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1.
Using the Australia Telescope Compact Array (ATCA), ATLAS (Australia Telescope Large Area Survey) is imaging two fields totalling 7 square degrees down to 10 μJy beam − 1 at 1.4 GHz. We have found 6 wide-angle tail galaxies (WATs), 4 of which have sufficient data to identify associated galaxy overdensities. The largest WAT, at a red-shift of 0.22, appears to be associated with an overdensity of galaxies that is spread over an unusually large extent of 12 Mpc, with a velocity range of 4500 km s − 1. Here we present the WATs in ATLAS and discuss the implications of these observations for future large-scale radio surveys such as ASKAP-EMU.  相似文献   

2.
We present results of the ATCA IDV Survey of southern extragalactic radio sources. We discuss briefly the properties of the 22 new intraday variable sources discovered in the Survey. The follow-up observations of a few extreme examples of strong intraday variability are presented. We find that the characteristics of the total flux density fluctuations at different wavelengths are consistent with intersteller scintillations (ISS) of the microarcsecondsize soorten components. However, the scintillating components of a few extreme IDVs are characterized by the brightness temperatures far exceeding the T B=1012 K limit. The relativistic beaming invoked in such sources would require Doppler factors up to as high as δ∼ 103. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3.
D. L. Croom 《Solar physics》1970,15(2):414-423
The results of 2 1/2 years (July 1967 – December 1969) monitoring of solar radio bursts at 71 GHz ( = 4.2 mm) at the Radio and Space Research Station, Slough are presented. During this period only seven events were positively identified as 71 GHz bursts. One of these events (6 July, 1968) is among the largest solar bursts ever recorded anywhere in the microwave-millimetre wave band (47000 × 10–22Wm–2Hz–1), and the associated magnetic field may possibly have exceeded 7200 G. Another event (27 March, 1969) has demonstrated that bursts at 71 GHz can be both intense (4700 × 10–22Wm–2Hz–1) and complex. On other occasions, the absence of any detectable event at 71 GHz helps to define the high frequency spectrum of the burst, this being an important factor in determining the initial energy distribution of the electrons ejected by the associated flare. On one such occasion (21 March, 1969) the derived energy distribution index is 8, in contrast with the more usual values of 2–4.1969–1970 NCR-OAR Senior Post-Doctoral Research Associate at Air Force Cambridge Research Laboratories, L. G. Hanscom Field, Bedford, Mass., U.S.A.  相似文献   

4.
There is no generally accepted evolutionary scheme for high mass star formation yet. A simple approach to address this problem is to cover several of the known stages during the formation of massive stars in the same cloud and then investigate their properties trying to construct an evolutionary sequence. Here we present such a project conducted with complementary APEX and ATCA observations. These observations show a compact and bright single hot core in the G327.3-0.6 region on a 0.03 pc scale with a mass of 500 M⊙ and 0.5–1.5 105 L⊙. Additionally a clumpy filament is seen in N2H+. Together with cm continuum observations, the data reveal like pearls on a string several stages of massive star formation, with likely the youngest stages hiding in the cold N2H+ cores analysed with a multilevel study of the APEX and ATCA observations.  相似文献   

5.
We analyze a special kind of temporal fine structure in microwave radio emission for the 25 August 1999 solar flare observed by the PMO spectrometer over the range of 4.5 – 7.5 GHz. This flare displays continuum emission after a group of reverse-slope type III bursts around 6 GHz. High-resolution dynamic spectra reveal three evolving emission lines (EELs) following the type III group. They are characterized by isolated, narrow, and continuous emission strips, which display frequency fluctuations with time. Their frequency-drift rates are between −2 and 3 GHz s−1. Distinct from the EELs at lower frequencies, three EELs have a very short duration of a few seconds. They show an average bandwidth of Δf≈330 MHz and a relative bandwidth of Δf/f≈0.057. This is the first time that this kind of fine structure has been observed around 6 GHz.  相似文献   

6.
We present a comparative analysis of 5 GHz VLA and 200 ks Chandra ACIS-I image. In the 5 GHz image the familiar jet and much weaker counterjet are seen, which bend as the jet propagates towards the hotspots. Furthermore, where the lobe detected in 5 GHz emission starts to interact with the jet, we see that the jet “threads”. In the 0.2–10 keV X-ray image we do not detect the jet, but do detect a relic of the counterjet. * This paper has previously been published in Astrophysics and Space Science, vol. 310:3–4.  相似文献   

