F. Cuttaia

Simultaneous Planck, Swift, and Fermi observations of X-ray and γ-ray selected blazars

We present simultaneous Planck, Swift, Fermi, and ground-based data for 105 blazars belonging to three samples with flux limits in the soft X-ray, hard X-ray, and -ray bands, and we compare our results to those of a companion paper presenting simultaneous Planck and multi-frequency observations of 104 radio-loud northern active galactic nuclei selected at radio frequencies. While we confirm several previous results, our unique data set has allowed us to demonstrate that the selection method strongly influences the results, producing biases that cannot be ignored. Almost all the BL Lac objects have been detected by Fermi Large Area Telescope (LAT), whereas 30 to 40% of the flat-spectrum radio quasars (FSRQs) in the radio, soft X-ray, and hard X-ray selected samples are still below the -ray detection limit even after integrating 27 months of Fermi-LAT data. The radio to sub-millimetre spectral slope of blazars is quite flat, withh i 0 up to about 70 GHz, above which it steepens toh i 0:65. BL Lacs have significantly flatter spectra than FSRQs at higher frequencies. The distribution of the rest-frame synchrotron peak frequency ( S ) in the spectral energy distribution (SED) of FSRQs is the same in all the blazar samples withh S i = 10 13:1 0:1 Hz, while the mean inverse-Compton peak frequency,h IC i, ranges from 10 21 to 10 22 Hz. The distributions of S and of IC of BL Lacs are much broader and are shifted to higher energies than those of FSRQs; their shapes strongly depend on the selection method. The Compton dominance of blazars ranges from less than 0.2 to nearly 100, with only FSRQs reaching values larger than about 3. Its distribution is broad and depends strongly on the selection method, with -ray selected blazars peaking at 7 or more, and radio-selected blazars at values close to 1, thus implying that the common assumption that the blazar power budget is largely dominated by high-energy emission is a selection e ect. A comparison of our multi-frequency data with theoretical predictions shows that simple homogeneous SSC models cannot explain the simultaneous SEDs of most of the -ray detected blazars in all samples. The SED of the blazars that were not detected by Fermi-LAT may instead be consistent with SSC emission. Our data challenge the correlation between bolometric luminosity and S predicted by the blazar sequence.

Planck Pre-Launch Status: Expected LFI Polarisation Capability

We present a system-level description of the Low Frequency Instrument (LFI) considered as a differencing polarimeter, and evaluate its expected performance. The LFI is one of the two instruments on board the ESA Planck mission to study the cosmic microwave background. It consists of a set of 22 radiometers sensitive to linear polarisation, arranged in orthogonally-oriented pairs connected to 11 feed horns operating at 30, 44 and 70 GHz. In our analysis, the generic Jones and Mueller-matrix formulations for polarimetry are adapted to the special case of the LFI. Laboratory measurements of flight components are combined with optical simulations of the telescope to investigate the values and uncertainties in the system parameters affecting polarisation response. Methods of correcting residual systematic errors are also briefly discussed. The LFI has beam-integrated polarisation efficiency >99% for all detectors, with uncertainties below 0.1%. Indirect assessment of polarisation position angles suggests that uncertainties are generally less than 0°.5, and this will be checked in flight using observations of the Crab nebula. Leakage of total intensity into the polarisation signal is generally well below the thermal noise level except for bright Galactic emission, where the dominant effect is likely to be spectral-dependent terms due to bandpass mismatch between the two detectors behind each feed, contributing typically 1–3% leakage of foreground total intensity. Comparable leakage from compact features occurs due to beam mismatch, but this averages to < 5 × 10^(-4) for large-scale emission. An inevitable feature of the LFI design is that the two components of the linear polarisation are recovered from elliptical beams which differ substantially in orientation. This distorts the recovered polarisation and its angular power spectrum, and several methods are being developed to correct the effect, both in the power spectrum and in the sky maps. The LFI will return a high-quality measurement of the CMB polarisation, limited mainly by thermal noise. To meet our aspiration of measuring polarisation at the 1% level, further analysis of flight and ground data is required. We are still researching the most effective techniques for correcting subtle artefacts in polarisation; in particular the correction of bandpass mismatch effects is a formidable challenge, as it requires multi-band analysis to estimate the spectral indices that control the leakage.

