High-Redshift Radio Galaxies from Deep Fields

Most of the radio galaxies with z > 3 have been found using the red-shift spectral index correlation. We have started a programme with the Giant Metrewave Radio Telescope (GMRT) to exploit this correlation at flux density levels about 100 times deeper than the known high-redshift radio galaxies, with an aim to detect candidate high-redshift radio galaxies. Here we present results from the deep 150 MHz observations of LBDS-Lynx field, which has been imaged at 327, 610 and 1412 MHz with the Westerbork Synthesis Radio Telescope (WSRT) and at 1400 and 4860 MHz with the Very Large Array (VLA). We find about 150 radio sources with spectra steeper than 1. About two-thirds of these are not detected in Sloan Digital Sky Survey (SDSS), hence are strong candidate high-redshift radio galaxies, which need to be further explored with deep infra-red imaging and spectroscopy to estimate the red-shift.     

应用ATA的对数周期馈源方案于FAST的可能性探讨

介绍应用于美国凤凰计划的Allen望远镜阵(ATA)的对数周期馈源(LPA)概况，初步给出此种馈源的基本参数及性能，仿真估算了其驻波比和方向图，并结合正在进行中的我国500m孔径球面射电望远镜(FAST)计划，探讨了应用这种宽带馈源的可能性及其限制。     

The OH Maser Line Receiving System for the Urumqi 25m Radio Telescope

A maser spectral line system is newly implemented on the Urumqi 25m Radio Telescope. The system consists mainly of a cooling receiver and a 4096 channels digital correlation spectrometer. The frequency resolution of the spectrometer at the maximum signal bandwidth of 80MHz is 19.5kHz. After careful calibrations observation at the 1665 MHz OH maser emission was made towards a number of sources, including W49N and W75N. The observed results demonstrate that the digital correlation spectrometer is suitable for astronomical spectral line observations.     

Observations of Interplanetary Scintillation (IPS) Using the Mexican Array Radio Telescope (MEXART)

The Mexican Array Radio Telescope (MEXART) consists of a 64×64 (4096) full-wavelength dipole antenna array, operating at 140 MHz, with a bandwidth of 2 MHz, occupying about 9660 square meters (69 m × 140 m) ( http://www.mexart.unam.mx ). This is a dedicated radio array for Interplanetary Scintillation (IPS) observations located at latitude 19°48′N, longitude 101°41′W. We characterize the performance of the system. We report the first IPS observations with the instrument, employing a Butler Matrix (BM) of 16×16 ports, fed by 16 east?–?west lines of 64 dipoles (1/4 of the total array). The BM displays a radiation pattern of 16 beams at different declinations (from ?48, to +88 degrees). We present a list of 19 strong IPS radio sources (having at least 3σ in power gain) detected by the instrument. We report the power spectral analysis procedure of the intensity fluctuations. The operation of MEXART will allow us a better coverage of solar wind disturbances, complementing the data provided by the other, previously built, instruments.     

RF Design of a Wideband CMOS Integrated Receiver for Phased Array Applications

New silicon CMOS processes developed primarily for the burgeoning wireless networking market offer significant promise as a vehicle for the implementation of highly integrated receivers, especially at the lower end of the frequency range proposed for the Square Kilometre Array (SKA). An RF-CMOS ‘Receiver-on-a-Chip’ is being developed as part of an Australia Telescope program looking at technologies associated with the SKA. The receiver covers the frequency range 500–1700 MHz, with instantaneous IF bandwidth of 500 MHz and, on simulation, yields an input noise temperature of < 50 K at mid-band. The receiver will contain all active circuitry (LNA, bandpass filter, quadrature mixer, anti-aliasing filter, digitiser and serialiser) on one 0.18 μm RF-CMOS integrated circuit. This paper outlines receiver front-end development work undertaken to date, including design and simulation of an LNA using noise cancelling techniques to achieve a wideband input-power-match with little noise penalty.     

