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Articles 1 - 23 of 23
Full-Text Articles in Physical Sciences and Mathematics
Gravitational Wave Burst Source Direction Estimation Using Time And Amplitude Information, J. Markowitz, M. Zanolin, L. Cadonati, E. Katsavounidis
Gravitational Wave Burst Source Direction Estimation Using Time And Amplitude Information, J. Markowitz, M. Zanolin, L. Cadonati, E. Katsavounidis
Publications
In this article we study two problems that arise when using timing and amplitude estimates from a network of interferometers (IFOs) to evaluate the direction of an incident gravitational wave burst (GWB). First, we discuss an angular bias in the least squares timing-based approach that becomes increasingly relevant for moderate to low signal-to-noise ratios. We show how estimates of the arrival time uncertainties in each detector can be used to correct this bias. We also introduce a stand alone parameter estimation algorithm that can improve the arrival time estimation and provide root-sum-squared strain amplitude (h(rss)) values for each site. In …
A Three-Dimensional Pattern-Space Representation For Volumetric Arrays, William C. Barott, Paul G. Steffes
A Three-Dimensional Pattern-Space Representation For Volumetric Arrays, William C. Barott, Paul G. Steffes
Publications
A three-dimensional pattern-space representation is presented for volumetric arrays. In this representation, the radiation pattern of an array is formed by the evaluation of the three-dimensional pattern-space on a spherical surface. The scan angle of the array determines the position of this surface within the pattern-space. This pattern-space representation is used in conjunction with a genetic algorithm to minimize the sidelobe levels exhibited by a thinned volumetric array during scanning.
Magnetohydrodynamic Effects In Propagating Relativistic Jets: Reverse Shock And Magnetic Acceleration, Yosuke Mizuno, Bing Zhang, Bruno Giacomazzo, Ken-Ichi Nishikawa, Phillip E. Hardee, Shigehiro Nagataki, Dieter H. Hartmann
Magnetohydrodynamic Effects In Propagating Relativistic Jets: Reverse Shock And Magnetic Acceleration, Yosuke Mizuno, Bing Zhang, Bruno Giacomazzo, Ken-Ichi Nishikawa, Phillip E. Hardee, Shigehiro Nagataki, Dieter H. Hartmann
Publications
We solve the Riemann problem for the deceleration of an arbitrarily magne-tized relativistic flow injected into a static unmagnetized medium in one dimen-sion. We find that for the same initial Lorentz factor, the reverse shock becomes progressively weaker with increasing magnetization σ (the Poynting-to-kinetic energy flux ratio), and the shock becomes a rarefaction wave when σ exceeds a critical value, σc, defined by the balance between the magnetic pressure in the flow and the thermal pressure in the forward shock. In the rarefaction wave regime, we find that the rarefied region is accelerated to a Lorentz factor that is significantly …
Geocoronal Hydrogen Observations Spanning Three Solar Minima, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, L. M. Haffner, R. J. Reynolds, R. C. Woodward
Geocoronal Hydrogen Observations Spanning Three Solar Minima, S. M. Nossal, E. J. Mierkiewicz, F. L. Roesler, L. M. Haffner, R. J. Reynolds, R. C. Woodward
Publications
The 11-year solar cycle is a dominant source of natural variability in the upper atmosphere, and its effect on atomic hydrogen distributions and emissions must be understood to investigate possible signs of longer-term climatic trends in this region. We present midlatitude geocoronal hydrogen Balmer α observations from solar cycle 23 (1997–2006) and three solar minimum periods, 1985, 1997, and 2006. The 1997 through 2006 observations were taken with the Wisconsin H-αMapper Fabry-Perot (WHAM), a ground-based CCD-annular summing instrument that began observations at the Kitt Peak Observatory in Arizona in 1997. The 1985 observations were made with a similarly …
