Predicted Planck extragalactic point-source catalogue

An estimation of the number and amplitude (in flux) of the extragalactic point sources that will be observed by the Planck Mission is presented in this paper. The study is based on the Mexican Hat wavelet formalism introduced by Cayón et al. Simulations at Planck observing frequencies are analysed, taking into account all the possible cosmological, Galactic and extragalactic emissions together with noise. With the technique used in this work, the Planck Mission will produce a catalogue of extragalactic point sources above the following flux values: 1.03 Jy (857 GHz), 0.53 Jy (545 GHz), 0.28 Jy (353 GHz), 0.24 Jy (217 GHz), 0.32 Jy (143 GHz), 0.41 Jy (100 GHz, high-frequency instrument), 0.34 Jy (100 GHz, low-frequency instrument), 0.57 Jy (70 GHz), 0.54 Jy (44 GHz) and 0.54 Jy (30 GHz), which are only slightly model dependent (see text). Amplitudes of these sources are estimated with errors below ∼15 per cent. Moreover, we also provide a complete catalogue (for the point-source simulations analysed) with errors in the estimation of the amplitude below ∼10 per cent. In addition we discuss the possibility of identifying different point-source populations in the Planck catalogue by estimating their spectral indices.     

A novel multifrequency technique for the detection of point sources in cosmic microwave background maps

In this work we address the problem of simultaneous multifrequency detection of extragalactic point sources in the maps of the cosmic microwave background. We apply a new linear filtering technique, the 'matched matrix filters', that incorporates full spatial information, including the cross-correlation among channels, without making any a priori assumption about the spectral behaviour of the sources. A substantial reduction of the background is achieved thanks to the optimal combination of filtered maps. We describe the new technique in detail and apply it to the detection of radio sources and estimation of their parameters in realistic all-sky Planck simulations at 30, 44, 70 and 100 GHz. Then, we compare the results with the single-frequency approach based on the standard matched filter, in terms of reliability, completeness and flux accuracy of the resulting point source catalogues. The new filters outperform the standard matched filters for all these indexes at 30, 44 and 70 GHz, whereas at 100 GHz both kinds of filters have a similar performance. We find a notable increment of the number of true detections for a fixed reliability level. In particular, for a 95 per cent reliability we practically double the number of detections at 30, 44 and 70 GHz.     

Some estimates of the source counts at Planck Surveyor frequencies, using the 9C survey at 15 GHz

We have used multifrequency follow-up observations of a sample of extragalactic sources from the 9C survey at 15 GHz to make deductions about the expected source population at higher radio frequencies, such as those in the lower frequency bands of the Planck Surveyor satellite. In particular, we have made empirical estimates of the source counts at 22, 30, 43 and 70 GHz and compared these with both known data and current theoretical predictions. We have also made an estimate of the count at the Atacama Large Millimeter Array (ALMA) frequency of 90 GHz, with a view to assessing the possible population of point sources available for the phase calibration of that instrument.     

Isotropic wavelets: a powerful tool to extract point sources from cosmic microwave background maps

It is the aim of this paper to introduce the use of isotropic wavelets to detect and determine the flux of point sources appearing in cosmic microwave background (CMB) maps. The most suitable wavelet to detect point sources filtered with a Gaussian beam is the 'Mexican Hat'. An analytical expression of the wavelet coefficient obtained in the presence of a point source is provided and used in the detection and flux estimation methods presented. For illustration the method is applied to two simulations (assuming Planck mission characteristics) dominated by CMB (100 GHz) and dust (857 GHz), as these will be the two signals dominating at low and high frequencies respectively in the Planck channels. We are able to detect bright sources above 1.58 Jy at 857 GHz (82 per cent of all sources) and above 0.36 Jy at 100 GHz (100 per cent of all), with errors in the flux estimation below 25 per cent. The main advantage of this method is that nothing has to be assumed about the underlying field, i.e. about the nature and properties of the signal plus noise present in the maps. This is not the case in the detection method presented by Tegmark & Oliveira-Costa. Both methods are compared, producing similar results.     

