M. Bersanelli

A Determination of the Spectral Index of Galactic Synchrotron Emission in the 1-10 GHz Range

We present an analysis of simultaneous multifrequency measurements of the Galactic emission in the 1-10 GHz range with 18° angular resolution taken from a high-altitude site. Our data yield a determination of the synchrotron spectral index between 1.4 and 7.5 GHz of βsyn = 2.81 ± 0.16. Combining our data with maps made by Haslam et al. and Reich & Reich, we find βsyn = 2.76 ± 0.11 in the 0.4-7.5 GHz range. These results are in agreement with the few previously published measurements. The variation of βsyn with frequency based on our results and compared with other data found in the literature suggests a steepening of the synchrotron spectrum toward high frequencies, as expected from theory because of the steepening of the parent cosmic-ray electron energy spectrum. Comparison between the Haslam data and the 19 GHz map of Cottingham also indicates a spatial variation of the spectral index on large angular scales. Additional high-quality data are necessary to provide a serious study of these effects.

The absolute temperature of the sky and the temperature of the cosmic background radiation at 600 MHz

The absolute temperature of the sky at delta = 46.5 deg has been measured at 600 MHz (50 cm wavelength) using a differential radiometer and a cold calibrator at liquid helium temperature. To separate the cosmic background radiation (CBR) from the remaining components of the sky temperature, observations at other frequencies, now under way, are necessary. A preliminary estimate of the CBR temperature at 600 MHz made using data of T(sky) at 600 MHz and maps of the sky at 408 MHz already in the literature gives T(cbr) = (3.0 + or - 1.2) K, in good agreement with previous measurements at nearby frequencies. 45 refs.

THE GEM PROJECT: AN INTERNATIONAL COLLABORATION TO SURVEY GALACTIC RADIATION EMISSION

The GEM (Galactic Emission Mapping) project is an international collaboration established with the aim of surveying the full sky at long wavelengths with a multi-frequency radio telescope. A total of 745 hours of observation at 408 MHz were completed from an Equatorial site in Colombia. The observations cover the celestial band 0h<α<24h, and −24° 22′<δ<+35° 37′. Preliminary results of this partial survey will be discussed. A review of the instrumental setup and a ∼10° resolution sky map at 408 MHz is presented.

A Measurement of the Cosmic Microwave Background Temperature at 7.5 GHz

The temperature of the cosmic microwave background (CMB) radiation at a frequency of 7.5 GHz (4 cm wavelength) is measured, obtaining a brightness temperature of T(CMB) = 2.70 +/- 0.08 K (68 percent confidence level). The measurement was made from a site near the geographical South Pole during the austral spring of 1989 and was part of an international collaboration to measure the CMB spectrum at low frequencies with a variety of radiometers from several different sites. This recent result is in agreement with the 1988 measurement at the same frequency, which was made from a different site with significantly different systematic errors. The combined result of the 1988 and 1989 measurements is 2.64 +/- 0.06 K. 11 refs.

The temperature of the cosmic microwave background radiation at a frequency of 10 GHz

We have measured the temperature of the cosmic microwave background radiation (CMBR) at a frequency of 10 GHz (wavelength 3.0 cm) as part of a larger effort to determine the spectrum of the CMBR in the Rayleigh-leans region. The instrument used is a superheterodyne Dicke-switched radiometer. We have repeated the measurement over four summers with successively improved techniques and equipment. Our best estimate of the CMBR thermodynamic temperature at 10 GHz is 2.61 ± 0.06 K, where the error estimate is a 68% confidence level limit. Subject headings: cosmic background radiation ..

The temperature of the cosmic background radiation : results from the 1987 and 1988 measurements at 3.8 GHz

The low-frequency (Rayleigh-Jeans) spectrum of the cosmic background radiation (CBR) is expected to contain information relevant to the physical processes that occurred in the early universe. In this paper, the authors have measured the temperature of the cosmic background radiation (CBR) at a frequency of 3.8 GHz (7.9 cm wavelength), during two consecutive summers, obtaining a brightness temperature, T{sub CBR}, of 2.56 {plus minus} 0.08 K in 1987 and 2.71 {plus minus} 0.07 K in 1988 (68% confidence level). The new results are in agreement with their previous measurement at 3.7 GHz obtained in 1986 and have smaller error bars. Combining measurements from all 3 years, they obtain T{sub CBR} = 2.64 {plus minus} 0.07 K.

