太阳射电三频率高时间分辨率三年同步观测的结果

本文总结了1987年2月到1989年12月三波段(1.42GHz、2.84GHz和4.0GHz)高时间分辨率同步观测的资料,介绍了各波段尖峰辐射出现的频次、持续时间以及与射电爆发、光学耀斑和X射线爆的统计关系.     

High time resolution observations of solar radio emission at four frequencies: evidence for energy release in microflares

As evidence for energy release in microflares, high time resolution observations of solar radio emission obtained with our “synchronous observation system of solar radio radiation with high time resolution at four frequencies (1.42, 2.13, 2.84 and 4.26 GHz)” from December 1989 to April 1993 are presented in this paper. The observed events include weak ms spikes, “spike-likes”, fast pulsations as well as two kinds of newly discovered fast fine structures, i.e., microwave type III bursts and microwave patch-like structures. A statistical study of the duration of fast fine structures has been made and on its basis the various types of phenomena are illustrated with actual examples.     

Solar microwave bursts as indicators of the occurrence of solar proton emission

A study has been made of the relation of 19 GHz( = 1.58 cm) solar radio bursts to solar proton emission, with particular reference to the usefulness of relatively long duration bursts with intensities exceeding 50% of the quiet Sun flux (or exceeding 350 × 10^–22 W m^–2 Hz^–1) as indicators of the occurrence of proton events during the four years from 1966–69. 76 to 88% of such bursts are directly associated with solar protons and 60 to 85% of the moderate to large proton events in the four year period could have been predicted from these bursts. The complete microwave spectra of the proton events have also been studied, and have been used to extend the results obtained at 19 GHz to other frequencies, particularly in the 5–20 GHz band. The widely used frequency of 2.8 GHz is not the optimum frequency for this purpose since proton events have a minimum of emission in this region. Most of the radio energy of proton events is at frequencies above 10 GHz. The radio spectra of proton events tend to peak at higher frequencies than most non-proton events, the overall range being 5 to 70 GHz, with a median of 10–12 GHz and a mean of 17 GHz.On leave from the Radio and Space Research Station, Slough, England, as 1969–1970 National Research Council-National Academy of Sciences Senior Post-Doctoral Research Associate at AFCRL.     

Solar microwave bursts recorded at 2.84 GHz with millisecond time resolution

A millisecond recorder for solar observation at 2.84 GHz was put to work in 1981. From April 1981 to September 1982 it recorded 250spike pulse events, which are here listed together with information on the associated solar flares, hard X-ray bursts and radio bursts. In defining these spike events, particular attention has been paid to ensure the reliability of the recorded data. Statistical analysis of the data has given some interesting results. The spike pulses have shorter duration and higher flux density than were previously known, and the basic units of the spike pulse events are single spike pulses crowded together forming separate clusters. Many spike pulses observed are not yet resolved at 1 ms. Fast spike pulse events are closely correlated with complex magnetic field regions, and are often accompanied by hard X-ray bursts and fast drifting radio bursts. Some such events showed no correspondence with the radio bursts at the same frequency, 2.84 GHz, but corresponded to those occurring at dm and short cm wavelengths. Some theoretical investigations of the spike phonomena have been carried out, the details of which will be discussed elsewhere.     

Observations of solar filaments at 8, 15, 22 and 43 GHz

On April 3, 4, 6, and 8, 1978, solar observations were made using the Haystack 120 ft telescope at 8, 15, 22, and 43 GHz. H filtergrams obtained at the Sacramento Peak Observatory on the same days showed an average of more than 30 filaments or filament fragments (per day) on the disk. Most of these appeared as depressions in brightness temperature at 15 and 22 GHz. Because of the relatively low spatial resolution at 8 GHz, only a few appeared at that frequency, and presumably because of lower opacity in filaments at higher frequencies, few depressions were visible at 43 GHz. At 15 and 22 GHz, more depressions appeared than H filaments, but virtually all the radio depressions overlay magnetic neutral lines. Taking the data sets for each day as independent samples, we found that at 22 GHz, 46 of the 77 radio depressions were associated with H filaments; at 15 GHz the correlation was smaller; only 27 out of 48 being associated with the H filaments. The data imply that the microwave depression features are the result of absorption by filaments and perhaps also the result of other effects of the associated filament channel, but not necessarily coronal depletion. The effects of filament absorption are, statistically, about twice as effective as other phenomena (such as absorption by material invisible in H, for example) in creating the radio depression. A center-to-limb study of a single large filament clearly showed that at 15 and 22 GHz the absorption by cool hydrogen supported above the neutral line was the predominant factor in producing the observed depression at radio frequencies.     

