Astrophysics and Astronomy Commons^™

Study The Mechanism Of The Prompt Emission Of Gamma-Ray Bursts, Wei Deng

UNLV Theses, Dissertations, Professional Papers, and Capstones

The prompt emission of Gamma-Ray Bursts (GRBs) has been detected over 40 years, but the mechanism of the prompt emission is still a mystery. The problem can be summarized as several debatable questions: What is the energy composition of the jets/outflows? What is the energy dissipation mechanism? How are the particles accelerated during the energy dissipation process? What is the radiation mechanism to produce the observed prompt emission? In order to solve these problems, several theoretical models have been proposed, including the classical "internal shock (IS)" model, the "dissipative photosphere" model, the "magnetic dissipation" model, and so on. Different models …

Multiperiodicity, Modulations, And Flip-Flops In Variable Star Light Curves. Iii. Carrier Fit Analysis Of Lq Hydrae Photometry For 1982–2014, Nigul Olspert, Maarit J. Käpylä, Jaan Pelt, Elizabeth M. Cole, Thomas Hackman, Jyri J. Lehtinen, Gregory W. Henry

Information Systems and Engineering Management Research Publications

Aims. We study LQ Hya photometry for 1982–2014 with the carrier fit (CF) method and compare our results to earlier photometric analysis and recent Doppler imaging maps.

Methods. As the rotation period of the object is not known a priori, we utilize different types of statistical methods first (least-squares fit of harmonics, phase dispersion statistics) to estimate various candidates for the carrier period for the CF method. Secondly, a global fit to the whole data set and local fits to shorter segments are computed with the period that is found to be optimal.

Results. The harmonic least-squares analysis of all …

Ultrafast Photoconductivity Measurements Of A Thermoelectric Nanocomposite: Tellurium Nanowire/Pedot:Pss, Brittany A. Ehmann

Macalester Journal of Physics and Astronomy

This project explores the conductivity properties of a novel thermoelectric hybrid material (Tellurium nanowires in a conducting polymer PEDOT:PSS) using both static and time-resolved conductivity measurements. We find that the effect of the conducting polymer PEDOT is weak and that the observed differences in conductivity measurements between the hybrid and non-hybrid material are most likely caused by the different sizes of the nanowires.

Mid-Ir Excitation Of Graphene, Andrew R. Banman, James Heyman

Macalester Journal of Physics and Astronomy

In this research we investigate how the conductivity of graphene changes in response to mid-infrared photoexcitation. Our p-type sample was formed through chemical vapor deposition. Pump/probe methodology produced the time-resolved Terahertz transmission, from which the photoconductivity was calculated. We probed the sample with energies above and below the Fermi energy, which was determined by Fourier transform infrared spectroscopy. Our results support a model in which heating of the electron gas, leading to high carrier scattering rates, is responsible for a decrease in conductivity. We observe this negative photoconductivity at all pump energies, allowing us to rule out the possibility of …

The Role Of Cold Gas In Low-Level Supermassive Black Hole Activity, Erik D. Alfvin

Macalester Journal of Physics and Astronomy

The nature of the relationship between low-level supermassive black hole activity and galactic cold gas, if any, is currently unclear. It has been hypothesized that feedback may heat or expel gas and quench star formation; alternatively, central black holes may feed at higher rates (either directly or as a secondary effect from stellar winds) in gas-rich galaxies. We use a combination of radio data from the on-going ALFALFA survey and from the literature, along with archival X-ray flux measurements from the Chandra X-ray observatory, to investigate this potential relationship. We construct a sample of 136 late-type galaxies, with MB < −18 out to 50 Mpc, that have both HI masses and sensitive X-ray coverage. Of these, 76 host a nuclear X-ray source, a 56% detection fraction. There is a highly significant correlation between LX and Mstar with a slope of 1.5±0.2, and a tentative correlation (significant at the 2.5σ level) between LX and MHI. However, a joint fit to LX as a function of both Mstar and MHI finds no significant dependence on MHI, and similarly the residuals of LX − LX(Mstar) show no trend with MHI. We conclude that the galaxy-wide cold gas content in these spirals does not strongly influence their low-level supermassive black hole activity.

