Context. CMB experiments aiming at a precise measurement of the CMB polarization, such as the Planck satellite, need a strong polarized absolute calibrator on the sky to accurately set the detectors ...polarization angle and the cross-polarization leakage. As the most intense polarized source in the microwave sky at angular scales of few arcminutes, the Crab nebula will be used for this purpose. Aims. Our goal was to measure the Crab nebula polarization characteristics at 90 GHz with unprecedented precision. Methods. The observations were carried out with the IRAM 30 m telescope employing the correlation polarimeter XPOL and using two orthogonally polarized receivers. Results. We processed the Stokes I, Q, and U maps from our observations in order to compute the polarization angle and linear polarization fraction. The first is almost constant in the region of maximum emission in polarization with a mean value of αSky = 152.1±0.3° in equatorial coordinates, and the second is found to reach a maximum of Π = 30% for the most polarized pixels. We find that a CMB experiment having a 5 arcmin circular beam will see a mean polarization angle of αSky = 149.9±0.2° and a mean polarization fraction of Π = 8.8±0.2%.
One of the major challenges of modern cosmology is the detection of B-mode polarization anisotropies in the Cosmic Microwave Background. These originate from tensor fluctuations of the metric ...produced during the inflationary phase. Their detection would therefore constitute a major step towards understanding the primordial Universe. The expected level of these anisotropies is however so small that it requires a new generation of instruments with high sensitivity and extremely good control of systematic effects.
We propose the QUBIC instrument based on the novel concept of bolometric interferometry, bringing together the sensitivity advantages of bolometric detectors with the systematics effects advantages of interferometry.
The instrument will directly observe the sky through an array of entry horns whose signals will be combined together using an optical combiner. The whole set-up is located inside a cryostat. Polarization modulation will be achieved using a rotating half-wave plate and the images of the interference fringes will be formed on two focal planes (separated by a polarizing grid) tiled with bolometers.
We show that QUBIC can be considered as a synthetic imager, exactly similar to a usual imager but with a synthesized beam formed by the array of entry horns. Scanning the sky provides an additional modulation of the signal and improve the sky coverage shape. The usual techniques of map-making and power spectrum estimation can then be applied. We show that the sensitivity of such an instrument is comparable with that of an imager with the same number of horns. We anticipate a low level of beam-related systematics thanks to the fact that the synthesized beam is determined by the location of the primary horns. Other systematics should be under good control thanks to an autocalibration technique, specific to our concept, that will permit the accurate determination of most of the instrumental parameters that would otherwise lead to systematics.
The Planck High Frequency Instrument (HFI) has been surveying the sky continuously from the second Lagrangian point (L2) between August 2009 and January 2012. It operates with 52 high impedance ...bolometers cooled at 100 mK in a range of frequency between 100 GHz and 1 THz with unprecedented sensitivity, but strong coupling with cosmic radiation. At L2, the particle flux is about 5
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2
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1
and is dominated by protons incident on the spacecraft. Protons with an energy above 40 MeV can penetrate the focal plane unit box causing two different effects: glitches in the raw data from direct interaction of cosmic rays with detectors (producing a data loss of about 15 % at the end of the mission) and thermal drifts in the bolometer plate at 100 mK adding non-Gaussian noise at frequencies below 0.1 Hz. The HFI consortium has made strong efforts in order to correct for this effect on the time ordered data and final Planck maps. This work intends to give a view of the physical explanation of the glitches observed in the HFI instrument in-flight. To reach this goal, we performed several ground-based experiments using protons and
α
particles to test the impact of particles on the HFI spare bolometers with a better control of the environmental conditions with respect to the in-flight data. We have shown that the dominant part of glitches observed in the data comes from the impact of cosmic rays in the silicon die frame supporting the micro-machined bolometric detectors propagating energy mainly by ballistic phonons and by thermal diffusion. The implications of these results for future satellite missions will be discussed.
A new observation of the distribution of the circular polarization over the Crab Nebula supernova remnant yields an upper limit of <0.2% at a radio frequency of 89.2 GHz. This limit is set by the ...uncertainty in correcting for the instrumental polarization. The raw data were dominated by the conversion of the strong linear polarization to circular in the crosspolarized sidelobes of the 30 m telescope. They were modeled as due to a differential phase gradient between the orthogonally linearly polarized far-field radiation patterns of the two receivers. As the source is tracked these rotate with respect to the radio source distribution on the sky since the telescope has an alt-azimuth mount and a Nasmyth focus. This allows the model to be fit to the raw data and a correction can be made. Our limit of <0.2% is to be compared with <0.03% derived at 610 MHz (Wilson & Weiler 1997, ApJ, 475, 661) and <6% measured at 23 GHz (Wright & Forster 1980, ApJ, 239, 873). These limits are consistent with the polarization expected from an optically thin synchrotron source with the known physical properties of the Crab Nebula. This non-detection does not allow an estimate to be made of the relative contribution to the radio emission from electrons and positrons.