Fine Time Structures in Solar Radio Bursts: A Summary of Observations at Four Frequencies

29 fine time structures (FTS) are found in 103 radio bursts observed with YRSOS of high temporal resolution of 1 ms at 4 frequencies (1.42, 2.00 (or2.13), 2.84 and 4.00 (or 4.26) GHz) from January 1990 to January 1994. The various morphologies of FTSs occurring in different phases of flares and the different FTS in the same event may reflect the transitional property of the low-frequency microwave bursts. Most FTSs are probably consisted with the four characteristics observed previously in literatures. The typical and representative events of FTSs and occurrence frequency of each kind are presented in order to explain the multiplicity, breadth and observational characteristics of FTSs in the range of long centimeter to short decimeter wavelengths. This revised version was published online in July 2006 with corrections to the Cover Date.     

Frequency Distributions of Microwave Pulses for the 18 March 2003 Solar Flare

We analyze the pulses in high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory (PMO) over the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. A number of individual pulses are determined from the drifting radio structures after the detected gradual component subtraction. The frequency distributions of microwave pulse occurrence as functions of peak flux, duration, bandwidth, and time interval between two adjacent pulses exhibit a power-law behavior, i.e. . From regression fitting in log-log space, we obtain the power-law indexes, α _P=7.38±0.40 for the peak flux, α _D=5.39±0.86 for the duration, and α _B=6.35±0.56 for the bandwidth. We find that the frequency distribution for the time interval displays a broken power law. The break occurs at about 500 ms, and their indexes are α _W1=1.56±0.08 and α _W2=3.19±0.12, respectively. Our results are consistent with the previous findings of hard X-ray pulses, type III bursts, and decimetric millisecond spikes.     

Evidence for an increase of the rate of rapid radio fluctuations before solar flares

Preflare phenomena have been analysed in 76 radio bursts observed in four frequencies (1.42, 2.13, 2.84, and 4.26 GHz). For 23 in the 76 events the rapid fluctuation rate of the radio radiation in one of the frequencies started to rise prior to the flare onsets by a time range from several minutes to tens of minutes. Three examples of the 23 events are presented in detail to demonstrate this kind of precursor.     

The microwave spectrum of solar millisecond spikes

The microwave radiation from solar flares sometimes shows short and intensive spikes which are superimposed on the burst continuum. In order to determine the upper frequency limit of their occurrence and the circular polarization, a statistical analysis has been performed on our digital microwave observations from 3.2 to 92.5 GHz. Additionally, fine structures have been investigated with a fast (5 ms) 32-channel spectrometer at 3.47 GHz. We found that 10% of the bursts show fine structures at 3.2 and 5.2 GHz, whereas none occurred above 8.4 GHz. Most of the observed spikes were very short ( 10 ms) and their bandwidth varied from below 0.5 MHz to more than 200 MHz. Simultaneous observations at two further frequencies showed no coincident spikes at the second and third harmonic. The observations can be explained by the theory of electron cyclotron masering if the observed bandwidths are determined by magnetic field inhomogeneities or if the rise times are independent of the source diameters. The latter would imply source sizes between 50 and 100 km.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.     

Ion-Sound Model of Microwave Spikes with Fast Shocks in the Reconnection Region

A new model for solar spike bursts is considered based on the interaction of Langmuir waves with ion-sound waves: l+st. Such a mechanism can operate in shock fronts, propagating from a magnetic reconnection region. New observations of microwave millisecond spikes are discussed. They have been observed in two events: 4 November 1997 between 05:52–06:10 UT and 28 November 1997 between 05:00–05:10 UT using the multichannel spectrograph in the range 2.6–3.8 GHz of Beijing AO. Yohkoh/SXT images in the AR and SOHO EIT images testify to a reconstruction of bright loops after the escape of a CME. A fast shock front might be manifested as a very bright line in T _e SXT maps (up to 20 MK) above dense structures in emission measure (EM) maps. Moreover one can see at the moment of spike emission (for the 28 November 1997 event) an additional maximum at the loop top on the HXR map in the AR as principal evidence of fast shock propagation. The model gives the ordinary mode of spike emission. Sometimes we observed a different polarization of microwave spikes that might be connected with the depolarization of the emission in the transverse magnetic field and rather in the vanishing magnetic field in the middle of the QT region. Duration and frequency band of isolated spikes are connected with parameters of fast particle beams and shock front. Millisecond microwave spikes are probably a unique manifestation of flare fast shocks in the radio emission.     

