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Articles 8371 - 8400 of 9203
Full-Text Articles in Physical Sciences and Mathematics
Random Spots On Chromospherically Active Stars, Joel A. Eaton, Gregory W. Henry, Francis C. Fekel
Random Spots On Chromospherically Active Stars, Joel A. Eaton, Gregory W. Henry, Francis C. Fekel
Information Systems and Engineering Management Research Publications
We have investigated the effect of large numbers of moderately sized spots placed randomly on a differentially rotating star as the explanation of the rotational light curves of magnetically active cool stars. This hypothesis produces light variation very similar to observed light curves of RS CVn binaries, provided there are of order 10-40 spots at any time and provided individual spots have a finite lifetime.
Hde 233517: Lithium And Excess Infrared Emission In Giant Stars, Francis C. Fekel, Richard A. Webb, Russel J. White, Benjamin Zuckerman
Hde 233517: Lithium And Excess Infrared Emission In Giant Stars, Francis C. Fekel, Richard A. Webb, Russel J. White, Benjamin Zuckerman
Information Systems and Engineering Management Research Publications
Recent studies have identified a small class of moderately rapidly rotating, chromospherically active, single giants, some of which are lithium rich. We present evidence suggesting the peculiar K-type star HDE 233517 is one such object. Previously, HDE 233517 has been suggested to be a young star, consistent with its large far-infrared excess and our log ε(Li) ~ 3.3. However, our high-resolution spectroscopic observations show it is likely a single, post-main-sequence K2 giant with v sin i = 15 km s-1 and modest Ca II H and K emission. The giant status of HDE 233517 is determined directly from luminosity-sensitive line …
Simulations Of Electrostatic Modes Of Non-Neutral Plasmas With Small Aspect Ratio In A Penning Trap, Grant W. Mason, Ross L. Spencer, Jonathan A. Bennett
Simulations Of Electrostatic Modes Of Non-Neutral Plasmas With Small Aspect Ratio In A Penning Trap, Grant W. Mason, Ross L. Spencer, Jonathan A. Bennett
Faculty Publications
The dependence on induced charge, experimental geometry, and temperature of electrostatic modes in very low aspect ratio non-neutral plasmas in a Penning trap is considered. The modes are of interest as non-destructive diagnostics of the shape of the plasmas. These investigations include equilibrium calculations of plasma shapes and profiles at finite temperature and particle-in-cell simulations of axisymmetric modes. The results of the simulations are compared to the zero-temperature theory by Dubin [Phys. Rev. Lett. 66, 2076 (1991)] taken to first-order in the aspect ratio and to experimental measurements by Weimer et al. [Phys. Rev. A 49, 3842 (1994)]. In general, …
An Optical And X-Ray Study Of Abell 576, A Galaxy Cluster With A Cold Core, Joseph J. S. Mohr, Margaret J. Geller, Daniel G. Fabricant, Gary Wegner, John Thorstensen, Douglas O. Richstone
An Optical And X-Ray Study Of Abell 576, A Galaxy Cluster With A Cold Core, Joseph J. S. Mohr, Margaret J. Geller, Daniel G. Fabricant, Gary Wegner, John Thorstensen, Douglas O. Richstone
Dartmouth Scholarship