The Receiver System for the Ooty Wide Field Array

The legacy Ooty Radio Telescope (ORT) is being reconfigured as a 264-element synthesis telescope, called the Ooty Wide Field Array (OWFA). Its antenna elements are the contiguous 1.92 m sections of the parabolic cylinder. It will operate in a 38-MHz frequency band centred at 326.5 MHz and will be equipped with a digital receiver including a 264-element spectral correlator with a spectral resolution of 48 kHz. OWFA is designed to retain the benefits of equatorial mount, continuous 9-hour tracking ability and large collecting area of the legacy telescope and use of modern digital techniques to enhance the instantaneous field-of-view by more than an order of magnitude. OWFA has unique advantages for contemporary investigations related to large scale structure, transient events and space weather watch. In this paper, we describe the RF subsystems, digitizers and fibre optic communication of OWFA and highlight some specific aspects of the system relevant for the observations planned during the initial operation.     

Efficiency Analysis of Focal Plane Arrays in Deep Dishes

In this paper we demonstrate the practical analysis of a dense Focal Plane Array (FPA) for a deep dish radio telescope. The analytical model is used to optimize efficiency and bandwidth of deep dish system by varying design parameters such as feed size and FPA aperture field. A prototype FPA was evaluated on the Westerbork Synthesis Radio Telescope (WSRT) and the resulting efficiency is discussed.     

Space Weather and Solar Wind Studies with OWFA

In this paper, we review the results of interplanetary scintillation (IPS) observations made with the legacy system of the Ooty Radio Telescope (ORT) and compare them with the possibilities opened by the upgraded ORT, the Ooty Wide Field Array (OWFA). The stability and the sensitivity of the legacy system of ORT allowed the regular monitoring of IPS on a grid of large number of radio sources and the results of these studies have been useful to understand the physical processes in the heliosphere and space weather events, such as coronal mass ejections, interaction regions and their propagation effects. In the case of OWFA, its wide bandwidth of 38 MHz, the large field-of-view of ~27^° and increased sensitivity provide a unique capability for the heliospheric science at 326.5 MHz. IPS observations with the OWFA would allow one to monitor more than 5000 sources per day. This, in turn, will lead to much improved studies of space weather events and solar wind plasma, overcoming the limitations faced with the legacy system. We also highlight some of the specific aspects of the OWFA, potentially relevant for the studies of coronal plasma and its turbulence characteristics.     

A digital signal pre-processor for pulsar search

A fast digital signal processor has been designed and built for survey and some observations of pulsars. The processor obtains spectral information over a bandwidth of 16 MHz (256 channels) every 25μsecs Wedescribethe design ofthisprocessor and present some test observations made with the Ooty Radio Telescope.     

Secondary radio eclipse of the transiting planet HD 189733 b: an upper limit at 307–347 MHz

We report the first attempt to observe the secondary eclipse of a transiting extra-solar planet at radio wavelengths. We observed HD 189733 b with the Robert C. Byrd Green Bank Telescope of the National Radio Astronomy Observatory (NRAO) over about 5.5 h before, during and after secondary eclipse, at frequencies of 307–347 MHz. In this frequency range, we determine the 3σ upper limit to the flux density to be 81 mJy. The data are consistent with no eclipse or a marginal reduction in flux at the time of secondary eclipse in all subsets of our bandwidth; the strongest signal is an apparent eclipse at the 2σ level in the 335.2–339.3 MHz region. Our observed upper limit is close to theoretical predictions of the flux density of cyclotron-maser radiation from the planet.     

MSRT的太阳观测能力

密云米波综合孔径射电望远镜（ ＭＳＲＴ） 是一架同时具有高空间分辨率和高时间分辨率,高灵敏度的大型设备,工作频率在２３２ ＭＨｚ。使用该望远镜能得到太阳爆发的空间分布及其随时间变化的丰富信息,所得数据将填补我国具有空间分辨率的太阳射电数据的空白。在国际太阳活动监测中,由于地理位置原因,也是其它同类设备不可取代的。可以期待在第２３ 周太阳峰年的观测与研究中,得到新的有意义的数据和研究成果     

Confirmation of three candidate Galactic supernova remnants from GMRT observations