Cosmological constraints from Archeops Benoît, A.; Ade, P.; Amblard, A. ...
Astronomy and astrophysics (Berlin),
03/2003, Letnik:
399, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We analyze the cosmological constraints that Archeops (Benoît et al. 2003) places on adiabatic cold dark matter models with passive power-law initial fluctuations. Because its angular power spectrum ...has small bins in $\ell$ and large $\ell$ coverage down to COBE scales, Archeops provides a precise determination of the first acoustic peak in terms of position at multipole $l_{\rm peak}=220\pm 6$, height and width. An analysis of Archeops data in combination with other CMB datasets constrains the baryon content of the Universe, $\Omega_{\rm b}h^2= 0.022^{+0.003}_{-0.004}$, compatible with Big-Bang nucleosynthesis and with a similar accuracy. Using cosmological priors obtained from recent non–CMB data leads to yet tighter constraints on the total density, e.g. $\Omega_{\rm tot}=1.00^{+0.03}_{-0.02}$ using the HST determination of the Hubble constant. An excellent absolute calibration consistency is found between Archeops and other CMB experiments, as well as with the previously quoted best fit model. The spectral index n is measured to be $1.04^{+0.10}_{-0.12}$ when the optical depth to reionization, τ, is allowed to vary as a free parameter, and $0.96^{+0.03}_{-0.04}$ when τ is fixed to zero, both in good agreement with inflation.
Summary
A total of 76 unrelated male patients with mild (n = 55) or moderate (n = 21) haemophilia A living in the southern Brazilian state of Rio Grande do Sul were studied by direct sequencing of ...all F8 26 exons, the 5′ UTR and 3′ UTR, intron–exon junctions and the promoter region. When no mutation was found, a multiplex ligation‐dependent probe amplification analysis was performed. We identified the disease‐causing mutations in 69 patients, who showed 33 different mutations: 27 missense, one small deletion, two small duplications and three splice site mutations. Seven missense and two splice site mutations were not previously reported in HAMSTeRS and were not identified in any current literature search. Nine recurrent mutations were found, one of them never described before (p.Tyr1786Phe). Haplotype analysis indicated that this mutation had originated in the Brazilian population as a single event in a common ancestor. The possible influence of these mutations in the determination of the disease was carefully considered, including bioinformatic tools. These data add to the general knowledge of the disease and can also be useful for HA diagnosis and detection of carriers in the southern Brazilian population.
Atmospheric emission is a dominant source of disturbance in ground-based astronomy at millimetric wavelengths. The Antarctic plateau is recognized as an ideal site for millimetric and submillimetric ...observations, and the French/Italian base of Dome Concordia (Dome C) is among the best sites on Earth for these observations. In this paper, we present measurements at Dome C of the atmospheric emission in intensity and polarization at a 2-mm wavelength. This is one of the best observational frequencies for cosmic microwave background (CMB) observations when considering cosmic signal intensity, atmospheric transmission, detector sensitivity and foreground removal. Using the B-mode radiation interferometer (BRAIN)-pathfinder experiment, we have performed measurements of the atmospheric emission at 150 GHz. Careful characterization of the airmass synchronous emission has been performed, acquiring more than 380 elevation scans (i.e. 'skydip') during the third BRAIN-pathfinder summer campaign in 2009 December/2010 January. The extremely high transparency of the Antarctic atmosphere over Dome C is proven by the very low measured optical depth, 〈τI〉= 0.050 ± 0.003 ± 0.011, where the first error is statistical and the second is the systematic error. Mid-term stability, over the summer campaign, of the atmosphere emission has also been studied. Adapting the radiative transfer atmosphere emission model am to the particular conditions found at Dome C, we also infer the level of the precipitable water vapor (PWV) content of the atmosphere, which is notoriously the main source of disturbance in millimetric astronomy (
mm). Upper limits on the airmass correlated polarized signal are also placed for the first time. The degree of circular polarization of atmospheric emission is found to be lower than 0.2 per cent 95 per cent confidence level (CL), while the degree of linear polarization is found to be lower than 0.1 per cent (95 per cent CL). These limits include signal-correlated instrumental spurious polarization.
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