Beecroft Institute for Particle Astrophysics and Cosmology

Abstract:

We describe the processing of data from the Low Frequency Instrument (LFI) used in production of the Planck Early Release Compact Source Catalogue (ERCSC). In particular, we discuss the steps involved in reducing the data from telemetry packets to cleaned, calibrated, time-ordered data (TOD) and frequency maps. Data are continuously calibrated using the modulation of the temperature of the cosmic microwave background radiation induced by the motion of the spacecraft. Noise properties are estimated from TOD from which the sky signal has been removed using a generalized least square map-making algorithm. Measured 1/f noise knee-frequencies range from 100mHz at 30GHz to a few tens of mHz at 70GHz. A destriping code (Madam) is employed to combine radiometric data and pointing information into sky maps, minimizing the variance of correlated noise. Noise covariance matrices required to compute statistical uncertainties on LFI and Planck products are also produced. Main beams are estimated down to the approx -10dB level using Jupiter transits, which are also used for geometrical calibration of the focal plane.

Abstract:

The escape fraction at infinity is evaluated for massless particles produced in collisions of weakly interacting particles accreted into a density spike near the particle horizon of an extremal Kerr black hole, for the case of equatorial orbits. We compare with the Schwarzschild case, and argue that in the case of extremal black holes, redshifted signatures can be produced that could potentially explore the physics of particle collisions at center of mass energies that extend beyond those of any feasible terrestrial accelerator. © 2011 The American Physical Society.

Abstract:

Here we present a number of improvements to weak lensing 3D power spectrum analysis, 3D cosmic shear, that uses the shape and redshift information of every galaxy to constrain cosmological parameters. We show how photometric redshift probability distributions for individual galaxies can be directly included in this statistic with no averaging. We also include the Limber approximation, considerably simplifying full 3D cosmic shear analysis, and we investigate its range of applicability. Finally we show the relationship between weak lensing tomography and the 3D cosmic shear field itself; the steps connecting them being the Limber approximation, a harmonic-space transform and a discretization in wavenumber. Each method has its advantages; 3D cosmic shear analysis allows straightforward inclusion of all relevant modes, thus ensuring minimum error bars, and direct control of the range of physical wavenumbers probed, to avoid the uncertain highly non-linear regime. On the other hand, tomography is more convenient for checking systematics through direct investigation of the redshift dependence of the signal. Finally, for tomography, we suggest that the angular modes probed should be redshift dependent, to recover some of the 3D advantages. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

We present the analysis of a new broad-band X-ray spectrum (0.6-180.0keV) of the radio-quiet quasar MR2251-178 which uses both Suzaku and Swift/Burst Alert Telescope data. In accordance with previous observations, we find that the general continuum can be well described by a power law with Γ= 1.6 and an apparent soft excess below 1keV. Warm absorption is clearly present, and absorption lines due to the Feunresolved transition array, FeL (Fexxiii-xxiv), Sxv and Sxvi are detected below 3keV. At higher energies, FeK absorption from Fexxv-xxvi is detected and a relatively weak (EW = 25+12-8eV) narrow FeKα emission line is observed (E= 6.44 ± 0.04keV) which is well modelled by the presence of a mildly ionized (ξ≲ 30) reflection component with a low reflection fraction (R < 0.2). At least five ionized absorption components with 1020≲NH≲ 1023 cm-2 and 0 ≲ logξ/ergcms-1≲ 4 are required to achieve an adequate spectral fit. Alternatively, we show that the continuum can also be fit if a Γ∼ 2.0 power law is absorbed by a column of NH∼ 1023cm-2 which covers ∼30 per cent of the source flux. Independent of which continuum model is adopted, the FeL and Fexxv Heα lines are well fit by a single absorber outflowing with vout∼ 0.14c. Such an outflow/disc-wind is likely to be substantially clumped (b∼ 10-3) in order to not vastly exceed the likely accretion rate of the source. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.

Abstract:

We present the results of a deep 300ks Chandra High Energy Transmission Grating (HETG) observation of the highly variable narrow-line Seyfert Type 1 galaxy NGC 4051. The HETG spectrum reveals 28 significant soft X-ray ionized lines in either emission or absorption; primarily originating from H-like and He-like K-shell transitions of O, Ne, Mg and Si (including higher order lines and strong forbidden emission lines from Ovii and Neix) plus high-ionization L-shell transitions from Fexvii to Fexxii and lower ionization inner-shell lines (e.g. Ovi). Modelling the data with xstar requires four distinct ionization zones for the gas, all outflowing with velocities <1000kms-1. A selection of the strongest emission/absorption lines appear to be resolved with full width at half-maximum (FWHM) of ~600kms-1. We also present the results from a quasi-simultaneous 350ks Suzaku observation of NGC 4051 where the X-ray Imaging Spectrometer (XIS) spectrum reveals strong evidence for blueshifted absorption lines at ~6.8 and ~7.1keV, consistent with previous findings. Modelling with xstar suggests that this is the signature of a highly ionized, high-velocity outflow (logξ= 4.1+0.2-0.1; vout~-0.02c) which potentially may have a significant effect on the host galaxy environment via feedback. Finally, we also simultaneously model the broad-band 2008 XIS+HXD (Hard X-ray Detector) Suzaku data with archival Suzaku data from 2005 when the source was observed to have entered an extended period of low flux in an attempt to analyse the cause of the long-term spectral variability. We find that we can account for this by allowing for large variations in the normalization of the intrinsic power-law component which may be interpreted as being due to significant changes in the covering fraction of a Compton-thick partial-coverer obscuring the central continuum emission. © 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS.