Magnetar-like X-ray bursts from an anomalous X-ray pulsar

Anomalous X-ray pulsars (AXPs) are a class of rare X-ray emitting pulsars whose energy source has been perplexing for some 20 years. Unlike other X-ray emitting pulsars, AXPs cannot be powered by rotational energy or by accretion of matter from a binary companion star, hence the designation 'anomalous'. Many of the rotational and radiative properties of the AXPs are strikingly similar to those of another class of exotic objects, the soft-gamma-ray repeaters (SGRs). But the defining property of the SGRs--their low-energy-gamma-ray and X-ray bursts--has not hitherto been observed for AXPs. Soft-gamma-ray repeaters are thought to be 'magnetars', which are young neutron stars whose emission is powered by the decay of an ultra-high magnetic field; the suggestion that AXPs might also be magnetars has been controversial. Here we report two X-ray bursts, with properties similar to those of SGRs, from the direction of the anomalous X-ray pulsar 1E1048.1 - 5937. These events imply a close relationship (perhaps evolutionary) between AXPs and SGRs, with both being magnetars.     

An X-ray outburst from the rapidly accreting young star that illuminates McNeil's nebula

Young, low-mass stars are luminous X-ray sources whose powerful X-ray flares may exert a profound influence over the process of planet formation. The origin of the X-ray emission is uncertain. Although many (or perhaps most) recently formed, low-mass stars emit X-rays as a consequence of solar-like coronal activity, it has also been suggested that X-ray emission may be a direct result of mass accretion onto the forming star. Here we report X-ray imaging spectroscopy observations which reveal a factor approximately 50 increase in the X-ray flux from a young star that is at present undergoing a spectacular optical/infrared outburst (this star illuminates McNeil's nebula). The outburst seems to be due to the sudden onset of a phase of rapid accretion. The coincidence of a surge in X-ray brightness with the optical/infrared eruption demonstrates that strongly enhanced high-energy emission from young stars can occur as a consequence of high accretion rates. We suggest that such accretion-enhanced X-ray emission from erupting young stars may be short-lived, because intense star-disk magnetospheric interactions are quenched rapidly by the subsequent flood of new material onto the star.     

Optical pulsations from the anomalous X-ray pulsar 4U0142+61

Anomalous X-ray pulsars (AXPs) differ from ordinary radio pulsars in that their X-ray luminosity is orders of magnitude greater than their rate of rotational energy loss, and so they require an additional energy source. One possibility is that AXPs are highly magnetized neuron stars or 'magnetars' having surface magnetic fields greater than 10(14) G. This would make them similar to the soft gamma-ray repeaters (SGRs), but alternative models that do not require extreme magnetic fields also exist. An optical counterpart to the AXP 4U0142+61 was recently discovered, consistent with emission from a magnetar, but also from a magnetized hot white dwarf, or an accreting isolated neutron star. Here we report the detection of optical pulsations from 4U0142+61. The pulsed fraction of optical light (27 per cent) is five to ten times greater than that of soft X-rays, from which we conclude that 4U0142+61 is a magnetar. Although this establishes a direct relationship between AXPs and the soft gamma-ray repeaters, the evolutionary connection between AXPs, SGRs and radio pulsars remains controversial.     

振动落砂机系统的拟周期碰撞设计

首先建立了落砂机系统周期运动的Poincaré映射,考虑到在设计过程中经典的Neimark-Sacker分岔临界准则需要直接计算特征值带来的局限性,利用不直接依赖于特征值计算的显式临界准则,获得了系统发生Neimark-Sacker分岔的两参数区域图,所获得的参数区域图有助于主动设计系统的拟周期碰撞运动.然后应用中心流形-正则形方法进一步分析了拟周期碰撞运动的稳定性.最后数值仿真表明在选定的系统参数处能产生稳定的拟周期碰撞运动.     

