Forward modeling of gyrosynchrotron intensity perturbations by sausage modes

To determine the observable radio signatures of the fast sausagestanding wave, we examine gyrosynchrotron (GS) emission modulation usinga linear three-dimensional magnetohydrodynamic model of a plasmacylinder. Effects of the line-of-sight angle and instrumental resolutionon perturbations of the GS intensity are analyzed for two models: a basemodel with strong Razin suppression and a low-density model in which theRazin effect was unimportant. Our finding contradicts previouspredictions made with simpler models: an in-phase variation of intensitybetween low (f fpeak) frequencies is found for the low-density model and ananti-phase variation for the base model in the case of a viewing angleof 45°. The spatially inhomogeneous character of the oscillatingemission source and the spatial resolution of the model are found tohave a significant effect on the resulting intensity.Publisher PDFPeer reviewe

Spatially resolved microwave pulsations of a flare loop

A microwave burst with quasi-periodic pulsations was studied with high spatial resolution using observations with the Nobeyama Radioheliograph (NoRH). We found that the time profiles of the microwave emission at 17 and 34 GHz exhibit quasi-periodic (with two well defined periods P 1 = 14–17 s and P 2 = 8–11 s) variations of the intensity at different parts of an observed flaring loop. Detailed Fourier analysis shows the P 1 spectral component to be dominant at the top, while the P 2 one near the feet of the loop. The 14–17 s pulsations are synchronous at the top and in both legs of the loop. The 8–11 s pulsations at the legs are well correlated with each other but the correlation is not so obvious with the pulsations at the loop top. For this P 2 spectral component, a definite phase shift, P 2 /4 ≈ 2.2 s, between pulsations in the northern leg and loop top parts of the loop have been found. The length of the flaring loop is estimated as L = 25 Mm (≈34 ) and its average width at half intensity at 34 GHz as about 6 Mm (≈8 ). Microwave diagnostics shows the loop to be filled with a dense plasma with the number density n 0 ≈ 10 11 cm −3, penetrated by the magnetic field changing from B 0 ≈ 100 G near the loop top up to B 0 ≈ 200 G near the north footpoint. A comparative analysis of different MHD modes of the loop demonstrates the possibility of the simultaneous existence of two modes of oscillations in the loop: the global sausage mode, with the period P 1 = 14–17 s and the nodes at the footpoints, and a higher harmonics mode (possibly with the radial wave number l > 1), with P 2 = 8–11 s

Three-minute oscillations above sunspot umbra observed with SDO/AIA and NoRH

Three-minute oscillations over sunspot's umbra in AR 11131 were observed simultaneously in UV/EUV emission by SDO/AIA and in radio emission by Nobeyama Radioheliograph (NoRH). We use 24-hours series of SDO and 8-hours series of NoRH observations to study spectral, spatial and temporal variations of pulsations in the 5-9 mHz frequency range at different layers of the solar atmosphere. High spatial and temporal resolution of SDO/AIA in combination with long-duration observations allowed us to trace the variations of the cut-off frequency and spectrum of oscillations across the umbra. We found that higher frequency oscillations are more pronounced closer to the umbra's center, while the lower frequencies concentrate to the peripheral parts. We interpreted this discovery as a manifestation of variation of the magnetic field inclination across the umbra at the level of temperature-minimum. Possible implications of this interpretation for the diagnostics of sunspot atmospheres is discussed.Comment: 29 pages, 7 figures, in press ApJ, 201

Quasi-Periodic Pulsations in Solar Flares: new clues from the Fermi Gamma-Ray Burst Monitor

In the last four decades it has been observed that solar flares show quasi-periodic pulsations (QPPs) from the lowest, i.e. radio, to the highest, i.e. gamma-ray, part of the electromagnetic spectrum. To this day, it is still unclear which mechanism creates such QPPs. In this paper, we analyze four bright solar flares which show compelling signatures of quasi-periodic behavior and were observed with the Gamma-Ray Burst Monitor (\gbm) onboard the Fermi satellite. Because GBM covers over 3 decades in energy (8 keV to 40 MeV) it can be a key instrument to understand the physical processes which drive solar flares. We tested for periodicity in the time series of the solar flares observed by GBM by applying a classical periodogram analysis. However, contrary to previous authors, we did not detrend the raw light curve before creating the power spectral density spectrum (PSD). To assess the significance of the frequencies we made use of a method which is commonly applied for X-ray binaries and Seyfert galaxies. This technique takes into account the underlying continuum of the PSD which for all of these sources has a P(f) ~ f^{-\alpha} dependence and is typically labeled red-noise. We checked the reliability of this technique by applying it to a solar flare which was observed by the Reuven Ramaty High-Energy Solar Spectroscopic Imager (RHESSI) which contains, besides any potential periodicity from the Sun, a 4 s rotational period due to the rotation of the spacecraft around its axis. While we do not find an intrinsic solar quasi-periodic pulsation we do reproduce the instrumental periodicity. Moreover, with the method adopted here, we do not detect significant QPPs in the four bright solar flares observed by GBM. We stress that for the purpose of such kind of analyses it is of uttermost importance to appropriately account for the red-noise component in the PSD of these astrophysical sources.Comment: accepted by A&