A research program to map the Galactic Emission at low frequencies

The need for accurate and complete maps of the galaxy at radio frequencies is made evident not only by the importance of the data in the study of galactic dynamics and structure formation but also in the analysis of cosmic background radiation data. A summary of the existing radio surveys of our galaxy is presented along with their limitations. A new program, the Galactic Emission Mapping (GEM) project, to obtain calibrated and complete maps of the galaxy in the 400 to 1400 MHz range, is outlined.

Trade - off between angular resolution and straylight contamination in CMB anisotropy experiments. 2. Straylight evaluation

The last generation of CMB anisotropy experiments operating either from space, like the WMAP and PLANCK satellite, from the atmosphere, such as balloons, or from the ground, like interferometers, make use of complex multi-frequency instruments at the focus of meter class telescopes to allow the joint study of CMB and foreground anisotropies, necessary to achieve an accurate component separation. Between ∼70 GHz and ∼300 GHz, where foreground contamination is minimum, it is extremely important to reach the best trade-off between the improvement of the angular resolution, necessary for measuring the high order acoustic peaks of CMB anisotropy, and the minimization of the straylight contamination mainly due to the Galactic emission. This is one ol the most critical systematic effects at large and intermediate angular scales (i.e. at multipoles f less than 100) and consists in unwanted radiation entering the beam at large angles from the direction of the antenna boresight direction. We consider here the 30 and 100 GHz channels of the PLANCK Low Frequency Instrument (LFI). Assuming the nominal PLANCK scanning strategy, we evaluate the straylight contamination introduced by the most relevant Galactic foreground components for a reference set of optical configurations, accurately simulated as described in Sandri et al. (2004, A&A, 428, 299) (hereafter Paper 1). Given the overall constraints to the LFI optical design, we show that it is possible to improve the angular resolution by 5-7% by keeping the overall peak-to-peak signal of the Galaxy straylight contamination (GSC) below the level of few μK (and about 10 times smaller in terms of rms). A comparison between the level of straylight introduced by the different Galactic components for different beam regions (intermediate and far beam) is presented. We provide approximate relations, both for the intermediate and the far beam, for the rms and the peak-to-peak levels of the GSC as functions of the corresponding contributions to the integrated beam or of the spillover. For some reference cases we compare the results based on Galactic foreground maps derived from radio, IR, and Hα templates with those based on WMAP maps including CMB and extragalactic source fluctuations. The implications for the GSC in the PLANCK LFI polarization data are discussed. Finally, we compare the results obtained at 100 GHz with those at 30 GHz, where the GSC is more critical.

Construction technique and performance of a 2 GHz rectangular corrugated horn

A large rectangular horn antenna with a center frequency of 2.0 GHz, corrugated on the E-plane walls, made out of aluminium sheet, has been designed, constructed, and tested. A technique has been developed to solder thin aluminium strips onto the back plane to form the corrugations. The radiation beam pattern shows half-power beamwidths of 12 degrees and 14 degrees in the H- and E-planes, respectively, and sidelobe response below -40 dB at angles greater than 50 degrees from the horn axis. The measured return loss is greater than 20 dB (VSWR >

Preliminary scanning strategy analysis for the LSPE-STRIP instrument

We present a preliminary study of the sky scanning strategy for the LSPE-STRIP instrument, a ground-based telescope that will be installed at the Teide Observatory (Tenerife, Canary Islands) in early 2019 and will observe the polarized emission of about 25% of the sky in the Northern Hemisphere at 43 and 95 GHz. The same sky portion will be observed at 140, 220 and 240 GHz by LSPE-SWIPE, a stratospheric balloon scheduled for a long-duration flight around the North Pole during the Arctic winter of 2019/2020. The combination of data from the two instruments aims at constraining the tensor-to-scalar ratio down to r ~ 0.03. In our paper we discuss the main scanning strategy requirements (overlap with SWIPE coverage, sensitivity distribution, observation of calibration sources) and show how we obtain a trade-off by spinning the telescope around the azimuth axis with constant elevation and angular velocity. The combination of the telescope motion with the Earth rotation will guarantee the access to the large angular scales. We will observe periodically the Crab Nebula as well as the Perseus molecular cloud. The Crab is one of the best known polarized sources in the sky and it will be observed for calibration purposes. The second one is a source of Anomalous Microwave Emission that could be characterized both in intensity and polarization.