Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We present a comparison of two Suzaku X-ray observations of the nearby (z = 0.184), luminous (L bol∼ 1047 erg s-1) type I quasar, PDS 456. A new 125 ks Suzaku observation in 2011 caught the quasar during a period of low X-ray flux and with a hard X-ray spectrum, in contrast with a previous 190 ks Suzaku observation in 2007 when the quasar appeared brighter and had a steep (Γ > 2) X-ray spectrum. The 2011 X-ray spectrum contains a pronounced trough near 9 keV in the quasar rest frame, which can be modeled with blueshifted iron K-shell absorption, most likely from the He- and H-like transitions of iron. The absorption trough is observed at a similar rest-frame energy as in the earlier 2007 observation, which appears to confirm the existence of a persistent high-velocity wind in PDS 456, at an outflow velocity of 0.25-0.30c. The spectral variability between 2007 and 2011 can be accounted for by variations in a partial covering absorber, increasing in covering fraction from the brighter 2007 observation to the hard and faint 2011 observation. Overall, the low-flux 2011 observation can be explained if PDS 456 is observed at relatively low inclination angles through a Compton-thick wind, originating from the accretion disk, which significantly attenuates the X-ray flux from the quasar. © 2014. The American Astronomical Society. All rights reserved.

Abstract:

We investigate the capabilities of various stages of the SKA to perform world-leading weak gravitational lensing surveys. We outline a way forward to develop the tools needed for pursuing weak lensing in the radio band. We identify the key analysis challenges and the key pathfinder experiments that will allow us to address them in the run up to the SKA. We identify and summarize the unique and potentially very powerful aspects of radio weak lensing surveys, facilitated by the SKA, that can solve major challenges in the field of weak lensing. These include the use of polarization and rotational velocity information to control intrinsic alignments, and the new area of weak lensing using intensity mapping experiments. We show how the SKA lensing surveys will both complement and enhance corresponding efforts in the optical wavebands through cross-correlation techniques and by way of extending the reach of weak lensing to high redshift.

Abstract:

Measuring spectral distortions of the cosmic microwave background (CMB) is attracting considerable attention as a probe of high energy particle physics in the cosmological context, since primordial inflation explorer (PIXIE) and polarized radiation imaging and spectroscopy mission (PRISM) have recently been proposed. In this paper, CMB distortions due to resonant conversions between CMB photons and light axionlike particles (ALPs) are investigated, motivated by the string axiverse scenario which suggests the presence of a plenitude of light axion particles. The distortions due to resonant conversions have a frequency-independent shape, in contrast to μ and y distortions. Therefore, one can distinguish the distortions due to resonant conversions from μ and y distortions. Since these resonant conversions depend on the strength of primordial magnetic fields, constraints on CMB distortions can provide an upper limit on the product of the photon-ALP coupling constant g and the comoving strength of primordial magnetic fields B. Potentially feasible constraints from PIXIE/PRISM can set a limit gBâ‰210-16 GeV-1 nG for ALP mass mφâ‰210-14 eV. Although this result is not a direct constraint on g and B, it is significantly tighter than the product of the current upper limits on g and B. © 2013 American Physical Society.