An array of lens-coupled antennas for cosmic microwave background measurements in the 30 Ghz band

An array of bow-tie slot antennas coupled through an extended hemispherical lens is proposed to operate in the 30?GHz frequency band. The design includes a combination of three microstrip Wilkinson power dividers (WPD) and transitions to coplanar wave guides (CPW) to form the feeding antenna network. This configuration is suitable for the integration with heterodyne imaging detectors commonly used in radioastronomy. Measurements and simulation results exhibit a frequency range of operation from 20 to 40?GHz with a bandwidth of 24% achieved for ?10?dB return loss at the central frequency. The measured radiation patterns show a maximum peak gain of around 13?dB with HPBW of 10° for the E-plane, and whose first side lobes are lower than 13?dB below the main lobe in both angular shift sides. The presented results will be considered as preliminary feasibility studies in the 30?GHz QUIJOTE-CMB Instrument, which is designed to study the anisotropies of the Cosmic Microwave Background (CMB).     

Neural networks and the separation of cosmic microwave background and astrophysical signals in sky maps

We implement an independent component analysis (ICA) algorithm to separate signals of different origin in sky maps at several frequencies. Owing to its self-organizing capability, it works without prior assumptions on either the frequency dependence or the angular power spectrum of the various signals; rather, it learns directly from the input data how to identify the statistically independent components, on the assumption that all but, at most, one of the components have non-Gaussian distributions.
We have applied the ICA algorithm to simulated patches of the sky at the four frequencies (30, 44, 70 and 100 GHz) used by the Low Frequency Instrument of the European Space Agency's Planck satellite. Simulations include the cosmic microwave background (CMB), the synchrotron and thermal dust emissions, and extragalactic radio sources. The effects of the angular response functions of the detectors and of instrumental noise have been ignored in this first exploratory study. The ICA algorithm reconstructs the spatial distribution of each component with rms errors of about 1 per cent for the CMB, and 10 per cent for the much weaker Galactic components. Radio sources are almost completely recovered down to a flux limit corresponding to ≃0.7 σ _CMB, where σ _CMB is the rms level of the CMB fluctuations. The signal recovered has equal quality on all scales larger than the pixel size. In addition, we show that for the strongest components (CMB and radio sources) the frequency scaling is recovered with per cent precision. Thus, algorithms of the type presented here appear to be very promising tools for component separation. On the other hand, we have been dealing here with a highly idealized situation. Work to include instrumental noise, the effect of different resolving powers at different frequencies and a more complete and realistic characterization of astrophysical foregrounds is in progress.     

System Optimisation Of Multi-Beam Aperture Synthesis Arrays For Survey Performance

Investigating the requirements for an aperture synthesis array that optimise the performance for surveying shows that, next to collecting area and system temperature, the field-of-view (FoV) is key parameter. However, the effective sensitivity not only depends on bandwidth and integration time but could be seriously limited by side lobe confusion and by gain errors that determine the effective dynamic range. From the basic sensitivity equation for a radiometric system we derive an optimum cost ratio between collecting area and processing electronics, where the latter should be less than a third of the total cost. For an instrument that has to cover a fraction of sky larger than its field-of-view, the FoV enters the equation for survey sensitivity and we identify the number of independent feed systems per unit collecting area as a key parameter. Then the optimum cost distribution allows the electronics to account for up to half the total cost. Further analysis of the sensitivity formula shows that there is an optimum design frequency for a survey instrument below 1 GHz. We discuss the impact of station size and array configuration on self-calibration, side lobe confusion and effective sensitivity and conclude that a minimum station size of 20 m diameter is required at 0.3 GHz as long as multi-patch self-calibration procedures need, per baseline, a signal-to-noise ratio of more than two for each ionospheric coherence patch.     

Spectrum of slowly varying component of solar radio emission on millimeter wavelengths

The spectrum of the S-component of solar radio emission has been investigated at 4 GHz, 17 GHz, 35 GHz, 70 GHz, and 94 GHz. The spectrum for a spot group which appeared late in March 1966 (McMath plage No. 8223), seems to be flat at the frequencies above about 35 GHz. This implies that the emission is due to pure free-free emission at the frequencies above 35 GHz.     