Decimetric type III radio bursts and associated hard X-ray spikes

A detailed comparison is made between hard X-ray spikes and decimetric type III radio bursts for a relatively weak solar flare on 1981 August 6 at 10: 32 UT. The hard X-ray observations were made at energies above 30 keV with the Hard X-Ray Burst Spectrometer on the Solar Maximum Mission and with a balloon-born coarse-imaging spectrometer from Frascati, Italy. The radio data were obtained in the frequency range from 100 to 1000 MHz with the analog and digital instruments from Zürich, Switzerland. All the data sets have a time resolution of 0.1 s or better. The dynamic radio spectrum shows many fast drift type III radio bursts with both normal and reverse slope, while the X-ray time profile contains many well resolved short spikes with durations of 1 s. Some of the X-ray spikes appear to be associated in time with reverse-slop bursts suggesting either that the electron beams producing the radio bursts contain two or three orders of magnitude more fast electrons than has previously been assumed or that the electron beams can trigger or occur in coincidence with the acceleration of additional electrons. One case is presented in which a normal slope radio burst at 600 MHz occurs in coincidence with the peak of an X-ray spike to within 0.1 s. If the coincidence is not merely accidental and if it is meaningful to compare peak times, then the short delay would indicate that the radio signal was at the harmonic and that the electrons producing the radio burst were accelerated at an altitude of 4 × 10⁹ cm. Such a short delay is inconsistent with models invoking cross-field drifts to produce the electron beams that generate type III bursts but it supports the model incorporating a MASER proposed by Sprangle and Vlahos (1983).     

A model of diffuse Galactic radio emission from 10 MHz to 100 GHz

Understanding diffuse Galactic radio emission is interesting both in its own right and for minimizing foreground contamination of cosmological measurements. cosmic microwave background experiments have focused on frequencies ≳10 GHz, whereas 21-cm tomography of the high-redshift universe will mainly focus on ≲0.2 GHz, for which less is currently known about Galactic emission. Motivated by this, we present a global sky model derived from all publicly available total power large-area radio surveys, digitized with optical character recognition when necessary and compiled into a uniform format, as well as the new Villa Elisa data extending the 1.42-GHz map to the entire sky. We quantify statistical and systematic uncertainties in these surveys by comparing them with various global multifrequency model fits. We find that a principal component based model with only three components can fit the 11 most accurate data sets (at 10, 22, 45 and 408 MHz and 1.42, 2.326, 23, 33, 41, 61, 94 GHz) to an accuracy around 1–10 per cent depending on frequency and sky region. Both our data compilation and our software returning a predicted all-sky map at any frequency from 10 MHz to 100 GHz are publicly available at http://space.mit.edu/home/angelica/gsm .     

Repeated activity of the 0.8–1.2 GHz radio source of March 20, 1993

During March 20, 1993, from 12:00 to 16:00 UT, repeated radio burst activity was observed in the 0.8–1.2 GHz frequency range. Periods in intervals 0.1–0.5, 0.7–1.0, 2.8–3.9, 75–170 s, and 15–25 min were recognized. This long-lasting narrowband activity consisted mainly of pulsations and continua. In some intervals it was accompanied not only by spikes, broadband pulsations, and fibers in the 1–2 GHz frequency range, but also by type III and U burst activity at lower frequencies as well as by hard X-ray bursts. From several radio bursts, two characterized by different fine structures were selected and compared. The observed differences are explained by different distribution functions of superthermal electrons. The position of the 0.8–1.2 GHz radio source above the photosphere and the magnetic field in the fiber burst source were estimated to be 66 000–75 000 km and 120–135 G, respectively.Presented at te CESRA-Workshop on Coronal Magnetic Energy Release at Caputh near Potsdam in May 1994.     

Spike observations in flares in China

Variations on short time-scales have been found in solar flares at different wavelengths. Millisecond scale radio spikes are a quickly developing area of solar radio astronomy. The solar radio astronomy group of Beijing Astronomical Observatory (BAO) has found fine structures of microwave bursts with millisecond time-scale at 2840 MHz. In this paper, we briefly summarize the observations. A joint-observation network for observing solar radio bursts with high time resolution has also been established. The equipment in the network covers a frequency domain of more than 10:1, including 1.3, 2.0, 6, 10, 15, 20 cm, and meter wavelengths. In particular, a multi-channel polarimeter with super-fast sampling (10 s) at 2600 MHz, an intensity interferometer with 1 ms sampling rate at 6 cm wavelength, and an auto-correlation radio spectrograph with 8 ms time constant at 21 cm wavelength are being established. We pay close attention to research on the spike emission features over wide bands, and their relationship to special characteristics in other spectral ranges.     

Two-frequency timing of the pulsar B1937+21 in Kalyazin and Kashima in 1997–2002

We present the results from our timing of the millisecond pulsar B1937+21, performed jointly since 1997 on two radio telescopes: the RT-64 in Kalyazin (Russia) at a frequency of 0.6GHz and RT-34 in Kashima (Japan) at a frequency of 2.15 GHz. The rms value of the pulse time of arrival (TOA) residuals for the pulsar at the barycenter of the Solar system is 1.8 μs (the relative variation is ≈10^?14 over the observing period). The TOA residuals are shown to be dominated by white phase noise, which allows this pulsar to be used as an independent time scale keeper. The upper limit for the gravitational background energy density Ω_gh² at frequencies ≈6.5 × 10^?9 Hz is estimated to be no higher than 10^?6. Based on the long-term timing of the pulsar, we have improved its parameters and accurately determined the dispersion measure and its time variation over the period 1984–2002, which was, on average, ?0.00114(3) pc cm^?3 yr^?1.     

