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This Week at Physics

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Events on Thursday, January 24th, 2013

NPAC (Nuclear/Particle/Astro/Cosmo) Forum
AGN as Multi-Messenger Probes of the High-Energy Universe: Observations with the HAWC Observatory
Time: 2:00 pm
Place: 4274 Chamberlin Hall
Speaker: Asif Imran, Los Alamos National Lab
Abstract: Ground-based gamma-ray observatories have opened up a new window into the high-energy universe. To date, exciting results reported by experiments such as VERITAS, H.E.S.S., and Milagro include the the detection of photons from nearly 50 relativistic AGN jets at TeV energies. However, the picture of the universe beyond 1 TeV is far from complete. The origin and composition of the extra-galactic ultrahigh energy cosmic rays (UHECR) remains a central problems in astrophysics. Based on energy considerations, recent studies have argued that highly relativistic jets in AGNs are the best candidates for the sites of UHECR acceleration. Consequently, we may be able to observe >20 TeV emission from nearby AGN contrary to conventional models that predict significant attenuations of the source gamma-ray photons via the diffuse extragalactic background light. The High Altitude Water Cherenkov (HAWC) observatory, a next-generation ground-based particle shower detector will be sensitive to photon energies from 50 GeV to 100 TeV with angular resolution of 0.3 degrees at E> 1 TeV. HAWC's high duty cycle (~100%) and wide field of view (~2 sr) is ideal to test AGN as possible sites for the acceleration of UHECR. Furthermore, HAWC's observations of an orphan flare from AGN coupled with the detection of coincident neutrinos by the IceCube observatory with allow us to independently probe the acceleration of UHECR in AGN.

In this talk, I will give an overview of the mechanism for the production of high energy photons from UHECR-induced cascade emission along with an update on the current status of the HAWC observatory. I'll also present the sensitivity of the HAWC detector to TeV emission from AGN.
Host: Westerhoff
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WIPAC Seminar
Exploring Fundamental Physics with the Cosmic Microwave Background: New Results from the South Pole Telescope
Time: 3:30 pm
Place: 4421 Sterling Hall
Speaker: Bradford Benson, University of Chicago
Abstract: The cosmic microwave background (CMB) is revolutionizing our understanding of the Universe. The CMB is the most powerful piece of evidence that we live in a geometrically flat Universe, dominated by non-baryonic cold dark matter and dark energy. Even with this basic cosmological model established, there are still many outstanding questions: What is dark energy? What are the neutrino masses? Are there missing standard model particles that we can detect cosmologically? Did Inflation happen, and what physics was responsible for it? The CMB remarkably is imprinted with information regarding each of these questions. In addition, the mm-wave CMB data is opening a new window into the extragalactic sky, simultaneously providing large catalogs of massive galaxy clusters, high-redshift lensed galaxies, and other mm-wave bright sources. I will present recent results from the South Pole Telescope, a 10-meter mm-wavelength telescope which recently completed a survey of 2500 sq. deg. of the sky with unprecedented depth and angular resolution. In particular, I will highlight SPT measurements of the CMB power spectrum, the Sunyaev-Zel'dovich galaxy cluster catalog, and the cosmological implications of the SPT data, including its constraints on dark energy, the sum of the neutrino masses, and the number of relativistic particle species.

Note: this is a joint WIPAC Seminar - Astronomy Colloquium.

Host: Naoko Kurahashi Neilson
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