Using the visual inspection and base difference method and data from the X-ray Telescope (XRT) onboard Hinode and TRACE with improved spatial and temporal resolution, we selected 48 X-ray transient brightenings (XTBs) and 237 EUV transient brightenings (ETBs) to study the connection between these two types of transient brightenings (TBs). These ETBs and XTBs have smaller areas (8.42 Mm 2 and 36.3 Mm 2 , respectively, on average) and shorter durations (9.0 min and 6.9 min, respectively, on average) than previous studies. These XTBs show three types of morphological structure: point-like, single-loop and multiple-loop. We find only 20% of the ETBs have corresponding XTBs while the other 80% have no X-ray signatures at all. This is presumably due to the small amount of released energy, which is not enough to heat the plasma to coronal temperatures which produce X-ray emission rather than being due to the limitation of spatial resolution and temperature sensitivity of the X-ray instrument. These small ETBs may significantly contribute to the coronal heating.
Based on a three-component description of partially ionized plasmas(i.e.,electrons,ions,and neutral atoms),effects of inelastic collisions between ions(neutrals)and electrons on Alfve′n waves(AWs)in a partially ionized plasma are studied.It is shown that for a fixed ionizability(i)or a fixed inelastic collision parameter(v,i.e.,the ratio of the inelastic to elastic collision frequency),the damping rate of AWs has a peak value round kz vA/min*1,where kz is the parallel wavenumber of AWs,vA is the Alfve′n velocity,and min is the elastic collision frequency between ions and neutrals.On the other hand,the damping rate of AWs decreases monotonously with the ionizabilityi for a fixed inelastic collision parameter,but has a peak value when the inelastic collision parameter varies for sufficiently small ionizability(i\0:1).For sufficiently large ionizability(i[0:1),it is found that the damping rate decreases with the inelastic collision parameter.The results may help us to understand the physics of AWs in partially ionized plasmas.
太阳耀斑中硬X射线(HXR)光子谱的低能变平过去一般认为是由于耀斑中非热电子的低能截止造成的,但现在也有作者认为耀斑光子与下层大气的逆康普顿散射(albedo效应)或者其他作用也能够使得HXR光子谱出现低能变平的情形.采用Gan et al.(2001,2002)中提出的求非热电子低能截止的方法,统计分析了Ramaty High Energy Solar Spectroscopy Imager(RHESSI)卫星在2002—2005年间观测的100个耀斑,发现经albedo校正,有18个耀斑的HXR光子谱可以利用单幂律谱来拟合,在80个可以用双幂律谱来拟合HXR光子谱的耀斑中,有21个耀斑可以直接用单幂律电子谱加一个低能截止来解释.低能截止范围为20—50keV,平均值约为30keV.同时也分析了耀斑光子谱特征的其他可能解释.
Among the RHESSI flare samples,we concentrated on a kind of flare that presents two successive peaks(that is,it presents both an impulsive phase and a gradual phase)in 12-25 keV light curves.Taking the C1.4 flare on 2002 August 12 as an example,we studied the light curves,spectra,and images in detail.Making full use of the capabilities of RHESSI,we showed some evidence to support the expected causal relationship between these two peaks:the first peak is mainly nonthermal,while the second peak is mainly thermal;the energy carried by nonthermal electrons during the first peak seems to be comparable to the thermal energy of the second peak.The morphologies of X-ray images and their evolutions provide additional evidence for this causality.We conclude that two such peaks in the 12-25 keV light curve are good evidence for the chromospheric evaporation.However,the maximum time of the second peak is later than the end time of the first peak,suggesting that for some events,a modification of the traditional Neupert effect could be necessary by inclusion of a time delay,which might be partly related to the filling of the loop by evaporated material.
We study the properties of the He I 10830 line in nine selected solar flares,using spectral data obtained with the Multi-channel Infrared Solar Spectrograph(MISS) at Purple Mountain Observatory(PMO) and photospheric images from the Michelson Doppler Imager(MDI) onboard the Solar and Heliospheric Observatory(SOHO).Our results indicate that,over an area of 3-8,the He I 10830 line shows emission exceeding the continuum in nearby quiet region when the Geostationary Operations Environmental Satellite(GOES) X-ray class of the flare reaches a threshold value(C4.5).The He I 10830 line emission is detected only in the kernels of the Hα brightenings,but is not associated with the size of the flare.It is found that,whenever the He I 10830 line shows excess emission over the nearby continuum both the Hα and the Ca II 8542 lines display enhanced intensities exceeding their preflare intensities.The He I 10830 line emission can occasionally extend into the umbra of the involved sunspot,which is inconsistent with previous studies.The weak com-ponent of He I 10830 line changes from emission to absorption earlier than does the main component.Our results favor the photoionization-reconnection mechanism for the excitation of the He I 10830 line.
The Kunming 40-meter radio telescope is situated in the yard ofthe Yunnan Astronomical Observatory(Longitude:1 02.8° East,Latitude:2 5.0° North)and saw its first light in 2006 May.The Kunming station successfully joined the VLBI tracking of China's first lunar probe "Chang'E-1" together with the other Chinese telescopes: the Beijing Miyun 50-meter radio telescope,Urumqi Nanshan 25-meter radio tele-scope,and Shanghai Sheshan 25-meter radio telescope,and received the downlinked scientific data together with the Miyun station from October of 2007 to March of 2009. We give an introduction to the new Chinese VLBI facility and investigate its potential applications.Due to its location,the Kunming station can significantly improve the u-v coverage of the European VLBI Network(EVN),in particular,in long base-line observations.We also report the results of the first EVN fringe-test experiment of N09SX1 with the Kunming station.The first fringes in the European telescopes were successfully detected at 2.3 GHz with the ftp-transferred data on 2009 June 1 7. From scheduling the observations to performing the post correlations,the Kunming station shows its good compatibility to work with the EVN.The imaging result of the extended source 11 56+295 further demonstrates that the Kunming station greatly enhances the EVN performance.
Magnetic field in the solar lower atmosphere can be measured by the use of the Zeeman and Hanle effects. By contrast, the coronal magnetic field well above the solar surface, which directly controls various eruptive phenomena, can not be precisely measured with the traditional techniques. Several attempts are being made to probe the coronal magnetic field, such as force-free extrapolation based on the photospheric magnetograms, gyroresonance radio emissions, and coronal seismology based on MHD waves in the corona. Compared to the waves trapped in the localized coronal loops, EIT waves are the only global-scale wave phenomenon, and thus are the ideal tool for the coronal global seismology. In this paper, we review the observations and modelings of EIT waves, and illustrate how they can be applied to probe the global magnetic field in the corona.
CHEN PengFei Department of Astronomy, Nanjing University, Nanjing 210093, China
