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GLAST and Suzaku: Study on Cosmic-Ray Acceleration And Interaction in the Cosmos

Description: The Gamma-Ray Large Area Space Telescope (GLAST) is an international and multiagency mission scheduled for launch in the fall 2007. The Large Area Telescope (LAT), the primary instrument of the mission, will survey the high energy sky found to be very dynamic and surprisingly diverse by its predecessor the Energetic Gamma Ray Experiment Telescope (EGRET). GLAST-LAT will have a much improved sensitivity when compared with EGRET and extend the higher energy coverage to {approx} 300 GeV. The instrument is now mounted on the spacecraft and undergoing a suite of pre-flight tests. Data analysis software has been tried out by collaborators in two rounds of 'Data Challenges' using simulated observations including backgrounds. The instrument performance and observational data on selected sources presented here have been obtained through the Data Challenges in the collaborative efforts. There are features in the GLAST-LAT observation possibly unfamiliar to X-ray astronomers: (1) GLAST will operate mostly in the survey mode; (2) the foreground objects (gas, dust, and star-light) become gamma-ray sources; (3) multiple sources will be 'confused' because of the wide point-spread-function. The last two features will pose a challenge for analysis on extended Galactic sources such as supernova remnants and pulsar wind nebulae: multi-wavelength study with X-ray instruments like Suzaku and atmospheric Chrenkov telescopes will become essential to dig out the underlying physics.
Date: May 23, 2008
Creator: Kamae, T. & /KIPAC, Menlo Park /SLAC
Partner: UNT Libraries Government Documents Department

Constraints on the Low-Energy Cutoff in the Electron Distributionof the PKS 0637--752 Jet

Description: We re-analyze the Chandra X-ray spectrum of the kpc-scale jet in PKS 0637-752 to investigate the possible low energy cutoff in the relativistic electron spectrum producing the non-thermal radiation in the scenario of inverse Compton emission off the cosmic microwave background. This was among the first objects targeted by the Chandra Observatory and gives a unique opportunity to study the low energy X-ray emission free of contamination. As previously noted, the spectrum can be fit by a power law, with the slope predicted by the radio spectrum, modified by low energy absorption through the Galaxy as determined from the spectrum of the quasar core and by HI 21 cm observations. We report evidence for a broad excess of emission below 1 keV, but are unable to constrain the shape very well. If we assume that this soft excess is unrelated to the electron population responsible for the power law emission, and that the electron spectrum cuts off at an energy of {gamma}{sub min}m{sub e}c{sup 2}, then we must have {gamma}{sub min} ({Lambda}/10) {approx}< 75 due to the absence of any low energy turn-over in the X-ray spectrum. This predicts that the observed radio spectrum should extend unbroken down below 2 MHz for the estimated jet restframe magnetic field B = 10 {micro} G. In addition, the observed optical flux can be used to place a lower limit on {gamma}{sub min}; the constraint is not very strong, but does suggest that {gamma}{sub min} must be higher than 1 to avoid overproducing the optical emission. The implication of these limits on the jet luminosity is discussed. An alternative phenomenological description of the soft excess is offered where the low-energy end of the electron spectrum is modified to account for the excess.
Date: June 26, 2007
Creator: Mueller, M. & /SLAC /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Recent and Future Observations in the X-ray and Gamma-ray Bands: Chandra, Suzaku, GLAST, and NuSTAR

Description: This paper presents a brief overview of the accomplishments of the Chandra satellite that are shedding light on the origin of high energy particles in astrophysical sources, with the emphasis on clusters of galaxies. It also discusses the prospects for the new data to be collected with instruments recently launched--such as Suzaku--or those to be deployed in the near future, and this includes GLAST and NuSTAR.
Date: December 2, 2005
Creator: Madejski, Greg & /SLAC /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Multi-Scale Initial Conditions For Cosmological Simulations

