Last updated: 01/07/08
Friday,19th January, 10:30am, ISB102 - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

H.E.S.S. Observations of Active Galactic Nuclei

Wystan Benbow ( MPI, Heidelberg, Germany)

The unprecedented sensitivity of the H.E.S.S experiment, an array of four imaging atmospheric-Cherenkov telescopes located Namibia, has enabled many groundbreaking studies of the gamma-ray sky at energies exceeding 100 GeV. A large fraction of these studies (~30% of the total observation time) are focused on Active Galactic Nuclei (AGN). A detailed overview of the H.E.S.S. AGN program, its many important results, and future plans will be presented.

Friday, 26th January, 10:30am, ISB102 - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

Using the Latest X-ray to TeV Instruments to Probe Blazars, GRBs, and Cosmological Parameters

Abe Falcone (Penn State)

During the past two years, new instruments have driven the study of jets from gamma ray bursts (GRBs) and blazars to new levels. In space, Swift has been producing exciting new results since its launch on 2004 November 20. From the ground, MAGIC and HESS have more than doubled the number of known TeV sources, while probing new parameter space due to improved sensitivity down to ~100 GeV. Since VERITAS is now moving from an engineering mode to a science program involving the full array of telescopes, it is poised to make dramatic contributions to the study of jets that produce TeV emission. The launch of GLAST, which is anticipated for the end of the year, will lead to record numbers of high energy sources across a broad range of categories, with unmatched sensitivity. When used simultaneously, this suite of instruments will be excellent for studies of jets from blazars and GRBs. These studies and their implications on both the source properties and cosmological parameters will be discussed. The potential for future observatories will also be discussed.

Monday, 29th January, 10:30am, ISB102 - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

Stratified Quasar Winds Revealed

Sarah Gallagher (UCLA)

Quasars are notable for the luminous power they emit across decades in frequency from X-rays through the far-infrared; emission at different frequencies emerges from physical scales ranging from AUs to parsecs. Each wavelength regime thus offers a different line of sight into the accreting supermassive black hole and a separate probe of outflowing material. Therefore, obtaining a complete accounting of the physical characteristics and kinetic power of quasar winds requires a panchromatic approach. High energy observations in particular are quite powerful as X-rays probe all of the material along the line-of-sight to the inner accretion flow. I present a stratified wind picture based on a synthesis of multiwavelength research programs designed to elucidate the nature of mass ejection from quasars. These empirical constraints set important limits for theoretical modeling of quasar outflows as well as high energy emission.

Friday, 2nd February, 10:30am, ISB102 - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

The Origin of the Diffuse X-ray Emission from the Galactic Plane

Michael Muno (CALTECH)

At X-ray energies (0.5--10 keV), the Galactic plane appears on the sky as a ridge of "diffuse" emission. Some of this emission can be attributed to plasma that is produced in the remnants of recent supernovae. However, there remains a hot component of the ridge emission that is difficult to explain, because it appears to result from a 10^8 K plasma. Such a plasma is hotter than is observed from known supernova remnants. Moreover, it is too hot to be gravitationally bound to the Galaxy, and so would require an enormous energetic input to replenish as it adiabatically expands. This has inspired exotic explanations for its origin, including unusual particle acceleration processes in supernovae, and even heat input from dark matter annihilation. I will describe Chandra observations of the central regions of our Galaxy that address this problem. I will quantify the amount of flux emerging from the large population of white dwarfs accreting from binary companions at the Galactic center, and show that the remaining emission can be attributed to plasma heated in star forming regions, and to past activity of the supermassive black hole at the Galactic center, Sagittarius A*.

Friday, 9th February, 10:30am, ISB102 - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

Recent Results and Future Prospects of the Cryogenic Dark Matter Search

Richard Schnee (Case Western)

Weakly interacting massive particles (WIMPs) form an excellent candidate for the universe's non-baryonic dark matter. The CDMS experiment has achieved unequaled discrimination of WIMP-search backgrounds using germanium and silicon detectors cooled to 50 mK. Results from the experiment's first runs with about a kg of Ge at the Soudan Underground Laboratory have led to the world's lowest exclusion limits on the WIMP-nucleon scalar cross-section, ruling out a significant range of neutralino supersymmetric models. The current 4.5-kg run promises an increase in sensitivity of an order of magnitude. By scaling the experiment up to a ton mass and siting it deep, three additional orders of magnitude in sensitivity can be achieved. Operation of these novel detectors, results from the recent and current runs, and the prospects for WIMP discovery will be discussed.