The 2d Distribution Of Iron-Rich Ejecta In The Remnant Of Sn 1885 In M31, Robert A. Fesen, Peter A. Höflich, Andrew J. S. Hamilton

Dartmouth Scholarship

We present Hubble Space Telescope (HST) ultraviolet Fe i and Fe ii images of the remnant of Supernova 1885 (S And) which is observed in absorption against the bulge of the Andromeda galaxy, M31. We compare these Fe i and Fe ii absorption line images to previous HST absorption images of S And, of which the highest quality and theoretically cleanest is Ca ii H and K. Because the remnant is still in free expansion, these images provide a 2D look at the distribution of iron synthesized in this probable Type Ia explosion, thus providing insights and constraints …

Accurate Determination Of The Free–Free Gaunt Factor – Ii. Relativistic Gaunt Factors, P. A. M. Van Hoof, Gary J. Ferland, R. J. R. Williams, K. Volk, Marios Chatzikos, M. Lykins, R. L. Porter

Physics and Astronomy Faculty Publications

When modelling an ionized plasma, all spectral synthesis codes need the thermally averaged free–free Gaunt factor defined over a very wide range of parameter space in order to produce an accurate prediction for the spectrum. Until now no data set exists that would meet these needs completely. We have therefore produced a table of relativistic Gaunt factors over a much wider range of parameter space than has ever been produced before. We present tables of the thermally averaged Gaunt factor covering the range ¹⁰log γ² = −6 to 10 and ¹⁰log u = −16 to 13 for …

Precision Measurements Of AN1 In The Deep Inelastic Regime, K. Allada, C. Dutta, A. Kolarkar, Wolfgang Korsch, D. S. Parno, D. Flay, M. Posik, W. Armstrong, T. Averett, F. Benmokhtar, W. Bertozzi, A. Camsonne, M. Canan, G. D. Cates

Physics and Astronomy Faculty Publications

We have performed precision measurements of the double-spin virtual-photon asymmetry A₁ on the neutron in the deep inelastic scattering regime, using an open-geometry, large-acceptance spectrometer and a longitudinally and transversely polarized ³He target. Our data cover a wide kinematic range 0.277 ≤ x ≤ 0.548 at an average Q² value of 3.078 (GeV/c)², doubling the available high-precision neutron data in this x range. We have combined our results with world data on proton targets to make a leading-order extraction of the ratio of polarized-to-unpolarized parton distribution functions for up quarks and for down quarks in …

P-Manga: Gradients In Recent Star Formation Histories As Diagnostics For Galaxy Growth And Death, Cheng Li, Enci Wang, Lin Lin, Matthew A. Bershady, Kevin Bundy, Christy A. Tremonti, Ting Xiao, Renbin Yan, Dmitry Bizyaev, Michael Blanton, Sabrina Cales, Brian Cherinka, Edmond Cheung, Niv Drory, Eric Emsellem, Hai Fu, Joseph Gelfand, David R. Law, Lahwai Lin, Nick Macdonald, Claudia Maraston, Karen L. Masters, Michael R. Merrifield, Kaike Pan, S. F. Sánchez, Donald P. Schneider, Daniel Thomas, David Wake, Lixin Wang, Anne-Marie Weijmans, David Wilkinson, Peter Yoachim, Kai Zhang, Tiantian Zheng

Physics and Astronomy Faculty Publications

We present an analysis of the data produced by the MaNGA prototype run (P-MaNGA), aiming to test how the radial gradients in recent star formation histories, as indicated by the 4000 Å break (D_n(4000)), Hδ absorption (EW(Hδ_A)), and Hα emission (EW(Hα)) indices, can be useful for understanding disk growth and star formation cessation in local galaxies. We classify 12 galaxies observed on two P-MaNGA plates as either centrally quiescent (CQ) or centrally star-forming (CSF), according to whether D_n(4000) measured in the central spaxel of each datacube exceeds 1.6. For …

A Wfc3 Grism Emission Line Redshift Catalog In The Goods-South Field, Aaron M. Morris, Dale D. Kocevski, Jonathan R. Trump, Benjamin J. Weiner, Nimish P. Hathi, Guillermo Barro, Tomas Dahlen, Sandra M. Faber, Steven L. Finkelstein, Adriano Fontana, Henry C. Ferguson, Norman A. Grogin, Ruth Grützbauch, Yicheng Guo, Li-Ting Hsu, Anton M. Koekemoer, David C. Koo, Bahram Mobasher, Janine Pforr, Mara Salvato, Tommy Wiklind, Stijn Wuyts