7.
We present 5.5 and 9.0 GHz Australia Telescope Compact Array (ATCA) observations of the cluster MACSJ0417.5-1154, one of the most massive galaxy clusters and one of the brightest in X-ray in the Massive Cluster Survey (MACS). We estimate diffuse emission at 5.5 and 9.0 GHz from our ATCA observations, and compare the results with the 235 MHz and 610 MHz GMRT observations and 1575 MHz VLA observations. We also estimate the diffuse emission at low frequencies from existing GLEAM survey data (using the MWA telescope (http://www.mwatelescope.org)), and find that the steepening reported in earlier studies may have been an artefact of underestimates of diffuse emission at low frequencies. High-frequency radio observations of galaxy cluster mergers therefore provide an important complement to low-frequency observations, not only for a probing the ‘on’ and ‘off’ state of radio halos in these mergers, but also to constrain energetics of cluster mergers. We comment on the future directions that further studies of this cluster can take.  相似文献   

8.
使用澳大利亚致密阵 (ATCA)在 1 .4GHz上观测了一个极高光度的IRAS星系样本。在这个样本所包括的 3 7个IRAS星系中 ,探测到 1 9个源的射电发射 ,获得了它们的射电参数 ,如峰值位置 ,射电流量等。该样本的射电功率范围在 2 2 .9相似文献   

9.
Supermassive black holes, with masses of 106 M to more than 109 M, are among the most spectacular objects in the Universe, and are laboratories for physics in extreme conditions. The primary goal of ARISE (Advanced Radio Interferometry between Space and Earth) is to use the technique of Space VLBI to increase our understanding of black holes and their environments, by imaging the havoc produced in the near vicinity of the black holes by their enormous gravitational fields. The mission will be based on a 25-meter space-borne radio telescope operating at frequencies between 8 and 86 GHz, roughly equivalent to an orbiting element of the Very Long Baseline Array. In an elliptical orbit with an apogee height of 40 000–100 000 km, ARISE will provide a resolution of 15 microarcsecond or better, 5–10 times better than that achievable on the ground. At frequencies of 43 and 86 GHz, the resolution of light weeks to light months in distant quasars will complement the gamma-ray and X-ray observations of high-energy photons, which come from the same regions near the massive black holes. At 22 GHz, ARISE will image the H2O maser disks in active galaxies more than 15 Mpc from Earth, probing accretion physics and giving accurate measurements of black-hole masses. ARISE also will study gravitational lenses at resolutions of tens of microarcseconds, yielding important information on the dark-matter distribution and on the possible existence of compact objects with masses of 103 M to 106 M.  相似文献   

10.
We report multi-frequency radio continuum and hydrogen radio recombination line observations of HII regions near l = 24.8°, b = 0.1° using the Giant Metrewave Radio Telescope (GMRT) at 1.28 GHz (n = 172), 0.61 GHz (n = 220) and the Very Large Array (VLA) at 1.42 GHz (n = 166). The region consists of a large number of resolved HII regions and a few compact HII regions as seen in our continuum maps, many of which have associated infrared (IR) point sources. The largest HII region at l = 24.83° and b = 0.1° is a few arcmins in size and has a shell-type morphology. It is a massive HII region enclosing ∼550 M⊙ with a linear size of 7 pc and an rms electron density of ∼110 cm−3 at a kinematic distance of 6 kpc. The required ionization can be provided by a single star of spectral type O5.5. We also report detection of hydrogen recombination lines from the HII region at l = 24.83° and b = 0.1° at all observed frequencies near V lsr = 100 km s−1. We model the observed integrated line flux density as arising in the diffuse HII region and find that the best fitting model has an electron density comparable to that derived from the continuum. We also report detection of hydrogen recombination lines from two other HII regions in the field.  相似文献   

11.
We use two independent methods to reduce the data of the surveys made with RATAN-600 radio telescope at 7.6 cm in 1988–1999 at the declination of the SS433 source. We also reprocess the data of the “Cold” survey (1980–1981). The resulting RCR (RATAN COLD REFINED) catalog contains the right ascensions and fluxes of objects identified with those of the NVSS catalog in the right-ascension interval 7 h ≤ R.A. < 17 h . We obtain the spectra of the radio sources and determine their spectral indices at 3.94 and 0.5 GHz. The spectra are based on the data from all known catalogs available from the CATS, Vizier, and NED databases, and the flux estimates inferred from the maps of the VLSS and GB6 surveys. For 245 of the 550 objects of the RCR catalog the fluxes are known at two frequencies only: 3.94 GHz (RCR) and 1.4 GHz (NVSS). These are mostly sources with fluxes smaller than 30mJy. About 65% of these sources have flat or inverse spectra (α > −0.5). We analyze the reliability of the results obtained for the entire list of objects and construct the histograms of the spectral indices and fluxes of the sources. Our main conclusion is that all 10–15 mJy objects found in the considered right-ascension interval were already included in the decimeter-wave catalogs.  相似文献   