Wednesday, 14th Feb, ISB102, 10:30am - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

X-Ray and Optical Flux Ratio Anomalies in Quadruply Lensed Quasars: Zooming in on Quasar Emission Regions

Dave Pooley (UC Berkley)

X-ray and optical observations of quadruply lensed quasars can provide a micro-arcsecond probe of the lensed quasar, corresponding to scale sizes of ~10^2-10^4 gravitational radii of the central black hole. This high angular resolution is achieved by taking advantage of microlensing by stars in the lensing galaxy. I will discuss X-ray observations of ten lensed quasars recorded with the Chandra X-ray Observatory as well as corresponding optical data obtained with either the Hubble Space Telescope or ground-based telescopes. These were analyzed in a systematic and uniform way with emphasis on the flux-ratio anomalies that are found relative to the predictions of smooth lens models. A comparison of the flux ratio anomalies between the X-ray and optical bands allows us to conclude that the optical emission regions of the lensed quasars are typically larger than expected from basic thin disk models by factors of ~3-30. I will also discuss how these same flux-ratio anomalies can be used to determine the amount of dark matter in the lensing galaxy.

Click to v iew animations from talk.

Tuesday, 20th Feb, 10:30am, ISB310

Detecting Diffuse Emission in the GLAST Era

Brian Baughman (SCIPP)

GLAST, due to launch in late 2007, is the next generation of space based gamma-ray detectors and will provide a significant improvement over previous experiments such as EGRET. Understanding of previous experiments as well as detailed knowledge of the performance characteristics of GLAST will be important for accurate diffuse gamma-ray measurements with GLAST. I have modified the detailed simulation and analysis framework developed for GLAST to be used with the EGRET geometry and low-level data. I will show the EGRET beam-test conditions are well reproduced. Additionally, I will show that a previously overlooked effect, which I have been able to treat with the more detailed simulation software, is important in estimating the EGRET experiment's response. Based on this work I will present a new estimate of the diffuse gamma-ray emission from the inner Galaxy made with EGRET data. GLAST will not only provide an improvement in basic performance characteristics it will also provide data products with more detailed information than previous experiments, I will discuss some possible uses for these new data.

Friday, 23rd February, 10:30am, ISB310

New limits on the density of the extragalactic background light in the optical to the far infrared from the spectra of all known TeV blazars

Daniel Mazin (Max-Planck-Institut fur Physik, Munich)

The diffuse extragalactic background light (EBL) in the UV to far IR wavelength regime carries important information about the galaxy and star formation history of the universe. The present level of the EBL is made up of the over all epochs integrated and, correspodingly to its formation epoch, redshifted electromagnetic radiation. Direct measurements of the EBL have proven to be a difficult task due to dominant foregrounds mainly from inter-planetary dust (zodiacal light) and it is not expected that the sensitivity of measurements will greatly improve over the next years. The observations of distant sources of TeV photons via Imaging Atmospheric Cherenkov Telescopes can provide an indirect measurement of the EBL: TeV photons are attenuated via pair production and the observed spectra therefore carry an imprint of the EBL. With assumptions about the source spectrum limits on the EBL can be derived. We adopted a grid scan on the EBL density using spline functions, which allowed us to test over 8 million different EBL shapes making the scan to be independent from any predefined shape between 0.8 and 80 microns. Here we present upper limits on the EBL density using spectra from all detected TeV blazars. Compared to previous studies, the derived limits are the strongest in the range between 3 and 60 microns so far.

