Paul F. Scott

INTERPLANETARY SCINTILLATION OF SMALL DIAMETER RADIO SOURCES

Previous observations 4 of flares on EV Lacertae in yellow and blue light have ~hown that 1/(yellow)/J/(blue) = 0·23 at maximum light, and this has been used as tho correction factor. The estimates of tho optical and radio energies in the flares on the three stars are given in Table 2. The optical energies havo been obtained by using the black-body equations to calculate the increased radiation appropriate to the observed brightness increase in the star over a 1,000 A.u. band-width at 5,400 A.u. The apparent photovisual magnitudes mpv quoted in Table 2 are for the combined light of both components of the binary in the case of UV Ceti, and it is assumed that the stars radiate uniformly into TC steradians. The energies are based on a stellar radius of 0·080 for UV Ceti and for radii typical of dM5e stars in the case of EV L acortao and Ross 882.

9C: a survey of radio sources at 15 GHz with the Ryle Telescope

The fields chosen for the first observations of the cosmic microwave background with the Very Small Array have been surveyed with the Ryle Telescope at 15 GHz. We have covered three regions around RA 00 h 20 m Dec. +30°, RA 09 h 40 m Dec. +32° and RA 15 h 40 m Dec. +43° (J2000.0), an area of 520 deg 2 . There are 465 sources above the current completeness limit of 25 mJy, although a total of 760 sources have been detected, some as faint as 10 mJy. This paper describes our techniques for observation and data analysis; it also includes source counts and some discussion of spectra and variability. Preliminary source lists are presented.

High-sensitivity measurements of the cosmic microwave background power spectrum with the extended Very Small Array

We present deep Ka-band (ν ≈ 33 GHz) observations of the cosmic microwave background (CMB) made with the extended Very Small Array (VSA). This configuration produces a naturally weighted synthesized FWHM beamwidth of ∼11 arcmin, which covers anrange of 300 to 1500. On these scales, foreground extragalactic sources can be a major source of contamination to the CMB anisotropy. This problem has been alleviated by identifying sources at 15 GHz with the Ryle Telescope and then monitoring these sources at 33 GHz using a single-baseline interferometer collocated with the VSA. Sources with flux densities20 mJy at 33 GHz are subtracted from the data. In addition, we calculate a statistical correction for the small residual contribution from weaker sources that are below the detection limit of the survey. The CMB power spectrum corrected for Galactic foregrounds and extragalactic point sources is presented. A totalrange of 150-1500 is achieved by combining the complete extended array data with earlier VSA data in a compact configuration. Our resolution of �� ≈ 60 allows the first three acoustic peaks to be clearly delineated. This is achieved by using mosaiced observations in seven regions covering a total area of 82 deg 2 . There is good agreement with the Wilkinson Microwave Anisotropy Probe (WMAP) data up to � = 700 where WMAP data run out of resolution. For highervalues out to � = 1500, the agreement in power spectrum amplitudes with other experiments is also very good despite differences in frequency and observing technique.

The cosmic microwave background power spectrum out to ℓ= 1400 measured by the Very Small Array

We have observed the cosmic microwave background (CMB) in three regions of sky using the Very Small Array (VSA) in an extended configuration with antennas of beamwidth 2 degrees at 34 GHz. Combined with data from previous VSA observations using a more compact array with larger beamwidth, we measure the power spectrum of the primordial CMB anisotropies between angular multipoles l = 160 - 1400. Such measurements at high l are vital for breaking degeneracies in parameter estimation from the CMB power spectrum and other cosmological data. The power spectrum clearly resolves the first three acoustic peaks, shows the expected fall off in power at high l and starts to constrain the position and height of a fourth peak.

First results from the Very Small Array — I. Observational methods

The Very Small Array (VSA) is a synthesis telescope designed to image faint structures in the cosmic microwave background on degree and sub-degree angular scales. The VSA has key differences from other CMB interferometers with the result that different systematic errors are expected. We have tested the operation of the VSA with a variety of blank-field and calibrator observations, and cross-checked its calibration scale against independent measurements. We find that systematic effects can be suppressed below the thermal noise level in long observations; the overall calibration accuracy of the flux density scale is 3.5 per cent and is limited by the external absolute calibration scale.

First results from the Very Small array: III. The cosmic microwave background power spectrum

We present the power spectrum of the fluctuations in the cosmic microwave background detected by the Very Small Array (VSA) in its first season of observations in its compact configuration. We find clear detections of first and second acoustic peaks at l≈ 200 and ≈550, plus detection of power on scales up to l= 800. The VSA power spectrum is in very good agreement with the results of the BOOMERanG, DASI and MAXIMA telescopes despite the differing potential systematic errors.

