共查询到20条相似文献，搜索用时 31 毫秒
1.
I. Yu. Grigor’eva A. N. Shakhovskaya M. A. Livshits I. S. Knyazeva 《Astronomy Reports》2012,56(11):887-894
Solar filtergrams obtained at the Crimean Astrophysical Observatory at the center and wings of the H?? line are used to study variations in filaments, in particular, in arch filament systems (AFSs). These are considered as an indicator of emerging new magnetic flux, providing information about the spatial locations of magnetic-field elements. Magnetic-field maps for the active region NOAA 10030 are analyzed as an example. A method developed earlier for detecting elements of emerging flux using SOHO/MDI magnetograms indicates a close link between the increase in flare activity in theNOAA 10030 group during July 14?C18, 2002 and variations in the topological disconnectedness of the magnetograms. Moreover, variations in the flare activity one day before a flare event are correlated with variations in the topological complexity of the field (the Euler characteristic) in regions with high field strengths (more than 700 G). Analysis of multi-wavelength polarization observations on the RATAN-600 radio telescope during July 13?C17, 2002 indicate dominance of the radio emission above the central spot associated with the increase in flare activity. In addition to the flare site near the large spot in the group, numerous weak flares developed along an extended local neutral line, far from the central line of the large-scale field. The statistical characteristics of the magnetic-field maps analyzed were determined, and show flare activity of both types, i.e., localized in spot penumbras and above the neutral line of the field. 相似文献
2.
We report the detection of long-lived sources of radio bursts accompanied by polarized background emission in solar active regions. Both types of radio sources were detected at several decimeter wavelengths in observations on the RATAN-600 radio telescope in one-dimensional scans in intensity and circular polarization with a sensitivity of about 5–10 Jy. The degree of polarization is from 70 to 100%. The microburst and background sources exist for several days and appear at sites of prolonged energy release. The typical duration of an individual microburst is about 1–2 s, and the time interval between microbursts is about 3–5 s. A negative microburst frequency drift of about 100 MHz/s or more is also observed. Some interpretations of the microburst and background sources are discussed. The most probable microburst model involves the generation of radio emission via the plasma mechanism, with the upward propagation of fast electrons above an active region. In this case, the required energy of the Langmuir waves is 2×10?8 of the heat energy of the background plasma. Microbursts appear in different places in an active region. New methods for determining the magnetic-field intensity in the regions of generation of the decimeter-wavelength emission are proposed. 相似文献
3.
Spectra of solar-flare active regions displaying peculiarities in their polarized radio emission observed on the RATAN-600
radio telescope at 2–16 GHz are considered. An appreciable dip of the circularly polarized emission (Stokes parameter V) in the middle of the microwave range (6–12 GHz), sometimes with a reversal of the sign of the polarization, is unusual.
In some cases, the ordinary emission also dominates at long microwave wavelengths. Expected peculiarities of the frequency
structure of microwave sources are calculated in simple models with loops in the form of hot and cool tori. Numerical calculations
of these spectra show that the above features of the polarized emission can be explained by the presence of a hot region in
the solar corona. It is shown that the parameters of the spectrum of the polarized emission can be used to determine the magnetic
field in this hot region and the product of the relative magnetic-field gradient and the loop thickness. 相似文献
4.
The recent publication of evidence for a new mechanism producing background radio emission of the Galaxy at centimeter wavelengths (in addition to synchrotron radiation, free—free transitions in ionized gas, and the weak radio emission of standard dust) gave rise to a strong reaction among observers, and requires independent experimental verification. This signal is of special concern in connection with studies of the polarization of the cosmic microwave background (CMB) using new-generation experiments. We have derived independent estimates of the validity of the “spinning-dust” hypothesis (dipole emission of macromolecules) using multi-frequency RATAN-600 observations. Test studies in the Perseus molecular cloud show evidence for anomalous extended emission in the absence of strong radio sources (compact HII regions) that could imitate an anomalous radio spectrum in this region. A statistical analysis at centimeter wavelengths over the Ratan Zenith Field shows that the upper limit for the polarized noise from this new component in the spinning-dust hypothesis is unlikely to exceed 1 µK at wavelengths of 1 cm or shorter on the main scales of the EE mode of Sakharov oscillations. Thus, this emission should not hinder studies of this mode, at least to within several percent of the predicted level of polarization of the CMB emission. 相似文献
5.
