首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 906 毫秒
1.
ASTRON has demonstrated the capabilities of a 4 m2, dense phased array antenna (Bij de Vaate et al., 2002) for radio astronomy, as part of the Thousand Element Array project (ThEA). Although it proved the principle, a definitive answer related to the viability of the dense phased array approach for the SKA could not be given, due to the limited collecting area of the array considered. A larger demonstrator has therefore been defined, known as “Electronic Multi-Beam Radio Astronomy Concept”, EMBRACE, which will have an area of 625 m2, operate in the band 0.4–1.550 GHz and have at least two independent and steerable beams. With this collecting area EMBRACE can function as a radio astronomy instrument whose sensitivity is comparable to that of a 25-m diameter dish. The collecting area also represents a significant percentage area (∼10%) of an individual SKA “station.” This paper presents the plans for the realisation of the EMBRACE demonstrator.  相似文献   

2.
In the rapidly developing field of study of the transient sky, fast radio transients are perhaps the most exciting objects of scrutiny at present. The SKA, with its wide field-of-view and significant improvement in sensitivity over existing facilities, is expected to detect a plethora of fast transients which, in addition to help resolve the mysteries surrounding their nature and origin, will also lead to other interesting applications in astrophysics. We explore some of these possibilities here, and also emphasize the current status and future plans of the Indian community working in this area, in the context of ongoing work and extension of this to the SKA.  相似文献   

3.
In this paper, we investigate how the Square Kilometre Array (SKA) can aid in determining the evolutionary history of active galactic nuclei (AGN) from redshifts z = 0 → 6. Given the vast collecting area of the SKA, it will be sensitive to both ‘radio-loud’ AGN and the much more abundant ‘radio-quiet’ AGN, namely the radio-quiet quasars and their ‘Type-II’ counterparts, out to the highest redshifts. Not only will the SKA detect these sources but it will also often be able to measure their redshifts via the Hydrogen 21-cm line in emission and/or absorption. We construct a complete radio luminosity function (RLF) for AGN, combining the most recent determinations for powerful radio sources with an estimate of the RLF for radio-quiet objects using the hard X-ray luminosity function of [ApJ 598 (2003) 886], including both Type-I and Type-II AGN. We use this complete RLF to determine the optimal design of the SKA for investigating the accretion history of the Universe for which it is likely to be a uniquely powerful instrument.  相似文献   

4.
The sensitivity and versatility of SKA will provide microarcsec astrometric precision and high quality milliarcsec-resolution images by simultaneously detecting calibrator sources near the target source. To reach these goals, we suggest that the long-baseline component of SKA contains at least 25% of the total collecting area in a region between 1000 and 5000 km from the core SKA. We also suggest a minimum of 60 elements in the long-baseline component of SKA to provide the necessary (u–v) coverage. For simultaneous all-sky observations, which provide absolute astrometric and geodetic parameters, we suggest using 10 independent subarrays each composed of at least six long-baseline elements correlated with the core SKA. We discuss many anticipated SKA long-baseline astrometric experiments: determination of distance, proper motion and orbital motion of thousands of stellar objects; planetary motion detections; mass determination of degenerate stars using their kinetics; calibration of the universal distance scale from 10 to 107 pc; the core and inner-jet interactions of AGN. With an increase by a factor of 10 in absolute astrometric accuracy using simultaneous all sky observations, the fundamental quasar reference frame can be defined to <10 μas and tied to the solar-system dynamic frame to this accuracy. Parameters associated with the earth rotation and orientation, nutation, and geophysical parameters, can be accurately monitored. Tests of fundamental physics include: solar and Jovian deflection experiments, the sky frame accuracy needed to interpret the gravity wave/pulsar-timing experiment, accurate monitoring of spacecraft orbits that impact solar system dynamics.  相似文献   

5.
With the high sensitivity and wide-field coverage of the Square Kilometre Array (SKA), large samples of explosive transients are expected to be discovered. Radio wavelengths, especially in commensal survey mode, are particularly well-suited for uncovering the complex transient phenomena. This is because observations at radio wavelengths may suffer less obscuration than in other bands (e.g. optical/IR or X-rays) due to dust absorption. At the same time, multiwaveband information often provides critical source classification rapidly than possible with only radio band data. Therefore, multiwaveband observational efforts with wide fields of view will be the key to progress of transients astronomy from the middle 2020s offering unprecedented deep images and high spatial and spectral resolutions. Radio observations of Gamma Ray Bursts (GRBs) with SKA will uncover not only much fainter bursts and verifying claims of sensitivity-limited population versus intrinsically dim GRBs, they will also unravel the enigmatic population of orphan afterglows. The supernova rate problem caused by dust extinction in optical bands is expected to be lifted in the SKA era. In addition, the debate of single degenerate scenario versus double degenerate scenario will be put to rest for the progenitors of thermonuclear supernovae, since highly sensitive measurements will lead to very accurate mass loss estimation in these supernovae. One also expects to detect gravitationally lensed supernovae in far away Universe in the SKA bands. Radio counterparts of the gravitational waves are likely to become a reality once SKA comes online. In addition, SKA is likely to discover various new kinds of transients.  相似文献   