Патогенетическое и клиническое обоснование применения N-ацетилцистеина (Флуимуцила) при идиопатическом фиброзирующем альвеолите

The aim of this study was to investigate free radical and lipid disorders in idiopathic pulmonary fibrosis (IPF), to assess clinical efficacy of Fluimucil and to substantiate its administration in different stages of the disease. We observed 127 IPF patients, of them 59 were treated typically with prednisolone, colchicines, or azathioprin, 68 ones received immunosuppressors and Fluimucil. The diagnosis of IPF was verified morphologically in open lung biopsy samples. The patients’ age was 25 to 74 yrs, the mean age, 46.7 ± 9.8 yrs. A control group included 20 healthy donors, the mean age, 41.2 ± 1.2 yrs. N-acetylcysteine (Fluimucil, Zambon group) was administered initially IV 1800 mg a day for 14 days, then orally 1 800 mg a day for a month, then 600 mg a day for 3 months. Clinical and free radical conditions were monitored before the treatment and 3, 6 and 12 months starting the therapy. Fluimucil improved thrombocyte antioxidant activity and plasma antioxidant activity, reduced CT signs of IPF, provided a stable growth in FEV1 and FVC (by 10 % and 12 % respectively) and DLco. Fluimucil was well-tolerated, adverse effects (nausea, stomach ache) were noted in 7 patients (10.2 %). Thus, the results confirmed antioxidant efficacy of Fluimucil in IPF. The long-term administration of Fluimucil combined with the immunosuppressive drugs in IPF patients was safe and reasonable as this inhibited progression of the disease.Цель нашего исследования — уточнить особенности свободнорадикальных и липидных нарушений при идиопатическом фиброзирующем альвеолите (ИФА), определить клиническую эффективность флуимуцила и патогенетически обосновать его применение на различных стадиях заболевания. Обследованы 127 больных с ИФА, из них 59 получали традиционную терапию (преднизолон, колхицин, азатиоприн), 68 — иммуносупрессивные препараты в сочетании с Флуимуцилом. Морфологическая верификация диагноза проводилась по материалу открытых легочных биопсий. Возраст больных варьировался от 25 до 74 лет, в среднем — 46,7 ± 9,8 лет. Контрольную группу составили 20 практически здоровых доноров, средний возраст — 41,2 ± 1,2 года. N-ацетилцистеин (Флуимуцил, «Zambon») назначался по двухэтапной схеме: внутривенно в дозе 1 800 мг в течение 14 дней, затем — реr os по 1 800 мг в сутки в течение месяца и по 600 мг в сутки в последующие 3 мес. Клиническое обследование и исследование свободнорадикальных процессов проводили до лечения, через 3, 6 и 12 мес. от начала терапии. Флуимуцил оказывал положительный эффект на антиоксидантную активность тромбоцитов, коэффициенты их ингибирующего влияния на генерацию АФК лейкоцитами и антиперекисную активность плазмы. Также Флуимуцил положительно влиял на компьютерно-томографические показатели активности альвеолита. У больных, получавших Флуимуцил, к концу наблюдения отмечен стойкий прирост ЖЕЛ и ФЖЕЛ (на 10 % и 12 % соответственно) и DLсо. Флуимуцил хорошо переносился больными, побочные эффекты в виде тошноты, болей в эпигастрии наблюдались только у 7 (10,2 %) больных. Таким образом, результаты исследования подтверждают эффективность Флуимуцила как антиоксиданта при ИФА. Длительное применение высоких доз Флуимуцила в сочетании с иммунносупрессивной терапией при ИФА безопасно и патогенетически обоснованно, т. к. препятствует прогрессированию заболевания