We report 327-MHz observations of three large (>15 arcmin) candidate supernova remnants (SNRs) at high Galactic latitudes using the Giant Metrewave Radio Telescope (GMRT). These objects were proposed by Duncan et al. as candidate SNRs in the Parkes 2.4-GHz survey. We detect extended 327-MHz emission in all three fields. G356.2+4.5 has a well-resolved shell of emission. This field also contains a 32-mJy pulsar situated at a distance of 1.4 kpc as derived from the dispersion measure of the pulsar. The field of G358.0+3.8 is highly confused and, although we confirm the presence of a partial ring, it has a lower signal-to-noise ratio detection. G004.8+6.2 (formerly G4.5+6.2) is located approximately 40 arcmin away from Kepler's SNR. Apart from GMRT observations of this field, this SNR lies in the field of view of a Very Large Array (VLA) D-array observation at 325 MHz and we detect a 17×18 arcmin SNR, possibly of shell morphology. All these fields show clear, well-resolved shells in the National Radio Astronomy Observatory/ VLA Sky Survey (NVSS) maps, which are also presented.     

325-MHz observations of the ELAIS-N1 field using the Giant Metrewave Radio Telescope

We present observations of the European Large-Area ISO Survey-North 1 (ELAIS-N1) at 325 MHz using the Giant Metrewave Radio Telescope (GMRT), with the ultimate objective of identifying active galactic nuclei and starburst galaxies and examining their evolution with cosmic epoch. After combining the data from two different days we have achieved a median rms noise of  ≈40 μJy  beam⁻¹, which is the lowest that has been achieved at this frequency. We detect 1286 sources with a total flux density above  ≈270 μJy  . In this paper, we use our deep radio image to examine the spectral indices of these sources by comparing our flux density estimates with those of Garn et al. at 610 MHz with the GMRT, and surveys with the Very Large Array at 1400 MHz. We attempt to identify very steep spectrum sources which are likely to be either relic sources or high-redshift objects as well as inverted-spectra objects which could be Giga-Hertz Peaked Spectrum objects. We present the source counts, and report the possibility of a flattening in the normalized differential counts at low flux densities which has so far been reported at higher radio frequencies.     

Deep low-frequency observations with the Giant Metrewave Radio Telescope: a search for relic radio emission

We present deep multifrequency observations using the Giant Metrewave Radio Telescope (GMRT) at 153, 244, 610 and 1260 MHz of a field centred on J0916+6348, to search for evidence of fossil radio lobes which could be due to an earlier cycle of episodic activity of the parent galaxy, as well as haloes and relics in clusters of galaxies. We do not find any unambiguous evidence of episodic activity in a list of 374 sources, suggesting that such activity is rare even in relatively deep low-frequency observations. We examine the spectra of all the sources by combining our observations with those from the Westerbork Northern Sky Survey (WENSS), NRAO (National Radio Astronomy Observatories) VLA (Very Large Array) Sky Survey (NVSS) and the Faint Images of the Radio Sky at Twenty-Centimeters Survey (FIRST). Considering only those which have measurements at a minimum of three different frequencies, we find that almost all sources are consistent with a straight spectrum with a median spectral index,  α∼ 0.8 [S(ν) ∝ν^−α  ], which appears steeper than theoretical expectations of the injection spectral index. We identify 14 very steep-spectrum sources with  α≥ 1.3  . We examine their optical fields and discuss the nature of some of these sources.     

Clusters of Galaxies and the Cosmic Web with Square Kilometre Array

The intra-cluster and inter-galactic media that pervade the large scale structure of the Universe are known to be magnetized at sub-micro Gauss to micro Gauss levels and to contain cosmic rays. The acceleration of cosmic rays and their evolution along with that of magnetic fields in these media is still not well understood. Diffuse radio sources of synchrotron origin associated with the Intra-Cluster Medium (ICM) such as radio halos, relics and mini-halos are direct probes of the underlying mechanisms of cosmic ray acceleration. Observations with radio telescopes such as the Giant Metrewave Radio Telescope, the Very Large Array and the Westerbork Synthesis Radio Telescope have led to the discoveries of about 80 such sources and allowed detailed studies in the frequency range 0.15–1.4 GHz of a few. These studies have revealed scaling relations between the thermal and non-thermal properties of clusters and favour the role of shocks in the formation of radio relics and of turbulent re-acceleration in the formation of radio halos and mini-halos. The radio halos are known to occur in merging clusters and mini-halos are detected in about half of the cool-core clusters. Due to the limitations of current radio telescopes, low mass galaxy clusters and galaxy groups remain unexplored as they are expected to contain much weaker radio sources. Distinguishing between the primary and the secondary models of cosmic ray acceleration mechanisms requires spectral measurements over a wide range of radio frequencies and with high sensitivity. Simulations have also predicted weak diffuse radio sources associated with filaments connecting galaxy clusters. The Square Kilometre Array (SKA) is a next generation radio telescope that will operate in the frequency range of 0.05–20 GHz with unprecedented sensitivities and resolutions. The expected detection limits of SKA will reveal a few hundred to thousand new radio halos, relics and mini-halos providing the first large and comprehensive samples for their study. The wide frequency coverage along with sensitivity to extended structures will be able to constrain the cosmic ray acceleration mechanisms. The higher frequency (>5 GHz) observations will be able to use the Sunyaev–Zel’dovich effect to probe the ICM pressure in addition to tracers such as lobes of head–tail radio sources. The SKA also opens prospects to detect the ‘off-state’ or the lowest level of radio emission from the ICM predicted by the hadronic models and the turbulent re-acceleration models.     

