Gamma-ray Continuum Research Articles

Nuclear line spectroscopy of the 1981 April 27 solar flare

The intensities, line centers, and widths of the 13 strongest narrow lines appearing in the observed count spectrum of April 27, 1981 solar flare are determined. It is found that the gamma-ray continuum underlying the narrow lines cannot be modeled solely with a power law, and must be modeled with more structure than simple shapes can provide. While the narrow-line centers are well-determined, both the line intensities and the line widths can vary considerably as the underlying continuum model is changed. Using a 'nuclear continuum' model based on theoretical considerations which provides a good fit to the data, it is found that, while the emission attributed to nuclear interaction and that attributed to electron interactions varied considerably as the flare progressed, the ratio of these two emissions was consistent with a constant value of 1.94 + or - 0.39 throughout the flare.

Secondary electron production and the millimeter to gamma-ray continuum of emission-line quasi-stellar objects

A model is outlined to explain the multifrequency continua of active galactic nucleus (AGN) and QSOs based on synchrotron and Compton emission of secondary electrons. 3C 273 is used as a particular guide for observational constraints since it so well observed from radio to gamma-ray photon energies. In this model the large blue bump and blue bump Compton components arise in the innermost region near a supermassive compact object with strong magnetic field. Infrared synchrotron emission and infrared Compton components arise in the low-field region. The model results in bumps, wiggles, and inflections in the multifrequency continuum that correspond to those observed. 47 refs.

The nature of the annihilation radiation and gamma-ray continuum from the Galactic center region

Analysis of the observations of the time-dependent, electron-positron annihilation line radiation and gamma-ray continuum emission from the region of the Galactic center shows that ther are two components to the emission: (1) a variable, compact source of 511 keV annihilation line and higher energy continuum emission active from about 1977 through 1979 at or near the Galactic center; and (2) a steady, diffuse interstellar source of 511 keV annihilation line and orthopositronium continuum emission, having a galactic longitudinal distribution consistent with that of the more than 70 MeV gamma rays or the molecular (CO) gas. It is found that the continuum spectrum of the compact source shows no evidence for orthopositronium annihilation. It is suggested that all of the three-photon orthopositronium continuum observed so far originates from the diffuse interstellar component. The continuum spectrum of the compact source is very similar to that of the black-hole candidate Cygnus X-1, supporting our earlier arguments that this object, at or near the Galactic center, is a black hole of stellar mass.

Annihilation Radiation and Gamma-Ray Continuum from the Galactic Center Region

Observations of the time-dependent, electron-positron annihilation line radiation and gamma-ray continuum emission from the region of the Galactic Center show that there are two components to the annihilation line emission: a variable, compact source at or near the Galactic Center, and a steady, diffuse interstellar distribution. We suggest that the annihilating positrons in the compact source, observed from 1977 through 1979, result from photon-photon pair production, most likely around an accreting black hole, and that the annihilating, interstellar positrons result from the decay of radionuclei produced by thermonuclear burning in supernovae.

Search for gamma-ray continuum emission at MeV energies from the Galactic center region

view Abstract Citations (6) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Search for Gamma-Ray Continuum Emission at MeV Energies from the Galactic Center Region Schoenfelder, V. ; von Ballmoos, P. ; Diehl, R. Abstract From balloon flight data of the MPE Compton telescope, constraints on the continuum emission of the Galactic center region at MeV energies were derived. The Galactic center point source flux was found to be less than 2.8×10-3cm-2s-1 between 0.6 to 3.0 MeV, which implies that the source was in a "low-intensity state" during the time of the observation (1982 October 31). The diffuse γ-ray flux from the central region of the Galactic plane was determined to be smaller than 7.2×10-3cm-2s-1rad-1 at l = 0 in the same energy interval. Publication: The Astrophysical Journal Pub Date: December 1988 DOI: 10.1086/166962 Bibcode: 1988ApJ...335..748S Keywords: Continuous Radiation; Galactic Nuclei; Gamma Ray Spectra; Milky Way Galaxy; Abundance; Balloon Flight; Heao 3; Space Radiation; COSMIC RAYS: ABUNDANCES; GALAXIES: NUCLEI; GALAXIES: THE GALAXY; GAMMA RAYS: GENERAL full text sources ADS | data products SIMBAD (4)

Directionality of continuum gamma rays from solar flares

Using hard X-ray burst spectrometer total counts as calibration, the changes in the brightness of gamma rays above 300 keV as a function of the heliocentric angle of a flare are investigated. The normalized gamma-ray brightness, on the average, increases with the heliocentric angle; a flare at the limb is estimated to be 13 times brighter in beam gamma rays than a similar flare near the central meridian. Both pancakelike electron distributions and downward beam distributions can be adjusted to produce the deduced limb brightening.

