Institution
Universities Space Research Association
Nonprofit•Columbia, Maryland, United States•
About: Universities Space Research Association is a nonprofit organization based out in Columbia, Maryland, United States. It is known for research contribution in the topics: Gamma-ray burst & Galaxy. The organization has 1921 authors who have published 5412 publications receiving 255681 citations. The organization is also known as: USRA.
Topics: Gamma-ray burst, Galaxy, Pulsar, Neutron star, Aerosol
Papers published on a yearly basis
Papers
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TL;DR: In this paper, the authors compared the long-term torque behavior of 4U 1626-67 to other disk-fed accreting pulsars and discuss the implications of their results for the various theories of magnetic accretion torques.
Abstract: Over 5 yr of hard X-ray (20-60 keV) monitoring of the 7.66 s accretion-powered pulsar 4U 1626-67 with the Compton Gamma Ray Observatory/BATSE large-area detectors has revealed that the neutron star is now steadily spinning down, in marked contrast to the steady spin-up observed during 1977-1989. This is the second accreting pulsar (the other is GX 1+4) that has shown extended, steady intervals of both spin-up and spin-down. Remarkably, the magnitudes of the spin-up and spin-down torques differ by only 15%, with the neutron star spin changing on a timescale |ν/dot ν| ≈ 5000 yr in both states. The current spin-down rate is itself decreasing on a timescale |dot ν/bar ν| ≈ 26 yr. The long-term timing history shows small-amplitude variations on a 4000 day timescale, which are probably due to variations in the mass transfer rate. The pulsed 20-60 keV emission from 4U 1626-67 is well-fitted by a power-law spectrum with photon index γ = 4.9 and a typical pulsed intensity of 1.5 × 10^(-10) ergs cm^(-2) s^(-1). The low count rates with BATSE prohibited us from constraining the reported 42 minute binary orbit, but we can rule out long-period orbits in the range 2 days lesssim Porb lesssim 900 days.
We compare the long-term torque behavior of 4U 1626-67 to other disk-fed accreting pulsars and discuss the implications of our results for the various theories of magnetic accretion torques. The abrupt change in the sign of the torque is difficult to reconcile with the extremely smooth spin-down now observed. The strength of the torque noise in 4U 1626-67, ~10^(-22) Hz^2 s^(-2) Hz^(-1), is the smallest ever measured for an accreting X-ray pulsar, and it is comparable to the timing noise seen in young radio pulsars. We close by pointing out that the core temperature and external torque (the two parameters potentially relevant to internal sources of timing noise) of an accreting neutron star are also comparable to those of young radio pulsars.
119 citations
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University of California, Santa Barbara1, Max Planck Society2, University of Michigan3, University of New South Wales4, Goddard Space Flight Center5, Sabancı University6, University of Arizona7, Middle East Technical University8, Universities Space Research Association9, Çağ University10, California Institute of Technology11, Louisiana State University12, Guilford College13, Los Alamos National Laboratory14, University of Texas at Austin15, College of Saint Benedict16
TL;DR: In this paper, a complete set of early optical afterglows of gamma-ray bursts was obtained with the Robotic Optical Transient Search Experiment (ROTSE-III) telescope network from 2005 March through 2007 June.
Abstract: We report on a complete set of early optical afterglows of gamma-ray bursts (GRBs) obtained with the Robotic Optical Transient Search Experiment (ROTSE-III) telescope network from 2005 March through 2007 June. This set is comprised of 12 afterglows with early optical and Swift/X-Ray Telescope observations, with a median ROTSE-III response time of 45 s after the start of γ-ray emission (8 s after the GCN notice time). These afterglows span 4 orders of magnitude in optical luminosity, and the contemporaneous X-ray detections allow multi-wavelength spectral analysis. Excluding X-ray flares, the broadband synchrotron spectra show that the optical and X-ray emission originate in a common region, consistent with predictions of the external forward shock in the fireball model. However, the fireball model is inadequate to predict the temporal decay indices of the early afterglows, even after accounting for possible long-duration continuous energy injection. We find that the optical afterglow is a clean tracer of the forward shock, and we use the peak time of the forward shock to estimate the initial bulk Lorentz factor of the GRB outflow, and find 100 ≲ Γ_0 ≲ 1000, consistent with expectations.
