Active galactic nuclei, which are powered by long-term accretion onto central supermassive black holes, produce relativistic jets with lifetimes of at least one million years, and the observation of ...the birth of such a jet is therefore unlikely. Transient accretion onto a supermassive black hole, for example through the tidal disruption of a stray star, thus offers a rare opportunity to study the birth of a relativistic jet. On 25 March 2011, an unusual transient source (Swift J164449.3+573451) was found, potentially representing such an accretion event. Here we report observations spanning centimetre to millimetre wavelengths and covering the first month of evolution of a luminous radio transient associated with Swift J164449.3+573451. The radio transient coincides with the nucleus of an inactive galaxy. We conclude that we are seeing a newly formed relativistic outflow, launched by transient accretion onto a million-solar-mass black hole. A relativistic outflow is not predicted in this situation, but we show that the tidal disruption of a star naturally explains the observed high-energy properties and radio luminosity and the inferred rate of such events. The weaker beaming in the radio-frequency spectrum relative to γ-rays or X-rays suggests that radio searches may uncover similar events out to redshifts of z ≈ 6.
We present an improved analysis of the final data set from the QUaD experiment. Using an improved technique to remove ground contamination, we double the effective sky area and hence increase the ...precision of our cosmic microwave background (CMB) power spectrum measurements by ~30% versus that previously reported. In addition, we have improved our modeling of the instrument beams and have reduced our absolute calibration uncertainty from 5% to 3.5% in temperature. The robustness of our results is confirmed through extensive jackknife tests, and by way of the agreement that we find between our two fully independent analysis pipelines. For the standard six-parameter Delta *LCDM model, the addition of QUaD data marginally improves the constraints on a number of cosmological parameters over those obtained from the WMAP experiment alone. The impact of QUaD data is significantly greater for a model extended to include either a running in the scalar spectral index, or a possible tensor component, or both. Adding both the QUaD data and the results from the Arcminute Cosmology Bolometer Array Receiver experiment, the uncertainty in the spectral index running is reduced by ~25% compared to WMAP alone, while the upper limit on the tensor-to-scalar ratio is reduced from r < 0.48 to r < 0.33 (95% c.l.). This is the strongest limit on tensors to date from the CMB alone. We also use our polarization measurements to place constraints on parity-violating interactions to the surface of last scattering, constraining the energy scale of Lorentz violating interactions to <1.5 X 10-43 GeV (68% c.l.). Finally, we place a robust upper limit on the strength of the lensing B-mode signal. Assuming a single flat band power between = 200 and = 2000, we constrain the amplitude of B-modes to be <0.57 Delta *mK2 (95% c.l.).
We constrain parity-violating interactions to the surface of last scattering using spectra from the QUaD experiment's second and third seasons of observations by searching for a possible systematic ...rotation of the polarization directions of cosmic microwave background photons. We measure the rotation angle due to such a possible "cosmological birefringence" to be 0.55 degrees +/-0.82 degrees (random) +/-0.5 degrees (systematic) using QUaD's 100 and 150 GHz temperature-curl and gradient-curl spectra over the spectra over the multipole range 200<l<2000, consistent with null, and constrain Lorentz-violating interactions to <2 x 10;{-43} GeV (68% confidence limit). This is the best constraint to date on electrodynamic parity violation on cosmological scales.
We report results from the second and third seasons of observation with the QUaD experiment. Angular power spectra of the cosmic microwave background are derived for both temperature and polarization ...at both 100 GHz and 150 GHz, and as cross-frequency spectra. All spectra are subjected to an extensive set of jackknife tests to probe for possible systematic contamination. For the implemented data cuts and processing technique such contamination is undetectable. We analyze the difference map formed between the 100 and 150 GHz bands and find no evidence of foreground contamination in polarization. The spectra are then combined to form a single set of results which are shown to be consistent with the prevailing LCDM model. The sensitivity of the polarization results is considerably better than that of any previous experiment-for the first time multiple acoustic peaks are detected in the E-mode power spectrum at high significance.
The Arcminute Microkelvin Imager Zwart, J. T. L.; Barker, R. W.; Biddulph, P. ...
Monthly notices of the Royal Astronomical Society,
12/2008, Letnik:
391, Številka:
4
Journal Article
Recenzirano
Odprti dostop
The Arcminute Microkelvin Imager is a pair of interferometer arrays operating with six frequency channels spanning 13.9–18.2 GHz, for observations on angular scales of 30 arcsec–10 arcmin and for ...declinations greater than −15°; the Small Array has a sensitivity of 30 mJy s−1/2 and the Large Array has a sensitivity of 3 mJy s−1/2. The telescope is aimed principally at Sunyaev–Zel'dovich imaging of clusters of galaxies. We discuss the design of the telescope and describe and explain its electronic and mechanical systems.
