A deep X-ray observation of M82 with XMM–Newton     

P. Ranalli †‡  A. Comastri  L. Origlia  R. Maiolino § 《Monthly notices of the Royal Astronomical Society》2008,386(3):1464-1480

We report on the analysis of a deep (100-ks) observation of the starburst galaxy M82 with the EPIC and RGS instruments onboard the X-ray telescope XMM–Newton . The broad-band (0.5–10 keV) emission is due to at least three spectral components: (i) continuum emission from point sources; (ii) thermal plasma emission from hot gas; and (iii) charge-exchange emission from neutral metals (Mg and Si). The plasma emission has a double-peaked differential emission measure, with the peaks at ∼0.5 and ∼7 keV. Spatially resolved spectroscopy has shown that the chemical absolute abundances are not uniformly distributed in the outflow, but are larger in the outskirts and smaller close to the galaxy centre. The abundance ratios also show spatial variations. The X-ray-derived oxygen abundance is lower than that measured in the atmospheres of red supergiant stars, leading to the hypothesis that a significant fraction of oxygen ions have already cooled off and no longer emit at energies ≳0.5 keV.  相似文献   

Radiative bubbles blown by slow stellar winds     

Christopher D. Matzner  Ruben Krasnopolsky 《Monthly notices of the Royal Astronomical Society》2008,386(2):903-908

  相似文献   

Studying the X-ray hysteresis in GX 339−4: the disc and iron line over one decade     

R. J. H. Dunn  R. P. Fender  E. G. Körding  C. Cabanac  T. Belloni 《Monthly notices of the Royal Astronomical Society》2008,387(2):545-563

We report on a comprehensive and consistent investigation into the X-ray emission from GX 339−4. All public observations in the 11 year RXTE archive were analysed. Three different types of model – single power law, broken power law and a disc + power law – were fitted to investigate the evolution of the disc, along with a fixed Gaussian component at 6.4 keV to investigate any iron line in the spectrum. We show that the relative variation in flux and X-ray colour between the two best sampled outbursts are very similar. The decay of the disc temperature during the outburst is clearly seen in the soft state. The expected decay is   S _Disc∝ T ⁴  ; we measure   T ^4.75±0.23  . This implies that the inner disc radius is approximately constant in the soft state. We also show a significant anticorrelation between the iron line equivalent width (EW) and the X-ray flux in the soft state while in the hard state the EW is independent of the flux. This results in hysteresis in the relation between X-ray flux and both line flux and EW. To compare the X-ray binary outburst to the behaviour seen in active galactic nuclei (AGN), we construct a disc fraction luminosity diagram for GX 339−4, the first for an X-ray binary. The shape qualitatively matches that produced for AGN. Linking this with the radio emission from GX 339−4 the change in radio spectrum between the disc and power-law-dominated states is clearly visible.  相似文献   

The role of Kelvin–Helmholtz instability in dusty and partially ionized outflows     

Mohsen Shadmehri  Turlough P. Downes 《Monthly notices of the Royal Astronomical Society》2008,387(3):1318-1322

We investigate the linear theory of Kelvin–Helmholtz instability at the interface between a partially ionized dusty outflow and the ambient material analytically. We model the interaction as a multifluid system in a planar geometry. The unstable modes are independent from the charge polarity of the dust particles. Although our results show a stabilizing effect for charged dust particles, the growth time-scale of the growing modes gradually becomes independent of the mass or charge of the dust particles when the magnetic-field strength increases. We show that growth time-scale decreases with increasing the magnetic field. Also, as the mass of the dust particles increases, the growth time-scale of the unstable mode increases.  相似文献   

Multiwavelength study of Cygnus A – II. X-ray inverse-Compton emission from a relic counterjet and implications for jet duty cycles     

Katrien C. Steenbrugge  Katherine M. Blundell  Peter Duffy 《Monthly notices of the Royal Astronomical Society》2008,388(4):1465-1472

