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This Week at Physics

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Events on Thursday, April 17th, 2014

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
Detection of degree angular scale B-mode polarization with BICEP2/Keck Array
Time: 2:30 pm
Place: 5280 Chamberlin Hall
Speaker: Grant Teply, Caltech
Abstract: The BICEP2 experiment is a cosmic microwave background (CMB) polarimeter specifically designed to search for the signal of inflationary gravitational waves in the B-mode power spectrum around l=80. BICEP2 observed from the South Pole for three seasons from 2010 to 2012. Using its full 3-year CMB data set, we report an excess of B-mode power at the angular scales of interest, inconsistent with the null hypothesis at a significance of >5σ. The observed B-mode power spectrum is well-fit by a lensed-LCDM + tensor theoretical model with tensor/scalar ratio r=0.20+0.07−0.05. We will describe the BICEP2 instrument, observing strategy, data analysis, and results. We will also describe Keck Array, a successor to BICEP2, which is actively collecting sky data at both 100 and 150 GHz at high sensitivity for improved constraints on galactic foregrounds.
Host: Vandenbroucke
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Astronomy Colloquium
The Fermi Bubbles: Possible Nearby Laboratory for AGN Jet Activity
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Karen Yang, University of Michigan
Abstract: One of the most important discoveries of the Fermi Gamma-ray Space Telescope is the detection of two giant bubbles extending 50 degrees above and below the Galactic center (GC). The symmetry about the GC of the Fermi bubbles suggests some episode of energy injection from the GC, possibly related to past jet activity of the central active galactic nuclei (AGN). Thanks to the proximity to the GC, the Fermi Bubbles are excellent laboratories for studying cosmic rays (CRs), Galactic magnetic field, and AGN feedback in general. Using three-dimensional magnetohydrodynamic simulations that include relevant CR physics, I will show how leptonic AGN jets can explain the key characteristics of the Fermi bubbles and the spatially correlated features observed in the X-ray, microwave, and radio wavelengths. I will also discuss how we use our simulations in combination with the multi-wavelength data to obtain constraints on the composition of the Fermi bubbles.
Host: Robert Lindner
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