We analyze the galaxy population and dynamics of the galaxy cluster A576; the observational constraints include 281 redshifts (230 new), R- band CCD galaxy photometry over a 2 h^-1^ Mpc x 2 h^-1^ Mpc region centered on the cluster, an Einstein IPC X-ray image, and an Einstein MPC X-ray spectrum. We focus on an 86% complete magnitude-limited sample (R_23.5_ < 17) of 169 cluster galaxies. The cluster galaxies with emission lines in their spectra have a larger velocity dispersion and are significantly less clustered on this 2 h^-1^ Mpc scale than galaxies without emission lines. We show that excluding the emission-line galaxies from the cluster sample decreases the velocity dispersion by 18% and the virial mass estimate by a factor of 2. The central cluster region contains a nonemission galaxy population and an intracluster medium which is significantly cooler (σ_core_ = 387_-105_^+250^ km s^-1^ and T_x_ = 1.6_-0.3_^+0.4^ keV at 90% confidence) than the global populations (σ = 977_-96_^+124^ km s^- 1^ for the nonemission population and T_X_ > 4 keV at 90% confidence). Because (1) the low-dispersion galaxy population is no more luminous than the global population and (2) the evidence for a cooling flow is weak, we suggest that the core of A576 may contain the remnants of …
Absence Of Open Strings In A Lattice-Free Simulation Of Cosmic String Formation, Julian Borrill
Absence Of Open Strings In A Lattice-Free Simulation Of Cosmic String Formation, Julian Borrill
Dartmouth Scholarship
Lattice-based string formation algorithms can, at least in principle, be reduced to the study of the statistics of the corresponding aperiodic random walk. Since in three or more dimensions such walks are transient, this approach necessarily generates a population of open strings. To investigate whether open strings are an artifact of the lattice we develop an alternative lattice-free simulation of string formation. Replacing the lattice with a graph generated by a minimal dynamical model of a first-order phase transition we obtain results consistent with the hypothesis that the energy density in string is due to a scale-invariant Brownian distribution of …
Modeling The Effects Of A Phase-Locked Higher Harmonic In Synchronous Sonoluminescence, Aaron Trickey
Modeling The Effects Of A Phase-Locked Higher Harmonic In Synchronous Sonoluminescence, Aaron Trickey
Honors Capstone Projects and Theses
No abstract provided.
Very High Density Clumps And Outflowing Winds In Qso Broad-Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, R. F. Carswell, F. Hamann, M. M. Phillips, D. A. Verner, Belinda J. Wilkes, R. E. Williams
Very High Density Clumps And Outflowing Winds In Qso Broad-Line Regions, J. A. Baldwin, Gary J. Ferland, K. T. Korista, R. F. Carswell, F. Hamann, M. M. Phillips, D. A. Verner, Belinda J. Wilkes, R. E. Williams
Physics and Astronomy Faculty Publications
Intercomparison of the spectra of seven high-luminosity quasi-stellar objects (QSOs) shows that there is a gradation of properties in their broad emission-line regions (BELRs) that can be understood as differing mixtures of different gas components. Six of these seven objects have unusually narrow BELR profiles, which greatly facilitates the disentangling of blends and measuring of weak lines. In the QSO 0207 - 398, the BELR is made up of at least three kinematically distinct components; its spectrum is in fact a composite of the spectra of the more homogeneous BELRs in the QSOs at either end of our sequence of …
High Metal Enrichments In Luminous Quasars, Gary J. Ferland, Jack A. Baldwin, Kirk T. Korista, Fred Hamann, R. F. Carswell, Mark Phillips, Belinda J. Wilkes, Robert E. Williams
High Metal Enrichments In Luminous Quasars, Gary J. Ferland, Jack A. Baldwin, Kirk T. Korista, Fred Hamann, R. F. Carswell, Mark Phillips, Belinda J. Wilkes, Robert E. Williams
Physics and Astronomy Faculty Publications