6.
The new generation of radio telescopes, such as the proposed Square Kilometer Array (SKA) and the Low-Frequency Array (LOFAR) rely heavily on the use of very large phased aperture arrays operating over wide band-widths at frequency ranges up to approximately 1.4?GHz. The SKA in particular will include aperture arrays consisting of many thousands of elements per station providing un-paralleled survey speeds. Currently two different arrays (from nominally 70?MHz to 450?MHz and from 400?MHz to 1.4?GHz) are being studied for inclusion within the overall SKA configuration. In this paper we aim to analyze the array contribution to system temperature for a number of regular and irregular planar antenna array configurations which are possible geometries for the low-frequency SKA (sparse disconnected arrays). We focus on the sub-500?MHz band where the real sky contribution to system temperature (T sys ) is highly significant and dominants the overall system noise temperature. We compute the sky noise contribution to T sys by simulating the far field response of a number of SKA stations and then convolve that with the sky brightness temperature distribution from the Haslam 408?MHz survey which is then scaled to observations at 100?MHz. Our analysis of array temperature is carried out by assuming observations of three cold regions above and below the Galactic plane. The results show the advantages of regular arrays when sampled at the Nyquist rate as well as their disadvantages in the form of grating lobes when under-sampled in comparison to non-regular arrays.  相似文献   

7.
  相似文献   

8.
The MRT survey will be by far one of the most extensive survey at low frequencies. This survey will provide a moderately deep radio catalog reaching a source density of about 2 × 104 sr-1over the southern sky with an angular resolution of 4' × 4' and a limiting flux density of 70 mJy (1 σ) at 151 MHz. The availability of zero spacing and short baselines in the MRT array will make it sensitive to the background temperature and to large scale features in the sky. In addition to this feature, the low frequency operation makes a study of continuum emission from large radio sources by MRT to have several interesting and important implications in the study of radio galaxies. This paper discusses the parameter space of radio galaxies which can be explored using the MRT. Images of a few extended radio galaxies are also presented. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
A sky model from CLEAN deconvolution is a particularly effective high dynamic range reconstruction in radio astronomy,which can effectively model the sky and remove the sidelobes of the point spread function(PSF)caused by incomplete sampling in the spatial frequency domain.Compared to scale-free and multi-scale sky models,adaptive-scale sky modeling,which can model both compact and diffuse features,has been proven to have better sky modeling capabilities in narrowband simulated data,especially for large-scale features in high-sensitivity observations which are exactly one of the challenges of data processing for the Square Kilometre Array(SKA).However,adaptive scale CLEAN algorithms have not been verified by real observation data and allow negative components in the model.In this paper,we propose an adaptive scale model algorithm with non-negative constraint and wideband imaging capacities,and it is applied to simulated SKA data and real observation data from the Karl G.Jansky Very Large Array(JVLA),an SKA precursor.Experiments show that the new algorithm can reconstruct more physical models with rich details.This work is a step forward for future SKA image reconstruction and developing SKA imaging pipelines.  相似文献   

10.
The emerging field of bioastronomy is beginning to address one of the oldest questions in science and philosophy: Are we alone? By virtue of its sheer sensitivity, high frequency coverage, and long baselines, the SKA will play a pivotal role in bioastronomical studies. It will be a unique instrument with the capability to image proto-planetary disks in nearby star-forming regions and monitor the evolution of structures within those disks (“movies of planetary formation”). It will also be able to assess the extent to which interstellar molecules are incorporated into proto-planetary disks. It will also be able to reach qualitatively new levels of sensitivity in the search for intelligence elsewhere in the Galaxy, including for the first time the realistic possibility of detecting unintentional emissions or “leakage” (such as from TV transmitters) from nearby stars.  相似文献   