  相似文献   

Vortical mechanism for collimation and acceleration of jets     

M. G. Abrahamyan 《Astrophysics》2008,51(3):357-371

A vortical mechanism for the collimation and acceleration of astrophysical jets is proposed on the basis of exact solutions of the hydrodynamic equations in a homogeneous gravitational field taking viscosity into account. Velocity profiles in the form of a jet structure with a uniformly rotating trunk whose pressure decreases in time, and longitudinal and converging radial flows of matter, are examined. Because of the radial flow, the angular velocity of the trunk and the velocity of the longitudinal flow of matter can accelerate exponentially or in the manner of an “explosive” instability. Flows of this type have low energy dissipation and can serve as unique channels for the acceleration and collimation of jet eruptions from young stars, as well as from active galactic nuclei and quasars. __________ Translated from Astrofizika, Vol. 51, No. 3, pp. 431–444 (August 2008).  相似文献   

Detection of CO Outflow in Rotating Cores     

Xin Guan  Yue-Fang Wu 《中国天文和天体物理学报》2008,8(2):230-236

We investigate the effect of bulk motion on the detection of molecular outflows in the sources S 146, GGD27, and IRAS 22566 5830. The traditional techniques do allow for bulk motions or systematic VLSR shifts of the core emissions, which may cause contamination of the high velocity gas emissions, and outflows may either fail to be detected or have their properties miscalculated. We used a program to follow the systematic shift of VLSR and better results have been obtained.  相似文献   

海南岛附近区域热带气旋低层风场的变化特征     

薛霖  李英  王丙兰  周荣卫 《气候与环境研究》2018,23(3):299-310

利用1979~2015年JTWC(Joint Typhoon Warning Center)最佳路径资料(2001~2015年资料用于台风风圈结构分析)及ERA-interim(0.5°×0.5°)再分析数据,统计分析我国海南岛附近区域(15.5°N~23.5°N,106°E~116°E)热带气旋(Tropical Cyclone,简称TC)低层风场的变化特征。结果表明:(1)年均5.5个TC于4~12月主要以西偏北路径进入该区域,其中海南岛东南侧海域TC出现频率最高且强TC比例最多,而岛西北区域出现频率最低,强TC比例最少。(2)TC中心位于海南岛不同方位时,其外围低层风场分布具有不同的非对称特征,且大风出现比率也各有差异;TC中心位于海南岛上时出现大风比率最高,位于岛南侧时次之,位于岛北侧时最小。(3)该区域TC平均最大风速半径(RMW)为58.3 km;TC位于岛上时RMW最大,而位于岛西南侧最小。(4)TC近中心最大风速由海上向陆地急剧减小,其高值中心主要位于雷州半岛东侧及西侧海域。(5)研究区域内TC的34节风圈半径在TC环流的东侧大而西侧小,强TC大而弱TC小。(6)不同区域TC变形程度有所差异。平均而言,位于岛西南侧TC变形最大而位于岛东南侧时变形最小。  相似文献   

Study on the gas-curtain generation characteristics by the multiple gas jets in a liquid-filled tube     

《Applied Ocean Research》2017

To further understand the gas-curtain generation characteristics during the launching process of the underwater guns, a simulated gas-injector with multiple nozzles is designed and the expansion process of these multiple combustion-gas jets is experimentally captured. Experiment results indicate that, with turbulent mixing between the gas jets and the liquid medium, the gas curtain is generated in the observation chamber. Based on the experiment, a three dimensional unsteady model is established to simulate the expansion process of the multiple jets. Numerical result shows, with the injection of the gas jets, pressure declines in the Taylor cavity along the axial direction at the beginning. During the expansion process, the multiple jets contact and interact with each other, and pressure rises in the mixing area. After merging, backflow vortexes interact and converge, and the vortexes move along the axial direction with the expansion of the combustion gas jets.  相似文献   

在6厘米波长对类星体3C454.3的九站VLBI观测     

吴盛殷  I.Pauliny-Toth  R.Porcas  A.Zensus 《中国天文和天体物理学报》1986,(2)

3C454.3是近几年引起广泛注意的一个强活动射电类星体,它有毫角秒尺度的核——喷流结构,其核在1981年的一次流量密度大爆发之后,显示出“超光速增亮”现象,在6厘米波长,用包括欧洲、美国及南非的9个射电望远镜,于1983年10月对3C454.3进行了甚长基线干涉网观测。观测结果除了证实其核——喷流结构,显示了从毫角秒到角秒尺度上该类星体结构的系统弯曲外,还清楚地揭示了“超光速增亮”所预期的,在1981年8月到1983年1月期间,核的超光速膨胀现象。  相似文献