We discuss observations of the broad emission line in luminous intermediate redshift quasars, with emphasis on Q0207 -398. This object has relatively sharp lines, allowing us to deconvolve the profiles into distinct components. In this paper we examine the high ionization region, which we show must be matter-bounded, partially transparent to ionizing radiation. We measure a large N V λ1240/He II λ1640 ratio in Q0207-398, but detailed calculations predict this ratio to be ~1 for standard cloud properties. We show that no choice of incident continuum, ionizing photon flux, density, or even the appeal to nonradiative energy sources, can reproduce …
The Chemical Enrichment Of Gas In Broad Absorption Line Qsos: Rapid Star Formation In The Early History Of Galaxies, Kirk Korista, Fred Hamann, Jason W. Ferguson, Gary J. Ferland
The Chemical Enrichment Of Gas In Broad Absorption Line Qsos: Rapid Star Formation In The Early History Of Galaxies, Kirk Korista, Fred Hamann, Jason W. Ferguson, Gary J. Ferland
Physics and Astronomy Faculty Publications
Utilizing spectra from ground-based and Hubble Space Telescope observations, Korista et al. identified at least 12 broad absorption lines in the broad absorption line (BAL) QSO 0226-1024 (zem = 2.256), many for the first time. In the present paper we use seven of their measured column densities to investigate the BAL gas ionization equilibrium and metallicity. We assume that the metal abundances follow the rapid star formation (RSF) models of Hamann & Ferland or are simply scaled from solar ratios to (1) limit the free parameters in constraining the overall metallicity and (2) test the applicability of such a …
Atomic Data For Astrophysics. I. Radiative Recombination Rates For H-Like, He-Like, Li-Like, And Na-Like Ions Over A Broad Range Of Temperature, D. A. Verner, Gary J. Ferland
Atomic Data For Astrophysics. I. Radiative Recombination Rates For H-Like, He-Like, Li-Like, And Na-Like Ions Over A Broad Range Of Temperature, D. A. Verner, Gary J. Ferland
Physics and Astronomy Faculty Publications
We present new calculations and analytic fits to the rates of radiative recombination towards H-like, He-like, Li-like and Na-like ions of all elements from H through Zn (Z=30). The fits are valid over a wide range of temperature, from 3 K to 109 K.
Stochastic Electron Acceleration By Cascading Fast Mode Waves In Impulsive Solar Flares, James A. Miller, Ted N. La Rosa, Ronald L. Moore
Stochastic Electron Acceleration By Cascading Fast Mode Waves In Impulsive Solar Flares, James A. Miller, Ted N. La Rosa, Ronald L. Moore
Faculty Articles
We present a model for the acceleration of electrons from thermal to ultrarelativistic energies during an energy release fragment in an impulsive solar flare. Long-wavelength low-amplitude fast mode waves are assumed to be generated during the initial flare energy release (by, for example, large-scale restructuring of the magnetic field). These waves nonlinearly cascade to higher wavenumbers and eventually reach the dissipation range, whereupon they are transit-time damped by electrons in the tail of the thermal distribution. The electrons, in turn, are energized out of the tail and into substantially higher energies. We find that for turbulence energy densities much smaller …
The Astrophysical Reaction Rate For The 18f(P,Α) 15o Reaction, K. E. Rehm, M. Paul, Andrew D. Roberts, C. L. Jiang, D. Blumenthal, J. Gehring, Robert J. Nickles, J. Nolen, R. C. Pardo, J. P. Schiffer, R. E. Segel
The Astrophysical Reaction Rate For The 18f(P,Α) 15o Reaction, K. E. Rehm, M. Paul, Andrew D. Roberts, C. L. Jiang, D. Blumenthal, J. Gehring, Robert J. Nickles, J. Nolen, R. C. Pardo, J. P. Schiffer, R. E. Segel
Physics and Astronomy Department Publications
Proton and alpha widths for a 3/2+ ( l p = 0) state in 19Ne at Ex-7.1 MeV have been extracted using the results of recent measurements of the 18F(p,α)15O reaction. This l p = 0 resonance dominates the astrophysical reaction rates at temperatures T9>0.5.