On the high-speed plasma streams,stormtime sudden commencements and cosmic-ray intensity: Relation amongst them during epoch 1978 to 1982

A new spectrometer has been put into operation that registers solar flare radio emission in the 0.1 to 3 GHz band. It is a frequency-agile system which can be fully programmed to measure both senses of circular polarization at any frequency within that range at selectable bandwidth. The time resolution has to be compromized with the number of frequency channels and can be in the range of 0.5 ms to 250 ms for 1 to 500 channels. First results mainly from the 1–3 GHz band are presented, a spectral region that has never been observed with high-resolution spectrometers. Most noteworthy are the frequent appearances of myriads of narrowband, fast-drifting bursts (microwave type III), diffuse patches of continuum emission, and broad clusters of millisecond spikes sometimes extending from 0.3 to 3 GHz.     

A study of filament transition sheath from radio observations

We have observed an H dark filament at 8, 15, and 22 GHz and derived the radio spectrum of the filament. We suggest that the filament has to be optically thick at radio frequencies and that the observed spectrum is due to the presence of a transition sheath surrounding the filament. We examine a model for the transition sheath in which the energy radiated away is balanced by the conduction of heat from the corona, and show that the radio observations indicate that little or no thermal energy is conducted into the main body of the filament. We compare the model with ultraviolet observations of filaments and discuss how the discrepancies can be removed.On leave of absence from Tata Institute of Fundamental Research, Bombay, India.     

Frequency dependence of solar flare occurrence rates—inferred from power-law distribution

Based on the frequency dependence of the power-law distribution of the peak fluxes in 486 radio bursts in 1–35 GHz observed by Nobeyama Radio Polarimeters (see Song et al. in Astrophys. J. 750:160, 2012), we have first suggested in this paper that the events with power-law behaviors may be emitted from the optically-thin regions, which can be considered as a good measure for the flare energy release. This result is supported by that both the power-law and optical-thin events gradually increase with radio frequencies, which are well fitted by a power-law function with similar indices of 0.48 and 0.80, respectively. Moreover, a flare occurrence rate is newly defined by the power-law event number in per unit frequency. Its values in lower frequencies are evidently larger than those in higher frequencies, which just imply that most flares are trigged in higher corona. Hence, the frequency variation of power-law event number may indicate different energy dissipation rates on different coronal heights.     

Nonlinear parametric instability and millisecond solar radio spikes

A model of nonlinear parametric instability (NLPI) modulation is suggested to explain the millisecond spikes in solar decimetric radio emission. The radio emission energy will periodically transfer to two other waves, and the intensity of the radio emission will be modified by NLPI processes in the corona, when the matching conditions of three-wave coupling are satisfied. This model can simultaneously explain the duration of spikes, why the millisecond spikes have not been observed in other solar radio emission, and the relation between the duration of the spikes and the intensity and the frequency of the radio emission as well.     

Short variability of the radio flux density from the blazar J0530+1331

The results of observations of the quasar J0530+1331 (B0528+134) with the radio telescopes RATAN-600 at frequencies of 4.6, 8.2, 11.2, 21.7 GHz and RT-32 at the Zelenchukskaya and Badary observatories of the Quasar network of the Institute of Applied Astronomy, the Russian Academy of Sciences, at frequencies of 4.84 and 8.57 GHz in 2014–2015 are presented. A strong variability on a timescale of 20 days at 4.6–11.2 GHz has been detected over three months of daily RATAN-600 observations; the variability indices are V = dS/〈S〉; = 0.65?0.39. The spectrum of the variable component is falling toward high frequencies with an index α = ?0.76. The structure and autocorrelation functions at 4.6 GHz show an additional process on a timescale of 7 days. No delay of the main process has been detected between 11.2 and 8.2 GHz; the delay between 8.2 and 4.6 GHz does not exceed two days. The most likely cause of the observed variability is the scattering by inhomogeneities of the interstellar medium. The variability has been obtained at theminimum activity phase of the source. The intraday variability (IDV) has been searched for at both RT-32 telescopes since April 2014. Out of 38 successful observing sessions for the source, only three have shown a variability on a timescale of four hours or more at a significance level no higher than 0.1%. This confirms our conclusion drawn from the previous IDV measurements for other sources that the IDV is observed mainly at the maximum phases of long-term variability of the sources.