The results of simultaneous high-resolution radio observations of the BL Lac object 1749+701 at 5, 8.4, 15, and 22 GHz are presented. The source has a rich, extended structure displaying a number of interesting features: a strongly bent jet, the presence of transverse and longitudinal magnetic field in different regions of the extended structure, and a very non-uniform rotation-measure distribution on parsec scales, in spite of the fact that the integrated rotation measure is modest. Gradients of the rotation measure across the jet are detected, suggesting the presence of a toroidal magnetic-field component. The rotation measure is higher in the core region, apparently due to an enhanced thermal-electron density and magnetic-field strength. A narrow feature is detected in the rotation-measure distribution, whose sign is opposite to that in the surrounding regions of the radio jet, possibly testifying to the presence of a sharp bend in the jet. Images were constructed using weighting in the uv plane, in order to reveal weak polarization in the extended jet structure. 相似文献
6.
Some mechanisms for Joule dissipation of electric currents flowing in partially ionized hydrogen plasmas are analyzed in a
three-fluid approximation. It is shown that ambipolar diffusion can be responsible for the annihilation of magnetic flux during
collisions of ions with neutral atoms. The relative influences of the electron conductivity and the Cowling conductivity on
the magnetic-field annihilation rate are examined in the frameworks of the Sweet-Parker reconnection model. The escape of
plasma is an efficient mechanism for cooling current sheetswith thicknesses of hundreds of kilometers in the solar chromosphere.
The origin of the solar chromospheric jets observed by the Hinode spacecraft is discussed. 相似文献
7.
The correlation between the magnetic flux in an active solar region and associated powerful solar flares is studied. The behavior
of the active regions AR 10486 and AR 10365 is considered. These regions produced a series of class X flares as they crossed
the solar disk. The flares appeared when the magnetic flux exceeded 1022 Mx. The magnetic flux remained constant during all the flares except for one. During this flare, the flux decreased by about
10%; this impulsive decrease of the flux was also recorded in the absence of flares. No energy flux from the photosphere to
the corona at the time of the flare was observed. The behavior of the photospheric field in AR 10486 and AR 10365 is consistent
with a slow accumulation of energy in the corona and the explosive release of energy stored in the magnetic field of a current
sheet above an active region during the flare. 相似文献
8.
Results of observations of circumstellar OH masers in lines with wavelengths near 18 cm are reported. The observations were
carried out on the radio telescope of the Nan cay Radio Astronomy Observatory (France). In 2007–2009, 70 late-type stars were
observed (including Mira and semi-regular variables). For 53 of these, emission was detected in at least one of three OH lines
(1612, 1665, or 1667 MHz). Circular and linear polarization of the maser emission was measured, yielding all four Stokes parameters.
Polarized emission features were detected in the OH line spectra of 41 stars. A summary of all the observations is given.
The results obtained for T Lep, R LMi, and R Crt are discussed. Emission in the 1665 and 1667 MHz OH lines was detected in
T Lep for the first time. Features probably due to Zeeman splitting were detected in the OH line profiles of all three stars.
Estimates of the magnetic-field strengths in the maser sources were obtained (0.46–2.32 mG). Variability of the polarization
characteristics of the maser emission of the stars on time intervals of several months was found. 相似文献
9.
M. A. Livshits I. Yu. Grigoryeva I. I. Myshyakov G. V. Rudenko 《Astronomy Reports》2016,60(10):939-948
Multi-wavelength observations and magnetic-field data for the solar flare of May 10, 2012 (04: 18 UT) are analyzed. A sign change in the line-of-sight magnetic field in the umbra of a small spot has been detected. This is at least partly associated with the emergence of a new magnetic field. A hard X-ray flare was recorded at almost the same time, and a “sunquake” was generated by the impact of the disturbance in the range of energy release on the photosphere. A sigmoid flare was recorded at the beginning of the event, but did not spread, as it usually does, along the polarity inversion (neutral) line. SDO/HMI full vectormagnetic-fieldmeasurements are used to extrapolate the magnetic field of AR 11476 into the corona, and to derive the distribution of vertical currents jz in the photosphere. The relationship between the distribution of currents in the active region and the occurrence of flares is quite complex. The expected “ideal” behavior of the current system before and after the flare (e.g., described by Sharykin and Kosovichev) is observed only in the sigmoid region. The results obtained are compared with observations of two other flares recorded in this active region on the same day, one similar to the discussed flare and the other different. The results confirm that the formation and eruption of large-scale magnetic flux ropes in sigmoid flares is associated with shear motions in the photosphere, the emergence of twisted magnetic tubes, and the subsequent development of the torus instability. 相似文献
10.