Planck-LFI: design and performance of the 4 Kelvin Reference Load Unit

The LFI radiometers use a pseudo-correlation design where the signal from the sky is continuously compared with a stable reference signal, provided by a cryogenic reference load system. The reference unit is composed by small pyramidal horns, one for each radiometer, 22 in total, facing small absorbing targets, made of a commercial resin ECCOSORB CRTM, cooled to ~ 4.5 K. Horns and targets are separated by a small gap to allow thermal decoupling. Target and horn design is optimized for each of the LFI bands, centered at 70, 44 and 30 GHz. Pyramidal horns are either machined inside the radiometer 20K module or connected via external electro-formed bended waveguides. The requirement of high stability of the reference signal imposed a careful design for the radiometric and thermal properties of the loads. Materials used for the manufacturing have been characterized for thermal, RF and mechanical properties. We describe in this paper the design and the performance of the reference system.

The Large-Scale Polarization Explorer (LSPE)

The LSPE is a balloon-borne mission aimed at measuring the polarization of the Cosmic Microwave Background (CMB) at large angular scales, and in particular to constrain the curl component of CMB polarization (B-modes) produced by tensor perturbations generated during cosmic inflation, in the very early universe. Its primary target is to improve the limit on the ratio of tensor to scalar perturbations amplitudes down to r = 0.03, at 99.7% confidence. A second target is to produce wide maps of foreground polarization generated in our Galaxy by synchrotron emission and interstellar dust emission. These will be important to map Galactic magnetic fields and to study the properties of ionized gas and of diffuse interstellar dust in our Galaxy. The mission is optimized for large angular scales, with coarse angular resolution (around 1.5 degrees FWHM), and wide sky coverage (25% of the sky). The payload will fly in a circumpolar long duration balloon mission during the polar night. Using the Earth as a giant solar shield, the instrument will spin in azimuth, observing a large fraction of the northern sky. The payload will host two instruments. An array of coherent polarimeters using cryogenic HEMT amplifiers will survey the sky at 43 and 90 GHz. An array of bolometric polarimeters, using large throughput multi-mode bolometers and rotating Half Wave Plates (HWP), will survey the same sky region in three bands at 95, 145 and 245 GHz. The wide frequency coverage will allow optimal control of the polarized foregrounds, with comparable angular resolution at all frequencies.

Planck pre-launch status: Low Frequency Instrument calibration and expected scientific performance

We present the calibration and scientific performance parameters of the Planck Low Frequency Instrument (LFI) measured during the ground cryogenic test campaign. These parameters characterise the instrument response and constitute our optimal pre-launch knowledge of the LFI scientific performance. The LFI shows excellent 1/f stability and rejection of instrumental systematic effects; its measured noise performance shows that LFI is the most sensitive instrument of its kind. The calibration parameters will be updated during flight operations until the end of the mission.

Design, development and verification of the 30 and 44 GHz front-end modules for the Planck Low Frequency Instrument

We give a description of the design, construction and testing of the 30 and 44 GHz Front End Modules (FEMs) for the Low Frequency Instrument (LFI) of the Planck mission to be launched in 2009. The scientific requirements of the mission determine the performance parameters to be met by the FEMs, including their linear polarization characteristics. The FEM design is that of a differential pseudo-correlation radiometer in which the signal from the sky is compared with a 4-K blackbody load. The Low Noise Amplifier (LNA) at the heart of the FEM is based on indium phosphide High Electron Mobility Transistors (HEMTs). The radiometer incorporates a novel phase-switch design which gives excellent amplitude and phase match across the band. The noise temperature requirements are met within the measurement errors at the two frequencies. For the most sensitive LNAs, the noise temperature at the band centre is 3 and 5 times the quantum limit at 30 and 44 GHz respectively. For some of the FEMs, the noise temperature is still falling as the ambient temperature is reduced to 20 K. Stability tests of the FEMs, including a measurement of the 1/f knee frequency, also meet mission requirements. The 30 and 44 GHz FEMs have met or bettered the mission requirements in all critical aspects. The most sensitive LNAs have reached new limits of noise temperature for HEMTs at their band centres. The FEMs have well-defined linear polarization characteristcs.