Equatorial Wind Compression Effects Across The H-R Diagram., R. Ignace, J. P. Cassinelli
Equatorial Wind Compression Effects Across The H-R Diagram., R. Ignace, J. P. Cassinelli
Richard Ignace
We investigate the degree to which moderate stellar rotation rates can influence the two-dimensional density structure in the winds of four classes of stars: WoIf-Rayet, B[e], asymptotic giant branch (AGB), and novae. These classes are distributed across the H-R diagram and have a wide range of escape speeds and wind acceleration. Furthermore, all have members which possess asymmetric circumstellar nebulae. It has been suggested that these asymmetries could result from stellar winds which have moderate equatorial density enhancements. Large enhancements may arise as the result of stellar rotation as demonstrated by the wind-compressed disk (WCD) model of Bjorkman & Cassinelli. …
A Search For Optical Flares In Chromospherically Active Stars, Gregory W. Henry, M. S. Newsom
A Search For Optical Flares In Chromospherically Active Stars, Gregory W. Henry, M. S. Newsom
Information Systems and Engineering Management Research Publications
We have surveyed four years of archival UBV photometry of 69 chromospherically active stars obtained with the Phoenix-10 automatic photoelectric telescope in search of optical flares on these stars. We demonstrate taht, while flares can be detected in these data, the number of events observed on evolved stars remains very small. Flares were found only on UX Arietis, II Pegasi, and AR Piscium.
Ground-Based Gamma-Ray Burst Follow-Up Efforts: Results Of The First Two Years Of The Batse/Comptel/Nmsu Rapid Response Network, B Mcnamara, T Harrison, James M. Ryan, R M. Kippen, Mark L. Mcconnell, John R. Macri, C Kouveliotou, Gerald J. Fishman, C Meegan, L O. Hanlon, K Bennett, T. A. Spoelstra, V. G. Metlov, N. V. Metlova, E. Feigelson, A. J. Beasley, D. M. Palmer, Scott Barthelmy, Dale E. Gary, E. T. Olsen, S. Levin, P. G. Wannier, M. A. Janssen, The Macho Collaboration, J. Borovicka, P. Pravec, R. Hudec, M. J. Coe
Ground-Based Gamma-Ray Burst Follow-Up Efforts: Results Of The First Two Years Of The Batse/Comptel/Nmsu Rapid Response Network, B Mcnamara, T Harrison, James M. Ryan, R M. Kippen, Mark L. Mcconnell, John R. Macri, C Kouveliotou, Gerald J. Fishman, C Meegan, L O. Hanlon, K Bennett, T. A. Spoelstra, V. G. Metlov, N. V. Metlova, E. Feigelson, A. J. Beasley, D. M. Palmer, Scott Barthelmy, Dale E. Gary, E. T. Olsen, S. Levin, P. G. Wannier, M. A. Janssen, The Macho Collaboration, J. Borovicka, P. Pravec, R. Hudec, M. J. Coe
Physics & Astronomy
No abstract provided.
Main Sequence Masses And Radii From Gravitational Redshifts, Ted Von Hippel
Main Sequence Masses And Radii From Gravitational Redshifts, Ted Von Hippel
Publications
Modern instrumentation makes it possible to measure the mass to radius ratio for main sequence stars in open clusters from gravitational redshifts. For stars where independent information is available for either the mass or the radius, this application of general relativity directly determines the other quantity. Applicable examples are: 1) measuring the radii of solar metallicity main sequence stars for which the mass - luminosity relation is well known, 2) measuring the radii for stars where model atmospheres can be used to determine the surface gravity (the mass to radius squared ratio), 3) refining the mass - radius relation for …
Search For Gamma-Ray Emission From The Lagrangian Points Of Psr 1957+20, R Buccheri, V. Salamone, K Bennett, M Busetta, L Kuiper, W Hermsen, Mark L. Mcconnell, R Much, James M. Ryan, H Steinle, V. Schonfelder
Search For Gamma-Ray Emission From The Lagrangian Points Of Psr 1957+20, R Buccheri, V. Salamone, K Bennett, M Busetta, L Kuiper, W Hermsen, Mark L. Mcconnell, R Much, James M. Ryan, H Steinle, V. Schonfelder
Physics & Astronomy
Compton Gamma Ray Observatory data of the COMPTEL and EGRET telescopes from 3 viewing periods have been used to search for gamma-ray emission from the Lagrangian points L_4_ and L_5_ of the binary system including the eclipsing pulsar PSR1957+20. The result was negative and the upper limits derived remain significantly below detections reported earlier.