Positron annihilation radiation from the Galactic center - 'Cheshire cat' Compton scattering and the origin of excess continuum

Two observations of the gamma-ray spectrum from the direction of the Galactic center were made by HEAO 3 in the fall of 1979 and the spring of 1980. The 2-gamma 511 keV annihilation line flux decreased by a factor of about three during the 6 months between these observations, while the excess gamma-ray continuum below the annihilation line, often interpreted as 3-gamma decay of orthopositronium, barely changed. This discrepancy in temporal behavior makes the identification of the bulk of excess continuum as 3-gamma decay of positronium difficult. It is shown that Compton scattering of the line and high-energy radiation provides a natural explanation for the surprisingly small changes seen in the excess continuum. Scattered photons are delayed by a time corresponding to the size of the scattering region. For the annihilation source in the Galactic center, this distance is probably a fraction of a parsec. Thus, even after the high-energy continuum and annihilation line are gone, low-energy Compton-scattered photons can still be detected with an almost unchanged flux.

Moderately deformed bands in the continuum of144Gd

The lifetimes of the gamma-ray continuum in144Gd were measured up to spin ∼ 50ħ via the DSAM technique following the74Ge(72Ge, 2n) reaction at 270 MeV beam energy. The average Doppler Shift of theE2 bump corresponds mostly to a structure with a deformation (β∼0.2–0.3), consistent with the triaxial structure predicted to lie close to the yrast line at spins 30–50ħ in this nucleus.

Simultaneous population of large and small deformation bands at very high spin in 152Dy.

The lifetimes of the gamma-ray continuum at spins above 40h-dash-bar were measured in /sup 152/Dy via the Doppler shift attenuation technique following the /sup 74/Ge(/sup 80/Se,2n) and /sup 76/Ge(/sup 80/Se,4n) reactions, at beam energies of 285 and 320 MeV, respectively. Although the deduced average quadrupole moments are smaller than the value expected for superdeformed bands, the variation of the observed Doppler shift as a function of gamma-ray energy suggests that both small deformation (..beta..approx.0.2) and more deformed structures (possibly superdeformed) are present in the very high spin continuum of this nucleus.

Prospects for observations of nucleosynthetic gamma-ray lines and continuum from SN 1987A

Expected flux levels for nucleosynthetic gamma-ray line and continuum emissions from SN 1987A are calculated for several models. The dominant line emission is from freshly synthesized Ni-56 and its decay daughters, and the continuum is from Compton scattering of line photons. For a 15 solar mass Type II model, the light curve for the 0.847 MeV gamma-ray line peaks in September 1988 at 3 x 10 to the -4th photons/sq cm/s. This is detectable only by new, ultrasensitive balloon-borne spectrometers. For models with substantial mass loss from their envelopes, the peak is in early 1988 at about 0.01 photons/sq cm/s, which is detectable at high significance levels by all current instruments. The continuum emission in the 0.05-0.5 MeV band peaks about 100 days before the 0.847 MeV line peak. This Compton precursor is observable at about the same significance level as the lines.

Investigation of Martian H2O and Co2 via orbital gamma ray spectroscopy

A number of presently unanswered questions concerning H2O and CO2 on Mars may be addressed using data from an orbital gamma ray spectrometer such as the one planned for the Mars Observer mission. Problems that could be addressed include the ice/dust ratio of the polar layered deposits; the dust content and thickness of polar perennial ice; the water content of hydrated silicates; the depth, distribution, and concentration of ground ice; the possible existence of liquid water “oases”; and the thickness, variability, and H2O content of the seasonal CO2 frost cap. We investigate the capability of an orbital gamma ray spectrometer to address these problems by calculating the gamma ray signal produced by the Martian atmosphere and by several simple models of Martian surface materials. The Martian surface is modeled as one or two layers composed of various arrangements of “Viking soil,” H2O, and CO2. We calculate (1) the production of neutrons in the atmosphere and in the subsurface material by cosmic ray interactions, (2) the scattering of neutrons and the resultant neutron energy spectrum and spatial distributions, (3) the production of gamma rays by neutron prompt capture and nonelastic scatter reactions, (4) the production of gamma rays by natural radionuclides, (5) the attenuation of the gamma ray signal by passage through surface materials and the Martian atmosphere, (6) the production of the gamma ray continuum background, and (7) the uncertainty in gamma ray line strengths that results from the combined signal and background observed by the detector. Two types of data give us information about the concentration and distribution of hydrogen: the strength of the 2.223‐MeV line of H and the ratio of gamma rays from inelastic scatter to gamma rays due to prompt capture for an element such as Si or Fe. The latter provides information about H by giving an indirect indication of the nature of the neutron energy spectrum. The two techniques are sensitive to the presence of H at different depths. Using both techniques then, we in many cases will be able to determine uniquely both the thicknesses and the H2O content of layers on the Martian surface from the gamma ray signal that will be observed. For investigation of CO2 layers, we can use both the 4.945‐MeV prompt capture line of carbon and, in some cases, the attenuation produced by passage of gamma rays from natural radionuclides through a CO2 layer to determine layer composition and thickness. Our results show that orbital gamma ray data can be used to extract a considerable amount of information about the quantity and vertical distribution of volatiles near the Martian surface. The addition of the capability to measure independently the neutron energy spectrum will further enhance the usefulness of this experiment.

