共查询到20条相似文献，搜索用时 31 毫秒
1.
Solar flares are known to release a large amount of energy. It is believed that the flares can excite velocity oscillations
in active regions. We report here the changes in velocity signals in three active regions which have produced large X-class
flares. The enhanced velocity signals appeared during the rise time of the GOES soft X-ray flux. These signals are located
close to the vicinity of the hard X-ray source regions as observed with RHESSI. The power maps of the active region show enhancement
in the frequency regime 5–6.5 mHz, while there is feeble or no enhancement of these signals in 2–4 mHz frequency band. High
energy particles with sufficient momentum seem to be the cause for these observed enhanced velocity signals. 相似文献
2.
We present an interferometric technique for the reconstruction of ultra-wide band impulsive signals from point sources. This highly sensitive method was developed for the search for ultra-high energy neutrinos with the ANITA experiment but is fully generalizable to any antenna array detecting radio impulsive events. Applications of the interferometric method include event reconstruction, thermal noise and anthropogenic background rejection, and solar imaging for calibrations. We illustrate this technique with applications from the analysis of the ANITA-I and ANITA-II data in the 200–1200 MHz band. 相似文献
3.
本文列举了云南天文台四波段太阳射电实测中得到的几种干扰实例及确认的太阳快速信号，在认识到太阳射电和干扰信号十分相似的基础上，探讨如何识别真伪信号问题。 相似文献
4.
We revisit the 1.3-year (yr) signals observed on the Sun, in the interplanetary space, and in the Earth’s magnetosphere to study the coupling among signals from the three regions for about 40 years (1970?–?2007) covering the three solar cycles 21, 22, and 23. For this, we make dynamic spectra of datasets including three different regions. From this, we estimate the peak frequency around 1.3 yr for each region and the corresponding band power. We found that coherent power only appears during 1987?–?1995 and the coherent behavior is found only in the interplanetary space and Earth, not in the Sun. Although the solar surface magnetic field shows significant power around 1.3 yr, their peak frequencies are statistically different from those of the outer regions, which make us dismiss the existence of coherence among the three regions. But it is notable that the peaks in band power corresponding to the 1.3-yr period are clearly simultaneous in the interplanetary space and Earth. 相似文献
5.
《Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science》1999,24(4):333-338
The characteristics of random ionospheric inhomogeneities are described including their dependency on the geophysical parameters. They are used in a propagation model to estimate the propagation errors and the fades of the transmitted signals. Margins to be included in a budget link are subsequently determined. Features of our propagation model are presented with typical results for VHF and L band links. 相似文献
6.
All-sky search algorithms for monochromatic signals in resonant bar gravitational wave detector data
In this paper we design and develop several filtering strategies for the analysis of data generated by a resonant bar gravitational wave (GW) antenna, with the goal of assessing the presence (or absence) therein of long-duration monochromatic GW signals, as well as the eventual amplitude and frequency of the signals, within the sensitivity band of the detector. Such signals are most likely generated in the fast rotation of slightly asymmetric spinning stars. We develop practical procedures, together with a study of their statistical properties, which will provide us with useful information on the performance of each technique. The selection of candidate events will then be established according to threshold-crossing probabilities, based on the Neyman–Pearson criterion. In particular, it will be shown that our approach, based on phase estimation, presents a better signal-to-noise ratio than does pure spectral analysis, the most common approach. 相似文献
7.
Carlos Frajuca Fabio da Silva Bortoli Natan Vanelli Garcia Nadja Simao Magalhaes 《Astronomische Nachrichten》2024,345(2-3):e230177
An experimental set up was proposed to determine the speed of gravitational signals traveling in air or in some other medium. It involves two vibrating masses—the emitters, which will be the sources of periodic tidal gravitational signals—and one sapphire-made mass that will act as a detector, positioned between the two emitters. The detector is planned to be suspended in vacuum and cooled down to 4.2 K, and its vibrational amplitude should be measured by a microwave signal (with ultra-low phase-noise) that is expected to resonate with the whispering gallery modes inside the detector. The mechanical and electrical quality factors of sapphire are quite high, yielding a very narrow detection band that reduces the detector sensitivity while amplifying the phase difference of the emitters' signals. The frequencies of the normal modes of the detector were previously determined using a finite element program. In this work, these frequencies are applied to the calculation of a first estimate of the sensitivity of the experiment. 相似文献
8.