Description: We discuss a new algorithm to generate multi-scale initial conditions with multiple levels of refinements for cosmological 'zoom-in' simulations. The method uses an adaptive convolution of Gaussian white noise with a real-space transfer function kernel together with an adaptive multi-grid Poisson solver to generate displacements and velocities following first- (1LPT) or second-order Lagrangian perturbation theory (2LPT). The new algorithm achieves rms relative errors of the order of 10{sup -4} for displacements and velocities in the refinement region and thus improves in terms of errors by about two orders of magnitude over previous approaches. In addition, errors are localized at coarse-fine boundaries and do not suffer from Fourier-space-induced interference ringing. An optional hybrid multi-grid and Fast Fourier Transform (FFT) based scheme is introduced which has identical Fourier-space behaviour as traditional approaches. Using a suite of re-simulations of a galaxy cluster halo our real-space-based approach is found to reproduce correlation functions, density profiles, key halo properties and subhalo abundances with per cent level accuracy. Finally, we generalize our approach for two-component baryon and dark-matter simulations and demonstrate that the power spectrum evolution is in excellent agreement with linear perturbation theory. For initial baryon density fields, it is suggested to use the local Lagrangian approximation in order to generate a density field for mesh-based codes that is consistent with the Lagrangian perturbation theory instead of the current practice of using the Eulerian linearly scaled densities.
Date: November 4, 2011
Creator: Hahn, Oliver; /KIPAC, Menlo Park; Abel, Tom & /KIPAC, Menlo Park /ZAH, Heidelberg /HITS, Heidelberg
Partner: UNT Libraries Government Documents Department

FIRST Winged And X-Shaped Radio Source Candidates

Description: A small number of double-lobed radio galaxies are found with an additional pair of extended low surface brightness 'wings' of emission giving them a distinctive 'X'-shaped appearance. One popular explanation for the unusual morphologies posits that the central supermassive black hole (SMBH)/accretion disk system underwent a recent realignment; in a merger scenario, the active lobes mark the post-merger axis of the resultant system (e.g., Merritt & Ekers 2002). However, this and other interpretations are not well tested on the few (about one dozen) known examples. In part to remedy this deficiency, a large sample of winged and X-shaped radio sources is being compiled for a systematic study. An initial sample of 100 new candidates is described as well as some of the follow-up work being pursued to test the different scenarios.
Date: May 30, 2007
Creator: Cheung, C.C.; /KIPAC, Menlo Park; Springmann, A. & /KIPAC, Menlo Park /Wellesley Coll.
Partner: UNT Libraries Government Documents Department

Demystifying an Unidentified EGRET Source by VHE gamma-ray Observations

Description: In a novel approach in observational high-energy gamma-ray astronomy, observations carried out by imaging atmospheric Cherenkov telescopes provide necessary templates to pinpoint the nature of intriguing, yet unidentified EGRET gamma-ray sources. Using GeV-photons detected by CGRO EGRET and taking advantage of high spatial resolution images from H.E.S.S. observations, we were able to shed new light on the EGRET observed gamma-ray emission in the Kookaburra complex, whose previous coverage in the literature is some-what contradictory. 3EGJ1420-6038 very likely accounts for two GeV gamma-ray sources (E>1 GeV), both in positional coincidence with the recently reported pulsar wind nebulae (PWN) by HESS in the Kookaburra/Rabbit complex. PWN associations at VHE energies, supported by accumulating evidence from observations in the radio and X-ray band, are indicative for the PSR/plerionic origin of spatially coincident, but still unidentified Galactic gamma-ray sources from EGRET. This not only supports the already suggested connection between variable, but unidentified low-latitude gamma-ray sources with pulsar wind nebulae (3EGJ1420-6038 has been suggested as PWN candidate previously), it also documents the ability of resolving apparently confused EGRET sources by connecting the GeV emission as measured from a large-aperture space-based gamma-ray instrument with narrow field-of-view but superior spatial resolution observations by ground-based atmospheric Cherenkov telescopes, a very promising identification technique for achieving convincing individual source identifications in the era of GLAST-LAT.
Date: April 17, 2007
Creator: Reimer, Olaf; /Stanford U., HEPL /KIPAC, Menlo Park; Funk, Stefan & /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