Polarization Of Astronomical Maser Radiation. Iii. Arbitrary Zeeman Splitting And Anisotropic Pumping, Moshe Elitzur
Polarization Of Astronomical Maser Radiation. Iii. Arbitrary Zeeman Splitting And Anisotropic Pumping, Moshe Elitzur
Physics and Astronomy Faculty Publications
General solutions of the maser polarization problem are presented for arbitrary absorption coefficients. The results are used to calculate polarization for masers permeated by magnetic fields with arbitrary values of χB, the ratio of Zeeman splitting to Doppler linewidth, and for anisotropic (m-dependent) pumping. In the case of magnetic fields, one solution describes the polarization for overlapping Zeeman components, χB < 1. The χB → 0 limit of this solution reproduces the linear polarization derived in previous studies, which were always conducted at this unphysical limit. Terms of higher order in χB have a negligible effect on …
The H Ii Region Complex G5.48-0.24: Radio Continuum, H I, And Co Observations, Bon-Chul Koo, Kee-Tae Kim, Ho-Gyu Lee, Min S. Yun, Paul T P Ho
The H Ii Region Complex G5.48-0.24: Radio Continuum, H I, And Co Observations, Bon-Chul Koo, Kee-Tae Kim, Ho-Gyu Lee, Min S. Yun, Paul T P Ho
Min S. Yun
We have carried out VLA radio continuum (6 and 20cm), VLA HI 21cm line, and 13CO J = 1 --> 0 line observations of the Galactic H II region G5.48-0.24. We present the continuum maps at 21 cm with 50" resolution and at 6 and 20 cm with 5" resolution. The radio continuum maps show that the H II region is composed of a bright component immersed in a diffuse emission of 6' (or 21 pc) radius. The bright component has a compact (0.7 pc) core surrounded by an extended (3.4 pc) halo. According to Wood & Churchwell (1989), the …
Comptel Measurements Of Mev Gamma-Ray Burst Spectra, R M. Kippen, James M. Ryan, A Connors, Mark L. Mcconnell, C Winkler, L O. Hanlon, V Schonfelder, J Greiner, M Varendorff, W Collmar, W Hermsen, L Kuiper
Comptel Measurements Of Mev Gamma-Ray Burst Spectra, R M. Kippen, James M. Ryan, A Connors, Mark L. Mcconnell, C Winkler, L O. Hanlon, V Schonfelder, J Greiner, M Varendorff, W Collmar, W Hermsen, L Kuiper
Space Science Center
We present results from the on-going spectral analysis of gamma-ray bursts measured by the COMPTEL instrument in its main Compton “Telescope” observing mode (0.75–30 MeV). Thus far, 18 bursts have been analyzed from three years (April 1991–April 1994) of observations. The time-averaged spectra of these events above 1 MeV are all consistent with a simple power law model with spectral index in the range 1.5–3.5. Exponential, thermal bremsstrahlung and thermal synchrotron models are statistically inconsistent with the burst sample, although they can adequately describe some of the individual burst spectra. We find good agreement between burst spectra measured simultaneously by …
Hard X‐Ray Polarimetry Of Solar Flares With Batse, Mark L. Mcconnell, D J. Forrest, W T. Vestrand, M Finger
Hard X‐Ray Polarimetry Of Solar Flares With Batse, Mark L. Mcconnell, D J. Forrest, W T. Vestrand, M Finger
Space Science Center
We describe a technique for measuring the polarization of hard X‐rays from solar flares based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Since the albedo component can represent a relatively large fraction …
Theoretical Hei Line Intensities In Gaseous Nebulae: Ngc 1976, 6572 And Ic 4997, J. B. Kingdon, Gary J. Ferland
Theoretical Hei Line Intensities In Gaseous Nebulae: Ngc 1976, 6572 And Ic 4997, J. B. Kingdon, Gary J. Ferland
Physics and Astronomy Faculty Publications
Smits has recently calculated theoretical He I intensities for a large number of lines for conditions appropriate to gaseous nebulae. These are likely to remain the definitive calculations for some time to come. A comparison of these line ratios with observed values in three nebulae reveals some discrepancies. We show that these discrepancies are reduced when collisional effects from the metastable 23S level are included, and that it is not necessary to invoke an unknown depopulation mechanism for the He I23S level.