Estimating the spectral indices of correlated astrophysical foregrounds by a second-order statistical approach

We present the first tests of a new method, the correlated component analysis (CCA) based on second-order statistics, to estimate the mixing matrix, a key ingredient to separate astrophysical foregrounds superimposed to the Cosmic Microwave Background (CMB). In the present application, the mixing matrix is parametrized in terms of the spectral indices of Galactic synchrotron and thermal dust emissions, while the free–free spectral index is prescribed by basic physics, and is thus assumed to be known. We consider simulated observations of the microwave sky with angular resolution and white stationary noise at the nominal levels for the Planck satellite, and realistic foreground emissions, with a position-dependent synchrotron spectral index. We work with two sets of Planck frequency channels: the low-frequency set, from 30 to 143 GHz, complemented with the Haslam 408 MHz map, and the high-frequency set, from 217 to 545 GHz. The concentration of intense free–free emission on the Galactic plane introduces a steep dependence of the spectral index of the global Galactic emission with Galactic latitude, close to the Galactic equator. This feature makes difficult for the CCA to recover the synchrotron spectral index in this region, given the limited angular resolution of Planck , especially at low frequencies. A cut of a narrow strip around the Galactic equator  (| b | < 3°)  , however, allows us to overcome this problem. We show that, once this strip is removed, the CCA allows an effective foreground subtraction, with residual uncertainties inducing a minor contribution to errors on the recovered CMB power spectrum.     

An update on Archeops: flights and data products

Archeops is a balloon-borne instrument dedicated to measuring cosmic microwave background (CMB) temperature anisotropies at high angular resolution (～ 8 arcminutes) over a large fraction (～ 30%) of the sky in the millimetre domain. The general design is based on Planck High Frequency Instrument (HFI) technology. Bolometers cooled to 0.1 K scan the sky in total power mode along large circles at constant elevation. Archeops is designed to observe a complete annulus on the sky covering all right ascensions between about 25 and 55 degrees during the course of a 24-hour Arctic-night balloon flight, in four frequency bands centered at 143, 217, 353 and 545 GHz. We describe the Archeops flights and the data products obtained during the three successful flights from Trapani (Sicily) to Spain in July 1999, and from Kiruna (Sweden) to Russia in January 2001 and February 2002. We discuss present Archeops results and the future use of Archeops data.     

基于100 nm砷化镓pHEMT工艺的C波段宽带低噪声放大器芯片

作为射电天文接收机系统的关键器件, 低噪声放大器的噪声和增益性能对接收机系统的灵敏度有重要影响. 采用100nm砷化镓赝配高电子迁移率晶体管(pseudomorphic High Electron Mobility Transistor, pHEMT)\lk工艺, 研制了一款可覆盖C波段(4--8GHz)的低噪声放大器(Low Noise Amplifier, LNA). 所设计的LNA采用3级共源级联放大拓扑结构, 栅极、漏极双电源供电. 常温下测试表明, 该LNA在4--8GHz频段内平均噪声温度为\lk60K, 在5GHz处获得最低噪声温度50K, 通带内增益($31\pm1.5$)dB, 输入输出回波损耗均优于10dB, 芯片面积为$2.1\times1.1$mm², 可以应用于C波段射电天文接收机以及卫星通信系统等.     

Measuring Cosmological Bulk Flows via the Kinematic Sunyaev-Zeldovich Effect in the Upcoming Cosmic Microwave Background Maps

We propose a new method for measuring the possible large-scale bulk flows in the universe from the cosmic microwave background (CMB) maps from the upcoming missions of the Microwave Anistropy Probe (MAP) and Planck. This can be done by studying the statistical properties of the CMB temperature field at many X-ray cluster positions. At each cluster position, the CMB temperature fluctuation will be a combination of the Sunyaev-Zeldovich (SZ) kinematic and thermal components, the cosmological fluctuations, and the instrument noise term. When averaged over many such clusters, the last three will integrate down, whereas the first one will be dominated by a possible bulk flow component. In particular, we propose to use all-sky X-ray cluster catalogs that should (or could) be available soon from X-ray satellites and then to evaluate the dipole component of the CMB field at the cluster positions. We show that for the MAP and Planck mission parameters, the dominant contributions to the dipole will be from the terms that are due to the SZ kinematic effect produced by the bulk flow (the signal we seek) and the instrument noise (the noise in our signal). Then, by computing the expected signal-to-noise ratio for such measurement, we find that at the 95% confidence level, the bulk flows on scales >/=100 h(-1) Mpc can be probed down to the amplitude of less than 200 km s(-1) with the MAP data and down to only approximately 30 km s(-1) with the Planck mission.     