12.
The slowly varying component of the solar radio emission (S-component) has been investigated from data obtained in the United States and Japan at 35, 17, 9.4 and 4 GHz. A good correlation occurs between the 35 GHz flux of the S-component and the corresponding plage area. This is interpreted by the assumption that the 35 GHz radiation is due to pure free-free emission, and the electron density in the coronal condensation is estimated to be about 2 × 109/cm3, assuming the electron temperature to be 2 × 106 K and the scale height of the coronal condensation to be 3 × 104 km.The S-component radiation at 17 GHz has, in turn, two components, one is due to pure free-free emission and the other is due to thermal-gyro emission. It is concluded that in the active regions a magnetic field of more than 2000 gauss extends horizontally over about 104 km.  相似文献   

13.
Data series for the same time interval of characteristic solar parameters (sunspot number R; flux at 2.8 GHz), ionospheric parameters (critical frequency of the E-region) and atmospheric parameters (stratospheric and tropospheric temperatures T) have been analysed by the maximum-entropy method, in order to study the occurrence of periodicities in those parameters in the range from 12 to 150 days. Digital filtering of the most pronounced of the detected periods (mainly in the range between 19 to 33 days) shows a similar but not identical feature in the time interval 1974–1978. It is demonstrated that sunspot number and solar radio flux at 2.8 GHz behave in a similar way on the average, and at periods greater than 20 days. Although a number of similar periods occurred in solar, ionospheric and atmospheric parameters, cross-correlation estimations only show a relationship between periods in solar and ionospheric data, but none between solar data and stratospheric and tropospheric temperatures; exception: T (35 km) correlates with R at 12.3 days. The most obvious correlation was found between the critical frequency of the E layer and the solar flux at 2.8 GHz at a frequency of approximately 1/23 days–1.Proceedings of the 14th ESLAB Symposium on Physics of Solar Variations, 16–19 September 1980, Scheveningen, The Netherlands.  相似文献   

14.
Radio images and spectra of an eruptive prominence were obtained from simultaneous multifrequency observations at 36 GHz, 89 GHz, and 110 GHz on May 28, 1991 with the 45-m radio telescope at Nobeyama Radio Observatory (NRO), the National Astronomical Observatory, Japan (NAOJ). The radio spectra indicated that the optical depth is rather thick at 36 GHz whereas it is thin at 89 and 110 GHz. The H data, taken at Norikura Solar Observatory, NAOJ, suggest that the eruption of an active region filament was triggered by an H flare. The shape and position of the radio prominence generally coincided with those of H images. The radio emission is explained with an isothermal cool thread model. A lower limit for the electron temperature of the cool threads is estimated to be 6100 K. The range of the surface filling factors of the cool threads is 0.3–1.0 after the H flare, and 0.2–0.5 in the descending phase of the eruptive prominence. The column emission measure and the electron number density are estimated to be of the order of 1028 cm–5 and 1010 cm–3, respectively. The physical parameters of a quiescent prominence are also estimated from the observations. The filling factors of the eruptive prominence are smaller than those of the quiescent prominence, whereas the emission measures and the electron densities are similar. These facts imply that each cool thread of the prominence did not expand after the eruption, while the total volume of the prominence increased.  相似文献   

