Jin Sheng-zhen

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 μs) 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.

The quasi-periodic oscillation of spike radiation in solar radio burst

Abstract We present the quasi-periodic oscillations found in the millisecond spikes of the microwave burst of 1981 May 16. Such oscilations may be connected with Alfven waves in the magnetic loops of solar activie regions, hence we can obtain from them certain basic physical conditions of the burst source region. Lastly we discuss the effect on the spike radiation by the quasi-periodic oscillation.

Detectivity of Fe Kα Lines in Gamma-Ray Bursts by Cerenkov Line Mechanism

The Fe Kα lines in gamma-ray bursts (GRBs) produced with the Cerenkov line mechanism are studied. We theoretically predict the Fe Kα line luminosities in both the early (before 1 hour) and late (~1 day) afterglows. Assuming about 200 GRBs could be detected by Swift per year, we sampled the redshift of these GRBs using the Monte Carlo method according to the GRB formation rate derived from the statistical correlation between the spectral peak energy and the peak luminosity of GRBs. Then we obtain the Fe Kα line flux distributions of the simulated GRB sample in the early and late phases. The simulated results show that the iron line flux is relatively low, so the line detection would be still a rare event at present. In addition, our results suggest that the iron lines from GRBs could be detected in the high redshift: z~3 for the early phase and z~6 for the late phase. Therefore, it is possible that the identification of Fe Kα lines in GRBs provides a tool to directly measure redshift and to study the high-redshift GRBs in the Swift era.

The intense microwave burst associated with a white light flare on 1991 June 6

Abstract This paper briefly reports on the intense microwave burst associated with a white light flare at 2545 and 2645 MHz on 1991 June 6. The burst had a very high flux density, a very high degree of polarization and very complex changes in polarization state. A chromospheric white light flare was observed during the first peak of the burst. We briefly discuss the time relation between the two and the cause for the changes in polarization.

Rapid reversals of polarization in spikes and fast fine structures

Abstract We briefly describe the polarization state of the spike groups and fast fine structures superimposed on the 47GB microwave burst of 1991 May 16. At two frequencies 100 MHz apart, namely, 2645 and 2545 MHz, the polarization showed rapid reversals on short time scales of the order of 50 ∼ 100ms. We think this is probably related to fluctuations on both short time and small spatial scales, in the plasma density and magnetic field of the emission region. These oscillations cause the plasma and cyclotron frequency ratio to vary around the value of 2 , thus making the electron cyclotron maser instability growth rate to be dominated alternately by the X mode and the O mode and the polarization state to switch from one sign to the other.

MHD oscillations in the solar spike radiation

Abstract In this paper the observed 1.4–1.6 s quasi-periodic oscillations in the spike radiation of the microwave outburst of 1981 May 16 are analysed in teras of MHD waves. We point out that the fast magnetoacoustic waves (“sausage” mode) propagating inside and outside a loop can modulate the magnetic field and the pitch angle distribution of the electron beams in the source region. The growth rate of electron-cyclotron-maser instability is then affected to give rise to the quasi-periodic oscillations. Quantitative estimates of relevant physical parameters are given.