The Square Kilometre Array (SKA)

Abstract:

The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and 95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to measure the anisotropy in the polarization of the CMB. QUIET primarily targets the B modes from primordial gravitational waves. The combination of these frequencies gives sensitivity to foreground contributions from diffuse Galactic synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of data were collected, first with the 19-element 43GHz array (3458hours) and then with the 90-element 95GHz array. Each array observes the same four fields, selected for low foregrounds, together covering ~1000deg^2. This paper reports initial results from the 43GHz receiver which has an array sensitivity to CMB fluctuations of 69uK sqrt(s). The data were extensively studied with a large suite of null tests before the power spectra, determined with two independent pipelines, were examined. Analysis choices, including data selection, were modified until the null tests passed. Cross correlating maps with different telescope pointings is used to eliminate a bias. This paper reports the EE, BB and EB power spectra in the multipole range ell=25-475. With the exception of the lowest multipole bin for one of the fields, where a polarized foreground, consistent with Galactic synchrotron radiation, is detected with 3sigma significance, the E-mode spectrum is consistent with the LCDM model, confirming the only previous detection of the first acoustic peak. The B-mode spectrum is consistent with zero, leading to a measurement of the tensor-to-scalar ratio of r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent boresight rotation leads to the lowest level of systematic contamination in the B-mode power so far reported, below the level of r=0.1

Abstract:

In this paper, we will present the design and the simulation of a 230GHz finline Ultra-wide IF Bandwidth SIS mixer. This mixer will be used in a novel millimeter-wave heterodyne interferometer: GUBBINS. GUBBINS is designed to demonstrate high surface brightness mm-wave interferometry at modest spatial and spectrum resolution. Its observational targets are the spectrum of the Sunyaev-Zel'dovich effect in the brightness galaxy cluster[3]. The archetype of the mixer design described here is an antipodal finline SIS mixer designed by Paul Grimes in Oxford Experimental Cosmology group in 2008[1]. Here several improvement and modification are made to simplify the design and fabrication, and also enhance the IF bandwidth. An unilateral finline replaces the complicated antipodal finline. No RF bandpass filter is needed after finline. The tuning circuit design presented here aims to achieve wider RF coupling bandwidth, even though only a single junction is used. A multi-stage IF transformer follows the IF bonding pad matching the IF output of the mixer to the input of the IF amplifier, as well as reducing the impact of the parasitical capacitance introduced by the RF finline and RF radial stub.

Abstract:

LOFT (Large area Observatory For x-ray Timing) is an innovative mission submitted in response to the Cosmic Vision "Call for a Medium-size mission opportunity for a launch in 2022" recently issued by ESA. LOFT is an ideal candidate for the next generation of (extremely) large experiments for X-ray timing dedicated to the study of the physics of compact objects and to the understanding of the behavior of matter in strong gravitational fields. Recent developments in the field of large area monolithic silicon detectors allowed us to reach an effective area ∼12 m2 (15 m2 goal), more than a order of magnitude larger that RXTE/PCA, in the energy range 2-30 keV (1-40 keV goal). This Large Area Detector (LAD) will have both high timing resolution (<10 μs, 5 μs goal) and good spectral capabilities (<260 eV, <180 eV goal). A Wide Field Monitor (WFM), sensitive in the ∼1-50 keV energy range, will observe simultaneously more than a quarter of the sky in order to both discover and localize transient events and study their long term evolution. © Copyright owned by the author(s) under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike Licence.

Abstract:

We present the first, complete 230 GHz feedhorn array manufactured by direct drilling of smooth-walled horns into a single plate of aluminium. The horn design process, based on a genetic algorithm, is described and the fabrication process, via direct drilling using shaped drill bits, is presented. We present cross coupling and beam pattern measurements of a close-packed pair of the smooth-walled horns fabricated in a single block of aluminium. We also present a prototype 37 horn array, again fabricated by drilling into a single block. Our measurements show that our designs and fabrication techniques will be robust when applied to large focal arrays of horns consisting of hundreds or thousands of feedhorns. We expect our smooth-walled horn designs and novel manufacturing techniques will offer an attractive, low-cost alternate to traditional horn arrays consisting of electroformed corrugated horns.

Abstract:

Recent studies of different X-ray binaries (XRBs) have shown a clear correlation between the radio and X-ray emission. We present evidence of a close relationship found between the radio and X-ray emission at different epochs for GRS 1915+105, using observations from the Ryle Telescope and Rossi X-ray Timing Explorer satellite. The strongest correlation was found during the hard state (also known as the "plateau" state), where a steady AU-scale jet is known to exist. Both the radio and X-ray emission were found to decay from the start of most plateau states, with the radio emission decaying faster. An empirical relationship of was then fitted to data taken only during the plateau state, resulting in a power-law index of ξ ~ 1.7 ± 0.3, which is significantly higher than in other black hole XRBs in a similar state. An advection-flow model was then fitted to this relationship and compared to the universal XRB relationship as described by Gallo et al. (2003, MNRAS, 344, 60). We conclude that either (I) the accretion disk in this source is radiatively efficient, even during the continuous outflow of a compact jet, which could also suggest a universal turn-over from radiatively inefficient to efficient for all stellar-mass black holes at a critical mass accretion rate (M c≈1018.5 g/s); or (II) the X-rays in the plateau state are dominated by emission from the base of the jet and not the accretion disk (e.g. via inverse Compton scattering from the outflow). © 2010 ESO.