A Hard X-ray View on Two Distant VHE Blazars: 1ES 1101-232 and 1ES 1553+113

Description: TeV-blazars are known as prominent non-thermal emitters across the entire electromagnetic spectrum with their photon power peaking in the X-ray and TeV-band. If distant, absorption of -ray photons by the extragalactic background light (EBL) alters the intrinsic TeV spectral shape, thereby affecting the overall interpretation. Suzaku observations for two of the more distant TeV-blazars known to date, 1ES 1101-232 and 1ES 1553+113, were carried out in May and July 2006, respectively, including a quasi-simultaneous coverage with the state of the art Cherenkov telescope facilities. We report on the resulting data sets with emphasis on the X-ray band, and set into context to their historical behavior. During our campaign, we did not detect any significant X-ray or {gamma}-ray variability. 1ES 1101-232 was found in a quiescent state with the lowest X-ray flux ever measured. The combined XIS and HXD PIN data for 1ES 1101-232 and 1ES 1553+113 clearly indicate spectral curvature up to the highest hard X-ray data point ({approx} 30 keV), manifesting as softening with increasing energy. We describe this spectral shape by either a broken power law or a log-parabolic fit with equal statistical goodness of fits. The combined 1ES 1553+113 very high energy spectrum (90-500 GeV) did not show any significant changes with respect to earlier observations. The resulting contemporaneous broadband spectral energy distributions of both TeV-blazars are discussed in view of implications for intrinsic blazar parameter values, taking into account the {gamma}-ray absorption in the EBL.
Date: May 2, 2008
Creator: Reimer, A.; Costamente, L.; /Stanford U., HEPL /KIPAC, Menlo Park; Madejski, G.; /KIPAC, Menlo Park /SLAC; Reimer, O. et al.
Partner: UNT Libraries Government Documents Department

Flux and Photon Spectral Index Distributions of Fermi-LAT Blazars and Contribution to the Extragalactic Gamma-ray Background

Description: We present a determination of the distributions of gamma-ray flux - the so called LogN-LogS relation - and photon spectral index for the 352 blazars detected with a greater than approximately seven sigma detection threshold and located above {+-} 20{sup o} Galactic latitude by the Large Area Telescope of the Fermi Gamma-ray Space Telescope in its first year catalog. Because the flux detection threshold depends on the photon index, the observed raw distributions do not provide the true LogN-LogS counts or the true distribution of the photon index. We use the non-parametric methods developed by Efron and Petrosian to reconstruct the intrinsic distributions from the observed ones which account for the data truncations introduced by observational bias and includes the effects of the possible correlation among the two variables. We demonstrate the robustness of our procedures using a simulated data set of blazars and then apply these to the real data and find that for the population as a whole the intrinsic flux distribution can be represented by a broken power law of slopes -2.37 {+-} 0.13 and -1.70 {+-} 0.26, and the intrinsic photon index distribution can be represented by a Gaussian with mean 2.41 {+-} 0.13 and 1{sigma} width of 0.25 {+-} 0.03. We also find the intrinsic distributions for the sub-populations of BL Lac and FSRQs type blazars separately. We then calculate the contribution of blazars to the diffuse cosmic gamma-ray background radiation to be 28% {+-} 19%.
Date: December 9, 2011
Creator: Singal, J.; /KIPAC, Menlo Park /SLAC /Stanford U.; Petrosian, V.; /KIPAC, Menlo Park /SLAC /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.; Ajello, M. & /KIPAC, Menlo Park /SLAC /Stanford U.
Partner: UNT Libraries Government Documents Department

On the Energy Spectra of GeV/TeV Cosmic Ray Leptons

Description: Recent observations of cosmic ray electrons from several instruments have revealed various degrees of deviation in the measured electron energy distribution from a simple power-law, in a form of an excess around 0.1 to 1 TeV energies. An even more prominent deviation and excess has been observed in the fraction of cosmic ray positrons around 10 and 100 GeV energies. These observations have received considerable attention and many theoretical models have been proposed to explain them. The models rely on either dark matter annihilation/decay or specific nearby astrophysical sources, and involve several additional assumptions regarding the dark matter distribution or particle acceleration. In this paper we show that the observed excesses in the electron spectrum may be easily reproduced without invoking any unusual sources other than the general diffuse Galactic components of cosmic rays. The model presented here assumes a power-law injection of electrons (and protons) by supernova remnants, and evaluates their expected energy spectrum based on a simple kinetic equation describing the propagation of charged particles in the interstellar medium. The primary physical effect involved is the Klein-Nishina suppression of the electron cooling rate around TeV energies. With a very reasonable choice of the model parameters characterizing the local interstellar medium, we can reproduce the most recent observations by Fermi and HESS experiments. Interestingly, in our model the injection spectral index of cosmic ray electrons becomes comparable to, or even equal to that of cosmic ray protons. The Klein-Nishina effect may also affect the propagation of the secondary e{sup {+-}} pairs, and therefore modify the cosmic ray positron-to-electron ratio. We have explored this possibility by considering two mechanisms for production of e{sup {+-}} pairs within the Galaxy. The first is due to the decay of {pi}{sup {+-}}'s produced by interaction of cosmic ray nuclei with ambient protons. The second ...
Date: August 19, 2011
Creator: Stawarz, Lukasz; /KIPAC, Menlo Park /Jagiellonian U., Astron. Observ.; Petrosian, Vahe; /KIPAC, Menlo Park /Stanford U., Phys. Dept. /Stanford U., Appl. Phys. Dept.; Blandford, Roger D. & /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