地基雷达观测可以提供太阳系天体目标的地形地貌、物理特征、轨道动力等信息。聚焦利用地基雷达天文技术开展月球观测的原理方法和科学意义,介绍了基于我国现有深空雷达上行装置、射电望远镜条件以及非相干散射雷达等系统,初步开展的特高频段(Ultra High Frequency,UHF)和X频段的地基雷达观测月球试验。通过月球反射回波的信号处理,获得了延迟、多普勒频移等参数,得到了一致的与近表层物质密度相关的月面雷达反射率,并得到了月球的左右旋圆极化率,反映了与波长同尺度的月球近表层结构。文章积累的数据处理经验将为我国的小行星预警、行星历表等地基雷达观测研究提供技术基础。 相似文献
9.
Fluorescent emissions from nitric oxide appear imposed upon the Rayleigh backscattered spectrum of the earth's atmosphere between 250 and 300 nm in wavelength. Satellite instruments designed to monitor the global ozone distribution can routinely observe these signals although techniques for exploiting the data are not yet available. Application of a radiative transfer equation developed for an atmosphere including absorption by ozone, molecular scattering, and nitric oxide fluorescence shows the three most prominent NO emissions relative to the 250–300 nm backscattered sunlight to be the (1,4), (1,6), and (0,3) gamma bands. Analysis of the contribution function for each emission band indicates that the fluorescent signals can provide useful information on the magnitude and variability of nitric oxide between 40 and 140 km in altitude. 相似文献
10.
Parasitic programs for the Search for Extraterrestrial Intelligence (SETI), carried out concurrently with conventional radio astronomical observing programs, can be an attractive and cost-effective means of exploring the large multidimensional search space intrinsic to this effort. We describe a microprocessor-based automated SETI acquisition system which searches for and records spectra of narrowband signals in the IF band of an observatory receiver. Data taken with this system over 35 days at the Hat Creek Radio Observatory at 1612 MHz are discussed. Out of approximately 105 spectra processed during this period, 4000 were identified by the system as containing narrowband signals and were recorded. Subsequent analysis indicates that over 3900 of these are due to local RF contamination. The remainder are undergoing further investigation. 相似文献
11.
3C273的光学光变周期 总被引：3，自引：0，他引：3
收录了类星体3C273约110年的光学资料，并在此基础上讨论了光变周期性.当用两种不同方法(Jurkevich方法及DCF(离散相关系数)法)分析时，发现光变曲线中存在周期为2.0年、(13.65±0.20)及(22.5±2.0)年的周期性.同时也讨论了这种周期的可能机制. 相似文献
12.
Yaroslaw A. Ilyushin 《Planetary and Space Science》2004,52(13):1195-1207
The propagation of electromagnetic waves in the northern polar ice sheet of Mars is considered. It is shown that the dispersion and attenuation of radio waves in the polar sheet are regulated by two groups of factors: the physical and chemical composition of the ice, and the geometrical parameters of the layered structure of polar sheet. Both analytical and numerical simulations of ultra wide band chirp radar pulse propagating through the cap are performed. Wide variety of combinations of the physical and geometrical parameters of the ice sheet, consistent with previously published observational data, has been considered. The frequency bands of transparency and opacity of the northern ice sheet for radar signals were found. The side clutter for this particular region of the planet is studied. 相似文献
13.