An optical counterpart to the anomalous X-ray pulsar 4U0142+61

The energy source of the anomalous X-ray pulsars (AXPs) is not understood, hence their designation as anomalous. Unlike binary X-ray pulsars, no companions are seen, so the energy cannot be supplied by accretion of matter from a companion star. The loss of rotational energy, which powers radio pulsars, is insufficient to power AXPs. Two models are generally considered: accretion from a large disk left over from the birth process, or decay of a very strong magnetic field (10(15) G) associated with a 'magnetar'. The lack of counterparts at other wavelengths has hampered progress in our understanding of these objects. Here we report deep optical observations of the field around 4U0142+61, which is the brightest AXP in X-rays. The source has no associated supernova remnant, which, together with its spin-down timescale of approximately 10(5) yr (ref. 5), suggests that it may be relatively old. We find an object with peculiar optical colours at the position of the X-ray source, and argue that it is the optical counterpart. The optical emission is too faint to admit the presence of a large accretion disk, but may be consistent with magnetospheric emission from a magnetar.     

Stability and Robustness Analysis of an Adaptive Algorithm for Quasi-periodic Disturbances Rejection

IntroductionThere exist several approaches to tackle periodicdisturbance rejection problems. One approach is based onrepetitive or learning control principles[1], it has gainedsome popularity in various applications where periodicdisturbances rejection or repetitive tracking is required.These applications include the control of disk drives[2],rejection of load disturbances in steel casting process[3],eccentricity compensation in rolling[4] and so on. This typeof …     

一种基于泊松分布的提高X射线脉冲星脉冲轮廓信噪比的方法

论述了X射线脉冲星辐射模型和脉冲轮廓构造算法,提出了以Kullback-leibler距离函数作为评价标准,提高具有泊松分布规律的X射线脉冲星脉冲轮廓信噪比的平滑算法,推导了平滑参数和平滑累积脉冲轮廓的计算公式.搭建了X射线脉冲星导航地面模拟系统,实现了对模拟X射线脉冲星单光子到达时间的记录及X射线脉冲星脉冲轮廓的构造,得到了X射线脉冲到达时间TOA.在X射线脉冲星导航地面模拟系统上,对平滑算法进行了验证,结果表明该算法对于提高累积脉冲轮廓的信噪比效果显著,信噪比提高大于10dB.     

Evidence for free precession in a pulsar

Pulsars are rotating neutron stars that produce lighthouse-like beams of radio emission from their magnetic poles. The observed pulse of emission enables their rotation rates to be measured with great precision. For some young pulsars, this provides a means of studying the interior structure of neutron stars. Most pulsars have stable pulse shapes, and slow down steadily (for example, see ref. 20). Here we report the discovery of long-term, highly periodic and correlated variations in both the pulse shape and the rate of slow-down of the pulsar PSR B1828-11. The variations are best described as harmonically related sinusoids, with periods of approximately 1,000, 500 and 250 days, probably resulting from precession of the spin axis caused by an asymmetry in the shape of the pulsar. This is difficult to understand theoretically, because torque-free precession of a solitary pulsar should be damped out by the vortices in its superfluid interior.     

单段爆破震动的动态响应分析

利用反应谱理论对单段爆破的地震效应进行研究。根据单自由度体系反应谱理论,采用计算量少、精确度高的三角插值解析公式法取代常用的分段线性插值法进行反应谱数值计算;结合工程爆破地震实测资料,对不同爆炸参量下产生的单段爆破震动信号进行反应谱分析,探讨爆炸参量对爆破震动反应谱的影响。研究结果表明,单段爆破产生的震动其频率成分相对简单;单段爆破震动的动态响应特征与爆炸参量有着密切的关系,特别是最大段药量对其影响最大。该方法可用于研究爆破地震效应特别是爆破震动危害控制和预测。     

神经网络LM算法在X射线探测器中的应用

介绍了1种探测X射线分布和剂量的方法.采用BP神经网络拟合图像灰度值与照射量率的关系曲线,实现了探测器的标定.分析了直接用CMOS图像传感器探测X射线的原理.探讨了神经网络参数选取的方法.利用LM算法优化BP神经网络,得到较为精确的拟合曲线和误差曲线,并且用测试数据验证该系统的误差性能指标.实验证明该算法能够较为精确的测量辐射的剂量信息,可应用于X射线探测器的标定.     

