On the Circular Polarization of Pulsar Radiation

We consider the polarization behaviour of radio waves propagating through an ultrarelativistic highly magnetized electron-positron plasma in a pulsar magnetosphere. The rotation of magnetosphere gives rise to the wave mode coupling in the polarization-limiting region. The process is shown to cause considerable circular polarization in the linearly polarized normal waves. Thus, the circular polarization observed for a number of pulsars, despite the linear polarization of the emitted normal waves, can be attributed to the limiting-polarization effect. This revised version was published online in August 2006 with corrections to the Cover Date.     

On the polarization of solar microwave bursts observed at 17 GHz

The polarization distribution of 17 GHz bursts is studied observed within a period of 1 yr after maximum solar activity. The typical variation of polarization with time of impulsive bursts leads to the conclusion of a thermalization of the emission region in the post-burst phase. The fine structure of the polarization curve of complex bursts is shown and two possible interpretations of the observed inversion of the polarization at 17 GHz during a complex event are given.     

On the origin of subsecond pulses at 17 GHz

We have analyzed three flare events with subsecond structures in hard X-rays (CGRO/ BATSE) and 17 GHz data (Nobeyama radioheliograph). It was shown that microwave subsecond brightenings (SSB) were generated by directly precipitating electrons with energy of 100–200 keV from tiny regions close to footpoints. In two events, when high correlation between microwaves and X-rays was observed, the SSB can be interpreted in terms of gyrosynchrotron emission. Plasma emission seems to be a more credible explanation of the spontaneous pulses in the event when poor correlation with X-rays was observed.     

Companion Event and Precursor of the X17 Flare on 28 October 2003

A major two-ribbon X17 flare occurred on 28 October 2003, starting at 11:01 UT in active region NOAA 10486. This flare was accompanied by the eruption of a filament and by one of the fastest halo coronal mass ejections registered during the October–November 2003 strong activity period. We focus on the analysis of magnetic field (SOHO/MDI), chromospheric (NainiTal observatory and TRACE), and coronal (TRACE) data obtained before and during the 28 October event. By combining our data analysis with a model of the coronal magnetic field, we concentrate on the study of two events starting before the main flare. One of these events, evident in TRACE images around one hour prior to the main flare, involves a localized magnetic reconnection process associated with the presence of a coronal magnetic null point. This event extends as long as the major flare and we conclude that it is independent from it. A second event, visible in Hα and TRACE images, simultaneous with the previous one, involves a large-scale quadrupolar reconnection process that contributes to decrease the magnetic field tension in the overlaying field configuration; this allows the filament to erupt in a way similar to that proposed by the breakout model, but with magnetic reconnection occurring at Quasi-Separatrix Layers (QSLs) rather than at a magnetic null point. Electronic supplementary material Electronic supplementary material is available for this article at and accessible for authorised users.     

1989年8月17日太阳边缘耀斑和速度场研究

本文利用云南天文台二维光谱仪观测的１９８９年８月１７日耀斑的Ｈβ波段光谱资料，采用多云模型的方法，得到此耀斑的观测视向速度分布，并在一定的简化和假设下，采用ＭＨＤ理论计算了几种情况下耀斑环内物质运动的视向速度分布，与观测的视向速度分布加以比较，研究和探讨耀斑环中的物质运动情况。通过分析比较，得出此耀斑环内物质运动可能属于下述两种模式：物质从环顶沿两环腿螺旋下落和物质从环足沿一环腿螺旋上升到环顶后沿另一腿螺旋下落     

Electron Acceleration and Transport During the November 5, 1998 Solar Flare At ∼13:34 UT