Tuesday, 27th February, 10:30am, ISB310

Light Higgses and Dark Matter

Bob McElrath (UC Davis)

We review the evidence, methods of detection, and models for light particle dark matter. We focus on dark matter particle mass less than 5 GeV, since this is the range in which low-energy electron-positron colliders such as BaBar and Belle could produce dark matter. We present a specific supersymmetric theory which can accommodate this light dark matter, that is coincident with low fine-tuning. We also review the constraints and methods of detection for light Higgses, which can mediate the Standard Model-Dark Matter interaction in this region.
Abstract: TBA

Friday, 2nd March, 11:00am, ISB102 - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

Probing the Dark with Gravitational Lensing

Ted Baltz (SLAC)

Gravitational lensing probes the matter content of the universe directly, without the bias of mass-to-light ratio. A wide variety of lensing techniques can be brought to bear to study dark matter and dark baryons. First, gravitational microlensing can be used to study dark stellar-mass objects, including stellar remnants and even primordial black holes. It is known that roughly half of the baryons are missing in the local universe. These may reside in stellar remnants accessible to microlensing surveys. We discuss such surveys of the local group, local supercluster, and beyond. Second, lensing by galaxies and clusters directly probes the matter distribution in the universe. We discuss preliminary work in several directions: studying rare lens configurations that may appear in large samples of lenses, studying the substructure in galaxies, and studying large samples of galaxy-galaxy lenses going beyond measurements of the shear. Each technique can add to our knowledge of the cosmic matter distribution.

Tuesday, 6th March, 10:30am, ISB310

IceCube Design, Construction, and First Results

Spencer Klein ( Lawrence Berkeley National Laboratory)

The IceCube Neutrino Observatory is being built at the South Pole. It is designed to search for neutrinos from astrophysical objects. In particular, it will study the sources of high energy cosmic-rays. After introducing cosmic-rays and IceCube , I will present the status of construction and analysis, including some first results.

Friday, 9th March, 10:30am, ISB 310

The Highest Energy Emission from Short Gamma-Ray Bursts

Pablo Saz Parkinson (SCIPP)

Gamma-ray bursts (GRBs) have been known now for about 40 years. The recent launch of the Swift satellite has resulted in significant progress being made in understanding these powerful explosions. Nevertheless, almost as many questions are being raised by the new observations as have been answered. This talk will focus primarily on GRBs of short duration: what they are, their differences (and similarities) to the more common long duration GRBs, and their expected (or observed) emission at high energies. I will present the results of our search for very high energy emission from short GRBs using data from the Milagro observatory spanning the last seven years. Finally, I will briefly describe the prospects for the future.

Tuesday, 13th March, 10:30am, ISB310

MadGraph/MadEvent 4 - SUSY, 2HDM, new models and more!

Johan Alwall (SLAC)

I'll present the new version of MadGraph/MadEvent and how to use it, on-line and locally. New developments include the addition of several new models, including MSSM and 2HDM, on-the-fly hadronization and detector simulation and a new structure to facilitate the addition of new models. I'll show how you can easily add your own model, and discuss some very recent development efforts, such as matching of matrix element jet production and parton showers.

Wednesday, March 14th, 10:00am, ISB 102 - JOB TALK - Asst. Prof. High Energy Astrophysics / Particle Physics

Stefano Profumo (CALtech)

Probing Supersymmetric Baryogenesis: from Electric Dipole Moments to Neutrino Telescopes

We study supersymmetric models that include a viable dark matter candidate and that generate the observed baryon asymmetry of the Universe at the electro-weak phase transition. We focus on the possibility of probing these models with searches for the permanent electric dipole moment (EDM) of the electron, with direct and indirect dark matter searches, and with high energy colliders. We point out that the lightest neutralino might play a key role for the generation of both baryonic and dark matter. Current constraints on the flux of energetic neutrinos from the Sun already put significant bounds on the available parameter space. Detectable signals are predicted in EDM searches, future neutrino telescopes, ton-sized direct detection experiments as well as, possibly, at the Large Hadron Collider and at a future International Linear Collider. This ensamble of probes makes ours a testable framework for the origin of both the dark matter and the baryonic matter-antimatter asymmetry in the Universe.