11.
Radio frequency interference (RFI) has plagued radio astronomy from its inception. The Workshop on the Mitigation of Radio Frequency Interference in Radio Astronomy (RFI2004) was held in Penticton, BC, Canada in July 2004 in order to consider the prognosis for the RFI problem, in particular as it impacts the planned Square Kilometre Array (SKA). This paper concludes that RFI is unlikely to be a “showstopper” in achieving SKA science goals, but that improved RFI mitigation technology may nevertheless be essential in order to take advantage of the vastly improved sensitivity, bandwidth, and field of view. Reported results provide some optimism that the desired improvements in RFI mitigation technology are possible, but indicate that much more work is required.  相似文献   

12.
The Square Kilometre Array (SKA) is expected to become the world’s most powerful radio telescope at meter and centimeter wavelength in the coming decades. The construction of SKA will be divided into two phases. The first phase (SKA1), scheduled for completion in 2023, will construct 10 % of the whole collecting area. The second phase (SKA2) will build the rest 90 % collecting area. The SKA1 consists of several types of arrays including SKA1-low and SKA1-mid. The latter is a dish array consisting of ~200 medium-size antennas. The integrated dish array in SKA2 will expand to 2500 dishes, spreading 3000 kilometers across the southern part of Africa. The demanding specifications and enormous number of the SKA dish raise challenges in the dish development such as mass production with high performance at low cost, quick installation and high reliability. Dish Verification Antenna China (DVA-C) was built as one of three initial prototypes. A novel single-piece panel reflector made of carbon fiber reinforced polymer (CFRP) was adopted. In this study, an L-band receiver is installed to make DVA-C a complete system for experiments on antenna performance test and preliminary observations. The performance of DVA-C including the system noise temperature, pointing accuracy, antenna pattern, and aperture efficiency has been tested. Preliminary observations such as pulsars and HI are then conducted, which indicates that the DVA-C can not only serve as an educational instrument and key technology test bed, but also be applied for scientific work such as pulsar timing, all-sky HI survey, multi-frequency monitoring of variable sources etc.  相似文献   

13.
In the standard galaxy formation scenario plasma clouds with a high thermal energy content must exist at high redshifts since the protogalactic gas is shock heated to the virial temperature, and extensive cooling, leading to efficient star formation, must await the collapse of massive haloes (as indicated by the massive body of evidence, referred to as downsizing ). Massive plasma clouds are potentially observable through the thermal and kinetic Sunyaev–Zel'dovich effects and their free–free emission. We find that the detection of substantial numbers of galaxy-scale thermal Sunyaev–Zel'dovich signals is achievable by blind surveys with next generation radio telescope arrays such as EVLA, ALMA and SKA. This population is even detectable with the 10 per cent SKA, and wide field of view options at high frequency on any of these arrays would greatly increase survey speed. An analysis of confusion effects and of the contamination by radio and dust emissions shows that the optimal frequencies are those in the range 10–35 GHz. Predictions for the redshift distributions of detected sources are also worked out.  相似文献   

14.
The unsurpassed sensitivity and resolution of the Square Kilometer Array (SKA) will make it possible for the first time to probe the continuum emission of normal star forming galaxies out to the edges of the universe. This opens the possibility for routinely using the radio continuum emission from galaxies for cosmological research as it offers an independent probe of the evolution of the star formation density in the universe. In addition it offers the possibility to detect the first star forming objects and massive black holes.In deep surveys SKA will be able to detect Hi in emission out to redshifts of z ≈ 2.5 and hence be able to trace the conversion of gas into stars over an era where considerable evolution is taking place. Such surveys will be able to uniquely determine the respective importance of merging and accreting gas flows for galaxy formation over this redshift range (i.e. out to when the universe was only one third its present age). It is obvious that only SKA will able to see literally where and how gas is turned into stars.These and other aspects of SKA imaging of galaxies will be discussed.  相似文献   

15.
We discuss the detection of redshifted line and continuum emission at radio wavelengths using a Square Kilometer Array (SKA), specifically from low-excitation rotational molecular line transitions of CO and HCN (molecular lines), the recombination radiation from atomic transitions in almost-ionized hydrogen (radio recombination lines; RRLs), OH and H2O maser lines, as well as from synchrotron and free–free continuum radiation and HI 21-cm line radiation. The detection of radio lines with the SKA offers the prospect to determine the redshifts and thus exact luminosities for some of the most distant and optically faint star-forming galaxies and active galactic nuclei, even those galaxies that are either deeply enshrouded in interstellar dust or shining prior to the end of reionization. Moreover, it provides an opportunity to study the astrophysical conditions and resolved morphologies of the most active regions in galaxies during the most active phase of star formation at redshift z 2. A sufficiently powerful and adaptable SKA correlator will enable wide-field three-dimensional redshift surveys at chosen specific high redshifts, and will allow new probes of the evolution of large-scale structure (LSS) in the distribution of galaxies. The detection of molecular line radiation favours pushing the operating frequencies of SKA up to at least 26 GHz, and ideally to 40 GHz, while very high redshift maser emissions requires access to about 100 MHz. To search for LSS the widest possible instantaneous field of view would be advantageous.  相似文献   

