Stanford Astrophysics Tea-time Talks
TUESDAYS 11:00AM, 3RD FLOOR CONFERENCE ROOM, VARIAN HALL
FRIDAYS 10:30AM, 3RD FLOOR CONFERENCE ROOM, FRED KAVLI BUILDING, SLAC
The regular astro-ph coffee times (both on campus and at SLAC) consist of a discussion of recent hot papers and a short talk from a member of the group. The aims of this exercise are to raise awareness of each other's activities, and provide a stage for the presentation of interesting new results, an upcoming conference paper, or a particular problem that would best be tackled with help from other members of the group. By keeping the atmosphere friendly and informal, these talks hopefully help to improve communication across the group. The carrot is finding out what others are up to (and hopefully being entertained in the process). The stick is that everyone is expected to contribute at some point (List of potential speakers).
The rules are as follows:
To reiterate, some suggestions for what you might talk about are:
The teatime talks are organised and regulated by a benign dictatorship - this job is fairly taxing so the current incumbents will step down at the end of the 2006-2007 financial year. Until then, you can volunteer for a slot by emailing Steven, (sfuerst@stanford.edu) at any time, otherwise you'll be hearing from him shortly. David, as deputy dictator, will fill in from time to time.
In addition, the speakers and their colleagues are formally invited to join Pierre Schwob for lunch at the Faculty Club on Friday at 12:00. You should sign up yourself and your colleagues before Thursday evening.
Finally, this webpage contains the current
schedule.
| Date | Name | Title | Abstract |
|---|---|---|---|
| Plans for SuperCDMS 25 kg Experiment | Proposals are going in this fall for the SuperCDMS 25 kg Experiment to extend the search for dark matter WIMPs by a factor of 120 beyond our present sensitivity, or a factor of 15 beyond the expected reach of the current CDMS II project which ends in at end of 2007. This sensitivity reach is exciting scientifically since it explores a common region of supersymmetric parameters at the same time as the LHC. We have demonstrated the operation of the new one inch thick sub-Kelvin detectors which are fabricated at Stanford. | ||
| Hard X-ray Polarization Experiment, PoGOLite | High energy astronomical sources have been studied using their spectrum, time variability and projected image. For many sources, such observations alone do not identify the dominant emission mechanism and polarization measurements are expected to play the decisive role. Orientation of the polarization plane will probe the distribution of magnetic and radiation fields, as well as the distribution of matter around these sources. Strong X-ray and gamma-ray polarization can arise from synchrotron emission in ordered magnetic fields, photon propagation in extremely strong magnetic fields and anisotropic Compton scattering. Despite potential importance of polarization measurement, there has been only one significant polarization detection in the X-ray band (2.6 and 5.2 keV) from the Crab nebula with an instrument aboard the OSO-8 satellite. Because of its small effective area, the instrument could not detect polarization from the Crab pulsar. PoGOLite is designed to detect 10% polarization of a 100 mCrab source in one 6-hour balloon observation in the 25-100 keV energy range. After three rounds of prototyping and beam tests, production of the flight model polarimeter has began. The instrument will be completed in the fall of 2008 and the maiden flight is scheduled in 2009 spring to observe the Crab pulsar and Cygnus X-1. Our future plan includes series of long duration balloon flights from northern Sweden to North America. | ||
| Replace this line with your talk title | Replace this line with a (short) abstract | ||
| Replace this line with your talk title | Replace this line with a (short) abstract | ||
| Replace this line with your talk title | Replace this line with a (short) abstract | ||
| Can we measure properties of the relativitic outflow in GRBs with the GLAST data ? | I will describe recent published work with two collaborators suggesting that the GLAST LAT data can be combined with low energy measurements to constrain the GRB Lorentz Factor and the radius of emission of gamma rays. | ||
| MRI in Accretion Disks: The Shearing Box Approximation | tI will discuss how magnetorotational instabilities in accretion disks can amplify an initially small magnetic field. This effect can be studied from the simplified framework of a shearing box simulation, which simulates a local patch of an accretion disk. As MRI can effect any system with differential rotation, and therefore can be applied to not only accretion disks but type II supernovae collapse as well. | ||
| After GLAST | I will discuss potential science drivers and design optimizations for a high-energy gamma-ray space mission after GLAST, and the many challenges that such a mission would face. | ||
| The DAMA/LIBRA Result | Replace this line with a (short) abstract | ||
| Life at Caltech - Gravitational Lensing and Chaotic Orbits | I will an overview for two projects that I am currently working on. First I will describe the effects of gravitational lensing on the CMB and efforts to make the first measurement of the convergence power spectrum with the final ACBAR datasets. Second I will discuss an analytic solution to a limit of the three body problem that is applicable to the outer Solar System. Using these these analytic results I will show the regions of the outer Solar System that should be chaotic due to Neptune's influence. | ||
| The Three Faces of Omega_m: Testing Gravity with Low and High Redshift SN Ia Surveys | It has been recognised recently that peculiar velocities of galaxies hosting Type Ia supernovae generate a significant systematic effect in deriving the dark energy equation of state parameters w, at level of a few percent. Here we illustrate how the peculiar velocity effect in SN Ia data can be turned from a "systematic" into a probe of cosmological parameters. We assume a flat Lambda-Cold Dark Matter model (w=-1) and use low and high redshift SN Ia data to derive simultaneously three distinct estimates of the matter density Omega_m which appear in the problem: from the geometry, from the dynamics and from the shape of the matter power spectrum. We find that each of the three Omega_m's agree with the canonical value Omega_m=0.25 to within 1-sigma, for reasonably assumed fluctuation amplitude and Hubble parameter. This is consistent with the standard cosmological scenario for both the geometry and the the growth of structure. For fixed Omega_m = 0.25 for all three Omega_m's, we constrain gamma = 0.72 +/- 0.21 in the growth factor Omega_m(z)^gamma, so we cannot currently distinguish between standard Einstein gravity and predictions from some modified gravity models. Future surveys of thousands of SN Ia could significantly improve the above tests. | ||
| Gamma-ray albedo of small solar system bodies and GLAST science | We calculate the gamma-ray albedo flux from cosmic-ray (CR) interactions with the solid rock and ice in Main Belt asteroids (MBAs), Jovian and Neptunian Trojan asteroids, and Kuiper Belt objects (KBOs) using the Moon as a template. We show that the gamma-ray albedo for the Main Belt, Trojans, and Kuiper Belt strongly depends on the small-body size distribution of each system. Based on an analysis of the Energetic Gamma Ray Experiment Telescope (EGRET) data we infer that the diffuse emission from the MBAs, Trojans, and KBOs has an integrated flux of less than ~6x10^{-6} cm^{-2} s^{-1} (100-500 MeV), which corresponds to ~12 times the Lunar albedo, and may be detectable by the forthcoming Gamma Ray Large Area Space Telescope (GLAST). If detected by GLAST, it can provide unique direct information about the number of small bodies in each system that is difficult to assess by any other method. Additionally, the KBO albedo flux can be used to probe the spectrum of CR nuclei at close-to-interstellar conditions. The orbits of MBAs, Trojans, and KBOs are distributed near the ecliptic, which passes through the Galactic center and high Galactic latitudes. Therefore, the asteroid gamma-ray albedo has to be taken into account when analyzing weak gamma-ray sources close to the ecliptic, especially near the Galactic center and for signals at high Galactic latitudes, such as the extragalactic gamma-ray emission. The asteroid albedo spectrum also exhibits a 511 keV line due to secondary positrons annihilating in the rock. This may be an important and previously unrecognized celestial foreground for the INTErnational Gamma-Ray Astrophysics Laboratory (INTEGRAL) observations of the Galactic 511 keV line emission including the direction of the Galactic center. | ||