We present gas constraints from Sunyaev-Zel'dovich (SZ) effect measurements in a sample of 11 X-ray and infrared (IR) selected galaxy clusters at z>=1, using data from the Sunyaev-Zel'dovich Array ...(SZA). The cylindrically integrated Compton-y parameter, Y, is calculated by fitting the data to a two-parameter gas pressure profile. Where possible, we also determine the temperature of the hot intracluster plasma from Chandra and XMM-Newton data and constrain the gas mass within the same aperture (r 2500) as Y. The SZ effect is detected in the clusters for which the X-ray data indicate gas masses above ~1013 M , including XMMU J2235 -- 2557 at redshift z = 1.39, which to date is one of the most distant clusters detected using the SZ effect. None of the IR-selected targets are detected by the SZA measurements, indicating low gas masses for these objects. For these and the four other undetected clusters, we quote upper limits on Y and M gas,SZ, with the latter derived from scaling relations calibrated with lower redshift clusters. We compare the constraints on Y and X-ray-derived gas mass M gas,X-ray to self-similar scaling relations between these observables determined from observations of lower redshift clusters, finding consistency given the measurement error.
ABSTRACT
We present a catalog of compact sources derived from the QUaD Galactic Plane
Survey. The survey covers ∼800 deg
2
of the inner galaxy
(|
b
| < 4°) in Stokes
I
,
Q
, and
U
parameters at 100 ...and 150 GHz,
with angular resolutions of 5 and 3.5 arcmin, respectively. Five hundred and
twenty-six unique sources are identified in
I
, of which 239 are
spatially matched between frequency bands, with 53 (234) detected at 100 (150)
GHz alone; 170 sources are identified as ultracompact H
ii
regions.
Approximating the distribution of total intensity source fluxes as a power law,
we find a slope of γ
S
, 100
= −1.8 ± 0.4 at 100 GHz
and γ
S
, 150
= −2.2 ± 0.4 at 150 GHz. Similarly, the
power-law index of the source two-point angular correlation function is γ
θ,
100
= −1.21 ± 0.04 and γ
θ, 150
= −1.25 ± 0.04. The total
intensity spectral index distribution peaks at α
I
∼
0.25, indicating that dust emission is not the only source of radiation produced
by these objects between 100 and 150 GHz; free–free radiation is likely
significant in the 100 GHz band. Four sources are detected in polarized
intensity
P
, of which three have matching counterparts in
I
. Three of the polarized sources lie close to the Galactic
center, Sagittarius A*, Sagittarius B2, and the Galactic Radio Arc, while the
fourth is RCW 49, a bright H
ii
region. An extended polarized source,
undetected by the source extraction algorithm on account of its ∼0.°5 size, is
identified visually, and is an isolated example of large-scale polarized
emission oriented distinctly from the bulk Galactic dust polarization.
We present measurements of the cosmic microwave background (CMB) radiation temperature anisotropy in the multipole range 2000 < < 3000 from the QUaD telescope's second and third observing seasons. ...After masking the brightest point sources our results are consistent with the primary Lambda CDM expectation alone. We estimate the contribution of residual (un-masked) radio point sources using a model calibrated to our own bright source observations, and a full simulation of the source finding and masking procedure. Including this contribution slightly improves the xi 2. We also fit a standard Sunyaev-Zel'dovich (SZ) template to the bandpowers and see no strong evidence of an SZ contribution, which is as expected for sigma 8 0.8.
In order to study inflationary cosmology and the Milky Way Galaxy's composition and magnetic field structure, Stokes I, Q, and U maps of the Galactic plane covering the Galactic longitude range 260 ...degree < l < 340 degree in three atmospheric transmission windows centered on 100, 150, and 220 GHz are presented. The maps sample an optical depth 1 less than or equal to AV less than or equal to 30, and are consistent with previous characterizations of the Galactic millimeter-wave frequency spectrum and the large-scale magnetic field structure permeating the interstellar medium. The polarization angles in all three bands are generally perpendicular to those measured by starlight polarimetry as expected and show changes in the structure of the Galactic magnetic field on the scale of 60 degree . The frequency spectrum of degree-scale Galactic emission is plotted between 23 and 220 GHz (including WMAP data) and is fit to a two-component (synchrotron and dust) model showing that the higher frequency BICEP data are necessary to tightly constrain the amplitude and spectral index of Galactic dust. Polarized emission is detected over the entire region within two degrees of the Galactic plane, indicating the large-scale magnetic field is oriented parallel to the plane of the Galaxy. A trend of decreasing polarization fraction with increasing total intensity is observed, ruling out the simplest model of a constant Galactic magnetic field orientation along the line of sight in the Galactic plane. A generally increasing trend of polarization fraction with electromagnetic frequency is found, varying from 0.5%-1.5% at frequencies below 50 GHz to 2.5%-3.5% above 90 GHz. The effort to extend the capabilities of BICEP by installing 220 GHz band hardware is described along with analysis of the new band.
QUaD is a bolometric CMB polarimeter sited at the South Pole, operating at frequencies of 100 and 150 GHz. In this paper we report preliminary results from the first season of operation (austral ...winter 2005). All six CMB power spectra are presented derived as cross spectra between the 100 and 150 GHz maps using 67 days of observation in a low foreground region of approximately 60 deg super(2). These data are a small fraction of the data acquired to date. The measured spectra are consistent with the ACDM cosmological model. We perform jackknife tests that indicate that the observed signal has negligible contamination from instrumental systematics. In addition, by using a frequency jackknife we find no evidence for foreground contamination.
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