Flash-Heating of Circumstellar Clouds by Gamma Ray Bursts

The blast-wave model for gamma-ray bursts (GRBs) has been called into question by observations of spectra from GRBs that are harder than can be produced through optically thin synchrotron emission. If GRBs originate from the collapse of massive stars, then circumstellar clouds near burst sources will be illuminated by intense gamma radiation, and the electrons in these clouds will be rapidly scattered to energies as large as several hundred keV. Low-energy photons that subsequently pass through the hot plasma will be scattered to higher energies, hardening the intrisic spectrum. This effect resolves the "line-of-death" objection to the synchrotron shock model. Illuminated clouds near GRBs will form relativistic plasmas containing large numbers of electron-positron pairs that can be detected within ~ 1-2 days of the explosion before expanding and dissipating. Localized regions of pair annihilation radiation in the Galaxy would reveal past GRB explosions.Comment: 9 pages, 1 figure, submitted to ApJ Letter

Spectral Hardness Decay with Respect to Fluence in BATSE Gamma-Ray Bursts

We have analyzed the evolution of the spectral hardness parameter Epk as a function of fluence in gamma-ray bursts. We fit 41 pulses within 26 bursts with the trend reported by Liang & Kargatis (1996) which found that Epk decays exponentially with respect to photon fluence. We also fit these pulses with a slight modification of this trend, where Epk decays linearly with energy fluence. In both cases, we found the set of 41 pulses to be consistent with the trend. For the latter trend, which we believe to be more physical, the distribution of the decay constant is roughly log-normal, with a mean of 1.75 +/- 0.07 and a FWHM of 1.0 +/- 0.1. Regarding an earlier reported invariance in the decay constant among different pulses in a single burst, we found probabilities of 0.49 to 0.84 (depending on the test used) that such invariance would occur by coincidence, most likely due to the narrow distribution of decay constant values among pulses.Comment: 17 pages, 7 figure pages, 2 table pages, submitted to The Astrophysical Journa

Evolution of the Low-Energy Photon Spectra in Gamma-Ray Bursts

We report evidence that the asymptotic low-energy power law slope alpha (below the spectral break) of BATSE gamma-ray burst photon spectra evolves with time rather than remaining constant. We find a high degree of positive correlation exists between the time-resolved spectral break energy E_pk and alpha. In samples of 18 "hard-to-soft" and 12 "tracking" pulses, evolution of alpha was found to correlate with that of the spectral break energy E_pk at the 99.7% and 98% confidence levels respectively. We also find that in the flux rise phase of "hard-to-soft" pulses, the mean value of alpha is often positive and in some bursts the maximum value of alpha is consistent with a value > +1. BATSE burst 3B 910927, for example, has a alpha_max equal to 1.6 +/- 0.3. These findings challenge GRB spectral models in which alpha must be negative of remain constant.Comment: 12 pages (including 6 figures), accepted to Ap

NOTES: ARE LAND-USE CHANGES REFLECTED IN DIETS OF MOURNING DOVES (ZENAIDA MACROURA) IN EASTERN SOUTH DAKOTA

Food habits of the mourning dove (Zenaida macroura) have been extensively studied in the southern United States (McClure 1943, Korschgen 1958, Carpenter 1971) and consist primarily of vegetable matter throughout their range (Beckwith 1959). Diet studies in several states have indicated agricultural crops, specifically corn and wheat, were the most readily consumed plant seeds (Korshgen 1958, Carpenter 1971). Similarities observed in diets of doves were dependent on the agricultural crops available within the area. For example, in Missouri, some seasonal variability was documented suggesting doves forage based on food availability as much as by food preference (Korschgen 1958). However, in the agriculturally- dominated landscape of east central South Dakota (SD), the two most important food items for doves were green (Setaria viridis) and yellow foxtail (S. glauca; Van’t Hul and Jenks 1992). Large-scale land use changes have occurred in eastern South Dakota in the past few decades and several factors have contributed to increased grassland to cropland conversion (Wright and Wimberly 2013). Conversion of grasslands to agricultural crops has increased as demand for biofuels and commodity prices increased (Secchi and Babcock 2007, Searchinger et al. 2008, Fargione et al. 2009, Wright and Wimberly 2013). In east central South Dakota, corn and soybean plantings have increased from 2,400,000 ha in 1991 to 4,400,000 ha in 2013 (United States Department of Agriculture 2014). These significant land-use changes that have occurred in the intervening 20 years may influence mourning dove feeding habits. We compared mourning dove diet composition in Minnehaha County, South Dakota, USA, to those published 20 years earlier from a study conducted approximately 60 km north (Van’t Hul and Jenks 1992)

The electric dipole response of 76^{76}Se above 4 MeV

The dipole response of $^{76}_{34}$Se in the energy range 4 to 9 MeV has been analyzed using a $(\vec\gamma,{\gamma}')$ polarized photon scattering technique, performed at the High Intensity $\gamma$-Ray Source facility, to complement previous work performed using unpolarized photons. The results of this work offer both an enhanced sensitivity scan of the dipole response and an unambiguous determination of the parities of the observed J=1 states. The dipole response is found to be dominated by $E1$ excitations, and can reasonably be attributed to a pygmy dipole resonance. Evidence is presented to suggest that a significant amount of directly unobserved excitation strength is present in the region, due to unobserved branching transitions in the decays of resonantly excited states. The dipole response of the region is underestimated when considering only ground state decay branches. We investigate the electric dipole response theoretically, performing calculations in a 3D cartesian-basis time-dependent Skyrme-Hartree-Fock framework.Comment: 20 pages, 18 figures, to be submitted to PR

Are Land-use Changes Reflected in Diets of Mourning Doves (Zenaida macroura) in Eastern South Dakota

Food habits of the mourning dove (Zenaida macroura) have been extensively studied in the southern United States (McClure 1943, Korschgen 1958, Carpenter 1971) and consist primarily of vegetable matter throughout their range (Beckwith 1959). Diet studies in several states have indicated agricultural crops, specifically corn and wheat, were the most readily consumed plant seeds (Korshgen 1958, Carpenter 1971). Similarities observed in diets of doves were dependent on the agricultural crops available within the area. For example, in Missouri, some seasonal variability was documented suggesting doves forage based on food availability as much as by food preference (Korschgen 1958). However, in the agriculturally dominated landscape of east central South Dakota (SD), the two most important food items for doves were green (Setaria viridis) and yellow foxtail (S. glauca; Van’t Hul and Jenks 1992)

Nuclear Structure of \u3csup\u3e76\u3c/sup\u3eGe from Inelastic Neutron Scattering Measurements and Shell Model Calculations

The low-lying, low-spin levels of 76Ge were studied with the (n,n′γ) reaction. Gamma-ray excitation function measurements were performed at incident neutron energies from 1.6 to 3.7 MeV, and γ-ray angular distributions were measured at neutron energies of 3.0 and 3.5 MeV. From these measurements, level spins, level lifetimes, γ-ray intensities, and multipole mixing ratios were determined. No evidence for a number of previously placed levels was found. Below 3.3 MeV, many new levels were identified, and the level scheme was re-evaluated. The B(E2) values support low-lying band structure. The 2+ mixed-symmetry state has been identified for the first time. A comparison of the level characteristics with large-scale shell model calculations yielded excellent agreement