| Evidences for an intermediate mass black hole in omega Centauri | I will present photometric and spectroscopic measurements for the central region of omega Centauri, as well as models that support the existence of a 40,000 solar mass black hole at the center of this cluster. | ||
| Gamma-ray pulsars and pulsar wind nebulae | Replace this line with a (short) abstract | ||
| Cosmological Constraints from the Observed Growth of X-ray Luminous Galaxy Clusters | I will briefly review my recent work deriving cosmological constraints from the growth of structure (read: repeat my talk from the HEAD meeting last week). Time permitting, I will go into greater detail on the important systematics for this experiment and the prospects for improving on them. | ||
| Importance Sampling for Finding Confidence Contours | I will discuss two algorithms for performing parameter space explorations, Metropolis-Hastings Markov Chain Monte Carlo and Importance Sampling, and their relative strengths and weaknesses in constructing contour plots in the limit where computation time is dominated by evaluating the likelihood. I will also present a hybrid algorithm which may be an improvement on traditional MCMC methods for finding confidence contours. Time permitting, I will conclude with some ultra-preliminary results. | ||
| Cosmological Parameters from Cosmic Shear - Including cosmology | In recent years weak lensing by the large-scale structure of the Universe, called cosmic shear, has become a valuable probe in cosmology. Large upcoming surveys like KIDS and Pan-STARRS will improve the quality of cosmic shear data significantly, enabling us to measure its signal with less than 1% statistical error. In order to obtain cosmological parameters from these high precision data properly, there remain issues to address. On the observational side, the systematic errors, mainly from insufficient PSF-correction, must be reduced and a possible contribution to the shear signal coming from intrinsic alignment must be excluded. On the theoretical side, we need accurate predictions for P_delta(k) and a precise method for the inference on cosmological parameters. In this talk I will briefly review the basics of cosmic shear, especially how to constrain cosmological parameters. I will focus on the impact of cosmic shear covariances on the parameter estimation, addressing the assumption of a covariance which is constant in parameter space, how this influences the likelihood contours and how to improve on this. Finally, I will quantify the difference between Gaussian and non-Gaussian covariances and the importance of the ellipticity shape noise for the latter case. | ||
| AMiBA: First-Year Results for Sunyaev-Zel'dovich Effect | AMiBA is an interferometric experiment designed to study cosmology through the observation of the anisotropy in Cosmic Microwave Background (CMB). In 2007 it focuses on the observation of galaxy clusters via the Sunyaev-Zel'dovich (S-Z) effect. Currently AMiBA operates at 86-104 GHz with 7 close-packed antennas of 60 cm in diameter giving a synthesized resolution of 6 arcminutes. In this talk, we will report the results of the first-year observation in 2007 on several massive low-redshift (0.08 < z < 0.33) clusters, including their images and preliminary science results. Data analysis and possible systematic effects will be also addressed. We will also discuss the prospects of the expanded AMiBA that will start operating in 2009. | ||
| Global X-ray Spectral Formation in HMXB Vela X-1 | Replace this line with a (short) abstract | ||
| Gravitational Wave Detection with Atom Interferometry | I will discuss an atom interferometer configuration that can detect gravitational waves. The terrestrial version of the experiment could be sensitive to gravitational waves from solar mass binaries out to megaparsec distances in the 1 Hz - 10 Hz band. The satellite experiment probes the same spectrum as LISA with comparable sensitivity. Each configuration compares two widely separated atom interferometers run using common lasers. The effect of the gravitational waves on the propagating laser field produces the main effect in this configuration and enables a large enhancement in the gravitational wave signal while significantly suppressing many backgrounds. The use of ballistic atoms as inertial test masses improves systematics coming from vibrations and acceleration noise, and reduces spacecraft control requirements. | ||
| A Hierarchical Markov Chain Monte Carlo Method for Confidence Contours | Monte Carlo Markov Chains (MCMCs) are in wide use among astronomers today to determine probability distributions for cosmological parameters. However, by virtue of the fact that most of the points in the chain are in high-probability regions, one must use a large chain length in order to accurately determine two-sigma or higher confidence contours in low-probability regions. This talk presents a method of joining together multiple short-length MCMCs which reduces the computational burden to find a 99% confidence contour by an order of magnitude or more. | ||
| Suzaku observation of TeV blazar 1ES 1218+304: clues on particle acceleration in an extreme TeV blazar | We observed a TeV blazar 1ES 1218+304 with an X-ray astronomy satellite Suzaku in 2006 May as a part of a multi-wavelength campaign in X-ray/TeV gamma-ray bands (Suzaku-MAGIC-Swift). At the beginning of the two-day continuous observation, we detected a large flare, in which the 2-10 keV flux changed by a factor of 2 on a timescale of 5×10^4 sec. During the flare, the increase in the hard X-ray flux clearly lagged behind that observed in the soft X-rays, with the maximum lag (2.5±0.7)×10^4 sec observed between 0.3-1 keV and 5-10 keV. Furthermore we discovered that the temporal profile of the flare clearly changes with energy, being more symmetric at higher energy band. Ascribing the energy dependent variability to differential acceleration timescale of relativistic electrons, we estimate the magnetic field B~0.05 G with a gyro-factor ?~ 1.0×10^5. Interestingly, this is in good agreement with an independent estimate through the spectral fitting of multi-wavelength data assuming a one-zone, homogeneous synchrotron self-Component model. We obtained B~0.05 G, emission region size R~3.0×10^16 cm for an appropriate beaming with a Doppler factor of ?=20. | ||
| New WIMP-exclusion results from CDMS | The CDMS II experiment is performing a direct search for Weakly Interacting Massive Particles (WIMP) dark matter candidates at the Soudan mine, Minnesota. A new exclusion WIMP limit will be reported that is both a world leader above 42 GeV/c2 WIMP mass for scalar-like WIMP-nucleon interactions, and excludes some interesting Minimal SuperSymmetry Model (MSSM) parameter space for interpreting a WIMP as the lightest supersymmetric particle (LSP) in MSSM. http://arxiv.org/abs/0802.3530v1 | ||
| The correlation of ultra-high-energy cosmic rays with AGN found by the AUGER experimen | One of the most interesting recent scientific results in particle astrophysics was the announcement of the AUGER collaboration that they have found an anisotropy in the arrival direction of their ultra-high-energy cosmic ray sample. Furthermore they find these arrival directions correlated with the positions of nearby AGN. However, the statistical significance of the observation was relatively weak and the details of the analysis are important for interpretation of the results. Following the initial Science article a longer more detailed paper (astro-ph/0712.2843) was published by the AUGER collaboration. As well one can find several articles discussing the nature and implications of this result. An overview of the results, discussions and possible implications for gamma-ray and neutrino astronomy will be presented. | ||
| Numerical Study on the Central Engine of Long GRBs | I have developed two numerical code to investigate the central engine of long GRBs: One is the newtonian code with some micophysics, and the other is the General Relativistic MHD (GRMHD) code without microphysics. As for the newtonian code, neutrino heating processes and magnetic fields are included in the ZEUS code to investigate the collapsar model. It is found that neutrino heating processes are insufficient to launch a jet in this study. A Jet is launched by magnetic fields, although this jet is non-relativistic at present. Simulations of the order of 10sec may be required to generate a powerful jet by special (general) relativistic MHD code. As for my GRMHD code, it has passed many test calculations. Now I am doing a preliminary simulation of a collapsar using my GRMHD code. In the future, I am planning to include some important microphysics into my GRMHD code and perform realistic simulations of collapsars. | ||
