Positively Drifting Structures During the 18 March 2003 Solar Flare     

Zongjun Ning  H. Wu  F. Xu  X. Meng 《Solar physics》2007,241(1):77-84

We analyze the high-frequency drift radio structures observed by the spectrometer at Purple Mountain Observatory (PMO) over the frequency range of 4.5 – 7.5 GHz during the 18 March 2003 solar flare. The drifting structures take place before the soft X-ray maximum, almost at the maximum of hard X-ray flux at 25 – 50 keV. For the first time, the positive drift in this kind of radio structures is detected in such a high frequency range. Their global drifting rate is roughly estimated as 3.6 GHz s⁻¹. They appear in four groups, lasting in total for less than 6 s, and have a broad bandwidth of more than 2 GHz but a smaller ratio of the bandwidth of the drifting structures to mean frequency than that of the lower frequency range. The lifetime of each individual burst in this event can be derived by using the high temporal resolution of the spectrometer at PMO and has an average value of 36.3 ms. Since the negative drifting structures observed in the 0.6 – 4.5 GHz frequency range were interpreted to be a radio signature of a plasmoid ejected upward (moving out of the Sun), the present observation may imply that it is possible for a plasmoid to move downward during a solar flare. However, for a confirmation of this suggestion direct radio imaging observation would be needed.  相似文献   

Cross-Correlation Detection of Point Sources in the WMAP First Year Data     

Jian-Yin Nie  Shuang-Nan Zhang  Department of Physics  Center for Astrophysics  Tsinghua University  Beijing  Key Laboratory of Particle Astrophysics  Institute of High Energy Physics  Chinese Academy of Sciences  Beijing 《中国天文和天体物理学报》2007,7(2):199-208

We apply a Cross-Correlation (CC) method developed previously for detecting gamma-ray point sources to the WMAP first year data by using the Point-Spread Function of WMAP and obtain a full sky CC coefficient map. We find that the CC method is a pow- erful tool to examine the WMAP foreground residuals which can be further cleaned accord- ingly. Evident foreground signals are found in the WMAP foreground cleaned maps and the Tegmark cleaned map. In this process 101 point sources are detected, and 26 of them are new sources additional to the originally listed WMAP 208 sources. We estimate the ?ux of these new sources and verify them by another method. As a result, a revised mask file based on the WMAP first year data is produced by including these new sources.  相似文献   

A statistical study of Galactic SNRs using the PMN survey     

M. Stupar  M. D. Filipović  Q. A. Parker  G. L. White  T. G. Pannuti  P. A. Jones 《Astrophysics and Space Science》2007,307(4):423-435

The Parkes–MIT–NRAO (PMN) radio survey has been used to generate a quasi all-sky study of Galactic Supernova Remnants (SNRs) at a common frequency of 4.85 GHz (λ=6 cm). We present flux densities estimated for the sample of 110 Southern Galactic SNRs (up to δ=−65°) observed with the Parkes 64-m radio telescope and an additional sample of 54 from the Northern PMN (up to δ=+64°) survey undertaken with the Green Bank 43-m (20 SNRs) and 91-m (34 SNRs) radio telescopes. Out of this total sample of 164 selected SNRs (representing 71% of the currently 231 known SNRs in the Green catalogue) we consider 138 to provide reliable estimates of flux density and surface brightness distribution. This sub-sample represents those SNRs which fall within carefully chosen selection criteria which minimises the effects of the known problems in establishing reliable fluxes from the PMN survey data. Our selection criteria are based on a judicious restriction of source angular size and telescope beam together with careful evaluation of fluxes on a case by case basis. Direct comparison of our new fluxes with independent literature values gives excellent overall agreement. This gives confidence in the newly derived PMN fluxes when the selection criteria are respected. We find a sharp drop off in the flux densities for Galactic SNRs beyond 4 Jy and then a fairly flat distribution from 5 to 9 Jy, a slight decline and a further flat distribution from 9 to 20 Jy though the numbers of SNR in each Jy bin are low. We also re-visit the contentious Σ–D (radio surface brightness–SNRs diameter) relation to determine a new power law index for a sub-sample of shell type SNRs which yields β=−2.2±0.6. This new evaluation of the Σ–D relation, applied to the restricted sample, provides new distance estimates and their Galactic scale height distribution. We find a peak in the SNR distribution between 7–11 kpc with most restricted to ±100 pc Galactic scale height.  相似文献   