Multiwavelength Analysis Of The Intriguing Grb 061126: The Reverse Shock Scenario And Magnetization, A. Gomboc, S. Kobayashi, C. Guidorzi, A. Melandri, V. Mangano, B. Sbarufatti, C. G. Mundell, P. Schady, R. J. Smith, A C. Updike, D A. Kann, K Misra, E Rol, A Pozanenko, A J. Castro-Tirado, G C. Anupama, D Bersier, M F. Bode, D Carter, P Curran, A Fruchter, J Graham, Dieter H. Hartmann, M Ibrahimov, A Levan, A Monfardini, C J. Mottram, P T. O'Brien, P Prema, D K. Sahu, I A. Steele, N R. Tanvir, K Wiersema
Multiwavelength Analysis Of The Intriguing Grb 061126: The Reverse Shock Scenario And Magnetization, A. Gomboc, S. Kobayashi, C. Guidorzi, A. Melandri, V. Mangano, B. Sbarufatti, C. G. Mundell, P. Schady, R. J. Smith, A C. Updike, D A. Kann, K Misra, E Rol, A Pozanenko, A J. Castro-Tirado, G C. Anupama, D Bersier, M F. Bode, D Carter, P Curran, A Fruchter, J Graham, Dieter H. Hartmann, M Ibrahimov, A Levan, A Monfardini, C J. Mottram, P T. O'Brien, P Prema, D K. Sahu, I A. Steele, N R. Tanvir, K Wiersema
Publications
We present a detailed study of the prompt and afterglow emission from Swift GRB 061126 using BAT, XRT, UVOT data and multicolor optical imaging from 10 ground-based telescopes. GRB 061126 was a long burst (T90 ¼191 s) with four overlapping peaks in its -ray light curve. The X-ray afterglow, observed from 26 minutes to 20 days after the burst, shows a simple power-law decay with X ¼1:290 Æ0:008. Optical observations presented here cover the time range from 258 s (Faulkes Telescope North) to 15 days (Gemini North) after the burst; the decay rate of the optical afterglow shows a steep-to-shallow …
Poet: Polarimeters For Energetic Transients, J. E. Hill, M. L. Mcconnell, P. Bloser, J. Legere, J. Macri, J. Ryan, S. Barthelmy, L. Angelini, T. Sakamoto, J K. Black, Dieter H. Hartmann, P Kaaret, B Zhang, K Ioka, T Nakamura, K Toma, R Yamazaki, X Wu
Poet: Polarimeters For Energetic Transients, J. E. Hill, M. L. Mcconnell, P. Bloser, J. Legere, J. Macri, J. Ryan, S. Barthelmy, L. Angelini, T. Sakamoto, J K. Black, Dieter H. Hartmann, P Kaaret, B Zhang, K Ioka, T Nakamura, K Toma, R Yamazaki, X Wu
Publications
POET (Polarimeters for Energetic Transients) is a Small Explorer mission concept proposed to NASA in January 2008. The principal scientific goal of POET is to measure GRB polarization between 2 and 500 keV. The payload consists of two wide FoV instruments: a Low Energy Polarimeter (LEP) capable of polarization measurements in the energy range from 2-15 keV and a high energy polarimeter (Gamma-Ray Polarimeter Experiment – GRAPE) that will measure polarization in the 60-500 keV energy range. Spectra will be measured from 2 keV up to 1 MeV. The POET spacecraft provides a zenith-pointed platform for maximizing the exposure to …
Neutrino-Nucleus Reaction Cross Sections For Light Element Systhesis In Supernova Explosions, Takashi Yoshida, Toshio Suzuki, Satoshi Chiba, Toshitaka Kajino, Hidekazu Yokomakura, Keiichi Kimura, Akira Takamura, Dieter H. Hartmann
Neutrino-Nucleus Reaction Cross Sections For Light Element Systhesis In Supernova Explosions, Takashi Yoshida, Toshio Suzuki, Satoshi Chiba, Toshitaka Kajino, Hidekazu Yokomakura, Keiichi Kimura, Akira Takamura, Dieter H. Hartmann
Publications
The neutrino-nucleus reaction cross sections of 4He and 12C are evaluated using new shell model Hamiltoni-ans. Branching ratios of various decay channels are calculated to evaluate the yields of Li, Be, and B producedthrough the ν -process in supernova explosions. The new cross sections enhance the yields of7Li and11B pro-duced during the supernova explosion of a 16.2 M⊙star model compared to the case using the conventionalcross sections by about 10%. On the other hand, the yield of10B decreases by a factor of two. The yieldsof6Li,9Be, and the radioactive nucleus10 Be are found at a level of ∼ 10−11M⊙. The temperature …
A Photometric Redshift Of Z = 1.8{+0.4}{-0.3} For The Agile Grb 080514b, A. Rossi, A. De Ugarte Postigo, P. Ferrero, D. A. Kann, S. Klose, S. Schulze, J. Greiner, P. Schady, R. Filgas, E E. Gonsalves, A Küpcü Yoldaş, T Krühler, G Szokoly, A Yoldas, P.M.J. Afonso, C Clemens, J S. Bloom, D A. Perley, J.P.U. Fynbo, A J. Castro-Tirado, J Gorosabel, P Kubanek, A C. Updike, Dieter H. Hartmann, A Giuliani, S T. Holland, L Hanlon, M Bremer, J French, G Melady, D A. Garcia-Hernandez