| Recent Results from the SDSS maxBCG Cluster Catalog |
The SDSS maxBCG cluster catalog contains nearly 14,000 clusters in the redshift range 0.1 |
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| Prospects for Direct Dark Matter Searches with Argon | Direct searches for WIMP Dark Matter are se poised for a quantum leap in sensitivty. The new generation of liquid noble gas detectors promises to increase the sensitivity of direct dark matter searches by many orders of magnitude in the next five years. I will discuss recent results with a 3-kg detector and prospects of the WARP 150-kg liquid argon currently under construction at Gran Sasso. I will also report on the recent discovery of the Princeton group of a first source of underground argon depleted in the cosmogenic 39Ar. This discovery opens a possibility for the construction of multi-ton argon-based detectors, capable of exploring a very broad range of WIMP Dark Matter candidates suggested by SUSY theories, with sensitivity to the WIMP-nucleon cross section extending below 10^-10 pbarn and sensitivity for the WIMP mass up to many TeV's. | ||
| Wide-band Observation of Gamma-ray Bursts with the Suzaku/WAM and GLAST | I will give the observational results of Gamma-ray Bursts (GRBs) with the Suzaku Wide-band All-sky Monitor (Suzaku/WAM), and describe the plan of the WAM/GLAST joint analysis as my current work. We can perform a wide-band spectroscopy with a good statistics up to the MeV energy band by using the WAM data, and we have revealed many spectral properties of prompt emission of GRBs. GLAST data will allow us to perform wider spectral analysis up to the GeV energy region. Combining the WAM data and GLAST, we will be able to impose a tighter constraint to the MeV-GeV high energy emission component from GRBs. | ||
| Complex Structures and High Energy Emission in Pulsar Wind Nebulae | I will outline some of the basic processes of pulsar wind nebulae (PWNe), and what can be learned from studying these systems. PWN are responsible for much of the galactic GeV and TeV emission and as such are of great interest with coming of GLAST and new generations of ground based Cherenkov telescopes. I will conclude with a brief case study of the PWN surrounding pulsar J2021 +3651. | ||
| The Evolution of Black Hole Mass and Spin in Active Galactic Nuclei | I will review and ask questions regarding recent estimates and simulations of the growth of black hole masses and evolution of spins thought to occur at high redshift. | ||
| Projects to Work on While Watching HEPL be Destroyed | I will give an overview of some of the projects I'm currently working on, including the production of mock galaxy catalogs for the DES survey, a large suite of cosmological N-Body simulations for generating statistics of dark matter halo properties, and the connection between halos accretion history and density profile. | ||
| A New Apparatus for Detecting Micron-Scale Deviations from Newtonian Gravity David M Weld, Jung Xia, Blas Cabrera, Aharon Kapitulnik | We describe the design and construction of a new apparatus for detecting or constraining deviations from Newtonian gravity at short length scales. The apparatus consists of a new type of probe with rotary mass actuation and cantilever-based force detection which is used to directly measure the force between two micromachined masses separated by tens of microns. We present the 1st data from the experiment, and discuss the prospects of more precisely constraining or detecting non-Newtonian e ects using this probe. Currently, the sensitivity to attractive mass-dependent forces is equal to the best existing limits at length scales near 5 micron. No non-Newtonian effects are detected at that level. | ||
| The Numerics of Scattering in General Relativistic Radiative Transfer | I describe the problem of how to solve for the radiation field in presence of scattering. The talk is in two parts. The first describes radiative transfer in curved space time, and the development of the algorithm used to tackle this problem. The second half describes the computer science required to make that algorithm efficiently parallel. | ||
| Physical interpretation of the near-infrared colors of low redshift galaxies. | Replace this line with a (short) abstract | ||
| Getting Weak Lensing Predictions Ready for Next-Generation Surveys | Weak lensing tomography is expected to become an extremely powerful probe of dark energy. The high precision of upcoming weak lensing experiments such as SNAP or LSST will require theorists to produce equally precise predictions of weak lensing statistics. I will discuss the validity of several common approximations in calculating weak lensing power spectra. In particular, surveys may be biased if they neglect the fact that galaxy ellipticity measures not shear but "reduced shear". The reduced shear correction may also have important consequences for weak lensing's ability to provide "purely geometrical" dark energy measurements, i.e. measurements that are insensitive to the cosmic matter distribution. | ||
| Visualizing and Information Mining of High Dynamic Range Adaptive Mesh Refinement Simulations | I'll give a quick overview over the software and techniques we have developed to deal with high dynamic range simulations. I will use a number of examples of simulations related to super massive black hole formation, star formation and galaxy formation to illustrate these tools and explain the type of questions we can address with them. | ||
| The "Death Star" Galaxy or FRII Radio Galaxy 3C 321 and its Companion | As an avid reader of news for nerds on Slashdot.org I came across this NASA press release on the FRII radio galaxy 3C 321. The Slashdot summary mentioned about the "Death Star" galaxy, as did the NASA press release. In this short talk I will discuss the radio galaxy 3C 321, describe its properties and explain why it was nicknamed the "Death Star" galaxy. Interestingly, 3C 321 does not have much in common with the Death Star in the Star Wars movies, but presumably the nickname gives average Joe a somewhat better insight into the concept of a jet and its destructive power. | ||
| How does galaxy morphology change? | I report our finding that the local environment set up by the nearest neighbor galaxy gives stong effects on the galaxy morphology. The probability for a galaxy to have an early morphological type depends critically on whether or not it is located within the virial radius of its neighbor. Large part of the morphology-local density relation is due to the effects of the nearest neighbor. We also found that galaxy luminosity depends on rho_n, and that more isolated galaxies are more likely to be recent merger products. We propose a scenario that a series of morphology and luminosity transformation occur through distant interactions and mergers, which results in the morphology-luminosity-local density relation. I will also add some recent findings on the environmental dependence of the activity of the type 2 AGNs. | ||
| Analysis Improvements For 2nd+3rd Season QUaD Data | The QUaD experiment recently published a measurement of the CMB temperature and polarisation power spectra from the 2005 observing season. With the second and third year data analysis almost complete, I will describe improvements in the analysis of this data and compare to the 2005 result. In particular I will focus on an interesting contamination mechanism that introduces a systematic polarised signal, and how we correct for it. | ||
| MHD turbulence in the intrastellar and intracluster medium. | Replace this line with a (short) abstract | ||
| Detecting non-virialized X-ray components in and around clusters of galaxies | We studied new Suzaku data and two archival XMM-Newton data sets of the cluster of galaxies Sérsic 159-03, which has a strong excess soft X-ray emission component. The Suzaku observation confirms the presence of the soft excess emission, but it does not confirm the presence of redshifted O VII lines in the cluster. We derived radial profiles and 2D maps which show that the soft excess emission has a strong peak at the position of the central cD galaxy and has no significant azimuthal variations. We concluded that the spatial distribution of the soft excess is neither consistent with the models of inter-cluster warm-hot filaments, nor with models of clumpy warm intra-cluster gas associated with infalling groups. Moreover, the XMM-Newton RGS observation does not show OVII line emission, which we would expect to see if the centrally peaked soft emission was of thermal origin. We concluded that a non-thermal model provides the best explanation for the observed properties of the soft excess in Sérsic 159-03. This non-thermal emission might be due inverse-Compton scattering of the cosmic microwave background photons on relativistic electrons. The total energy in relativistic electrons needed to explain the excess emission within the radius of 600 kpc does not exceed 1×10^61 erg, while the total thermal energy within the same radius is 3×10^63 erg. Furthermore, we discuss the prospects of a search for the missing baryons in the warm-hot phase of the inter-cluster filaments with the current instruments using pairs of clusters of galaxies, in which the filament connecting them has a favourable geometry. | ||