Physics and Astronomy Faculty Publications

We combine Hubble Space Telescope (HST)/Wide Field Camera3 (WFC3) imaging and G141 grism observations from the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and 3D-HST surveys to produce a catalog of grism spectroscopic redshifts for galaxies in the CANDELS/GOODS-South field. The WFC3/G141 grism spectra cover a wavelength range of 1.1 ≼ λ ≼ 1.7 μm with a resolving power of R ~ 130 for point sources, thus providing rest-frame optical spectra for galaxies out to z ~ 3.5. The catalog is selected in the H-band (F160W) and includes both galaxies with and without previously …

Periodicity In Some Light Curves Of The Solar Analogue V352 Canis Majoris, Perttu Kajatkari, Lauri Jetsu, Elizabeth M. Cole, Thomas Hackman, Gregory W. Henry, Sirkka-Liisa Joutsiniemi, Jyri J. Lehtinen, V. Mäkelä, Sebastian Porceddu, Kyösti Ryynänen, V. Solea

Information Systems and Engineering Management Research Publications

Aims. We applied the Continuous Period Search (CPS) method to 14 yr of V-band photometry of the active G6.5 solar analog V352 CMa. Our aim was to show that CPS can successfully model the presence or absence of periodicity in low-amplitude light curves.

Methods. CPS computes values for the mean brightness, photometric period, amplitude and minimum of selected datasets. We also applied the Power Spectrum Method (PSM) to these datasets and compared the performance of this frequently applied method to that of CPS.

Results. We found an apparent 11.7 ± 0.5 yr cycle in the mean brightness. The mean of …

Bootstrapping Dielectronic Recombination From Second-Row Elements And The Orion Nebula, N. R. Badnell, Gary J. Ferland, T. W. Gorczyca, D. Nikolić, Gururaj Anil Wagle

Physics and Astronomy Faculty Publications

Dielectronic recombination (DR) is the dominant recombination process for most heavy elements in photoionized clouds. Accurate DR rates for a species can be predicted when the positions of autoionizing states are known. Unfortunately such data are not available for most third- and higher-row elements. This introduces an uncertainty that is especially acute for photoionized clouds, where the low temperatures mean that DR occurs energetically through very low-lying autoionizing states. This paper discusses S²⁺ → S⁺ DR, the process that is largely responsible for establishing the [S iii]/[S ii] ratio in nebulae. We derive an empirical rate coefficient using …

Magnetism Of Fept Nanoclusters In Polyimide, Mircea Chipara, Tom George, Yingfan Xu, Ralph Skomski, Lanping Yue, Nasar Ali, David J. Sellmyer

Physics & Astronomy Faculty Publications

FePt nanoclusters have been implanted onto polyimide films and subjected to thermal annealing in order to obtain a special magnetic phase (L10) dispersed within the polymer. SQUID measurements quantified the magnetic features of the as-prepared and annealed hybrid films. As-implanted FePt nanoparticles in polyimide films exhibited a blocking temperature of 70 ± 5 K. Thermal annealing in zero and 10 kOe applied magnetic field increased the magnetic anisotropy and coercivity of the samples. Wide Angle X-Ray Scattering confirmed the presence of FePt and L10 phase. All samples (as deposited and annealed) exhibited electron spin resonance spectra consisting of two overlapping …

Atomic Data For Zn Ɪɪ: Improving Spectral Diagnostics Of Chemical Evolution In High-Redshift Galaxies, Romas Kisielius, Varsha P. Kulkarni, Gary J. Ferland, Pavel Bogdanovich, Debopam Som, Matt L. Lykins

Physics and Astronomy Faculty Publications

Damped Lyα (DLA) and sub-DLA absorbers in quasar spectra provide the most sensitive tools for measuring the element abundances of distant galaxies. The estimation of abundances from absorption lines depends sensitively on the accuracy of the atomic data used. We have started a project to produce new atomic spectroscopic parameters for optical and UV spectral lines using state-of-the-art computer codes employing a very broad configuration interaction (CI) basis. Here we report our results for Zn ii, an ion used widely in studies of the interstellar medium (ISM) as well as DLAs and sub-DLAs. We report new calculations of many …

Unraveling The Drivers Of The Storm Time Radiation Belt Response, E. K.J. Kilpua, H. Hietala, D. L. Turner, H. E.J. Koskinen, T. I. Pulkkinen, J. V. Rodriguez, Geoffrey Reeves, S. Claudepierre, Harlan E. Spence