Cosmological parameter estimation using Very Small Array data out to ℓ = 1500

We estimate cosmological parameters using data obtained by the Very Small Array (VSA) in its extended configuration, in conjunction with a variety of other cosmic microwave background (CMB) data and external priors. Within the flat A cold dark matter (ACDM) model, we find that the inclusion of high-resolution data from the VSA modifies the limits on the cosmological parameters as compared to those suggested by the Wilkinson Microwave Anisotropy Probe (WMAP) alone, while still remaining compatible with their estimates. We find that Omega(b)h(2) = 0.0234(-0.0014)(+0.0012), Omegadmh2 = 0.111(-0.016)(+0.014), h = 0.73(-0.05)(+0.09), n(S) = 0.97(-0.03)(+0.06), 10(10) A(S) = 23(-3)(+7) and tau = 0.14(-0.07)(+0.14) for WMAP and VSA when no external prior is included. On extending the model to include a running spectral index of density fluctuations, we find that the inclusion of VSA data leads to a negative running at a level of more than 95 per cent confidence (n(run) = -0.069 +/- 0.032), something that is not significantly changed by the inclusion of a stringent prior on the Hubble constant. Inclusion of prior information from the 2dF galaxy redshift survey reduces the significance of the result by constraining the value of Omega(m). We discuss the veracity of this result in the context of various systematic effects and also a broken spectral index model. We also constrain the fraction of neutrinos and find that f(v) < 0.087 at 95 per cent confidence, which corresponds to m(v) <0.32 eV when all neutrino masses are equal. Finally, we consider the global best fit within a general cosmological model with 12 parameters and find consistency with other analyses available in the literature. The evidence for nrun < 0 is only marginal within this model.

Measurements of Structure in the Cosmic Background Radiation with the Cambridge Cosmic Anisotropy Telescope

We have observed a 2° × 2° area of sky at frequencies of 15.5 and 16.5 GHz with the Cambridge Cosmic Anisotropy Telescope (CAT). Comparison with earlier measurements at 13.5 GHz shows that the observed structure at 16.5 GHz arises predominantly from the cosmic microwave background. The broadband power, averaged over spherical harmonic multipole orders between 330 and 680, is (ΔT/T) = 2.0+ 0.4−0.4 × 10-5, which is consistent with the predictions of a standard COBE-normalized, cold dark matter model.

First results from the Very Small Array – II. Observations of the cosmic microwave background

We have observed the cosmic microwave background temperature fluctuations in eight fields covering three separated areas of sky with the Very Small Array at 34 GHz. A total area of 101 square degrees has been imaged, with sensitivity on angular scales 3. ◦ 6–0. ◦ 4 (equivalent to angular multipoles l=150–900). We describe the field selection and observing strategy for these observations. In the full-resolution images (with synthesised beam of FWHM ≃ 17 arcmin) the thermal noise is typically 45 � K and the CMB signal typically 55 � k. The noise levels in each field agree well with the expected thermal noise level of the telescope, and there is no evidence of any residual systematic features. The same CMB features are detected in separate, overlapping observations. Discrete radio sources have been detected using a separate 15 GHz survey and their effects removed using pointed follow-up observations at 34 GHz. We estimate that the residual confusion noise due to unsubtracted radio sources is less than 14 mJy beam −1 (15 � K in the full-resolution images), which added in quadrature to the thermal noise increases the noise level by 6 %. We estimate that the rms contribution to the images from diffuse Galactic emission is less than 6 � K. We also present images which are convolved to maximise the signal-to-noise of the CMB features and are co-added in overlapping areas, in which the signal-to-noise of some individual CMB features exceeds 8.

10C Survey of Radio Sources at 15.7 GHz: I - Observing, mapping and source extraction ?

We have observed an area of�27 deg 2 to an rms noise level of/ 0: 2 mJy at 15.7 GHz, using the Arcminute Microkelvin Imager Large Array. These observations constitute the most sensitive radio-source survey of any extent (& 0: 2 deg 2 ) above 1.4 GHz. This paper presents the techniques employed for observing, mapping and source extraction. We have used a systematic procedure for extracting information and producing source catalogues, from maps with varying noise and uv-coverage. We have performed simulations to test our mapping and source-extraction procedures, and developed methods for identifying extended, overlapping and spurious sources in noisy images. In an accompanying paper, AMI Consortium: Davies et al. (2010), the first results from t he 10C survey, including the deep 15.7-GHz source count, are presented.