16.
Five out of six Square Kilometre Array (SKA) science programs need extensive surveys at frequencies below 1.4 GHz and only four need high-frequency observations. The latter ones drive to expensive high surface accuracy collecting area, while the former ask for multi-beam receiver systems and extensive post correlation processing. In this paper, we analyze the system cost of a SKA when the field-of-view (Fov) is extended from 1 deg2 at 1.4 GHz to 200 deg2 at 0.7 GHz for three different antenna concepts. We start our analysis by discussing the fundamental limitations and cost issues of wide-band focal plane arrays (FPA) in dishes and cylinders and of wide-band receptors in aperture arrays. We will show that a hybrid SKA in three different antenna technologies will give the highest effective sensitivity for all six key science programs.  相似文献   

17.
L.I. Gurvits   《New Astronomy Reviews》2004,48(11-12):1211
Several recent global and Space VLBI surveys of quasars, Active Galactic Nuclei of other types and star-burst galaxies provide a wealth of material on milli- and sub-milliarcsecond radio structures in hundreds of sources. Results of these projects are presented with an emphasis on the statistics of redshift- and angular-scale-dependent properties of the milli- and sub-milliarcsecond radio structures. These studies make possible disentanglement of intrinsic (possibly, evolutionary) phenomena of parsec-scale radio structures and the imprints of the cosmological model. The studies indicate a very promising potential of high-resolution applications of the Square Kilometer Array. Based on our pilot projects we estimate that a sample containing of the order of 104 faint radio sources in the luminosity range 1022–1026 W/Hz can be surveyed by a high-resolution SKA with the milliarcsecond resolution at cm wavelengths. Such the high resolution radio survey, including those conducted jointly by SKA and Space VLBI missions, in conjunction with data from other domains, will provide a new ground for extragalactic studies.  相似文献   

18.
The Australian SKA Pathfinder (ASKAP) is a new radio-telescope being built in Western Australia. One of the key surveys for which it is being built is EMU (Evolutionary Map of the Universe), which will make a deep (∼10 μJy/bm rms) radio continuum survey covering the entire sky as far North as +30°. EMU may be compared to the NRAO VLA Sky Survey (NVSS), except that it will have about 45 times the sensitivity, and five times the resolution. EMU will also have much better sensitivity to diffuse emission than previous large surveys, and is expected to produce a large catalogue of relics, tailed galaxies, and halos, and will increase the number of known clusters by a significant factor. Here we describe the EMU project and its impact on the astrophysics of clusters.  相似文献   

19.
The present-day Universe is seemingly dominated by dark energy and dark matter, but mapping the normal (baryonic) content remains vital for both astrophysics – understanding how galaxies form – and astro-particle physics – inferring properties of the dark components.The Square Kilometer Array (SKA) will provide the only means of studying the cosmic evolution of neutral hydrogen (HI) which, alongside information on star formation from the radio continuum, is needed to understand how stars formed from gas within dark-matter over-densities and the rôles of gas accretion and galaxy merging.‘All hemisphere’ HI redshift surveys to z 1.5 are feasible with wide-field-of-view realizations of the SKA and, by measuring the galaxy power spectrum in exquisite detail, will allow the first precise studies of the equation-of-state of dark energy. The SKA will be capable of other uniquely powerful cosmological studies including the measurement of the dark-matter power spectrum using weak gravitational lensing, and the precise measurement of H0 using extragalactic water masers.The SKA is likely to become the premier dark-energy-measuring machine, bringing breakthroughs in cosmology beyond those likely to be made possible by combining CMB (e.g. Planck), optical (e.g. LSST, SNAP) and other early-21st-century datasets.  相似文献   

20.
In the paper we present the results of search for transient sources using the data from the surveys conducted onRATAN-600 at 7.6 cmin the time period of 1980–1994.We detected three events at a level of 3–5σ. A search for coincidenceswith detected transient events was carried out. Using the data from radio and optical surveys and the VizieR, SIMBAD, and NED databases, we made assumptions on the possible nature of these events. The first transient is probably associated with AGN activity, the second—with a cataclysmic GRB event or with a supernova, the origin of the third is not determined. The inference on the possibility of search for variable sources and transients using the data from the RATAN-600 blind surveys was drawn. Searching for transients, we have found twenty-two radio sources which are associated with the NVSS objects but are not included in the RCR catalog. Three of them turned out to be presumably variable.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号