Rotational Periods And Starspot Activity Of Young Solar-Type Dwarfs In The Open Cluster Ic 4665, S. Allain, C. Prosser, Laurence A. Marschall, Bentley D. Laaksonen
Rotational Periods And Starspot Activity Of Young Solar-Type Dwarfs In The Open Cluster Ic 4665, S. Allain, C. Prosser, Laurence A. Marschall, Bentley D. Laaksonen
Physics and Astronomy Faculty Publications
We present the results of a V-band photometric monitoring survey of 15 late-type dwarfs in the young open cluster IC 4665. Low-amplitude periodic light variations are found for 8 stars and ascribed to the modulation by starspots that cover typically a few percent of the stellar disk. Periods range from 0.6 to 3.7d, translating to equatorial velocities between 13 and 93 km.s-1. That no period longer than 4d was detected suggests a relative paucity of extremely slow rotators (Veq << 10 km.s-1) among late-type dwarfs in IC 4665. The fractional number of slow rotators in IC 4665 is similar to that of Alpha Per cluster, suggesting that IC 4665 is close in age to Alpha Per (~50 Myr).
A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour
A Simple Model For Nonequilibrium Fluctuations In A Fluid, Alejandro Garcia, F. Baras, M. Malek Mansour
Faculty Publications
Presents a train model that shows the long-range spatial correlations of fluctuations in nonequilibrium fluid systems. Illustration of model through analysis of flat-car trains running on parallel tracks; Simulation of train model in computers; Theoretical analysis for fluctuations in the train model; Relationship between train model and the fluctuating hydrodynamic theory of fluids.
Hd 12545, A Study In Spottedness, Melissa Hampton, Gregory W. Henry, Joel A. Eaton, Richard A. Nolthenius, Douglas S. Hall
Hd 12545, A Study In Spottedness, Melissa Hampton, Gregory W. Henry, Joel A. Eaton, Richard A. Nolthenius, Douglas S. Hall
Information Systems and Engineering Management Research Publications
We have solved two sets of light curves of HD 12545 at its epoch of extreme spottedness in 1990-91, one of which coincides with an independent set analyzed recently by Strassmeier and Olah. Even for the huge amplitudes observed, these light-curve solutions did not give reliable determinations of several important spot properties. Specifically, we find that we could obtain acceptable solutions for a wide range of inclination; that spot temperature depends on inclination assumed, falling in the range Delta-T = Tstar - Tspot = 650-1200 K for inclinations of 70-30 deg; that spot latitudes derived from the light curves are …
A Group Of Galaxies At Redshift 2.38, Paul J. Francis, Bruce E. Woodgate, Stephen J. Warren, Palle Møller, Margaret Mazzolini, Andrew J. Bunker, James D. Lowenthal, Ted B. Williams, Takeo Minezaki, Yukiyasu Kobayashi, Yuzuru Yoshii
A Group Of Galaxies At Redshift 2.38, Paul J. Francis, Bruce E. Woodgate, Stephen J. Warren, Palle Møller, Margaret Mazzolini, Andrew J. Bunker, James D. Lowenthal, Ted B. Williams, Takeo Minezaki, Yukiyasu Kobayashi, Yuzuru Yoshii
Astronomy: Faculty Publications
We report the discovery of a group of galaxies at redshift 2.38. We imaged ∼ 10% of a claimed supercluster of QSO absorption lines at z = 2.38. In this small field (2′ radius), we detect two Lyα-emitting galaxies. The discovery of two such galaxies in our tiny field supports Francis & Hewett's interpretation of the absorption-line supercluster as a high-redshift Great Wall. One of the Lyα galaxies lies 22″ from a background QSO and may be associated with a multicomponent Lyα absorption complex seen in the QSO spectrum. This galaxy has an extended (∼50 kpc), lumpy Lyα morphology surrounding …
