Microwave Type III-Like Bursts as Possible Signatures of Magnetic Reconnection

Magnetic reconnection is commonly accepted to play a key role in flare energy release, but only poor information about the main characteristics of this process is available so far. An intrinsic feature of reconnection is plasma density enhancement in current sheets. A unique method to detect this effect is provided by analysis of drifting bursts, whose emission frequency is close to the local Langmuir frequency or its harmonics. With this purpose, we analyze a series of several tens of drifting microwave bursts during the 30 March 2001 flare. The burst drift rates range from −10 to 20 GHz s⁻¹. Using one-dimensional scans recorded with the SSRT interferometer at two different frequencies near 5.7 GHz, we have measured relative positions of burst sources and their velocities along a flare loop revealed from soft X-ray and extreme-ultraviolet images. It is argued that the contribution of the increasing density effect into the observed frequency drift rates is about 6 GHz s⁻¹, which is shown to be consistent with theoretical models of magnetic reconnection with reasonable boundary conditions.     

北京天文台85cm望远镜光电视向速度仪

本文介绍了北京天文台８５ｃｍ望远镜的光电视向速度仪，其主要特点为：１．包括两个通道，可准同时测量恒星视向速度和光度．２．采用光导纤维将卡焦的星光引导到分光仪上．３．采用阶梯光栅作为分光仪色散元件．该仪器已投入试观测，文中给出了１０颗视向速度标准星的测量结果和几颗星的极小值曲线．     

A simple tool for assessing the completeness in apparent magnitude of magnitude–redshift samples

A new tool is proposed for finding out the completeness limit in apparent magnitude of a magnitude–redshift sample. The technique, closely related to the statistical test proposed by Efron & Petrosian, presents a real improvement compared to standard completeness tests. Namely, no a priori assumptions are required concerning the redshift-space distribution of the sources. It means in particular that neither the clustering nor the evolution of the mean number density of the galaxies affects the result of the search.     

Buoyant radio plasma in clusters of galaxies

Radio galaxies are known to inflate lobes of hot relativistic plasmas into the intergalactic medium. Here we present hydrodynamical and magnetohydrodynamical simulations of these hot plasma bubbles in FR II objects. We focus on the later stages of their evolution after the jet has died down and after the bow shock that surrounded the lobes at earlier stages has vanished. We investigate the evolution of the plasma bubbles as they become subject to Rayleigh–Taylor instabilities. From our simulations we calculate the radio and X-ray emissivities of the bubbles and discuss their appearance in observations. Finally, we investigate the influence of large-scale magnetic fields on the evolution of the bubbles. The issues of re-acceleration and diffusion of relativistic particles are briefly discussed.     

An analysis of the line shape for H2O maser emission peaks in star-forming regions

We analyze the line shape for emission peaks of H₂O maser sources associated with star-forming regions by using the spectra obtained with the RT-22 radio telescope at the Pushchino Radio Astronomy Observatory. For five sources, we found the line profile of emission peaks to be asymmetric. In all cases, the left (high-frequency) line wing is higher than the right wing. Our analysis of the line shape yielded additional information on the structure and evolution of the maser sources under study. In G43.8-0.1, the emission feature was found to split up into two components. To explain the evolution of the 16.8 km s^?1 line in NGC 2071, we propose a model in which the line-of-sight velocity gradient changes under the effect of a (non-shock) wave. The observed short-duration flares of individual emission features in W75N can emerge due to a chance projection of the numerous clumps of matter involved in Keplerian motion onto each other.     

Closed loop model of turbulent acceleration for the gradual phase of the radio burst of 1981 April 27

We propose a closed loop model of turbulent stochastic acceleration for the gradual phase of the radio burst of 1981 April 27. It can explain the various observed features in the spectrum, the rather long time of rise, the absence of X-ray bursts below 56 keV and of any detectable proton events.