| Improved statistics for obtaining cosmological parameter constraints from the nonlinear matter power spectrum | I will describe and demonstrate a statistical framework for using limited numbers of N-body simulations to build a model for the sample variance distribution of the nonlinear matter and shear power spectra. It is well known that nonlinear evolution of the mass density field skews the sampling distribution away from Gaussian and can potentially change the cosmological information content. Our machinery is designed to make efficient use of tractable numbers of simulations to improve the accuracy of cosmological parameter constraints obtained from small-scale galaxy clustering and cosmic shear measurements. Our model retains the common assumption of a multivariate Normal distribution for the band-powers, but is extended to include the full parameter dependence of the power spectrum covariance matrix in the nonlinear regime. | ||
| Using Galaxies as Cosmic Tracers | A widely used cosmic mapping technique is to use galaxies as tracers of the underlying cosmic matter distribution. I will address some of the challenges of this method with SDSS measurements of galaxy bias that quantify its stochasticity and its dependence on scale, luminosity, and color. I will also present new tools I have developed for the MANGLE software package for managing angular masks of next-generation galaxy surveys and other cartographic applications that have recently been made publicly available. | ||
| From the very first PopIII stars to high redshift galaxies and quasars | Replace this line with a (short) abstract | ||
| Galaxy Mythology | Observational studies of the individual and collective properties of galaxies are coming in thick and fast. To keep pace, the galaxy formation model built originally at Durham University has recently been refined to incorporate advances in theories of galactic dynamics, star formation and the evolution of the ISM. This provides an ideal theoretical standpoint from which to review the compatibilty between the predictions based on the concordance cosmology and real galaxies. | ||
| Primordial black holes in the Dark Ages | I will discuss the effect of evaporating primordial black holes on the ionization history of the universe, with an emphasis on the limits derivable from future 21-cm observations of high-redshift neutral hydrogen. | ||
| The First Light Instrument on the Atacama Cosmology Telescope | I'll talk about CCAM, an instrument designed to map the CMB on the Atacama Cosmology Telescope (ACT) at 145 GHz. CCAM uses an 8x32 CCD-like camera of millimeter-wave TES bolometers. It employs new detector technology, read-out electronics, cold re-imaging optics, and cryogenics to obtain high sensitivity CMB anisotropy measurements. | ||
| Why X-ray Cosmology with Clusters needs Lensing | X-ray studies of clusters provide important constraints on cosmological parameters. Currently at higher redshifts (z ~ .3 - 1), systematic errors are dominated by uncertainties in mass measurements. Combined gravitational lensing data from ground and space of large surveys such as the Massive Cluster Survey (MACS) will allow us to bring these systematics under control. I will discuss where the x-ray systematic errors arise and how lensing will fix the problem. I will also briefly discuss my efforts to remove the 'black magic' stigma from weak lensing analyses. | ||
| Optimizing CDMS detectors | Replace this line with a (short) abstract | ||
| Polarization of Pulsar High-Energy Light Curves | Only a handful of gamma-ray pulse profiles are available, but some characteristics are already clear. Gamma-ray emission occurs in ~30-50% of the light curve, often with two distinct peaks, generally well separated from the radio pulsations. This implicates magnetospheric emission from well above the star surface, and several model geometries have been proposed to produce the pulses. Simulations of such models have been run, with light curves computed in the vacuum (Deutsch field) approximation. GLAST should provide many more high quality light curves to match, but additional probes of the geometry are important in resolving degeneracies in the models. Polarization is, of course, an excellent probe but is only available at lower energies. High quality optical data measured for the Crab pulsar by Kanbach and colleagues present the most detailed challenge. Synchrotron emission from the magnetospheric model can reproduce many of the complex polarization features seen in these data. This match is quite constraining, requiring emission anisotropies linked to the geometry. While many features have been successfully simulated, the quest for the perfect polarization curve continues... | ||
| Baryon Wiggles and Information Plateaux in Cosmological Power-Spectrum Covariance Matrices | When analyzing large-scale structure clustering data, it is essential for precision cosmology to use an accurate covariance matrix. I will discuss surprisingly large baryon acoustic oscillations (BAO's) in the covariance matrix of galaxy or matter power spectra. These slightly affect the precision of cosmological parameter estimation. As a bonus, these BAO's in the covariance matrix are potentially observable in themselves, but probably only at small significance from gigaparsec-scale redshift surveys. If time permits, I will also mention some work we have done concerning a plateau in cosmological information which exists on scales just smaller than linear. This plateau seems to come largely from cosmic variance in the number of large haloes in a given volume. | ||
| Searching for WIMP Lines with GLAST | I will present work in preparation for detecting gamma ray lines produced by WIMPS with GLAST. Implications of the gamma ray production method, "line theory", on the analysis timeline will be discussed. I will give an outline of the analysis procedure including the role of the LAT calorimeter and filtering software, and some ideas for statistical methods. Lastly, an instructive calculation of the GLAST sensitivity to lines from WIMP annihilation will be presented. | ||
| NeXT mission | The NeXT (New X-ray Telescope/Non-thermal Energy eXploration Telescope) mission has been proposed in Japan as a successor to the Suzaku mission. Two major scientific objectives include: study of dark energy through structure formation history and study of the high-energy non-thermal Universe (particle acceleration). The instrument design of the NeXT satellite is optimized to achieve the above science goals: a high resolution spectrometer (SXS) with an energy resolution better than 7 eV at iron, two hard X-ray imagers (HXI) with hard X-ray telescopes (HXTs) to achieve two orders of magnitudes of sensitivity improvement in the energy range from 10 keV up to 80 keV, two soft gamma-ray detectors (SGDs) with one order of magnitude better sensitivity in the 80-300 keV energy band, in addition to a soft X-ray telescope (SXT)/soft X-ray imager (SXI) for modest spectroscopy/imaging in the 0.1-10 keV energy band. The continuum sensitivity of the mission will reach several x10^(-8) photons/s/keV/cm^2 in the hard X-ray region and a few x 10^(-7) photons/s/keV/cm^2 in the soft gamma-ray region. Recently, the NeXT mission is approved by ISAS/JAXA for phase-A study. I will describe the science of the NeXT mission followed by the development of Si/CdTe detectors and ASICs (Application Specific Integrated Circuits) for HXI/SGD. | ||
