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Deviations of the observed cosmic microwave background (CMB) from the standard model, known as anomalies, are obviously highly significant and deserve to be pursued more aggressively in order to discover the physical phenomena underlying them. Through intensive investigation we have discovered that there are equally surprising features in the digits of the number $pi$, and moreover there is a remarkable correspondence between each type of peculiarity in the digits of $pi$ and the anomalies in the CMB. Putting aside the unreasonable possibility that these are just the sort of flukes that appear when one looks hard enough, the only conceivable conclusion is that, however the CMB anomalies were created, a similar process imprinted patterns in the digits of $pi$.
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We present results from a total of 459 repeated 3.1 GHz radio continuum observations (of which 379 were used in a search for transient sources) of the ELAIS-N1, Coma, Lockman Hole, and NOAO Deep Wide Field Survey fields as part of the Pi GHz Sky Survey (PiGSS). The observations were taken approximately once per day between 2009 May and 2011 April. Each image covers 11.8 square degrees and has 100 arcsecond FWHM resolution. Deep images for each of the four fields have rms noise between 180 and 310 uJy and the corresponding catalogs contain ~200 sources in each field. Typically 40 - 50 of these sources are detected in each single-epoch image. This represents one of the shortest cadence, largest area, multi-epoch surveys undertaken at these frequencies. We compare the catalogs generated from the combined images to those from individual epochs, and from monthly averages, as well as to legacy surveys. We undertake a search for transients, with particular emphasis on excluding false positive sources. We find no confirmed transients, defined here as sources that can be shown to have varied by at least a factor 10. However, we find one source which brightened in a single-epoch image to at least six times the upper limit from the corresponding deep image. We also find a source associated with a z = 0.6 quasar which appears to have brightened by a factor of about three in one of our deep images, when compared to catalogs from legacy surveys. We place new upper limits on the number of transients brighter than 10 mJy: fewer than 0.08 transients / sq. deg. with characteristic timescales of months to years; fewer than 0.02 / sq. deg. with timescales of months; and fewer than 0.009 / sq. deg with timescales of days. We also plot upper limits as a function of flux density for transients on the same timescales.
We present a numerical code to simulate maps of Galactic emission in intensity and polarization at microwave frequencies, aiding in the design of Cosmic Microwave Background experiments. This Python code builds on existing efforts to simulate the sky by providing an easy-to-use interface and is based on publicly available data from the WMAP and Planck satellite missions. We simulate synchrotron, thermal dust, free-free, and anomalous microwave emission over the whole sky, in addition to the Cosmic Microwave Background, and include a set of alternative prescriptions for the frequency dependence of each component that are consistent with current data. We also present a prescription for adding small-scale realizations of these components at resolutions greater than current all-sky measurements. The code is available at https://github.com/bthorne93/PySM_public.
An important, and potentially detectable, signature of a non-trivial topology for the universe is the presence of so called circles-in-the-sky in the cosmic microwave background (CMB). Recent searches, confined to antipodal and nearly antipodal circles, have however failed to detect any. This outcome, coupled with recent theoretical results concerning the detectability of very nearly flat universes, is sufficient to exclude a detectable non-trivial cosmic topology for most observers in the inflationary limit ($0< |Omega_{tot}-1| lesssim 10^{-5}$). In a recent paper we have studied the consequences of these searches for circles if the Universe turns out to be exactly flat ($Omega_{tot} = 1 $) as is often assumed. More specifically, we have derived the maximum angles of deviation possible from antipodicity of pairs of matching circles associated with the shortest closed geodesic for all multiply-connected flat orientable $3$-manifolds. These upper bounds on the deviation from antipodicity demonstrate that in a flat universe for some classes of topology there remains a substantial fraction of observers for whom the deviation from antipodicity of the matching circles is considerably larger than zero, which implies that the searches for circles-in-the-sky undertaken so far are not enough to exclude the possibility of a detectable non-trivial flat topology. Here we briefly review these results and discuss their consequences in the search for circles-in-the-sky in a flat universes.
We investigate the scientific impact of the Wide Field X-ray Telescope mission. We present simulated images and spectra of X-ray sources as observed from the three surveys planned for the nominal 5-year WFXT lifetime. The goal of these simulations is to provide WFXT images of the extragalactic sky in different energy bands based on accurate description of AGN populations, normal and star forming galaxies, groups and clusters of galaxies. The images are realized using a detailed PSF model, instrumental and physical backgrounds/foregrounds, accurate model of the effective area and the related vignetting effect. Thanks to this comprehensive modelization of the WFXT properties, the simulated images can be used to evaluate the flux limits for detection of point and extended sources, the effect of source confusion at very faint fluxes, and in general the efficiency of detection algorithms. We also simulate the spectra of the detected sources, in order to address specific science topics which are unique to WFXT. Among them, we focus on the characterization of the Intra Cluster Medium (ICM) of high-z clusters, and in particular on the measurement of the redshift from the ICM spectrum in order to build a cosmological sample of galaxy clusters. The end-to-end simulation procedure presented here, is a valuable tool in optimizing the mission design. Therefore, these simulations can be used to reliably characterize the WFXT discovery space and to verify the connection between mission requirements and scientific goals. Thanks to this effort, we can conclude on firm basis that an X-ray mission optimized for surveys like WFXT is necessary to bring X-ray astronomy at the level of the optical, IR, submm and radio wavebands as foreseen in the coming decade.
An apparatus to search for optical flashes in the sky is described. It has been optimized for gamma ray bursts (GRB) optical counterparts. It consists of 2x16 cameras covering all the sky. The sky is monitored continuously and the data are analysed on-line. It has self-triggering capability and can react to external triggers with negative delay. The prototype with two cameras has been installed at Las Campanas (Chile) and is operational from July 2004. The paper presents general idea and describes the apparatus in detail. Performance of the prototype is briefly reviewed and perspectives for the future are outlined.
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