Observations of the RRAT pulsars J0627+16, J0628+09, J1819?1458, J1826?1419, J1839?01, J1840?1419, J1846?0257, J1848?12, J1850+15, J1854+0306, J1919+06, J1913+1330, J1919+17, J1946+24, and J2033+00 observed earlier on the 64-m Parkes telescope (Australia) and the 300-m Arecibo radio telescope (Puerto Rico) at 1400 MHz were conducted at 111 MHz on the LSA radio telescope of the Pushchino Radio Astronomy observatory in 2010–2012. A characteristic feature of these pulsars is their sporadic radio emission during rare active epochs and the absence of radio emission during long time intervals. No appreciable flare activity of these pulsars was detected in the Pushchino observations. However, processing the observations using the Fast Folding Algorithm taking into account known information about the pulsar dispersion measures and periods shows that, even during quiescent intervals, the majority of the studied pulsars generate weak radio pulses with a period corresponding to that of the radio emission of the sporadic pulses observed at active epochs. The flux of this radio emission does not exceed 100 mJy at the pulse peak, even at the low frequency of 111 MHz. This considerably hinders detection of the radio emission of RRAT pulsars at high frequencies, since the radio fluxes of RRAT pulsars decreases with increasing frequency. 相似文献
11.
A comparative analysis of sunspot oscillations and related radio sources in the active regions AR 8949, AR 8951, and AR 8953 is carried out using SOHO MDI data and simultaneous observations with the Nobeyama Radioheliograph, with a one-minute time resolution on scales of tens to hundreds of minutes. The radio sources in the selected active regions are ～40 000–60 000 km away from the corresponding spots, with the periods of long-term oscillations of the radio sources being ～12% longer. 相似文献
12.
M. V. Popov V. A. Soglasnov V. I. Kondrat’ev S. V. Kostyuk Yu. P. Ilyasov V. V. Oreshko 《Astronomy Reports》2006,50(1):55-61
The paper presents an analysis of dual-polarization observations of the Crab pulsar obtained on the 64-m Kalyazin radio telescope at 600 MHz with a time resolution of 250 ns. A lower limit for the intensities of giant pulses is estimated by assuming that the pulsar radio emission in the main pulse and interpulse consists entirely of giant radio pulses; this yields estimates of 100 and 35 Jy for the peak flux densities of giant pulses arising in the main pulse and interpulse, respectively. This assumes that the normal radio emission of the pulse occurs in the precursor pulse. In this case, the longitudes of the giant radio pulses relative to the profile of the normal radio emission turn out to be the same for the Crab pulsar and the millisecond pulsar B1937+21, namely, the giant pulses arise at the trailing edge of the profile of the normal radio emission. Analysis of the distribution of the degree of circular polarization for the giant pulses suggests that they can consist of a random mixture of nanopulses with 100% circular polarization of either sign, with, on average, hundreds of such nanopulses within a single giant pulse. 相似文献
13.
14.
Two solar radio bursts exhibiting narrow-band millisecond pulsations in intensity and polarization are analyzed. There were considerable time delays between the left-and right-circularly polarized components of the radio emission. The observed oscillations of the degree of polarization are due to the different group velocities of the ordinary and extraordinary modes in their propagation from the source to the observer; the frequency dependence of the delay is in excellent agreement with the theoretically calculated group delay in a magnetoactive plasma. It unambiguously follows that the pulsed radio emission is generated near the double upper hybrid frequency by the nonlinear plasma mechanism, since the source emission has a low degree of polarization. In addition to dispersion effects, a Fourier analysis also reveals effects associated with the source inhomogeneity. We detected a frequency drift of pulsations (autodelays) with different signs for different polarization components. This drift suggests that, apart from the dispersion effects, there are also the effects related to inhomogeneity of the radio source. It is shown, in particular, that the upper hybrid modes (generating the radio emission) are unstable in regions with enhanced gradients of the plasma density and/or magnetic field. 相似文献
15.
We have carried out a search for compact radio sources in the cores of 16 nearby radio galaxies. We detected compact components in four radio galaxies, and found upper limits for the flux density in compact components in ten radio galaxies. VLBI observations enabled the detection of a turnover in the spectra of the two nearby radio galaxies 3C 111 and 3C 465. Using a method based on an inhomogeneous model for a synchrotron source, we estimate the magnetic-field strength and the energy densities in the magnetic field and relativistic electrons in the cores of these radio galaxies. Strong inhomogeneity in the distribution of the magnetic fields in the cores of 3C 111 and 3C 465 is implied by our analysis. The magnetic-field strengths in the central regions of these galactic nuclei, on scales of ～0.1 pc, exceed the mean strength by four to five orders of magnitude, and lie in the range 102 G < H < 104 G. 相似文献
16.
A topological method for detecting the new emergence of magnetic flux using SOHO/MDI magnetograms of the full solar disk is
proposed. This method uses the number of pixels in the image that can be distinguished from a specified value to within a
predetermined threshold (the number of disconnected components). We study more than ten very powerful active regions (ARs)
with very high flare activity and show that the number of disconnected components increases directly before the development
of a series of M and X flares, or accompanies this process. This behaviour is evident not only when there is an explicit emergence
of a new flux and a series of fast flares, such as in AR 9236 (November 2000), but also in groups with many non-stationary
processes developing along a neutral line of the large-scale magnetic field. We also discuss the possibility of using the
obtained results for flare prediction. 相似文献
17.