The Angular Distribution Of Comptel Gamma-Ray Bursts, R M. Kippen, James M. Ryan, A Connors, Mark L. Mcconnell, H Hartmann, C Winkler, L O. Hanlon, V Schonfelder, J Greiner, M Varendorff, W Collmar, W Hermsen, L Kuiper
The Angular Distribution Of Comptel Gamma-Ray Bursts, R M. Kippen, James M. Ryan, A Connors, Mark L. Mcconnell, H Hartmann, C Winkler, L O. Hanlon, V Schonfelder, J Greiner, M Varendorff, W Collmar, W Hermsen, L Kuiper
Space Science Center
The superior burst location capability of the COMPTEL instrument aboard the Compton Gamma-Ray Observatory allows us to study the small-scale angular distribution of burst sources with good sensitivity even though the number of burst detections is small. We accumulate four years (April 1991–April 1995) of observations to form a catalog of 27 burst locations whose mean 1σ uncertainty is ∼1°. We find that the COMPTEL bursts are consistent with an isotropic distribution of sources, yet the spatial coincidence of two of the bursts within COMPTEL’s angular resolution indicates the possibility of repetition. This possibility is studied using the two-point angular …
Using Batse To Measure Gamma-Ray Burst Polarization, Mark L. Mcconnell, D J. Forrest, W T. Vestrand, M H. Finger
Using Batse To Measure Gamma-Ray Burst Polarization, Mark L. Mcconnell, D J. Forrest, W T. Vestrand, M H. Finger
Space Science Center
We describe a technique for measuring the polarization of hard x-rays from γ-ray bursts based on the angular distribution of that portion of the flux which is scattered off the top of the Earth’s atmosphere. The scattering cross section depends not only on the scatter angle itself, but on the orientation of the scatter angle with respect to the incident polarization vector. Consequently, the distribution of the observed albedo flux will depend on the direction and the polarization properties (i.e., the level of polarization and polarization angle) of the source. Although the BATSE design (with its large field-of-view for each …
Looking For The Source Of ∼Hour-Long Soft X-Ray Emission Following Grb 780506, A Connors, Mark L. Mcconnell
Looking For The Source Of ∼Hour-Long Soft X-Ray Emission Following Grb 780506, A Connors, Mark L. Mcconnell
Space Science Center
GRB 780506, a gamma-ray burst discovered in HEAO 1 A-4 data, was unusual in three respects. First, it was well-measured (by HEAO 1 A-2) in 2–60 keV X-rays. Second, two minutes after it ended, HEAO 1 A-2 detected a faint resurgence of 2–10 keV flux, lasting roughly an hour. From recently calculated position constraints, it appears the source of the extended flux is consistent with the source of the burst, and probably not from a serendipitous transient along the Galactic plane. Third, it now appears GRB 780506 belongs to a newly discovered softer subclass of gamma-rays bursts. This subclass is …
Extended Γ‐Ray Emission In Solar Flares, G Rank, K Bennett, H Bloemen, H Debrunner, J Lockwood, Mark L. Mcconnell, James M. Ryan, V Schonfelder, R Suleiman
Extended Γ‐Ray Emission In Solar Flares, G Rank, K Bennett, H Bloemen, H Debrunner, J Lockwood, Mark L. Mcconnell, James M. Ryan, V Schonfelder, R Suleiman
Space Science Center
During the solar flare events on 11 and 15 June 1991, COMPTEL measured extended emission in the neutron capture line for about 5 hours after the impulsive phase. The time profiles can be described by a double exponential decay with decay constants on the order of 10 min for the fast and 200 min for the slow component. Within the statistical uncertainty both flares show the same long‐term behaviour. The spectrum during the extended phase is significantly harder than during the impulsive phase and pions are not produced in significant numbers before the beginning of the extended emission. Our results …