FERMI view of the TeV blazar Markarian 421

Description: The high energy component of the TeV blazar Markarian 421 has been extensively studied since the beginning of the 90s, when the source was first detected at gamma-rays with EGRET and the Whipple Telescope, yet the source is still far from being understood. The high sensitivity, large dynamic range, and excellent time coverage of the Fermi Large Area Telescope (LAT), all representing significant advances over previous gamma-ray observations, will play a key role in the elucidation of the physical processes underlying the high energy emission of this blazar. In this presentation we show the results from almost 6 months (4 August 2008 to 20 January 2009) of observation with LAT. We report significant flux/spectral variability on a range of time scales from weeks to days, and an energy spectrum from 0.1 GeV to 300 GeV, overlapping with the energy ranges covered by the current generation of Cherenkov Telescopes. Results on the observations of the BLLac object Markarian 421 collected in the first months of operation of the Fermi satellite have been presented. Light curves on weekly and daily timescales have been shown, as well as the results of the spectral analysis in the energy range between 100 MeV and 300 GeV, covered for the first time by a satellite experiment overlapping the lower energy observations from Cherenkov telescopes on earth. These results are still preliminary and will be enriched and completed soon by a forthcoming publication. The results shown here demonstrate the great performance of Fermi-LAT to study the gamma-emission from Mrk421 (and blazars in general) over a large dynamic range and also on short timescales, which is expected to be of key importance for the study of the emission of the source in a coordinated way with other instruments covering other energy ranges.
Date: August 26, 2010
Creator: Paneque, D; /SLAC /KIPAC, Menlo Park; Raino, S.; /Bari Polytechnic /INFN, Bari; Chiang, J.; /SLAC /KIPAC, Menlo Park et al.
Partner: UNT Libraries Government Documents Department

Analysis Methods for Milky Way Dark Matter Halo Detection

Description: We present methods for the analysis of dark matter annihilation in the smooth halo of the Milky Way galaxy. We model the diffuse gamma-ray background using GALPROP, and model the halo using an NFW profile and the gamma-ray spectrum for WIMP pair annihilation. We plan to combine these models with the point source catalog and a simple model for the extragalactic gamma ray background. Using the downhill simplex method to converge on the maximum likelihood value, we can vary key parameters in these models and fit them to the gamma-ray data. Through the use of the Markov Chain Monte Carlo (MCMC) method we can then map out the likelihood as a function of the model parameters to estimate the correlated errors on these parameters.
Date: October 11, 2007
Creator: Sander, Aaron; Winer, Brian; Hughes, Richard; U., /Ohio State; Wai, Larry; /KIPAC, Menlo Park et al.
Partner: UNT Libraries Government Documents Department

Galaxy Mergers with Adaptive Mesh Refinement: Star Formation and Hot Gas Outflow

Description: In hierarchical structure formation, merging of galaxies is frequent and known to dramatically affect their properties. To comprehend these interactions high-resolution simulations are indispensable because of the nonlinear coupling between pc and Mpc scales. To this end, we present the first adaptive mesh refinement (AMR) simulation of two merging, low mass, initially gas-rich galaxies (1.8 x 10{sup 10} M{sub {circle_dot}} each), including star formation and feedback. With galaxies resolved by {approx} 2 x 10{sup 7} total computational elements, we achieve unprecedented resolution of the multiphase interstellar medium, finding a widespread starburst in the merging galaxies via shock-induced star formation. The high dynamic range of AMR also allows us to follow the interplay between the galaxies and their embedding medium depicting how galactic outflows and a hot metal-rich halo form. These results demonstrate that AMR provides a powerful tool in understanding interacting galaxies.
Date: June 22, 2011
Creator: Kim, Ji-hoon; /KIPAC, Menlo Park /Stanford U., Phys. Dept.; Wise, John H.; /NASA, Goddard; Abel, Tom & /KIPAC, Menlo Park /Stanford U., Phys. Dept.
Partner: UNT Libraries Government Documents Department