This paper deals with a detailed analysis of spectral and imaging observations of the November 5, 1998 (Hα 1B, GOES M1.5) flare obtained over a large spectral range, i.e., from hard X-rays to radiometric wavelengths. These observations allowed us to probe electron acceleration and transport over a large range of altitudes that is to say within small-scale (a few 10³ km) and large-scale (a few 10⁵ km) magnetic structures. The observations combined with potential and linear force-free magnetic field extrapolations allow us to show that: (i) Flare energy release and electron acceleration are basically driven by loop–loop interactions at two independent, low lying, null points of the active region magnetic field; (ii) <300 keV hard X-ray-producing electrons are accelerated by a different process (probably DC field acceleration) than relativistic electrons that radiate the microwave emission; and (iii) although there is evidence that hard X-ray and decimetric/metric radio-emitting electrons are produced by the same accelerator, the present observations and analysis did not allow us to find a clear and direct magnetic connection between the hard X-ray emitting region and the radio-emitting sources in the middle corona.     

On the Nature of the Compact Star in 4U 1728-34

The discovery of kilohertz quasi-periodic oscillations (kHz QPOs) in low-mass X-ray binaries (LMXBs) with the Rossi X-Ray Timing Explorer has stimulated extensive studies of these sources. Recently, Osherovich & Titarchuk suggested a new model for kHz QPOs and the related correlations between kHz QPOs and low-frequency features in LMXBs. Here we use their results to study the mass-radius relation for the atoll source 4U 1728-34. We find that, if this model is correct, 4U 1728-34 is possibly a strange star rather than a neutron star.     

Images of Gradual Millimeter Emission and Multi-Wavelength Observations of the 17 august 1994 Solar Flare

We present a comprehensive analysis of the 17 August 1994 flare, the first flare imaged at millimeter (86 GHz) wavelengths. The temporal evolution of this flare displays a prominent impulsive peak shortly after 01:02 UT, observed in hard X-rays and at microwave frequencies, followed by a gradual decay phase. The gradual phase was also detected at 86 GHz. Soft X-ray images show a compact emitting region (20), which is resolved into two sources: a footpoint and a loop top source. Nonthermal emissions at microwave and hard X-ray wavelengths are analyzed and the accelerated electron spectrum is calculated. This energy spectrum derived from the microwave and hard X-ray observations suggests that these emissions were created by the same electron population. The millimeter emission during the gradual phase is thermal bremsstrahlung originating mostly from the top of the flaring loop. The soft X-rays and the millimeter flux density from the footpoint source are only consistent with the presence of a multi-temperature plasma at the footpoint.     

The Two Mini-lobes of the CSO OQ208—— VLBI Observations at 5 GHz and 8.4 GHz

We present the results of VLBI observations at 5 GHz and 8.4 GHz of the compact symmetric object (CSO) OQ208. Images taken on four epochs at 5GHz and one at 8.4GHz show that the parsec radio structure of the source consists of two mini-lobes, both of them are resolved into two hot-spots. We note that the component D is stronger than the component C in the south-west region at 5 GHz, indicating that component D is less free-free absorbed than C at low frequency. On the basis of the separation of components A and D, a proper motion of 0.032±0.02 mas yr~(-1) between the two mini-lobes is estimated. This value is about half the previous estimates based on the separation of components A and C with 8.4 GHz VLBI data. The reason for the decrease in the expansion velocity is discussed.     

Gamma-Rays and Neutrons as a Probe of Flare Proton Spectra: the Solar Flare of 11 June 1991

The large flare of 11 June 1991 (GOES class X12) was detected by the Total Absorption Shower Counter (TASC) segment of the EGRET gamma-ray telescope on board the Compton Gamma Ray Observatory. Significant gamma-ray emission was observed over the entire energy range to which the TASC was sensitive –1 to 140 MeV. Several phases were identified which showed major changes in the intensity and spectral shape of the flare gamma-rays. Furthermore, a 'delayed' phase during which a response consistent with the detection of energetic neutrons and pion-decay gamma-rays was seen, implying a qualitative change in the spectral shape of the accelerated ion spectrum. The similarity of the characteristics of this delayed phase (pion and energetic neutron production) to those in other large flares hint at a common particle acceleration mechanism.     

