена особливість у вигляді зламу поблизу температури TM ≃ 135 K. Для досліджуваних сполук здійснено ab initio розрахунки електронної структури й парамагнітної сприйнятливості в залежності від атомного об’єму і структурного параметру Z, що визначає висоту атомів халькогену відносно площини атомів заліза. Розрахунки індукованих полем магнітних моментів та їх об’ємних похідних вказують на близькість цих сполук до квантової критичної точки. Для сполук FeSe й FeTe розраховані парамагнітні сприйнятливості виявляють значний магнітооб’ємний ефект та екстремальну чутливість до параметру Z.Изучены эффекты давления на электронную структуру и магнитные свойства сверхпроводников на основе железа FeSe1−xTex (x ≃ 0, 0.5 и 1.0) и LaFeAsO. Переход в сверхпроводящее состояние в соединениях FeSe₀.₉₆₃, FeSe₀.₅Te₀.₅ и LaFeAsO₀.₈₅F₀.₁ наблюдался соответственно при TC ≃ 8, 13.6−14.2 и 26 K. Установлено, что присущая соединениям магнитная восприимчивость χ в ряду FeSe₀.₉₆₃, FeSe₀.₅Te₀.₅ и FeTe монотонно возрастает примерно на порядок величины с повышением концентрации теллура. Для соединения LaFeAsO₀.₈₅F₀.₁ в измеренной в слабом поле зависимости χ(T) была обнаружена особенность в виде излома при TM ≃ 135 K. Для исследуемых соединений выполнены ab initio расчеты электронной структуры и парамагнитной восприимчивости в зависимости от атомного объема и структурного параметра Z, который определяет относительную высоту атомов халькогена над плоскостью железа. Расчеты индуцированных полем магнитных моментов и их объемных производных указывают на близость этих соединений к квантовой критической точке. Для соединений FeSe и FeTe рассчитанные парамагнитные восприимчивости свидетельствуют о значительном магнитообъемном эффекте и сильной чувствительности к структурному параметру Z

Study of flare energy release using events with numerous type III-like bursts in microwaves

The analysis of narrowband drifting of type III-like structures in radio bursts dynamic spectra allows to obtain unique information about primary energy release mechanisms in solar flares. The SSRT spatially resolved images and a high spectral and temporal resolution allow direct determination not only the positions of its sources but also the exciter velocities along the flare loop. Practically, such measurements are possible during some special time intervals when the SSRT (about 5.7 GHz) is observing the flare region in two high-order fringes; thus, two 1D scans are recorded simultaneously at two frequency bands. The analysis of type III-like bursts recorded during the flare 14 Apr 2002 is presented. Using-muliwavelength radio observations recorded by SSRT, SBRS, NoRP, RSTN we study an event with series of several tens of drifting microwave pulses with drift rates in the range from -7 to 13 GHz/s. The sources of the fast-drifting bursts were located near the top of the flare loop in a volume of a few Mm in size. The slow drift of the exciters along the flare loop suggests a high pitch-anisotropy of the emitting electrons.Comment: 16 pages, 6 figures, Solar Physics, in press, 201

Multiwavelength Study on Solar and Interplanetary Origins of the Strongest Geomagnetic Storm of Solar Cycle 23

We study the solar sources of an intense geomagnetic storm of solar cycle 23 that occurred on 20 November 2003, based on ground- and space-based multiwavelength observations. The coronal mass ejections (CMEs) responsible for the above geomagnetic storm originated from the super-active region NOAA 10501. We investigate the H-alpha observations of the flare events made with a 15 cm solar tower telescope at ARIES, Nainital, India. The propagation characteristics of the CMEs have been derived from the three-dimensional images of the solar wind (i.e., density and speed) obtained from the interplanetary scintillation data, supplemented with other ground- and space-based measurements. The TRACE, SXI and H-alpha observations revealed two successive ejections (of speeds ~350 and ~100 km/s), originating from the same filament channel, which were associated with two high speed CMEs (~1223 and ~1660 km/s, respectively). These two ejections generated propagating fast shock waves (i.e., fast drifting type II radio bursts) in the corona. The interaction of these CMEs along the Sun-Earth line has led to the severity of the storm. According to our investigation, the interplanetary medium consisted of two merging magnetic clouds (MCs) that preserved their identity during their propagation. These magnetic clouds made the interplanetary magnetic field (IMF) southward for a long time, which reconnected with the geomagnetic field, resulting the super-storm (Dst_peak=-472 nT) on the Earth.Comment: 24 pages, 16 figures, Accepted for publication in Solar Physic

An Extreme Solar Event of 20 January 2005: Properties of the Flare and the Origin of Energetic Particles

The extreme solar and SEP event of 20 January 2005 is analyzed from two perspectives. Firstly, we study features of the main phase of the flare, when the strongest emissions from microwaves up to 200 MeV gamma-rays were observed. Secondly, we relate our results to a long-standing controversy on the origin of SEPs arriving at Earth, i.e., acceleration in flares, or shocks ahead of CMEs. All emissions from microwaves up to 2.22 MeV line gamma-rays during the main flare phase originated within a compact structure located just above sunspot umbrae. A huge radio burst with a frequency maximum at 30 GHz was observed, indicating the presence of a large number of energetic electrons in strong magnetic fields. Thus, protons and electrons responsible for flare emissions during its main phase were accelerated within the magnetic field of the active region. The leading, impulsive parts of the GLE, and highest-energy gamma-rays identified with pi^0-decay emission, are similar and correspond in time. The origin of the pi^0-decay gamma-rays is argued to be the same as that of lower energy emissions. We estimate the sky-plane speed of the CME to be 2000-2600 km/s, i.e., high, but of the same order as preceding non-GLE-related CMEs from the same active region. Hence, the flare itself rather than the CME appears to determine the extreme nature of this event. We conclude that the acceleration, at least, to sub-relativistic energies, of electrons and protons, responsible for both the flare emissions and the leading spike of SEP/GLE by 07 UT, are likely to have occurred simultaneously within the flare region. We do not rule out a probable contribution from particles accelerated in the CME-driven shock for the leading GLE spike, which seemed to dominate later on.Comment: 34 pages, 14 Postscript figures. Solar Physics, accepted. A typo corrected. The original publication is available at http://www.springerlink.co

Magnetic and superconducting properties of FeSe₁–xTex (x≃0, 0.5, and 1.0)

Magnetization studies for FeSe₁–xTex (x≃0, 0.5, and 1.0) compounds were carried out in magnetic fields up to 50 kOe and in the temperature range 2–300 K. The superconducting transition was observed at Tc≃8 K and 13.6–14.2 K in FeSe₀.₉₆₃ and FeSe₀.₅Te₀.₅, respectively. For the most samples, a nonlinear behavior of the magnetization curves in the normal state gives evidence of a commonly observed substantial presence of ferromagnetic impurities in the compounds under study. By taking these impurity effects into account, the intrinsic magnetic susceptibility χ of FeSe₀.₉₆₃ and FeSe₀.₅Te₀.₅, and FeTe was estimated to increase gradually with Te content. For FeTe a drastic drop in χ(T) with decreasing temperature was found at TN≃70 K, which is presumably related to antiferromagnetic ordering. To shed light on the observed magnetic properties, ab initio calculations of the exchange enhanced magnetic susceptibility are performed for FeSe and FeTe within the local spin density approximation