Superdiscs in radio galaxies: jet–wind interactions     

Gopal-Krishna    Paul J. Wiita  Santosh Joshi † 《Monthly notices of the Royal Astronomical Society》2007,380(2):703-711

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Density gradients in Galactic ultra-compact H ii regions     

J. P. Phillips 《Monthly notices of the Royal Astronomical Society》2007,380(1):369-373

We have used recent radiative transfer solutions for cavity-centred shells to investigate the prevalence of density gradients in Galactic ultra-compact H  ii regions. We find that an analysis of 5 and 1.4 GHz data, taken from the recent compilation of Giveon et al., implies that ∼76 per cent of sources may have appreciable density gradients. It would also seem that the central cavities of these sources must be relatively small, with radii no greater than ∼20 per cent of those of the outer shells. The remainder of these sources are presumably homogenous, have much larger cavities, or possess reverse density gradients (densities which increase with increasing radius). A good fraction of the H  ii regions also appear to have high brightness temperatures, implying mean electron temperatures  〈 T _e〉  of the order of  ≈1.3 × 10⁴ K  . This value is higher than has been determined for other such sources.  相似文献   

Radio galaxies in the 2SLAQ Luminous Red Galaxy Survey – I. The evolution of low-power radio galaxies to  z∼ 0.7      

Elaine M. Sadler  Russell D. Cannon  Tom Mauch  Paul J. Hancock  David A. Wake  Nic Ross  Scott M. Croom  Michael J. Drinkwater  Alastair C. Edge  Daniel Eisenstein  rew M. Hopkins  Helen M. Johnston  Robert Nichol  Kevin A. Pimbblet  Roberto De Propris  Isaac G. Roseboom  Donald P. Schneider  Tom Shanks 《Monthly notices of the Royal Astronomical Society》2007,381(1):211-227

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High-redshift Fanaroff–Riley type II radio sources: large-scale X-ray environment     

E. Belsole  D. M. Worrall  M. J. Hardcastle  J. H. Croston 《Monthly notices of the Royal Astronomical Society》2007,381(3):1109-1126

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Constraining the nature of dark energy using the Square Kilometer Array Telescope     

A. Torres-Rodríguez  C. M. Cress 《Monthly notices of the Royal Astronomical Society》2007,376(4):1831-1837

We investigate the potential of the Square Kilometer Array Telescope (SKA) to constrain the sound speed of dark energy. The Integrated Sachs Wolfe (ISW) effect results in a significant power spectrum signal when Cosmic Microwave Background (CMB) temperature anisotropies are cross-correlated with galaxies detectable with the SKA in H  i . We consider using this measurement, the autocorrelation of H  i galaxies and the CMB temperature power spectrum to derive constraints on the sound speed. We study the contributions to the cross-correlation signal made by galaxies at different redshifts and use redshift tomography to improve the signal-to-noise. We use a  χ²  analysis to estimate the significance of detecting a sound speed different from that expected in quintessence models, finding that there is potential to distinguish very low sound speeds from the quintessence value.  相似文献   

On the origins of part-time radio pulsars   总被引：1，自引：0，他引：1  

Bing Zhang  Janusz Gil  Jaroslaw Dyks 《Monthly notices of the Royal Astronomical Society》2007,374(3):1103-1107

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关于太阳厘米-分米波段频谱日像仪研究进展   总被引：4，自引：4，他引：0  

颜毅华  张坚  陈志军  姬国枢  王威  刘飞 《天文研究与技术》2006,3(2):91-98

摘要：在无线电波段进行射电观测是研究太阳的一个十分重要的手段，不同波段的无线电波反映出不同的特性和状态，其辐射频率与环境参数密切相关。当探测出某一频率上的无线电辐射后，即可诊断源区的电子密度或磁场。因此，建设厘米-分米波段频谱日像仪将首次在该波段上实现同时以高空间、高时间和高频率分辨率观测太阳活动的动力学性质，探测日冕大气。对于太阳物理研究具有重要作用。本文介绍该项目的科学意义、技术方案及预研进展情况。  相似文献