KICP Seminars & Colloquia
KICP Seminars & Colloquia, Spring 2006
FRIDAY NOON SEMINARS
High Resolution Imaging of Cerenkov Light from Air Showers
Elizabeth Hays, The University of Chicago and Argonne National Laboratory
Above TeV energies, the cosmic-ray flux becomes prohibitively small for direct observations by balloon-borne detectors. However, large ground-based arrays cannot be used to identity the type of nucleus initiating an air shower on an event-by-event basis and so, the inferences of cosmic-ray composition depend heavily on simulations and have large uncertainties. The Cerenkov emission accompanying an air shower includes light from the primary nucleus passing through the upper atmosphere before the first interaction. This "direct" Cerenkov component is a very fast and compact signal that provides a measurement of the charge of the primary particle using an air Cerenkov telescope with sufficiently high angular and timing resolution. In addition to a precision measurement of composition at TeV energies, the ability to identify the type of particle generating an air shower has potential applications to ground-based gamma-ray observations, where cosmic-rays are a dominant background. The Track Imaging Cerenkov Experiment, TrICE, is a prototype instrument to test the use of a high resolution camera in a Cerenkov telescope and to look for the "direct" Cerenkov component of cosmic-ray-induced air showers. TrICE has been constructed at Argonne National Lab and is currently being commissioned. I will discuss the "direct" Cerenkov measurement and show some of the first data taken with TrICE this Spring.
Digging for new (Astro-)Physics in the old CMB
Niayesh Afshordi, Harvard University
The residents of KICP need little reminder that there is much more to CMB than the last scattering surface. The secondary anisotropies, even though a foreground to the high redshift universe, illuminate the nature of different astrophysical processes, and may even open a window to new physics on large scales. I start by summarizing different attempts to detect the Integrated Sachs-Wolfe (ISW) effect, and the constraints that they put on theories of dark energy, or modified gravity, including a theory which may only be distinguished from LCDM through its ISW signature. Turning focus onto small scales, I outline an optimized method to extract the SZ signature of the intracluster medium (ICM) from a low resolution CMB map (such as WMAP), in combination with an X-ray cluster catalog. I then report an 11sigma, model-independent detection of the SZ signal in the WMAP 3yr, and the resulting ICM pressure profile around the virial radius.
ASTRONOMY SPECIAL SEMINARS