On the Quasi-Five-Year Variation of Nitrate Abundance in Polar ice and Solar Flare Activity in the Past

The quasi-five-year variation in the abundance of nitrate in Central Greenland ice is revealed. Probable origin of the variation is the connection of solar proton events with the period of declining solar activity. Such a connection exists during more than 200 years and appears to be a fundamental property of solar activity.     

POlarization Emission of Millimeter Activity at the Sun (POEMAS): New Circular Polarization Solar Telescopes at Two Millimeter Wavelength Ranges

We present a new system of two circular polarization solar radio telescopes, POEMAS, for observations of the Sun at 45 and 90 GHz. The novel characteristic of these instruments is the capability to measure circular right- and left-hand polarizations at these high frequencies. The two frequencies were chosen so as to bridge the gap at radio frequencies between 20 and 200 GHz of solar flare spectra. The telescopes, installed at CASLEO Observatory (Argentina), observe the full disk of the Sun with a half power beam width of 1.4^°, a time resolution of 10 ms at both frequencies, a sensitivity of 2?–?4 K that corresponds to 4 and 20 solar flux unit (=10⁴ Jy), considering aperture efficiencies of 50±5 % and 75±8 % at 45 and 90 GHz, respectively. The telescope system saw first light in November 2011 and is satisfactorily operating daily since then. A few flares were observed and are presented here. The millimeter spectra of some flares are seen to rise toward higher frequencies, indicating the presence of a new spectral component distinct from the microwave one.     

Current-sheet-associated radio sources and development of the magnetosphere of an active region revealed from 17 GHz and Yohkoh data

We study the evolution of the active region (AR) NOAA 7321 in which appeared a so-called `neutral-line-associated source' (NLS) on the basis of data of the Nobeyama Radioheliograph and Yohkoh/SXT. We provide a physical interpretation of the NLS in terms of a topological magnetic reconnection model in a quadrupole magnetic configuration and discuss its relation to the evolution of the active region. Two kinds of the NLS were observed at 17 GHz. One of them, `rising NLS', was found in the growth stage. The other was `stationary NLS' detected in the maximal stage of the AR. Their presence was associated with substantial expansion of the active region's magnetosphere and accompanied by gradual development of spine-like structures visible in soft X-rays before homologous long-duration arcade flares. We suggest that the rising 17 GHz NLS corresponded to a fragment of a `horizontal' current sheet moving upward. Bright X-ray spines were boundaries of that current sheet. Almost all bursts observed from 26 to 28 October 1992 which accompanied class C and M flares occurred in the rising NLS. Formation of magnetic X-point singularities is believed to be responsible for the low-lying NLS. Reversal of circular polarization due to the effect of radio wave propagation was detected in that NLS on the limb. The initial stage of the microwave burst of the long-duration X9 class flare on 2 November 1992 occurred in this NLS. We also revealed observational manifestations of the presence of `vertical' non-neutral current sheet in the spatial structure of this NLS before the flare.     

On the Evolution of Orbits in a Photo-Gravitational Circular Three-Body Problem: The Inner Problem

Astronomy Letters - We consider the spatial restricted circular three-body problem in the nonresonant case. The massless body (satellite) is assumed to have a large sail area and, therefore, the...     

On the Origin of the Spin of Planets and Stars and its Connection with Gravitomagnetism

The origin of the spin of planets and stars is, to a certain extent, still unexplained. In general, we attribute their rotation to the swirl of their constituent primitive gases. In this paper, we try to show that the rotation of celestial bodies depends only on their mass, apparent radius and tilt of their spin axes. We reach this conclusion within the framework of gravitomagnetism, implied by the Einstein’s general relativity theory (GR). Our results show that it might possible, in principle, to calculate the mass of spinning objects by measuring their apparent radius, the speed of rotation and the tilt of the axis of rotation.     

Four New Eclipsing Binary Systems in the TESS field:CD-34 13220,HD 295082,TYC 6484-426-1 and TYC 6527-2310-1

We present the first evidence for the binarity of four targets in the TESS field.The temperatures are estimated by SED analysis and the orbital periods are dete...