| Quasi-Periodic Flares From Star-Accretion Disc Collisions | We propose a theory of relating the observed quasi-periodoic IR/X-ray signals at the Galactic center with the collisions between the accretion disc and stars orbiting around the Black Hole. When an orbiting star crashes into the black hole's accretion disc, part of the star's orbital energy is lost in the collision and transformed to radiation of a flare. As the star continues to orbit around the black hole, it hits the disc and produces the energetic flares repeatedly. Due the to precesion of the star's orbit and the bending of light near black hole, these signals will not be periodic but quasi-periodic. The features of the signals, such as the patten of the time divisions between two consecutive signals and the intensity profiles of them, can be affected by the following parameters: mass/spin of the black hole, disc structure, eccentricity of the star, star's distance from the black hole, inclination angle of the star's orbit, and the inclination of the observer w.r.t the spinning axis of the black hole. We will show simulation results of the star's orbit, the disc image, and the flux VS time plot of the observed signals. By comparing different stars' orbits around a Schwarzschild or a Kerr metric black hole and the corresponding flux's patten, we will come to see how the paramters of the star and black hole results in different features of the signals. Furthermore, we will show one case where the simulated results fit the observed IR signals in the Galactic center. | ||
| The prospects for constraining dark energy with future X-ray cluster gas mass fraction measurements | We examine the ability of a future X-ray observatory to constrain dark energy via measurements of the cluster X-ray gas mass fraction, fgas. We find that fgas measurements for a sample of ~500 hot, X-ray bright, dynamically relaxed clusters, to a precision of ~5 per cent, can be used to constrain dark energy with a Dark Energy Task Force (DETF) figure of merit of 20-50. Such constraints are comparable to those predicted by the DETF for other leading, planned dark energy experiments. A future fgas experiment will be preceded by a large X-ray or SZ survey that will find hot, X-ray luminous clusters out to high redshifts. Short `snapshot' observations with the new X-ray observatory should then be able to identify a sample of ~500 suitably relaxed systems. The redshift, temperature and X-ray luminosity range of interest has already been partially probed by existing X-ray cluster surveys which allow reasonable estimates of the fraction of clusters that will be suitably relaxed for fgas work. Our analysis uses a Markov Chain Monte Carlo method which fully captures the relevant degeneracies between parameters and facilities the incorporation of priors and systematic uncertainties in the analysis. We explore the effects of such uncertainties, for scenarios ranging from optimistic to pessimistic. We conclude that the fgas experiment offers a competitive and complementary approach to the best other planned dark energy experiments. In particular, the fgas experiment will provide tight constraints on the mean matter and dark energy densities, with a peak sensitivity for dark energy work at redshifts midway between those of supernovae and baryon acoustic oscillation/weak lensing/cluster number counts experiments. In combination, these experiments should enable a precise measurement of the evolution of dark energy. | ||
| Some speculation about Gamma-ray Bursts | Replace this line with a (short) abstract | ||
| Image Reconstruction for GLAST/LAT Data using EMC2 | A major challenge for the analysis of GLAST/LAT data will be the detection and characterization of sources of spatially extended gamma-ray emission. The major source of such emission seen by the LAT will be cosmic-ray interactions with the Galactic interstellar gas; and this Galactic diffuse component is itself is not well measured and must be modeled with considerable uncertainties. Discerning contributions from smaller structures such as supernova remnants or even collections of point sources in the presence of the much stronger Galactic diffuse emission will be quite difficult given the relatively limited angular resolution of the LAT and the expected low numbers of counts for sources near the detection limit. I will describe some on-going work on an image reconstruction method known as EMC2 that considers low-count Poisson data using a Bayesian multiscale framework. A key feature of this method is that it offers a means of assessing the significance of extended structures that are found via the posterior distribution of the parameters describing the null hypothesis; and because of the multiscale framework, EMC2 allows for differing levels of smoothness and structure at the various resolution scales of the underlying image, thereby addressing a problem faced by earlier reconstruction methods such as Richardson-Lucy. EMC2 has been applied to Chandra and EGRET data, and we are extending it to handle LAT data. | ||
| Self-Calibration and Assembly Bias in Galaxy Cluster Surveys | Galaxy cluster abundances are sensitive probes of cosmological parameters. Theoretically, the halo mass function and the halo bias are both sensitive to dark energy; observationally, the halo mass needs to be inferred from observable quantities (e.g. X-ray temperature and luminosity, SZ signal, optical richness, etc.). In self-calibration, we use information from both mass function and bias to calibrate the observable-mass distribution and to constrain dark energy. Previous analyses of self-calibration were all based on the assumption that halo bias depends on mass only. However, recent studies show that the halo bias also depends on the assembly history (the so-called "assembly bias") and other parameters which are correlated with this history. This extra dependence could affect the efficacy of self-calibration. In particular, if assembly bias exists in data but we ignore it, the cosmological parameters estimated from galaxy cluster surveys may be biased. We apply a modified Fisher matrix formalism to analyze the systematics caused by assembly bias. This talk will give a sense how large the systematics would be and under what circumstances the effect is important. | ||
| GALLEX-GNO Solar Neutrino Data | The GALLEX solar neutrino flux histogram looks bimodal, but that of the follow-on GNO experiment does not. Using a "bimodality index," I find that the GALLEX measurements really are bimodal, and the GNO measurements are not. The bimodality is strongest for a limited time interval, that coincides with an interval of strong periodic modulation that may be attributed to solar rotation. | ||
| Image formation studies for the LSST telescope and control of systematics for its weak lensing mission | I'll briefly review the weak lensing systematics issue and our control plan as it relates to LSST's promise to routinely provide immaculate imaging across its outrageous field-of-view. | ||
| I will describe a method for reconstructing event location in CDMS detectors. | Replace this line with a (short) abstract | ||
| HETDEX and BAO | Our HET colleagues are working up a massive fiber instrument to do a large survey for Ly-alpha emitters. The idea for this HET Dark Energy eXperiment is to measure the Baryon Acoustic Oscillations at z~1.8-3.7 and use these to constrain Lambda(z). How can they do this? What would the Instrument look like? Why use the HET? Who are the principal proponents? How long would it take? and What is the cost? I pose, and partially answer, these question in this brief review. | ||
| The LSST and Survey Science | I will review the various programs that are currently performing surveys and identify the survey projects which are planned. Emphasis will be placed on how the LSST fits into "Survey Astrophysics" | ||
| What I Did On My Summer Vacation: Fully Self-Consistent Protostellar Collapse From First Principles | I will present on the latest results from high-resolution simulations of cosmological initial conditions leading to the collapse of the first star in the universe. I follow these calculations well-beyond the point at which previous studies have terminated, and I will discuss the constraints these calculations place on the primordial initial mass function, as well as the future directions for this line of inquiry. Additionally, I will briefly present on the analysis methods I use for these enormous datasets, as well as the meta-simulational techniques I have used to introduce new physical an chemical models, many of which may have uses outside this domain. | ||
| Diskoseismology | I will summarize our analyses of the normal modes of oscillation of accretion disks around black holes (and neutron stars or white dwarfs); then compare them with the Reynolds and Miller simulations and with observations by RXTE. | ||