Physics & Astronomy

We present a new framework to study the time evolution and dynamics of the outer Van Allen belt electron fluxes. The framework is entirely based on the large-scale solar wind storm drivers and their substructures. The Van Allen Probe observations, revealing the electron flux behavior throughout the outer belt, are combined with continuous, long-term (over 1.5 solar cycles) geosynchronous orbit data set from GOES and solar wind measurements A superposed epoch analysis, where we normalize the timescales for each substructure (sheath, ejecta, and interface region) allows us to avoid smearing effects and to distinguish the electron flux evolution during various …

Section Abstracts: Astronomy, Mathematics And Physics With Material Science

Virginia Journal of Science

Abstracts of the Astronomy, Mathematics, and Physics with Material Science Section for the 93rd Annual Meeting of the Virginia Academy of Science, May 21-23, 2015, James Madison University, Richmond, Virginia

Energetic, Relativistic And Ultra-Relativistic Electrons: Comparison Of Long-Term Verb Code Simulations With Van Allen Probes Measurements, A. Drozdov, Y. Y. Shprits, K. Orlova, A. C. Kellerman, D. A. Subbotin, D. N. Baker, Harlan E. Spence, Geoffrey Reeves

Physics & Astronomy

In this study, we compare long-term simulations performed by the Versatile Electron Radiation Belt (VERB) code with observations from the Magnetic Electron Ion Spectrometer and Relativistic Electron-Proton Telescope instruments on the Van Allen Probes satellites. The model takes into account radial, energy, pitch angle and mixed diffusion, losses into the atmosphere, and magnetopause shadowing. We consider the energetic (>100 keV), relativistic (~0.5–1 MeV), and ultrarelativistic (>2 MeV) electrons. One year of relativistic electron measurements (μ = 700 MeV/G) from 1 October 2012 to 1 October 2013 are well reproduced by the simulation during varying levels of geomagnetic …

Analysis Of Plasmaspheric Hiss Wave Amplitudes Inferred From Low-Altitude Poes Electron Data: Technique Sensitivity Analysis, M. De Soria-Santacruz, W. Li, R. M. Thorne, Q. Ma, J. Bortnik, B. Ni, C A. Kletzing, W. S. Kurth, G. B. Hospodarsky, Harlan E. Spence, Geoffrey Reeves, J. B. Blake, Joseph F. Fennell

Physics & Astronomy

A novel technique capable of inferring wave amplitudes from low-altitude electron measurements from the Polar Operational Environmental Satellites (POES) spacecraft has been previously proposed to construct a global dynamic model of chorus and plasmaspheric hiss waves. In this paper we focus on plasmaspheric hiss, which is an incoherent broadband emission that plays a dominant role in the loss of energetic electrons from the inner magnetosphere. We analyze the sensitivity of the POES technique to different inputs used to infer the hiss wave amplitudes during three conjunction events with the Van Allen Probes. These amplitudes are calculated with different input models …

How Elevated Is The Dynamical-To-Stellar Mass Ratio Of The Ultracompact Dwarf S999?, Joachim Janz, Duncan Forbes, Mark Norris, Jay Strader, Samantha Penny, Martina Fagioli, Aaron Romanowsky

Faculty Publications

No abstract provided.

Measurement Of The Formation Rate Of Muonic Hydrogen Molecules, V. A. Andreev, T. I. Banks, R. M. Carey, T. A. Case, S. M. Clayton, K. M. Crowe, J. Deutsch, J. Egger, S. J. Freedman, V. A. Ganzha, Tim Gorringe, F. E. Gray, D. W. Hertzog, M. Hildebrandt, P. Kammel, B. Kiburg, S. Knaack, P. A. Kravtsov, A. G. Krivshich, B. Lauss, K. R. Lynch, E. M. Maev, O. E. Maev, F. Mulhauser, C. Petitjean, G. E. Petrov, R. Prieels, G. N. Schapkin, G. G. Semenchuk, M. A. Soroka, Vladimir Tishchenko, A. A. Vasilyev, A. A. Vorobyov, M. E. Vznuzdaev, P. Winter

Physics and Astronomy Faculty Publications

Background: The rate λ_ppμ characterizes the formation of ppμ molecules in collisions of muonic pμ atoms with hydrogen. In measurements of the basic weak muon capture reaction on the proton to determine the pseudoscalar coupling g_P, capture occurs from both atomic and molecular states. Thus knowledge of λ_ppμ is required for a correct interpretation of these experiments.

Purpose: Recently the MuCap experiment has measured the capture rate Λ_S from the singlet pμ atom, employing a low-density active target to suppress ppμ formation [V. Andreev et al. (MuCap Collaboration), Phys. Rev. Lett. 110, 012504 (2013) …