An Inside Look at Sunspot Oscillations with Higher Azimuthal Wavenumbers

Solar chromospheric observations of sunspot umbrae offer an exceptional view of magneto-hydrodynamic wave phenomena. In recent years, a wealth of wave signatures related to propagating magneto-acoustic modes have been presented, which demonstrate complex spatial and temporal structuring of the wave components. Theoretical modelling has demonstrated how these ubiquitous waves are consistent with an m=0 slow magneto-acoustic mode, which are excited by trapped sub-photospheric acoustic (p-mode) waves. However, the spectrum of umbral waves is broad, suggesting that the observed signatures represent the superposition of numerous frequencies and/or modes. We apply Fourier filtering, in both spatial and temporal domains, to extract chromospheric umbral wave characteristics consistent with an m=1 slow magneto-acoustic mode. This identification has not been described before. Angular frequencies of 0.037 +/- 0.007 rad/s (2.1 +/- 0.4 deg/s), corresponding to a period approximately 170 s for the m=1 mode are uncovered for spatial wavenumbers in the range of 0.45<k<0.90 arcsec^-1 (5000-9000 km). Theoretical dispersion relations are solved, with corresponding eigenfunctions computed, which allows the density perturbations to be investigated and compared with our observations. Such magnetohydrodynamic modelling confirms our interpretation that the identified wave signatures are the first direct observations of an m=1 slow magneto-acoustic mode in the chromospheric umbra of a sunspot

The Frequency-dependent Damping of Slow Magnetoacoustic Waves in a Sunspot Umbral Atmosphere

High spatial and temporal resolution images of a sunspot, obtained simultaneously in multiple optical and UV wavelengths, are employed to study the propagation and damping characteristics of slow magnetoacoustic waves up to transition region heights. Power spectra are generated from intensity oscillations in sunspot umbra, across multiple atmospheric heights, for frequencies up to a few hundred mHz. It is observed that the power spectra display a power-law dependence over the entire frequency range, with a significant enhancement around 5.5 mHz found for the chromospheric channels. The phase-difference spectra reveal a cutoff frequency near 3 mHz, up to which the oscillations are evanescent, while those with higher frequencies propagate upwards. The power-law index appears to increase with atmospheric height. Also, shorter damping lengths are observed for oscillations with higher frequencies suggesting frequency-dependent damping. Using the relative amplitudes of the 5.5 mHz (3 minute) oscillations, we estimate the energy flux at different heights, which seems to decay gradually from the photosphere, in agreement with recent numerical simulations. Furthermore, a comparison of power spectra across the umbral radius highlights an enhancement of high-frequency waves near the umbral center, which does not seem to be related to magnetic field inclination angle effects

Multiwavelength studies of MHD waves in the solar chromosphere: An overview of recent results

The chromosphere is a thin layer of the solar atmosphere that bridges the relatively cool photosphere and the intensely heated transition region and corona. Compressible and incompressible waves propagating through the chromosphere can supply significant amounts of energy to the interface region and corona. In recent years an abundance of high-resolution observations from state-of-the-art facilities have provided new and exciting ways of disentangling the characteristics of oscillatory phenomena propagating through the dynamic chromosphere. Coupled with rapid advancements in magnetohydrodynamic wave theory, we are now in an ideal position to thoroughly investigate the role waves play in supplying energy to sustain chromospheric and coronal heating. Here, we review the recent progress made in characterising, categorising and interpreting oscillations manifesting in the solar chromosphere, with an impetus placed on their intrinsic energetics.Comment: 48 pages, 25 figures, accepted into Space Science Review

Forward modeling of standing kink modes in coronal loops. I. Synthetic views

Kink magnetohydrodynamic (MHD) waves are frequently observed in various magnetic structures of the solar atmosphere. They may contribute significantly to coronal heating and could be used as a tool to diagnose the solar plasma. In this study, we synthesize the Fe ix λ171.073 emission of a coronal loop supporting a standing kink MHD mode. The kink MHD wave solution of a plasma cylinder is mapped into a semi-torus structure to simulate a curved coronal loop. We decompose the solution into a quasi-rigid kink motion and a quadrupole term, which dominate the plasma inside and outside of the flux tube, respectively. At the loop edges, the line of sight integrates relatively more ambient plasma, and the background emission becomes significant. The plasma motion associated with the quadrupole term causes spectral line broadening and emission suppression. The periodic intensity suppression will modulate the integrated intensity and the effective loop width, which both exhibit oscillatory variations at half of the kink period. The quadrupole term can be directly observed as a pendular motion at the front view