We present the results of numerical simulations of the development of a current sheet in the solar corona over a bipolar region during the emergence of two new sunspots arranged collinearly with older spots. Two fronts of increased plasma density form at the boundary of the rising new magnetic flux. One of these is due to the generation of a current sheet, whose magnetic field accumulates energy for a flare. The other front is a branch of the density perturbation, and separates the old and new magnetic fluxes in a region where the magnetic field lines have the same direction on both sides of the boundary. The development of this perturbation is not associated with the energy accumulation in the corona, and hinders observation of the preflare state and complicates analysis of the results. This second front can be interpreted as the eruption of a filament before the onset of the flare. A scheme conservative with respect to magnetic flux was introduced in the Peresvet code that solves the MHD equations, in order to suppress numerical instabilities in regions of large magnetic-field gradients. 相似文献
18.
N. N. Kardapolova T. P. Borisevich N. G. Peterova S. V. Lesovoĭ 《Astronomy Reports》2008,52(5):409-418
The results of a study of the coronal mass ejection (CME) of April 27, 2003, which was intrinsically associated with the active region NOAA 10338, are reported. Particular attention is paid to the initial stage of the event, which was accompanied by X-ray bursts of class C9.3 and C6.7, with the aim of determining the origin of CMEs. The energy source of the ejection was in the active region NOAA 10338. This region had a complicated and dynamic magnetic-field topology, and produced a series of CME-type events. The basis for the study was observations at wavelengths of 1.92–17 cm with high spatial resolution, 17″–20″, obtained on the Siberian Solar Radio Telescope (SSRT) and RATAN-600, together with simultaneous data from the Nobeyama Radio Heliograph (NoRH, wavelength 1.76 cm) and 195 Å ultraviolet data from the TRACE spacecraft. The development of the event was followed over three hours, first through observations against the disk at heights of 10,000–100,000 km from the photosphere, then in the post-limb stage to distances of the order of 106 km from the solar center, i.e., in the zone inaccessible to the LASCO coronographs. According to the radio observations, ～10 min before the beginning of the event, the radio structure of the active region NOAA 10338 had an S-shaped (sigmoid) configuration. A rising, gradually expanding dark loop originated at the points where this structure was observed; according to the TRACE data, this loop initiated the event. Subsequently, the structure of the radio image drastically changed, suggesting that coronal plasma was heated and cooled at different sites of the emission region (or was shielded by the cooler material of the ejection). Profiles of the burst that accompanied the ejection are presented for four points in the region. The post-limb part of the event first had a compact (～50″) structure receding from the Sun and visible to distances ～106 km. An asymmetric loop was then formed, with its material falling back onto the Sun at the end of the event. The brightness temperature of the loop was ～15 × 103 K, and its emission was weakly polarized (P ≈16%). The mean speed of the material was 160 km/s. It is concluded that the observations of the event of April 27, 2003 are most consistent with the model of Amari et al., in which the formation of an eruptive twisted magnetic rope, taken to be responsible for CME-type events, is explained by the emergence of new magnetic flux within an old field of opposite polarity. 相似文献
19.
利用玉树隆宝湿地2015年的涡动相关系统观测资料,分析了高寒湿地CO2通量的变化特征及影响因子。结果表明：玉树隆宝湿地生长季CO2通量日变化呈倒单峰型,夏季日变化幅度大,冬季日变化幅度小。4-9月CO2净交换量为负值,其余各月CO2净交换量为正值。全年CO2净吸收量为465 g·m-2。白天CO2通量随着光合有效辐射的增大而减小。CO2排放量与土壤温度和气温日较差均呈正相关。高寒湿地土壤体积含水量对CO2通量的影响很微弱。降雨事件发生后, CO2排放量在短期内有所升高。各影响因子中,光合有效辐射对高寒湿地CO2通量影响的相关度最高,其次为气温日较差,土壤温度,而土壤体积含水量对CO2通量影响的相关度最低。 相似文献
20.
We have carried out 3D MHD modeling of the solar corona above the active region AR 0365 before a series of flares observed on May 26–27, 2003. Maps of the evolving photospheric magnetic fields preceding the flares were used as boundary conditions. An emergence of new flux equal to ～1.5 × 1022 Maxwell preceded the observed series of X-ray flares. Modeling a large region 4 × 1010 cm in size demonstrates the formation of several current sheets in the vicinities of coronal Xlines, both already existing in the initial potential field and arising due to the emergence of the new magnetic flux. Each current sheet could be responsible for an elementary flare. 相似文献