15.
We describe an observational programme aimed at understanding the radio emission from distant, rapidly evolving galaxy populations. These observations were carried out at 1.4 and 8.5 GHz with the VLA, centred on the Hubble Deep Field, obtaining limiting flux densities of 40 and 8 μJy respectively. The differential count of the radio sources is marginally sub-Euclidean to the completeness limits(γ = − 2.4 ± 0.1) and fluctuation analysis suggests nearly 60 sources per arcmin2 at the 1 μJy level. Using high-resolution 1.4 GHz observations obtained with MERLIN, we resolve all radio sources detected in the VLA complete sample and measure a median angular size for the microjansky radio population of 1-2". This clue, coupled with the steep spectral index of the 1.4 GHz selected sample, suggests diffuse synchrotron radiation in z ∼ 1 galactic discs. The wide-field HST and ground-based optical exposures show that the radio sources are identified primarily with disc systems composed of irregulars, peculiars, interacting/merging galaxies and a few isolated field spirals. Only 20% of the radio sources can be attributed to AGN – the majority are probably associated with starburst activity. The available redshifts range from 0.1 to 3, with a mean of about 0.8. We are plrobably witnessing a major episode of starburst activity in these luminous (L > L *) systems, occasionallyaccompanied by an embedded AGN.About 20% of the radio sources remain unidentified to I = 26-28 inthe HDF and flanking fields. Several of these objectshave extremely red counterparts. We suggestthat these are high-redshift dusty protogalaxies. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

16.
We present an analysis of multi-epoch global VLBI observations of the Compact Symmetric Objects: 2352+495 and 0710+439 at 5 GHz. Analysis of data spread over almost two decades shows strong evidence for an increase in separation of the outer components of both sources at a rate of 0.2h−1c (for q=0.5 and H=100h km s−1Mpc−1). Dividing the overall sizes of the sources by their separation rates implies that these Compact Symmetric Objects have a kinematic age 104 years. These results (and those for other CSOs) strongly argue that CSOs are indeed very young sources that probably evolve into much larger classical doubles.  相似文献   

17.
Schrijver  Carolus J.  Title  Alan M. 《Solar physics》1999,188(2):331-344
Eleven microwave spike events observed with the 2.6–3.8 GHz spectrometer of Beijing Astronomical Observatory (BAO) are analysed. The polarization degrees of spikes are variable, some spikes have frequency drift with the drift rate of several GHz s–1. In particular, the time delay (8 ms) between the two polarization modes of spike is detected, which is different from previous results. According to the leading spot rule, we conclude that the o-modes arrive first. Moreover, the reversal of polarization sense versus frequency is also found. A change of the emission mode may be the cause of the polarization reversal.  相似文献   

18.
I investigate the problem of high dynamic range continuum synthesis imaging in the presence of confusing sources, using scaling arguments and simulations. I derive a quantified cost equation for the computer hardware needed to support such observations for the EVLA and the SKA. This cost has two main components – from the data volume, scaling as D−6 (where D is the antenna diameter), and from the non-coplanar baselines effect, scaling as D−2, for a total scaling of D−8. A factor of two in antenna diameter thus corresponds to 12 years of Moore’s law (18 month doubling time) cost reduction in computing hardware. For a SKA built with 12.5 m antennas observing with 1 arcsecond at 1.4 GHz, I find the computing load to be about 150 Petaflops (costing about $500 million in 2015). For 25 m antennas, the load is about 256 times lower, costing $2 million in 2015. This new cost equation differs from that of Perley and Clark (2003), which has scaling as D−6. This is because I find that the excellent Fourier plane coverage of the small antenna design does not significantly change the convergence rate of the Clean algorithm, which is already satisfactory in this regime.The National Radio Astronomy Observatory is operated by Associated Universities, Inc., under cooperative agreement with the National Science Foundation.  相似文献   

19.
The results of 21/2 yr (July 1967–December 1969) monitoring of solar radio bursts at 19 GHz ( = 1.58 cm) at the Radio and Space Research Station, Slough, are presented. Observations at this frequency are important in helping to define the form of the microwave spectrum of solar bursts since many of the more intense bursts have their spectral peak in the frequency region above 10 GHz. Fifteen bursts with peak flux increases exceeding 1000 × 10–22 Wm–2 Hz–1 were observed during this period.  相似文献   

20.
We report the first detection of DCO+ in a circumstellar disk. The DCO+ J=5–4 line at 360.169 GHz is observed with the 15 m James Clerk Maxwell Telescope in the disk around the pre-main sequence star TW Hya. Together with measurements of the HCO+ and H13CO+ J=4–3 lines, this allows an accurate determination of the DCO+/HCO+ ratio in this disk. The inferred value of0.035±0.005 is close to that found in cold pre-stellar cores and is somewhat higher than that measured in the envelope around the low-mass proto star IRAS 16293-2422. It is also close to the DCN/HCN ratio obtained for pristine cometary material in the jet of comet Hale-Bopp. The observed DCO+/HCO+ ratio for TW Hya is consistent with theoretical models of disks which consider gas-phase fractionation processes within a realistic 2-D temperature distribution and which include the effects of freeze-out onto grains. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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