Noise properties of the Planck-LFI receivers

The Planck Low Frequency Instrument (LFI) radiometers have been tested extensively during several dedicated campaigns. The present paper reports the principal noise properties of the LFI radiometers. A brief description of the LFI radiometers is given along with details of the test campaigns relevant to determination of noise properties. Current estimates of flight sensitivities, 1/f parameters, and noise effective bandwidths are presented. The LFI receivers exhibit exceptional 1/f noise, and their white noise performance is sufficient for the science goals of Planck.

Planck-LFI radiometers' spectral response

The Low Frequency Instrument (LFI) is an array of pseudo-correlation radiometers on board the Planck satellite, the ESA mission dedicated to precision measurements of the Cosmic Microwave Background. The LFI covers three bands centred at 30, 44 and 70 GHz, with a goal bandwidth of 20% of the central frequency. The characterization of the broadband frequency response of each radiometer is necessary to understand and correct for systematic effects, particularly those related to foreground residuals and polarization measurements. In this paper we present the measured band shape of all the LFI channels and discuss the methods adopted for their estimation. The spectral characterization of each radiometer was obtained by combining the measured spectral response of individual units through a dedicated RF model of the LFI receiver scheme. As a consistency check, we also attempted end-to-end spectral measurements of the integrated radiometer chain in a cryogenic chamber. However, due to systematic effects in the measurement setup, only qualitative results were obtained from these tests. The measured LFI bandpasses exhibit a moderate level of ripple, compatible with the instrument scientific requirements.

Design, development, and verification of the Planck Low Frequency Instrument 70 GHz Front-End and Back-End Modules

70 GHz radiometer front-end and back-end modules for the Low Frequency Instrument of the European Space Agencys Planck Mission were built and tested. The operating principles and the design details of the mechanical structures are described along with the key InP MMIC low noise amplifiers and phase switches of the units. The units were tested in specially designed cryogenic vacuum chambers capable of producing the operating conditions required for Planck radiometers, specifically, a physical temperature of 20 K for the front-end modules, 300 K for the back-end modules and 4 K for the reference signal sources. Test results of the low noise amplifiers and phase switches, the front and back-end modules, and the combined results of both modules are discussed. At 70 GHz frequency, the system noise temperature of the front and back end is 28 K; the effective bandwidth 16 GHz, and the 1/f spectrum knee frequency is 38 mHz.The test results indicate state-of-the-art performance at 70 GHz frequency and fulfil the Planck performance requirements.

A coherent polarimeter array for the Large Scale Polarization Explorer (LSPE) balloon experiment

We discuss the design and expected performance of STRIP (STRatospheric Italian Polarimeter), an array of coherent receivers designed to fly on board the LSPE (Large Scale Polarization Explorer) balloon experiment. The STRIP focal plane array comprises 49 elements in Q band and 7 elements in W-band using cryogenic HEMT low noise amplifiers and high performance waveguide components. In operation, the array will be cooled to 20 K and placed in the focal plane of a ~0.6 meter telescope providing an angular resolution of ~1.5 degrees. The LSPE experiment aims at large scale, high sensitivity measurements of CMB polarization, with multi-frequency deep measurements to optimize component separation. The STRIP Q-band channel is crucial to accurately measure and remove the synchrotron polarized component, while the W-band channel, together with a bolometric channel at the same frequency, provides a crucial cross-check for systematic effects.