Inner-Shell Absorption Lines of Fe 6-Fe 16: a Many-Body Perturbation Theory Approach

Description: We provide improved atomic calculation of wavelengths, oscillator strengths, and autoionization rates relevant to the 2 -> 3 inner-shell transitions of Fe VI-XVI, the so-called Fe M-shell unresolved transition array (UTA). A second order many-body perturbation theory is employed to obtain accurate transition wavelengths, which are systematically larger than previous theoretical results by 15-45 mA. For a few transitions of Fe XVI and Fe XV where laboratory measurements exist, our new wavelengths are accurate to within a few mA. Using these new calculations, the apparent discrepancy in the velocities between the Fe M-shell UTA and other highly ionized absorption lines in the outflow of NGC 3783 disappears. The oscillator strengths in our new calculation agree well with the previous theoretical data, while the new autoionization rates are significantly larger, especially for lower charge states. We attribute this discrepancy to the missing autoionization channels in the previous calculation. The increased autoionization rates may slightly affect the column density analysis of the Fe M-shell UTA for sources with high column density and very low turbulent broadening. The complete set of atomic data is provided as an electronic table.
Date: January 17, 2006
Creator: Gu, Ming F.; /KIPAC, Menlo Park; Holczer, Tomer; Behar, Ehud; /Technion; Kahn, Steven M. et al.
Partner: UNT Libraries Government Documents Department

Application of a XMM-Newton EPIC Monte Carlo to Analysis And Interpretation of Data for Abell 1689, RXJ0658-55 And the Centaurus Clusters of Galaxies

Description: We propose a new Monte Carlo method to study extended X-ray sources with the European Photon Imaging Camera (EPIC) aboard XMM Newton. The Smoothed Particle Inference (SPI) technique, described in a companion paper, is applied here to the EPIC data for the clusters of galaxies Abell 1689, Centaurus and RXJ 0658-55 (the ''bullet cluster''). We aim to show the advantages of this method of simultaneous spectral-spatial modeling over traditional X-ray spectral analysis. In Abell 1689 we confirm our earlier findings about structure in temperature distribution and produce a high resolution temperature map. We also confirm our findings about velocity structure within the gas. In the bullet cluster, RXJ 0658-55, we produce the highest resolution temperature map ever to be published of this cluster allowing us to trace what looks like the motion of the bullet in the cluster. We even detect a south to north temperature gradient within the bullet itself. In the Centaurus cluster we detect, by dividing up the luminosity of the cluster in bands of gas temperatures, a striking feature to the north-east of the cluster core. We hypothesize that this feature is caused by a subcluster left over from a substantial merger that slightly displaced the core. We conclude that our method is very powerful in determining the spatial distributions of plasma temperatures and very useful for systematic studies in cluster structure.
Date: April 17, 2007
Creator: Andersson, Karl E.; /SLAC, /Stockholm U.; Peterson, J.R.; /Purdue U. /KIPAC, Menlo Park; Madejski, G.M. & /SLAC /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Can Astrophysical Gamma Ray Sources Mimic Dark Matter Annihilation in Galactic Satellites?

Description: The nature of the cosmic dark matter is unknown. The most compelling hypothesis is that dark matter consists of weakly interacting massive particles (WIMPs) in the 100 GeV mass range. Such particles would annihilate in the galactic halo, producing high-energy gamma rays which might be detectable in gamma ray telescopes such as the GLAST satellite. We investigate the ability of GLAST to distinguish between the WIMP annihilation spectrum and the spectrum of known astrophysical source classes. Focusing on the emission from the galactic satellite halos predicted by the cold dark matter model, we find that the WIMP gamma-ray spectrum is unique; the separation from known source classes can be done in a convincing way. We discuss the follow-up of possible WIMP sources with Imaging Atmospheric Cerenkov Telescopes. Finally we discuss the impact that Large Hadron Collider data might have on the study of galactic dark matter.
Date: November 1, 2006
Creator: Baltz, Edward A.; /KIPAC, Menlo Park; Taylor, James E.; U., /Waterloo; Wai, Lawrence L. & /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