A Photometric Redshift Of Z = 1.8{+0.4}{-0.3} For The Agile Grb 080514b, A. Rossi, A. De Ugarte Postigo, P. Ferrero, D. A. Kann, S. Klose, S. Schulze, J. Greiner, P. Schady, R. Filgas, E E. Gonsalves, A Küpcü Yoldaş, T Krühler, G Szokoly, A Yoldas, P.M.J. Afonso, C Clemens, J S. Bloom, D A. Perley, J.P.U. Fynbo, A J. Castro-Tirado, J Gorosabel, P Kubanek, A C. Updike, Dieter H. Hartmann, A Giuliani, S T. Holland, L Hanlon, M Bremer, J French, G Melady, D A. Garcia-Hernandez
Publications
The AGILE gamma-ray burst GRB 080514B is the first detected to have emission above 30 MeV and an optical afterglow. However, no spectroscopic redshift for this burst is known. We report on our ground-based optical/NIR and millimeter follow-up observations of this event at several observatories, including the multi-channel imager GROND on La Silla, supplemented by Swift UVOT and Swift XRT data. The spectral energy distribution (SED) of the optical/NIR afterglow is found to decline sharply bluewards to the UV bands, which can be utilized in estimating the redshift. Fitting the SED from the Swift UVOT uvw2bandto the H band, we …
Erratum: "Warm Hcn, C2h2, And Co In The Disk Of Gv Tau'', E L. Gibb, K A. Vanbrunt, Sean D. Brittain, T W. Rettig
Erratum: "Warm Hcn, C2h2, And Co In The Disk Of Gv Tau'', E L. Gibb, K A. Vanbrunt, Sean D. Brittain, T W. Rettig
Publications
This is an Erratum for the article 2007 ApJ 660 1572
The Rapidly Flaring Afterglow Of The Very Bright And Energetic Grb 070125, Adria C. Updike, Josh B. Haislip, Melissa C. Nysewander, Andrew S. Fruchter, D. Alexander Kann, Sylvio Klose, Peter A. Miline, G. Grant Williams, Weikang Zheng, Carl W. Hergenrother
The Rapidly Flaring Afterglow Of The Very Bright And Energetic Grb 070125, Adria C. Updike, Josh B. Haislip, Melissa C. Nysewander, Andrew S. Fruchter, D. Alexander Kann, Sylvio Klose, Peter A. Miline, G. Grant Williams, Weikang Zheng, Carl W. Hergenrother
Publications
We report on multiwavelength observations, ranging from X-ray to radio wave bands, of the IPN-localized gamma-ray burst GRB 070125. Spectroscopic observations reveal the presence of absorption lines due to O i,Si ii,and C iv, implying a likely redshift of z ¼1:547. The well-sampled light curves, in particular from 0.5 to 4 days after the burst, suggest a jet break at 3.7 days, corresponding to a jet opening angle of $7.0, and implying an intrinsic GRB energy in the 1Y10,000 keV band of around E ¼(6:3Y6:9) ; 1051 ergs (based on the fluences measured by the gamma-ray de-tectorsof the IPN).GRB070125 is …
Constraining The Surface Inhomogeneity And Settling Times Of Metals On Accreting White Dwarfs, Michael H. Montgomery, S.E. Thompson, Ted Von Hippel
Constraining The Surface Inhomogeneity And Settling Times Of Metals On Accreting White Dwarfs, Michael H. Montgomery, S.E. Thompson, Ted Von Hippel
Publications
Due to the short settling times of metals in DA white dwarf atmospheres, any white dwarfs with photospheric metals must be actively accreting. It is therefore natural to expect that the metals may not be deposited uniformly on the surface of the star. We present calculations showing how the temperature variations associated with white dwarf pulsations lead to an observable diagnostic of the surface metal distribution, and we show what constraints current data sets are able to provide. We also investigate the effect that time-variable accretion has on the metal abundances of different species, and we show how this can …
Book Review: Guide To Observing Deep-Sky Objects: A Complete Global Resource For Astronomers, T. D. Oswalt
Book Review: Guide To Observing Deep-Sky Objects: A Complete Global Resource For Astronomers, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Guide to Observing Deep-Sky Objects : a Complete Global Resource for Astronomers by Jeff A. Farinacci. Springer, 2007 189p, 9780387728506 $29.95
The First Mid-Infrared Spectra Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
The First Mid-Infrared Spectra Of Cool White Dwarfs, Mukremin Kilic, Ted Von Hippel, Et Al.