119 citations
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TL;DR: In this paper, two 3-year integrations were carried out with a version of the GLA GCM that contains the Simple Biosphere Model (SiB) for simulating land-atmosphere interactions.
Abstract: Two 3-year (1979–1982) integrations were carried out with a version of the GLA GCM that contains the Simple Biosphere Model (SiB) for simulating land-atmosphere interactions. The control case used the usual SiB vegetation cover (comprising 12 vegetation types), while its twin, the deforestation case, imposed a scenario in which all tropical rainforests were entirely replaced by grassland. Except for this difference, all other initial and prescribed boundary conditions were kept identical in both integrations. An intercomparison of the integrations shows that tropical deforestation • decreases evapotranspiration and increases land surface outgoing longwave radiation and sensible heat flux, thereby warming and drying the planetary boundary layer. This happens despite the reduced absorption of solar radiation due to higher surface albedo of the deforested land. • produces significant and robust local as well as global climate changes. The local effect includes significant changes (mostly reductions)...
119 citations
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TL;DR: In this paper, the authors describe the composition of a new soil texture data set and its implementation into a specific land surface modeling system, namely, the Catchment land surface model (LSM) of the NASA Goddard Earth Observing System version 5 (GEOS-5) modeling and assimilation framework.
Abstract: The advent of new data sets describing soil texture and associated soil properties offers the promise of improved hydrological simulation. Here we describe the composition of a new soil texture data set and its implementation into a specific land surface modeling system, namely, the Catchment land surface model (LSM) of the NASA Goddard Earth Observing System version 5 (GEOS-5) modeling and assimilation framework. First, global soil texture composites are generated using data from the Harmonized World Soil Database version 1.21 (HWSD1.21) and the State Soil Geographic (STATSGO2) project, with explicit consideration of different levels of organic material. Then, the LSM's soil parameters are upgraded using the new texture data, with hydraulic parameters derived for the more extensive set of texture classes using pedotransfer functions. Other changes to the LSM parameters are included to further support simulations at increasingly fine resolutions. A suite of simulations with the original and new parameter versions shows modest yet significant improvements in the Catchment LSM's simulation of soil moisture and surface hydrological fluxes. The revised LSM parameters will be used for the forthcoming Soil Moisture Active Passive (SMAP) soil moisture assimilation product.
119 citations
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TL;DR: In this paper, a summary of data obtained with the 350m polarimeter, Hertz, at the Caltech Submillimeter Observatory is presented, along with tabulated results and maps showing polarization vectors and intensity contours.
Abstract: We present a summary of data obtained with the 350 {mu}m polarimeter, Hertz, at the Caltech Submillimeter Observatory. We give tabulated results and maps showing polarization vectors and intensity contours. The summary includes over 4300 individual measurements in 56 Galactic sources and two galaxies. Of these measurements, 2153 have P {>=} 3{sigma} {sub p} statistical significance. The median polarization of the entire data set is 1.46%.
119 citations
Authors
Showing all 1930 results
Name | H-index | Papers | Citations |
---|---|---|---|
Alexander S. Szalay | 166 | 936 | 145745 |
Naomi J. Halas | 140 | 435 | 82040 |
Krzysztof M. Gorski | 132 | 380 | 105912 |
William T. Reach | 131 | 535 | 90496 |
David C. Koo | 119 | 568 | 49040 |
Ranga B. Myneni | 114 | 393 | 53054 |
Chryssa Kouveliotou | 109 | 671 | 47748 |
Darren L. DePoy | 99 | 554 | 38932 |
Mario Hamuy | 95 | 389 | 30391 |
A. A. Moiseev | 95 | 263 | 36948 |
Holland C. Ford | 93 | 347 | 29661 |
Alistair R. Walker | 93 | 580 | 35142 |
Jonathan F. Ormes | 89 | 306 | 27022 |
Andreas Quirrenbach | 89 | 678 | 33504 |
Tyson Littenberg | 89 | 297 | 61373 |