Multiwavelength study of Cygnus A – III. Evidence for relic lobe plasma

We study the particle energy distribution in the cocoon surrounding Cygnus A, using radio images between 151 MHz and 15 GHz and a 200 ks Chandra Advanced CCD Imaging Spectrometer-Imaging (ACIS-I) image. We show that the excess low-frequency emission in the lobe further from the Earth cannot be explained by absorption or excess adiabatic expansion of the lobe or a combination of both. We show that this excess emission is consistent with emission from a relic counterlobe and a relic counterjet that are being re-energized by compression from the current lobe. We detect hints of a relic hotspot at the end of the relic X-ray jet in the more distant lobe. We do not detect relic emission in the lobe nearer to the Earth as expected from light traveltime effects assuming intrinsic symmetry. We determine that the duration of the previous jet activity phase was slightly less than that of the current jet-active phase. Further, we explain some features observed at 5 and 15 GHz as due to the presence of a relic jet.     

Broadband submillimeter measurements of the full Moon center brightness temperature and application to a lunar eclipse

We report on observations of the full Moon brightness temperature covering the frequency range of 300-950 GHz, and also on observations of the lunar eclipse of July 16, 2000, though only covering the frequency range of 165-365 GHz due to poor atmospheric transmission at higher frequencies. All observations were performed from the summit of Mauna Kea (HI) using a Fourier Transform Spectrometer mounted on the Caltech Submillimeter Observatory and supplemented by measurements of the atmospheric opacity using a 183 GHz Water Vapor Monitor. The telescope was pointed to the center of the lunar disk (with a footprint of ∼45-15 km on the Moon at 300 through 900 GHz). In order to obtain the correct values of the Moon brightness temperatures at all frequencies we carefully corrected for the atmospheric absorption, which varies across the submillimeter domain. This correction is fully described. The measured pre-eclipse brightness temperature is around 337 K in the 165-365 GHz range. This temperature slightly increases with frequency to reach ∼353 K at 950 GHz, according to previous broader band data. The magnitude of the temperature drop observed during the eclipse at 265 GHz (central frequency of the band covered) was about ∼70 K, in very good agreement with previous millimeter-wave measurements of other lunar eclipses. We detected, in addition, a clear frequency trend in the temperature drop that has been compared to a thermal and microwave emission model of the lunar regolith, with the result of a good match of the relative flux drop at different frequencies between model and measurements.     

Characterization of the atmosphere above a site for millimeter wave astronomy

The Sardinia Radio Telescope (SRT) is a challeging scientific project managed by the National Institute for Astrophysics (INAF), it is being developed at 30 km North of the city of Cagliari, Italy. The goal of the SRT project is to build a general purpose, fully steerable, 64 m diameter radio telescope, capable of operating with high efficiency in the centimeter and millimeter frequency range (0.3–100 GHz). In portions of this frequency range, especially towards the high end, astronomical observations can be heavily deteriorated by non-optimal atmospheric conditions, especially by water vapor content. The water molecule permanent electric dipole in fact, leads to pressure broadened rotational transitions around the 22.23 GHz spectral line. Furthermore, water vapor’s continuum absorption and emission may influence higher frequency observations too. To a lower degree, cloud liquid black body radiation can also affect centimeter and millimeter observations. In addition to this, inhomogeneities in water vapor distributions can cause signal phase errors which introduce a great amount of uncertainty to VLBI mode observations. The Astronomical Observatory of Cagliari (OA-CA) has obtained historical timeseries of radiosonde profiles conducted at the airport of Cagliari. Through the radiosonde measurements and an appropriate radiative transfer model, we have performed a statistical analysis of the SRT site’s atmosphere which accounts for atmospheric opacity at different frequencies, integrated water vapor (IWV), integrated liquid water (ILW) and cloud cover distributions during the year. This will help to investigate in which period of the year astronomical observations at different frequencies should be performed preferably. The results show that, at the SRT site, K-band astronomical observations are possible all year round, the median opacity at 22.23 GHz is 0.10 Np in the winter (Dec-Jan-Feb) and 0.16 Np in the summer (Jun-Jul-Aug). Integrated water vapor during winter months ranges, on average, between 7 and 15 mm. Cloud cover is usually not present for more than 36% of the time during the year. The atmospheric opacity study indicates that observations at higher frequencies (50–100 GHz) may be performed usefully: the median opacity at 100 GHz is usually below or equal to 0.2 Np in the period that ranges from January to April.     