Design of a compact C-band high brightness photoinjector for an ultra-fast electron diffraction

A compact C-band high brightness photoinjector for ultra-fast electron diffraction （UED） is under development at Tsinghua Uni- versity. The C-band photoinjector, operating at 5.172 GHz, uses a 1.45-cell C-band RF gun as the electron source. The design of the RF gun has addressed the physics, beam dynamics and mechanical aspects, and based on these design studies, a prototype has been fabricated. In order to obtain optimized performance for the UED, beam dynamics simulation has been carried out using the particle tracking code Astra for the photoinjector consisting of an alternative multi-cell RF gun design and a C-band compressor downstream. The beam dynamics parameters that are optimized include the bunch length, peak current, horizontal emittance, and position of the minimum bunch length.     

电子加速器X射线发射率的MCNP分析

为满足现代X射线应用和设计电子加速器的靶结构和束流参数的需要,采用MCNP4B程序对2～20MeV能量范围内的电子束入射不同厚度钨靶的X射线发射率进行了系统的模拟计算和研究.结果表明在电子能量小于10MeV时,MCNP4B的结果与NCRP-51报告一致,但在10MeV以上,它们间的差别增大.该文结果对早期NCRP-51报告的结果有重要的改进,对于现代产生X射线的电子加速器靶的设计具有参数作用.     

非中性相对论等离子体在脉冲星磁层中的运动

探讨了脉冲星磁层加速区外磁流管中非中性相对论等离子体的运动学特征.在满足净电荷密度处处等于Goldreich-Julian电荷密度的条件下,计算了不同磁倾角和不同磁力线上的次级正负电子速度分布.结果表明,电子速度经历显著的加速或减速.在靠近自转轴一侧的上半磁层和靠近赤道一侧的下半磁层,次级电子加速或减速的图像有显著不同.沿磁力线平行电场的总电压差所引起的电子动能改变与电子初始动能相当,但该电压差远小于磁层加速区的总电压差.该结果对研究磁层中粒子能谱的不均匀性是有意义的.     

Atomic inner-shell X-ray laser at 1.46 nanometres pumped by an X-ray free-electron laser

Since the invention of the laser more than 50 years ago, scientists have striven to achieve amplification on atomic transitions of increasingly shorter wavelength. The introduction of X-ray free-electron lasers makes it possible to pump new atomic X-ray lasers with ultrashort pulse duration, extreme spectral brightness and full temporal coherence. Here we describe the implementation of an X-ray laser in the kiloelectronvolt energy regime, based on atomic population inversion and driven by rapid K-shell photo-ionization using pulses from an X-ray free-electron laser. We established a population inversion of the Kα transition in singly ionized neon at 1.46 nanometres (corresponding to a photon energy of 849 electronvolts) in an elongated plasma column created by irradiation of a gas medium. We observed strong amplified spontaneous emission from the end of the excited plasma. This resulted in femtosecond-duration, high-intensity X-ray pulses of much shorter wavelength and greater brilliance than achieved with previous atomic X-ray lasers. Moreover, this scheme provides greatly increased wavelength stability, monochromaticity and improved temporal coherence by comparison with present-day X-ray free-electron lasers. The atomic X-ray lasers realized here may be useful for high-resolution spectroscopy and nonlinear X-ray studies.     

露天矿微差爆破振动对多层建筑的影响

基于十堰市高家沟堰口采石场爆破开挖工程现场试验,对矿山附近一栋多层建筑物进行爆破振动监测,分析了该建筑物不同楼层的振动速度及谐波频率的变化规律。结果表明:爆破远区的多层建筑物受爆破振动影响时,垂直方向振动速度随着楼层高度的增加而变大,水平方向振动速度随着楼层高度的增加而变小;爆破振动产生的谐波频率丰富,较高楼层谐波频率分布范围小于较低楼层且更接近建筑物的固有频率。