Publications
We present the first mid-infrared spectra of two cool white dwarfs obtained with the Spitzer Space Telescope. We also present 3.5–8 μ m photometry for 19 cool white dwarfs with 5000 K ≤Teff ≤ 9000 K. We perform a detailed model atmosphere analysis of these white dwarfs by fitting their UBVRIJHK and Spitzer photometry with state-of-the-art model atmospheres, and demonstrate that the optical and infrared spectral energy distributions of cool white dwarfs are well reproduced by our grid of models. Our mid-infrared photometry and 7.5-14.5 μm spectrum of WD 0018–267 are consistent with a Teff = 5720 …
A New Look At The Local White Dwarf Population, J. B. Holberg, E. M. Sion, Terry D. Oswalt, G. P. Mccook, S. Foran, John P. Subasavage
A New Look At The Local White Dwarf Population, J. B. Holberg, E. M. Sion, Terry D. Oswalt, G. P. Mccook, S. Foran, John P. Subasavage
Publications
We have conducted a detailed new survey of the local population of white dwarfs lying within 20 pc of the Sun. A new revised catalog of local white dwarfs containing 122 entries (126 individual degenerate stars) is presented. This list contains 27 white dwarfs not included in a previous list from 2002, as well as new and recently published trigonometric parallaxes. In several cases new members of the local white dwarf population have come to light through accurate photometric distance estimates. In addition, a suspected new double degenerate system (WD 0423+120) has been identified. The 20 pc sample is currently …
Book Review: The Road To Galaxy Formation 2nd Ed, T. D. Oswalt
Book Review: The Road To Galaxy Formation 2nd Ed, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of The road to galaxy formation 2nd ed by William C. Keel. Springer/Praxis, 2007 262p, 9783540725343 $99.00.
The Robotic Super-Lotis Telescope: Results & Future Plans, G. G. Williams, P. A. Milne, H. S. Park, S. D. Barthelmy, Dieter H. Hartmann, A. Updike, K. Hurley
The Robotic Super-Lotis Telescope: Results & Future Plans, G. G. Williams, P. A. Milne, H. S. Park, S. D. Barthelmy, Dieter H. Hartmann, A. Updike, K. Hurley
Publications
We provide an overview of the robotic Super-LOTIS (Livermore Optical Transient Imaging System) telescope and present results from gamma-ray burst (GRB) afterglow observations using Super-LOTIS and other Steward Observatory telescopes. The 0.6-m Super-LOTIS telescope is a fully robotic system dedicated to the measurement of prompt and early time optical emission from GRBs. The system began routine operations from its Steward Observatory site atop Kitt Peak in April 2000 and currently operates every clear night. The telescope is instrumented with an optical CCD camera and a four position filter wheel. It is capable of observing Swift Burst Alert Telescope (BAT) error …
Relativistic Particle-In-Cell Simulation Of Prompt And Early Afterglows From Grbs, K.-I. Nishikawa, P. Hardee, Y. Mizuno, M. Medvedev, B. Zhang, Dieter H. Hartmann, G. J. Fishman
Relativistic Particle-In-Cell Simulation Of Prompt And Early Afterglows From Grbs, K.-I. Nishikawa, P. Hardee, Y. Mizuno, M. Medvedev, B. Zhang, Dieter H. Hartmann, G. J. Fishman
Publications
Nonthermal radiation observed from astrophysical systems containing relativistic jets and shocks, e.g., gamma-ray bursts (GRBs), active galactic nuclei (AGNs), and microquasars commonly exibit power-law emission spectra. Recent PIC simulations of relativistic electro-ion (or electron-positron) jets injected into a stationary medium show that particle acceleration occurs within the downstream jet. In collisionless, relativistic shocks, particle (electron, positron, and ion) acceleration is due to plasma waves and their associated instabilities (e.g., the Weibel (filamentation) instability) created in shock region. The simulations show that the Weibel instability in responsible for generating and amplifying highly non-uniform, small-scale magnetic fields. These fields contribute to the …
Implications Of Cosmological Gamma-Ray Absorption. Ii. Modifications Of Gamma-Ray Spectra, Dieter H. Hartmann, T. M. Kneiske, T. Bretz, K. Mannheim
Implications Of Cosmological Gamma-Ray Absorption. Ii. Modifications Of Gamma-Ray Spectra, Dieter H. Hartmann, T. M. Kneiske, T. Bretz, K. Mannheim
Publications
