从一个微波C型爆推算到的高能电子数

本文分析了Sag。Hill天文台观测到的1989年3月6日在1353 UT左右发生的一个罕见的大C型爆,即延伸型耀斑大爆发。假设射电辐射来自处于磁环顶部的均匀源,采用合适的日冕磁场值(100高斯),可推算出射电源中的非热电子总数N_R(5.6×10^(37)),这与一个标准硬X射线发射(I_p=10~6ε^(-3.5))的薄靶模型所预计的非热电子总数N_X(2.8×10^(37))相近。由此表明这两类辐射可能有共同的或紧密相关的非热电子分布起源。文中还用统计规律估算该事件的硬X射线大于30keV以上各通道的总记数率,即HXRBS峰率F_X为1.1×10~5s^(-1)。 文中还分析了长期存有争论的N_R与N_X相差10~3—10~5的原因,可能主要是N_R估计不准。这种估计不准,除理论原因外,还有流量测量精度不够的原因。如流量测量误差在±30％时,就可使N_R的估计值相差10~2—10~3。

Diagnostics from three rising submillimeter bursts

In this paper we investigate three novel rising submillimeter （THz） bursts that occurred sequen- tially in Super Active Region NOAA 10486. The average rising rate of the flux density above 200 GHz is only 20 sfu GHz-1 （corresponding to spectral index α of 1.6） for the THz spectral components of the 2003 October 28 and November 4 bursts, but it attained values of 235 sfu GHz-1 （α = 4.8） in the 2003 November 2 burst. The steeply rising THz spectrum can be produced by a population of highly relativistic electrons with a low-energy cutoff of 1 MeV, but it only requires a low-energy cutoff of 30 keV for the two slowly rising THz bursts, via gyrosynchrotron （GS） radiation based on our numerical simulations of burst spectra in the magnetic dipole field case. The electron density variation is much larger in the THz source than in the microwave （MW） source. It is interesting that the THz source radius decreased by 20%-50% during the decay phase for the three events, but the MW source increased by 28% for the 2003 November 2 event. In the paper we will present a formula that can be used to calculate the energy released by ultrarel- ativistic electrons, taking the relativistic correction into account for the first time. We find that the energy released by energetic electrons in the THz source exceeds that in the MW source due to the strong GS radi- ation loss in the THz range, although the modeled THz source area is 3-4 orders smaller than the modeled MW source one. The total energies released by energetic electrons via the GS radiation in radio sources are estimated, respectively, to be 5.2 × 10^33, 3.9 × 10^33 and 3.7 × 10^32 erg for the October 28, November 2 and 4 bursts, which are 131, 76 and 4 times as large as the thermal energies of 2.9 × 10^31, 2.1 × 10^31 and 5.2 × 10^31 erg estimated from soft X-ray GOES observations.

Study of temporal evolution of emission spectrum in a steeply rising submillimeter burst

The temporal evolution of a spectrum during a steeply rising submillimeter（THz） burst that occurred on 2003 November 2 was investigated in detail for the first time.Observations show that the flux density of the THz spectrum increased steeply with frequency above 200 GHz.Their average rising rates reached a value of 235 sfu GHz^（-1）（corresponding to spectral index α of 4.8） during the burst.The flux densities reached about 4 000 and 70 000 sfu at 212 and 405 GHz at the maximum phase,respectively.The emissions at 405 GHz maintained such a continuous high level that they largely exceeded the peak values of the microwave（MW） spectra during the main phase.Our studies suggest that only energetic electrons with a low-energy cutoff of~ 1 MeV and number density of ~ 10~6-10~8 cm^（-3） can produce such a strong and steeply rising THz component via gyrosynchrotron radiation based on numerical simulations of burst spectra in the case of a nonuniform magnetic field.The electron number density N,derived from our numerical fits to the THz temporal evolution spectra,increased substantially from 8 ×10~6 to 4 × 10~8 cm^（-3）,i.e.,the N value increased 50 times during the rise phase.During the decay phase it decreased to 7 ×10~7 cm^（-3）,i.e.,it decreased by about five times from the maximum phase.The total electron number decreased an order of magnitude from the maximum phase to the decay phase.Nevertheless,the variation in amplitude of N is only about one time in the MW emission source during this burst,and the total electron number did not decrease but increased by about 20%during the decay phase.Interestingly,we find that the THz source radius decreased by about 24%while the MW source radius,on the contrary,increased by 28%during the decay phase.

一个太阳硬X射线爆的观测特性

本文分析了1981年4月27日的一个特大高能爆发。它在硬X射线(HXR)、γ射线和微波(MW)记录上显示一一对应的多脉冲结构。文中讨论了这些脉冲的寿命、时延与HXR的能量、MW的波长之间的关系,发现时延量与湍动加速所预期的值相符合。提出了各脉冲期间的谱呈软→硬→软的演化,可能是由高能电子受到加速的看法。还对产生HXR的高能电子的谱指数、电子总数和MW源区的磁场也作了估计。