A new spectroscopic facility at millimetre wavelengths

A new millimeter-wave facility is in operation at the Bordeaux Observatory for spectroscopic observations of interstellar and stratospheric molecules. A cooled receiver has been installed on a 2·5m radio telescope. The overall system temperature is in the range 400 to 600 K (single side band) in the operating frequency range 75 to 115 GHz. The relatively broad beam of the telescope (∼ 5 arcmin) combined with a sensitive receiver will permit studies of extended molecular cloud complexes.     

Repetition rates of fast pulses in a solar burst observed at MM-waves and hard X-rays

The solar burst of 21 May, 1984, 13 26 UT, showed radio spectral emission with a turnover frequency above 90 GHz, well correlated in time with the hard X-ray emission. It consisted of seven major time structures (1–3 s in duration), of which each was composed of several fast pulses with rise times between 30 and 60 ms. The spectral indices of the millimeter and hard X-ray emission exhibited sudden changes during each major time structure. The subsecond pulses were nearly in phase at 30 and 90 GHz, but their relative amplitude at 90 GHz ( 50%) were considerably larger than at 30 GHz (<5%). It was also found that the 90 GHz and the 100 keV X-rays fluxes were proportional to the repetition rate of the subsecond pulses, and that the hard X-ray power law index hardens with increasing repetition rate.Proceedings of the Second CESRA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

The spectrum of Cosmic Microwave Background at low frequency

The spectrum of Cosmic Microwave Background at frequency close or below 1 GHz is currently known with a large uncertainty. The difficulties arise both from the calibration technique and the presence of large foreground signals. In this spectral region large deviations from the Planck distribution are still permitted. In this paper the current status of our knowledge is described. Experiments involved and techniques employed are also discussed.     

The microwave spectrum of solar millisecond spikes

The microwave radiation from solar flares sometimes shows short and intensive spikes which are superimposed on the burst continuum. In order to determine the upper frequency limit of their occurrence and the circular polarization, a statistical analysis has been performed on our digital microwave observations from 3.2 to 92.5 GHz. Additionally, fine structures have been investigated with a fast (5 ms) 32-channel spectrometer at 3.47 GHz. We found that 10% of the bursts show fine structures at 3.2 and 5.2 GHz, whereas none occurred above 8.4 GHz. Most of the observed spikes were very short ( 10 ms) and their bandwidth varied from below 0.5 MHz to more than 200 MHz. Simultaneous observations at two further frequencies showed no coincident spikes at the second and third harmonic. The observations can be explained by the theory of electron cyclotron masering if the observed bandwidths are determined by magnetic field inhomogeneities or if the rise times are independent of the source diameters. The latter would imply source sizes between 50 and 100 km.Proceedings of the Workshop on Radio Continua during Solar Flares, held at Duino (Trieste), Italy, 27–31 May, 1985.     

Correlation effects in microwave observations of selected RS CVn-like stars

Sets of dual frequency microwave data on selected chromospherically active stars, from the Australia Telescope Compact Array, have been investigated for their auto and cross-correlation effects. Comparison of cross-correlation peak values with theoretical expectation indicates a high degree of real physical connection between the emission at the pairs of frequencies (4.8 and 8.64 GHz) compared. This fact should help constrain models for the emission mechanism.The timescale of observed time-shifts between the emissions at the two frequencies is consistent, in general, with the underlying energization being propagated by magnetohydrodynamic waves in a compact turbulent medium.