边带分离(Sideband-separating, 2SB)接收可实现上边带(Upper Sideband, USB)和下边带(Lower Sideband, LSB)信号同时观测,观测效率高且上、下两边带不会出现混叠.因此在射电天文观测应用中越来越受到重视.由于全模拟边带分离接收机存在难以克服的幅度和相位误差,导致了边带抑制率较低,影响了系统的性能.数字边带分离接收机可通过数字信号处理方法,有效改善系统边带抑制率.在3–18 GHz频段构建数字边带分离接收机原理实验,并基于边带分离理论和数字校准方法,实现实验系统的边带不平衡度校准,大大改善了系统的边带抑制率. 相似文献
14.
Since 1973 an all-sky, full-time search for narrowband radio radiation (presumably of intelligent origin) near 21 cm has been underway at the Ohio State University Radio Observatory. The search concentrates on a band 380 kHz wide centered on the hydrogen line, corrected to the Galactic Standard of Rest. The search is limited by lack of funding and personnel. It has been found that beam switching is an important technique for reducing terrestrial interference, and that galactic hydrogen emission does not cause significant extraterrestrial interference. A number of small-diameter cold hydrogen clouds have been discovered. No confirmed narrowband extraterrestrial signals have been found between +48° and +14° in declination above the detection limit of 1.5 × 10?21 W/m2. 相似文献
15.
The North Atlantic Oscillation (NAO) is the leading mode of atmospheric variability in the North Atlantic region, influencing storm tracks and creating a dipole pattern of precipitation from north to south across Western Europe. This distinct spatial distribution of precipitation provides a framework that can be potentially used to identify and reconstruct patterns of past NAO-forced climate variability. In this study we use tree-ring width series from Western Europe, in conjunction with principal components analysis and advanced spectral methods, to prospect for quasi-periodic climate signals that are forced by the NAO. We identify a robust 25-yr anti-phased synchronization in climate variability between Scandinavia and the Mediterranean during the 17th–20th centuries. The amplitude of the 25-yr beat displays a long-term modulation in northern and southern Europe, with minimum amplitude during the late Maunder Minimum. This amplitude minimum coincides with a maximum in Δ14C, suggesting a potential solar or oceanic influence on the intensity of the 25-yr band of quasi-periodic variability. 相似文献
16.
Yuan-Chuan Zou Yi-Zhong Fan Tsvi Piran 《Monthly notices of the Royal Astronomical Society》2009,396(2):1163-1170
We calculate the high-energy (sub-GeV to TeV) prompt and afterglow emission of GRB 080319B that was distinguished by a naked-eye optical flash and by an unusual strong early X-ray afterglow. There are three possible sources for high-energy emission: the prompt optical and γ-ray photons IC scattered by the accelerated electrons, the prompt photons IC scattered by the early external reverse-forward shock electrons, and the higher band of the synchrotron and the synchrotron self-Compton emission of the external shock. There should have been in total hundreds of high-energy photons detectable for the Large Area Telescope onboard the Fermi satellite, and tens of photons of those with energy >10 GeV. The >10 GeV emission had a duration about twice that of the soft γ-rays. Astro-rivelatore Gamma a Immagini Leggero (AGILE) could have observed these energetic signals if it was not occulted by the Earth at that moment. The physical origins of the high-energy emission detected in GRB 080514B, GRB 080916C and GRB 081024B are also discussed. These observations seem to be consistent with the current high-energy emission models. 相似文献
17.
Hongtao Wang 《Astrophysics and Space Science》2014,351(1):281-287
BL Lac object AO 0235+164 is a well-known object. We collect a large number of effective observation in B, V, R and I band from historical literatures. The possible periods are analyzed by means of discrete correlation function (DCF) method, structure function (SF) method and Jurkevich (J-K) method. The results show that there are possible periodic variations of 2.63–2.66 years in B band, 2.79–2.84 years in V band, 2.57–2.87 years in R band, 2.62–2.88 years in I band, respectively. 相似文献
18.