| Toward a handle on the low-energy end of the electron distribution in large-scale jets: The case of PKS 0637--752 | I present the results from a re-analysis of the Chandra X-ray spectrum of the kpc-scale jet in PKS 0637--752. In the scenario of inverse Compton scattering on the cosmic microwave background, the soft X-ray band is the best place to look for clues about the shape of the low-energy end of the electron distribution, specifically whether or not it cuts off at some minimum Lorentz factor. We find no such cut-off, but rather an excess of emission over that predicted by the radio observations and the extension of the higher-energy X-ray spectrum. An interpretation of this excess will be offered, but the audience is invited to actively participate in a discussion about its origin. | ||
| KIPAC Computing: Status, Resources & Future Plans | KIPAC's computing needs and capabilities have grown significantly within the overall SLAC computing system. I will briefly go over the current status and resources of KIPAC computing with the goal of bringing everyone up-to-date on what is available and where to get assistance. Finally I will sketch our plans (in progress) to update the visualization facilities in bldg 50. | ||
| Hough Transformations and You: How an image processing technique can help you identify contamination and pass jackknives. | Showing that QUaD's power spectra are free from contamination using jackknife tests is crucial to publishing the strongest possible result. One major source of contamination is the moon shining on parts of the focal plane, contaminating the half-day, single-channel polarization maps at levels under human perception. A standard image processing technique, the Hough transformation, can be used to identify contaminated channels on days when the moon is above the horizon and toss them out of the data set. This talk will be an example of an exercise in data analysis, and the technique presented should be both accessible and generally applicable by first year graduate students. | ||
| Spectral Energy Distributions of Infrared Bright Galaxies | The dusty infrared-bright galaxies now commonly dubbed as LIRGs and ULIRGs (luminous infrared galaxies and ultraluminous infrared galaxies) were discovered in large numbers by the IRAS satellite. Here, we use a new approach to study the SEDs of these galaxies. We calculate the infrared spectral energy distributions from simulations of major mergers and study the effect of AGN and starburst feedback on the evolution of the SED as a function of time. We find that feedback processes critically determine the evolution of the SED. In particular, AGN feedback is very effective at dispersing gas mass and rapidly injecting energy into the ISM. The observational signature of such powerful feedback is a warm SED. In general, simulations performed with AGN feedback have warmer spectra in the main outflow phases than (otherwise equivalent) simulations performed with starburst feedback. This suggests that the warm-cold IRAS classification of ULIRGs is naturally explained within the context of a dynamical model where AGN feedback disperses gas mass effectively to produce warm SEDs. | ||
| Testing gravity on cosmological scales | I will discuss our framework for testing gravity on cosmological scales using the relationship between metric perturbations and the cosmological matter distribution. This framework allows for a simple, observer friendly characterization of departures from the flat LCDM model. | ||
| Plasma suppression of large scale structure formation in the universe: Theory and simulation. | This talk will be shared by Pisin Chen and Alice Allafort. We point out that during the reionization epoch of the cosmic history, the plasma collective effect among the ordinary matter would suppress the large scale structure formation. The imperfect Debye shielding at finite temperature would induce a residual long-range electrostatic potential which, working together with the baryon thermal pressure, would counter the gravitational collapse. As a result the effective Jean's length, lambda-J-eff, is increased by a factor, lambda-J-eff/lambda-J=sqrt{8/5}, relative to the conventional one. For scales smaller than the effective Jean's scale the plasma would oscillate at the ion-acoustic frequency. The modes that would be influenced by this effect depend on the starting time and the initial temperature of reionization, but roughly lie in the range 0.5 h.Mpc^-1< k, which corresponds to the region of the Lyman-alpha forest from the inter-galactic medium. We predict that in the linear regime of density-contrast growth, the plasma suppression of the matter power spectrum would approach 1-(Omega-dm/Omega-m)^2 = 1-(5/6)^2 = 30%. We also report on our simulation results of this effect using the code GADGET. | ||
| Gamma-ray absorption in quasars: some theoretical perspectives | Replace this line with a (short) abstract | ||
| Turbulence Cascade and Damping in the MHD Regime and Beyond: Application to Solar Wind Magnetic Fluctuations | Using the diffusion approximation and the exact dispersion relation, we study the cascade and damping of turbulent plasma waves in the magnetohydrodynamic (MHD) regime and beyond. We test several approximations for the wave-wave coupling rate $\tau_W^{-1}$ to derive the cascade time and the diffusion coefficient. Different rates result in the same anisotropic cascade and Kolmogoroff spectra in the inertia range but somewhat different wave spectra beyond that. We also calculate anisotropic thermal damping and combined it with cascading in our numerical simulations. We found that the combined anisotropic effects from cascading and damping can produce the broken power-law wave spectra observed in the solar wind. The model suggests that the break frequency depends on turbulence level and Alfven velocity, which can be tested by further observations. | ||
| Updates on the Candidate Gamma-Ray Blazar Survey (CGRaBS) | CGRaBS is a survey of radio-selected candidate blazars that are likely to be detected by GLAST. The focus of our work is an optical campaign to secure redshifts and identifications for 1,625 sources. I will briefly summarize our sample selection and report on our progress. I will also subject you to gruesome images of horrifying violence toward stick figures. | ||
| Short flux variations in TeV blazars : what do we learn from them ? | The talk will be mostly based on the following two papers: Mrk 501: astro-ph/0702008 PKS 2155-304: astro-ph/0706797 | ||
| My talk title is "The search for dark matter satellites using GLAST LAT". | The cold dark matter model implies a significant number of as yet unobserved dark matter satellites in our galaxy. The spectra of these satellites have some distinct features. I will briefly talk about the GLAST LAT instrument and feasibility study for the indirect detection of dark matter satellites in the Milky Way using the GLAST LAT. | ||
| First use of a Hybrid Silicon Pin Array on the Sky | I recently took pictures with a 4K x 4K hybrid cmos visible imager at the Kitt Peak 2.1 meter telescope. I'll talk a little about some of the appealing and unappealing sides of these devices as compared to charge coupled devices and present some preliminary results for this particular detector. | ||
| Non-linear gravitational lensing in A1689 cluster and UDF | Replace this line with a (short) abstract | ||
| Testing for relaxed Galaxy Clusters | Researchers determine that galaxy clusters are relaxed by looking at their X-ray features. I will talk about the work being done to quantify this with various tests. | ||
| Solar and stellar dynamos | Solar and stellar activity is a result of complex interaction between magnetic field, turbulent convection and differential rotation in a star's interior. Magnetic field is believed to be generated by a dynamo process in the convection zone. It emerges on the surface forming sunspots and starspots. Localization of the magnetic spots and their evolution with the activity cycle is determined by large-scale interior flows. Thus, the internal dynamics of the Sun and other stars hold the key to understanding the dynamo mechanism and activity cycles. Recently, significant progress has been made for modeling magnetohydrodynamics of the stellar interiors and probing the internal rotation and large-scale dynamics of the Sun by helioseismology. Also, asteroseismology is beginning to probe interiors of distant stars. I'll briefly review key achievements and challenges in our quest to understand the basic mechanisms of solar and stellar activity. | ||
| Exoplanets: Past, Present and Future | I will briefly summarize our understanding of planets outside of our Solar System. Emphasis will be placed on recent discoveries. I will also discuss NASA's upcoming Kepler mission to search for extrasolar planets similar to Earth. | ||