Bearing on the model for the time-dependent metagalactic radiation field developed in the first paper of this series, we compute the gamma-ray attenuation due to pair production in photon-photon scattering. Emphasis is on the effects of varying the star formation rate and the fraction of UV radiation assumed to escape from the star forming regions, the latter being important mainly for high-redshift sources. Conversely, we investigate how the metagalactic radiation field can be measured from the gamma-ray pair creation cutoff as a function of redshift, the Fazio-Stecker relation. For three observed TeV-blazars (Mkn501, Mkn421, H1426+428) we study the effects of …
Exist's Gamma-Ray Burst Sensitivity, D. L. Band, J. E. Grindlay, A. Garson Iii, H. Krawczynski, Dieter H. Hartmann, S. Barthemy, N. Gehrels, G. Skinner
Exist's Gamma-Ray Burst Sensitivity, D. L. Band, J. E. Grindlay, A. Garson Iii, H. Krawczynski, Dieter H. Hartmann, S. Barthemy, N. Gehrels, G. Skinner
Publications
We use semianalytic techniques to evaluate the burst sensitivity of designs for the EXIST hard X-ray survey mis-sion. Applying these techniques to the mission design proposed for the Beyond Einstein program,we find that with its very large field of view and faint gamma-ray burst detection threshold, EXIST will detect and localize approximately two bursts per day, a large fraction of which may be at high redshift. We estimate that EXIST’s maximum sensitivity will be ~4 times greater than that of Swift’s Burst Alert Telescope. Bursts will be localized to better than 40" at thresh-old, with a burst position as good …
A Magnetohydrodynamic Boost For Relativistic Jets, Yosuke Mizuno, Phillip Hardee, Dieter H. Hartmann, Ken-Ichi Nishikawa, Bing Zhang
A Magnetohydrodynamic Boost For Relativistic Jets, Yosuke Mizuno, Phillip Hardee, Dieter H. Hartmann, Ken-Ichi Nishikawa, Bing Zhang
Publications
We performed relativistic magnetohydrodynamic simulations of the hydrodynamic boosting mechanism for relativistic jets explored by Aloy & Rezzolla (2006) using the RAISHIN code. Simulation results show that the presence of a magnetic field changes the properties of the shock interface between the tenuous, overpressured jet (Vzj) flowing tangentially to a dense external medium. Magnetic fields can lead to more efficient acceleration of the jet, in comparison to the pure-hydrodynamic case. A "polodial" magnetic field (Bz), tangent to the interface and parallel to the jet flow, produces both a stronger outward moving shock and a stronger inward moving rarefaction wave. This …
White Dwarf Luminosity And Mass Functions From Sloan Digital Sky Survey Spectra, Steven Degennaro, Ted Von Hippel, D. E. Winget, S. O. Kepler, Atsuko Nitta, Detlev Koester, Leandro Althaus
White Dwarf Luminosity And Mass Functions From Sloan Digital Sky Survey Spectra, Steven Degennaro, Ted Von Hippel, D. E. Winget, S. O. Kepler, Atsuko Nitta, Detlev Koester, Leandro Althaus
Publications
We present the first phase in our ongoing work to use Sloan Digital Sky Survey (SDSS) data to create separate white dwarf (WD) luminosity functions (LFs) for two or more different mass ranges. In this paper, we determine the completeness of the SDSS spectroscopic WD sample by comparing a proper-motion selected sample of WDs from SDSS imaging data with a large catalog of spectroscopically determined WDs. We derive a selection probability as a function of a single color (g − i) and apparent magnitude (g) that covers the range −1.0 < g − i < 0.2 and 15 < g < 19.5. We address the observed upturn in log g for WDs with Teff 12,000 K and offer arguments that the problem is limited to the line profiles and is not present in the continuum. We offer an empirical method of removing the upturn, recovering a reasonable mass function for WDs with Teff < 12,000 K. Finally we present a WD LF with nearly an order of magnitude (3358) more spectroscopically confirmed WDs than any previous work.
Book Review: The Telescope: Its History, Technology, And Future, T. D. Oswalt
Book Review: The Telescope: Its History, Technology, And Future, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of The Telescope : Its History, Technology, and Future by Geoff Andersen. Princeton, 2007 248p, 0691129797 $29.95, 9780691129792 $29.95.
Book Review: Your Cosmic Context: An Introduction To Modern Cosmology, T. D. Oswalt
Book Review: Your Cosmic Context: An Introduction To Modern Cosmology, T. D. Oswalt
Publications
This document is Dr. Oswalt’s review of Your Cosmic Context : an Introduction to Modern Cosmology by Todd Duncan and Craig Tyler Pearson Addison-Wesley, 2008 466p, 0132400103 $80.00, 9780132400107 $80.00.