We conducted spectral analysis of central region of the Mare Moscoviense area on the far side of the Moon using the Hyperspectral Imager (HySI) data from the Chandrayaan-1 mission in an effort to identify and map the major lithological units present in the area. Various spectral band parameters, namely, band curvature, band tilt and band strength have been used for lithological discrimination based on the nature of the spectral profile. These band parameters essentially measure the shape, position and strength of the absorption feature near 1000 nm arising due to electronic transition of Fe2+ in crystallographic sites of major rock forming silicates. Spectral band parameters have been used for generating rock type composite image. Based on spectral studies and rock type composite image as obtained using band parameters, five major compositional units have been identified: highland basin soils, ancient mature mare, highland contaminated mare, buried unit with abundant low-Ca pyroxene (LCP), and youngest mare unit. In the present study, a multispectral approach in the form of spectral band parameters has been adopted for analysing the HySI hyperspectral data from Chandrayaan-1 mission. Present study clearly shows that the spectral band parameters obtained using selected HySI channels could efficiently be used to discriminate and delineate the major litho-units present across the central part of Mare Moscoviense and the same approach can thus be used for lithological mapping of other parts of lunar surface using HySI data. 相似文献
19.
Investigation of the polarization observed in infrared absorption bands in the spectra of protostars
T. V. Zinov’eva 《Astronomy Letters》2006,32(10):671-687
We investigate the linear polarization in the two deepest infrared absorption bands observed in the spectra of protostars,
the water-ice band with the center near 3.1 μm and the silicate band with the center near 9.7 μm, using a core-mantle confocal
spheroid model with various axial ratios a/b and relative volumes of the core material. We consider the effect of the grain shape, structure, and type (oblate, prolate)
as well as the type of grain orientation and its location relative to the incident ray of light and the magnetic field direction
on the central wavelengths of the two bands and the polarizability in the bands. We have found that the observed relationships
between the polarizability in the bands and the ratio of their optical depths at the band centers can be explained if we choose
slightly oblate or prolate particles (a/b ≲2 for the silicate band and 1.3 ≲ a/b ≲ 2 for the ice band). For any type of orientation, the core-mantle confocal spheroid model requires different axial ratios
for the ice and silicate bands to account for the observed polarization. We show that picket-fence-oriented particles can
explain the observed polarization in the ice band at angles α between the particle rotation axis and the incident ray ≳30°
and in the silicate band at any α. Perfectly Davis-Greenstein-oriented particles can explain the observed polarization in
the ice band at angles Ω between the line of sight and the magnetic field direction ≳60° and in the silicate band at any Ω.
The orientation parameter ζ (imperfect Davis-Greenstein orientation) must be no more than 0.5 (oblate particles) and 0.1 (prolate
particles) for the ice band and can be arbitrary for the silicate band.
Original Russian Text ? T.V. Zinov’eva, 2006, published in Pis’ma v Astronomicheskiĭ Zhurnal, 2006, Vol. 32, No. 10, pp. 748–766. 相似文献
20.
In this paper, we present the design of a high resolution Chirp Transform Spectrometer (CTS) which is part of the GREAT (German
REceiver for Astronomy at Terahertz frequencies) instrument onboard SOFIA, the Stratospheric Observatory For Infrared Astronomy.
The new spectrometer will provide unique spectral resolving power and linearity response, since the analog Fourier transform
performed by the CTS spectrometer was improved through a new design, that we call “Adaptive Digital Chirp Processor (ADCP)”.
The principle behind the ADCP consists on digitally generating the dispersive signal which adapts to the compressor dispersive
properties, achieving maximum spectral resolution and higher dynamic range. Excellent test results have been obtained such
as a white noise dynamic range of 30 dB, and a spectral resolution (FWHM) of 41.68 kHz which would mean if analyzing signals
with the high frequency band receiver on the GREAT instrument (4.7 THz) a spectral resolving power (λ/Δ λ) higher than 108. 相似文献