| The relation between accretion rate and jet power in elliptical galaxies. | An ingredient in the recipe for galaxy formation ... | ||
| Renaissance of stellar winds in the quest for Cosmic Ray acceleration? | Recent (HESS J1023-575) and not-so-recent (TEV J2032+4130) VHE gamma-ray source detections supported the revival of the concept that Galactic Cosmic Rays might be accelerated, besides in supernova remnants, presumably in the winds of hot and massive stars as well. The respective gamma-ray observations are put in context of suggested MWL associations in order to shed light if current modeling allows us to conclude on the respective radiative particle population already. | ||
| Observing Cosmic Strings Via Lensing Pairs in Surveys | Observing a cosmic string would provide a window into super high energy (GUT) scales. Cosmic strings would produce two images of an source translated by a "deficit" angle which is proportional to the linear energy density of the string. Indirect studies constrain this angle to be less than 3". Previous observations of close pairs have led to significant excitement and eventual disappointment. I will discuss future work in observing close pairs to set competitive limits on string energies and densities. | ||
| Impromptu on DM burning neutrinos at the Galactic Center | In light of the renewed fashion of 'rough and tough' tea-time talks I will present some work in progress concerning DM Burners at the Galactic Center. DM annihilation 'catalyzed' from WIMP stellar capture can give rise to a (directional) neutrino signal comparable with the free-space annihilation one. | ||
| Highlights of recent observations of clusters of galaxies with Chandra | Replace this line with a (short) abstract | ||
| Measuring masses of black holes in active galaxies with megamasers | In my short talk, I will present a recent result regarding a new, precise measurement of mass of a black hole in active galaxy IC 2560, using megamaser techniques. | ||
| CMB Absolute Spectrum Measurements with the ARCADE 2 Experiment | Recent measurements of the spatial anisotropy and polarization of the Cosmic Microwave Background radiation (CMB) have yielded exciting and well publicized results. However, a third type of structure in the CMB, that of deviations in the overall absolute intensity vs. frequency spectrum from a blackbody form, encodes additional important cosmological and astrophysical information, and remains inconclusively studied. | ||
| Hypervelocity stars | I will talk about the mechanisms of ejecting hypervelocity stars by interactions with massive black holes at galactic centers. I will also talk about kinematics of hypervelocity stars and how they can be used as a diagnostic tool for constraining the triaxial shape of the Galactic halo potential, which is a generic prediction of the hierarchical, cold dark matter models of structure formation. | ||
| Coordinated LAT - Near IR Observations of AGN | I will describe a newly redesigned near IR camera, plans for mounting the camera on the Magdalena Ridge Observatory's 2.4-meter telescope, and capabilities for simultaneous NIR observations of AGN alerted by the GLAST/LAT, as well as GRB afterglows alerted by Swift and GLAST. | ||
| Galaxy Formation on AMR | One of the most fundamental challenges in astrophysics is understanding the process of galaxy formation. To fully model and comprehend galaxy formation with computers, we need very high resolution simulations, as it is consistent of numerous constituent micro-processes occurring on a very wide range of distance scales: from ~Mpc (distance between the galaxies) to ~few pc (star forming regions.) Now, thanks to the tremendous progress in computational resources and the help of parallel programming, we are poised to realize these kinds of simulations. I will first go through the basics of galaxy formation theory and several different approaches to galaxy simulations, and then present a way of putting galaxies on AMR (Adaptive Mesh Refinement) grids and following their collapse. I will also describe the possible future research topics that I will be able to explore by taking advantage of this AMR approach. | ||
| A connection between bulge properties and the color bimodality of galaxies | The global colors and structural properties of galaxies have recently been shown to follow bimodal distributions. Galaxies separate into a ``red sequence'' and a ``blue cloud''. Intermediate-type (Sa-Sbc) galaxies populate both regions. It has been suggested that this bimodality reflects the two-component nature of disk-bulge galaxies. However, it has now been established that there are two types of bulges: ``classical bulges'' that are dynamically hot systems resembling (little) ellipticals, and ``pseudobulges'', dynamically cold, flattened, disk-like structures that could not have formed via violent relaxation. We identify classical bulges and pseudobulges morphologically with HST images in a sample of nearby galaxies. Detailed surface photometry reveals that: (1) The red -- blue dichotomy is a function of bulge type: at the same $B/T$, pseudobulges are in globally blue galaxies and classical bulges are in globally red galaxies. (2) Bulge type also predicts where the galaxy lies in other dichotomous global structural parameters: global S\'ersic index and central surface brightness. (3) Hence, the red -- blue dichotomy is not due to decreasing bulge prominence alone, and the bulge type of a galaxy carries significance for the galaxy's evolutionary history. | ||
| What do we see from a hot neutron star's surface when we observe it from a distance? | Optical and kev x-ray emission from a hot, strongly magnetized, neutron star's surface must pass through regions of the star's magnetosphere where there could be cyclotron-resonant scattering of it by electrons and/or positrons. Significant relativistic electron-positron flow is expected even in the "closed field line" regions around neutron stars which sustain "open field line" accelerators. Scattering by the the associated pair-densities and velocities can give significant modifications of the energy distribution of the suface emission. It is proposed that these can account for a number of features of observed radiation which have generally been given quite different interpretations (eg. spectral "absorption"-line features, anomalously large optical emission areas in older pulsars and extremely small ones for thermal x-rays from many very young neuton stars). | ||
| Particle acceleration, magnetic field generation, and associated emission in relativistic jets | Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., active galactic nuclei (AGNs), gamma-ray bursts (GRBs), and Galactic microquasar systems usually have power-law emission spectra. Fermi acceleration is the mechanism usually assumed for the acceleration of particles in astrophysical environments. Recent PIC simulations using injected relativistic electron-ion (electro-positron) jets show that acceleration occurs within the downstream jet, rather than by the scattering of particles back and forth across the shock as in Fermi acceleration. Shock acceleration is a ubiquitous phenomenon in astrophysical plasmas. Plasma waves and their associated instabilities (e.g., the Buneman instability, other two-streaming instability, and the Weibel instability) created in the shocks are responsible for particle (electron, positron, and ion) acceleration. The simulation results show that the Weibel instability is responsible for generating and amplifying highly nonuniform, small-scale magnetic fields. These magnetic fields contribute to the electron's transverse deflection behind the jet head. The ``jitter'' radiation from deflected electrons has different properties than synchrotron radiation which is calculated in a uniform magnetic field. This jitter radiation may be important to understanding the complex time evolution and/or spectral structure in gamma-ray bursts, relativistic jets, and supernova remnants. | ||
| A Magnetic Bootstrap? | Some undeveloped ideas that may be relevant to the acceleration of PeV cosmic rays in supernova remnants and MHD in collisionless plasmas more generally will be described. | ||
| Status of EXO | I will review the status of double beta decay and flash a few photos describing the progress of the EXO detector | ||
| Spectroscopic CdZnTe Detectors | In recent years, CdZnTe has increased in use for x-ray detection due to its operation at room temperature. Yet, other material parameters impact the operation and resolution of such detectors. These material properties and their impact on resolution will be discussed along with techniques used to mitigate the impact on performance. | ||