巨射电星系3C236的326.5MHz射电研究

用4km Ooty综合孔径射电望远镜,在326.5MHz频率上,对巨射电星系3C236进行了射电观测。该文给出了巨射电星系3C236在326.5MHz上的射电图,并作了简单的分析讨论,得到一些初步结果。     

Spectral ageing analysis of the double–double radio galaxy J1453+3308

We present new radio observations at frequencies ranging from 240 to 4860 MHz of the well-known, double–double radio galaxy (DDRG), J1453+3308, using both the Giant Metrewave Radio Telescope (GMRT) and the Very Large Array (VLA). These observations enable us to determine the spectra of the inner and outer lobes over a large frequency range and demonstrate that while the spectrum of the outer lobes exhibits significant curvature, that of the inner lobes appears practically straight. The break frequency, and hence the inferred synchrotron age of the outer structure, determined from 16-arcsec strips transverse to the source axis, increases with distance from the heads of the lobes. The maximum spectral ages for the northern and southern lobes are ∼47 and 58 Myr, respectively. Because of the difference in the lengths of the lobes, these ages imply a mean separation velocity of the heads of the lobes from the emitting plasma of 0.036 c for both the northern and southern lobes. The synchrotron age of the inner double is about 2 Myr which implies an advance velocity of ∼0.1 c , but these values have large uncertainties because the spectrum is practically straight.     

L-band RFI Measurement and Mitigation at the NSRT Site

近些年,南山台址内部各类电子设备不断引入,此过程忽视了有效的设备管理及电磁防护,且台址周边无线电业务增多,以致电波环境恶化。为改善台址电波环境,采用一种准实时电波环境测量方法测量分析了台址周边瞬态信号的影响;另外,为提高微弱信号检测能力,采用便携式电磁干扰测量系统和26m射电望远镜对台址主要干扰信号特征及来源进行测量分析。依据测量和分析结果,采用屏蔽及滤波技术对望远镜观测室内部主要干扰源进行电磁防护,并针对屏蔽工程的有效性进行测量评估,结果表明,采用的电磁屏蔽措施有效。另外,提出了初步南山无线电宁静区保护办法缓解台址外部电磁干扰。     

Intermittent jet activity in the radio galaxy 4C 29.30?

We present radio observations at frequencies ranging from 240 to 8460 MHz of the radio galaxy 4C 29.30 (J0840+2949) using the Giant Metrewave Radio Telescope (GMRT), the Very Large Array (VLA) and the Effelsberg telescope. We report the existence of weak extended emission with an angular size of ∼520 arcsec (639 kpc) within which a compact edge-brightened double-lobed source with a size of 29 arcsec (36 kpc) is embedded. We determine the spectrum of the inner double from 240 to 8460 MHz and show that it has a single power-law spectrum with a spectral index of ∼0.8. Its spectral age is estimated to be ≲33 Myr. The extended diffuse emission has a steep spectrum with a spectral index of ∼1.3 and a break frequency ≲240 MHz. The spectral age is ≳200 Myr, suggesting that the extended diffuse emission is due to an earlier cycle of activity. We re-analyse archival X-ray data from Chandra and suggest that the X-ray emission from the hotspots consists of a mixture of non-thermal and thermal components, the latter being possibly due to gas which is shock heated by the jets from the host galaxy.