The Impact of Theoretical Uncertainties in the Halo Mass Function and Halo

Description: We study the impact of theoretical uncertainty in the dark matter halo mass function and halo bias on dark energy constraints from imminent galaxy cluster surveys. We find that for an optical cluster survey like the Dark Energy Survey, the accuracy required on the predicted halo mass function to make it an insignificant source of error on dark energy parameters is {approx}1%. The analogous requirement on the predicted halo bias is less stringent ({approx}5%), particularly if the observable-mass distribution can be well constrained by other means. These requirements depend upon survey area but are relatively insensitive to survey depth. The most stringent requirements are likely to come from a survey over a significant fraction of the sky that aims to observe clusters down to relatively low mass, M{sub th}{approx} 10{sup 13.7} h{sup -1} M{sub sun}; for such a survey, the mass function and halo bias must be predicted to accuracies of {approx}0.5% and {approx}1%, respectively. These accuracies represent a limit on the practical need to calibrate ever more accurate halo mass and bias functions. We find that improving predictions for the mass function in the low-redshift and low-mass regimes is the most effective way to improve dark energy constraints.
Date: June 4, 2010
Creator: Wu, Hao-Yi; Zentner, Andrew R.; Wechsler, Risa H. & /KIPAC, Menlo Park /SLAC /Pittsburgh U. /KIPAC, Menlo Park /SLAC
Partner: UNT Libraries Government Documents Department

Annealing a Follow-up Program: Improvement of the Dark Energy Figure of Merit for Optical Galaxy Cluster Surveys

Description: The precision of cosmological parameters derived from galaxy cluster surveys is limited by uncertainty in relating observable signals to cluster mass. We demonstrate that a small mass-calibration follow-up program can significantly reduce this uncertainty and improve parameter constraints, particularly when the follow-up targets are judiciously chosen. To this end, we apply a simulated annealing algorithm to maximize the dark energy information at fixed observational cost, and find that optimal follow-up strategies can reduce the observational cost required to achieve a specified precision by up to an order of magnitude. Considering clusters selected from optical imaging in the Dark Energy Survey, we find that approximately 200 low-redshift X-ray clusters or massive Sunyaev-Zel'dovich clusters can improve the dark energy figure of merit by 50%, provided that the follow-up mass measurements involve no systematic error. In practice, the actual improvement depends on (1) the uncertainty in the systematic error in follow-up mass measurements, which needs to be controlled at the 5% level to avoid severe degradation of the results; and (2) the scatter in the optical richness-mass distribution, which needs to be made as tight as possible to improve the efficacy of follow-up observations.
Date: June 2, 2010
Creator: Wu, Hao-Yi; Rozo, Eduardo; Wechsler, Risa H. & /KIPAC, Menlo Park /SLAC /CCAPP, Columbus /KICP, Chicago /KIPAC, Menlo Park /SLAC
Partner: UNT Libraries Government Documents Department

A Southern Sky Survey with Fermi LAT and ASKAP

Description: We present the prospects for a future joint gamma-ray and radio survey of southern hemisphere sources using the Fermi Large Area Telescope (LAT) and the upcoming Australian Square Kilometre Array Pathfinder (ASKAP) radio telescope. ASKAP is a next generation radio telescope designed to perform surveys at GHz frequencies at a much higher survey speed than previous radio telescopes, and is scheduled to start engineering observations in 2011. The survey capabilities of both Fermi LAT and ASKAP are described, and the planned science surveys for ASKAP are summarized. We give some expected details of the Variable and Slow Transient (VAST) survey using ASKAP, which will search for transients on timescales from 5 seconds to years. Some observational properties of faint and transient sources seen at gamma-ray and radio wavelengths are summarized, and prospects and strategies for using ASKAP survey data for LAT source counterpart identification are summarized.
Date: April 29, 2010
Creator: Cameron, Robert A. & /SLAC /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department

Persistent Patterns in Accretion Disks

Description: We present a set of new characteristic frequencies associated with accretion disks around compact objects. These frequencies arise from persistent rotating patterns in the disk that are finite in radial extent and driven purely by the gravity of the central body. Their existence depends on general relativistic corrections to orbital motion and, if observed, could be used to probe the strong gravity region around a black hole. We also discuss a possible connection to the puzzle of quasi-periodic oscillations.
Date: April 3, 2006
Creator: Amin, Mustafa A.; Frolov, Andrei V. & /KIPAC, Menlo Park
Partner: UNT Libraries Government Documents Department