| Relativistic flows with adaptive mesh refinement. | Astrophysical relativistic flow problems require high resolution three-dimensional numerical simulation. I will describe a new parallel three-dimensional code for simulation of special relativistic hydrodynamics using both spatially and temporally structured adaptive mesh refinement. I will discuss some preliminary results on 3d AGN jet and GRB simulation using this code. | ||
| The build-up of massive galaxies & the intracluster light since z=1. | Replace this line with a (short) abstract | ||
| Can Gamma-Ray Bursts be used as cosmological tools? | Discovery of many Gamma-Ray Bursts (GRBs) with high redshifts has open the possibility of testing cosmological models using GRBs as standard candles or correlations between a distant independent and a distant dependent variable. Under the light of the latest data, I will report on the feasibility of using GRBs for such analysis. The main conclusion is that, at this stage of our understanding of GRBs, care is required and many aspects of these sources must be examined before this question can be answered. In particular it will be shown that new observations are not fully consistent with the assumptions made earlier in using these properties of GRBs for global cosmological studies. One important question to be addressed is about the cosmological evolution of GRB properties. With the new data from SWIFT we can begin to investigate this aspect, by carefully taking into account the limiting sensitivity of the instruments. Some preliminary results from such an analysis will be presented. | ||
| Host Galaxy Subtraction and Spectra Diversity of SDSS-II Supernovae Survey Ia Sample | The SDSS-II Supernova Survey team have pursued extensive follow-up spectroscopy campaigns at a number of telescopes (especially HET, APO, WHT, Subaru, MDM, Keck, NTT and SALT). The observations to date (Fall 2006, 2006) have yielded spectra of several hundred SNe, focusing on type Ia's, but including classification spectra and synoptic monitoring of a variety of other supernova types, as well. The Ia data, in particular, allow us to explore the diversity of SN spectra and make connections with the SDSS-measured light curves. In our sample, dominated by supernovae at redshifts ~0.1-0.35, most spectra have significant contamination from the host galaxy, making host subtraction a critical step for the SN identification and subsequent spectral analysis. In this talk, I will briefly describe spectral results from 2005 and 2006, emphasizing our efforts to improve host galaxy subtraction with PCA and chi-square fitting methods and describing some spectral diversity in the SN Ia sample. | ||
| Time dependence of pair opacity in GRB internal shocks | I will discuss in slightly more details the current work that I am doing in collaboration with Jonathan Granot and Eduardo do Couto e Silva, which was summarized by Jonathan during his plenary talk at the 1st GLAST symposium, and which was also presented in the poster P16.6. | ||
| Automatic Quenching of High Ebergy Gamma-ray Sources by Synchrotron | We investigate evolution of a magnetized system, in which continuously produced high energy emission undergoes annihilation on a soft photon field, such that the synchrotron radiation of the created electron-positron pairs increases number density of the soft photons. This situation is important in high energy astrophysics, because, for an extremely wide range of magnetic field strengths (nano to mega Gauss), it involves gamma-ray photons with energies between 0.3 GeV and 30 TeV. We derive and analyze the conditions for which the system is unstable to runaway production of soft photons and ultrareltivistic electrons, and for which it can reach a steady state with an optical depth to photon-photon annihilation larger than unity, as well those for which efficient pair loading of the emitting volume takes place. We also discuss the application of our analysis to a realistic situation involving astrophysical sources of a broad-band gamma-ray emission. In particular, we point out the possibility for measuring magnetic field intensity in astrophysical objects by using the presented analysis. Particular case of sources close to active supermassive black holes is also briefly discussed. | ||
| Simulation of Cosmic Ray Acceleration, Propagation and Interaction for a 3D Toy Model SNR | Observations of non-thermal emission, from soft X-ray to TeV gamma rays, from a number of supernova remnants (SNRs) such as SN1006 and RXJ1713-3946 have been reported, suggesting that SNRs can be potential acceleration sites of Galactic cosmic rays with energies up to hundreds of TeV. This work aims to develop a realistic code capable of simulating particle acceleration, propagation and interaction in any given SNR environment, in 3 dimensions. By obtaining multi-waveband photon spectrum and emission profile from the code, we can compare with observations to gain insight into how these high energy photons are possibly produced in the SNR being studied. A toy model will be used to illustrate how this can be done. | ||
| Present status and future plans of the Cryogenic Dark Matter Search (CDMS) | Presently CDMS is part-way through the operation of the CDMS-II experiment, housed at the Soudan mine, Minnesota, and has released the most sensitive WIMP-nucleon cross-section exclusion limits to date. We report on the ongoing activites at Soudan, which include the operation of the full CDMS-II payload since mid-2006. The expected final reach of CDMS-II by the end of 2007 is a WIMP-nucleon cross-section sensitivity of 2.1 x10^-44 cm2, at a WIMP mass of 60 GeV/c2. To proceed further, we have proposed the SuperCDMS program. In the first phases, each detector element is 2.5 times thicker than the CDMS-II crystals, thus allowing the more rapid deployment of a larger payload. The first phase we have recently proposed for funding is the Detector Project which will deploy the new detectors at the Soudan mine, followed by a 25~kg experiment which will need to be performed at a site deeper than Soudan in order not to be limited by a muon-induced neutron background and reach a desired goal of 1.3x10^-45 cm. These cross-sections, and approximate WIMP mass determinations from the kinematics of discovery events, are of interest and are complimentary to Supersymmetry investigations at the LHC and future linear colliders. | ||
| Observational probes of early structure formation and reionization | The cosmic dark ages ended when the first stars and quasars formed, emitting radiation which altered the state of the intergalactic medium and eventually reionized the universe. Several direct observational probes of this epoch exist, among which are the redshifted 21-cm background and secondary anisotropies in the cosmic microwave background (CMB). I will present recent theoretical predictions for the imprint of early structure formation and reionization on both the CMB and the 21-cm background. In particular, I will focus on Ly-alpha pumping by the first sources and the CMB-21cm cross-correlation, ending with a brief discussion on the detectability of the predicted signals. | ||
| Large Separation Lensed Quasars | Large separation lensed quasars are a new class of strong lensing events which serve as a powerful probe of our universe. After briefly reviewing the science and history, I will describe our effort to find such lenses from the SDSS data, with a particular emphasis on a recent discovery of the largest separation (22.5 arcseconds) lensed quasar. | ||
| GLAST, Cygnus X-3, and maybe some other binaries | Cygnus X-3 is one of the most puzzling objects in the gamma-ray sky. In the early days of TeV astronomy, it was one of the two reliable sources that everyone saw. Newer, more sensitive, instruments can't see it. At ~100 MeV, COS-B didn't see it, but it was spectacularly bright for SAS II. EGRET split the difference with a detection at a moderate level. There is no optical data to help unravel its mysteries. What will GLAST see? What about other x-ray binaries? | ||
| SuZIE: on the Sky, and Dipoles | I will describe the Sunyaev-Zel'dovich effect and the recent commissioning of our new instrument, SuZIE-III, to study the effect. I'll also say a bit about one of measurement this and future instruments make possible: the measurement of the intrinsic dipole moment of the CMB, referenced to a frame of rest defined by the matter in the universe averaged over very large scales. | ||
| Status of the CDMS-II Experiment | The CDMS-II experiment upgrade to 5 towers is complete and has been taking commissioning data since late June. I will give a status report on the commissioning of the completed 5 tower experiment. |