Photoerosion of nuclei in quasar emission-line regions

The possible occurrence of photoerosion in active galactic nuclei (AGN) emission-line region gas is examined. The effect of with h(nu) radiation greater than 10 MeV on the emission-line gas for an AGN is investigated. It is determined that the flux of h(nu) greater than 10 MeV protons at the inner edge emission-line region is 2.9 x 10 to the 15th photons/sq cm per sec. The relations between the mean cross section and atomic mass, abundance of nuclei and adjacent atomic masses, and the chemical composition and time are studied. It is noted that photoerosion explains the presence of an inner boundary in the emission-line region of AGN; and the gamma-ray continuum observed in AGN is related to the composition of BLR clouds. 29 references.

Electromagnetic cascades in the magnetosphere of a very young pulsar - A model for the positron production near the Galactic center

A detailed model for positron production by a young pulsar is presented. It is shown that electromagnetic cascades can develop in a young pulsar's magnetosphere, and the model results are applied to the pulsar which is hypothesized to lie near the Galactic center. It is found that such a pulsar would be expected to produce relatively low energy electron-positron pairs with an efficiency rating high enough to explain the observed luminosity of the Galactic center annihilation line. Virtually all of the gamma ray continuum radiation produced in the cascades would be beamed along the magnetic poles of the neutron star, and therefore probably would not be observed from earth. Some observational predictions generated by the proposed model for the Galactic center positron source are given.

Hard X-ray and gamma-ray bremsstrahlung production by high-energy protons in solar flares

The production rates of hard X-rays and the gamma-ray continuum by protons during solar flares are computed exactly, paying special attention to the Lorentz transformation of the radiation. The maximal quantum of the radiation in proton-electron bremsstrahlung is addressed, and angle and energy differential cross sections of X-rays and gamma rays and the rates of these radiations in the thick-target model are presented. A model is proposed for solar X-rays and gamma-rays. It is found that when an energetic proton interacts with an ambient electron, there is a maximum of energy of the emitted photon in each direction whose highest value is in the direction in which the photon is moving and whose lowest value is on the opposite side. At small angles the maximal energy is greater than the energy of an electron having the same velocity as the proton. 42 references.

Acceleration of interplanetary solar electrons in the 1982 August 14 flare

The solar flare on August 14, 1982 (about 0507 UT) produced hard X-rays, gamma-rays, and an electron-rich interplanetary particle event. Because of its location (N11, W61), the flare site was magnetically well connected to the ISEE 3 spacecraft. The ISEE 3 observations have provided a detailed time history of 15 keV-1.9 MeV photon emission from the flare and the relativistic (greater than 3 MeV) solar electrons in interplanetary space. These observations indicate that a significant fraction of the relativistic electrons escaping from the sun were accelerated during the impulsive phase simultaneously with the energetic electrons producing the hard X-ray and gamma-ray continuum at the sun.

Analysis of continuum gamma-ray emission in precompound-decay reactions

Abstract A model is developed for the statistical description of continuum γ-ray emission in precompound reactions. Consistency requirements are derived and discussed. An ambiguity in the generalization of the Brink-Axel hypothesis to precompound decay is pointed out.

Effect of γ-softness on continuum gamma-ray spectra

In the case that a nuclear system has a large fluctuation in the direction of triaxiality, we examine the possible feature expected to appear in the continuum gamma-ray spectra, especially a possibility of the filling in the central valley of the two-dimensional gamma-energy coincidence spectra.

Spin precession of unresolved high-spin states in 153–156Dy

Abstract Fast Dy recoils produced by the inverse reactions 24 Mg ( 136 Xe , x n ) and 26 Mg ( 132 Xe , x n ) were subjected to transient fields in ferromagnetic gadolinium. Spin precession results from continuous and discrete gamma rays were used to deduce average g -factors and collectivities at spins I = 20–30 h . We observe marked differences in the two bombardments, with 156 Dy exhibiting large collectivity and reduced g -factors ( g ≈ 0.2), whereas 154 Dy shows decreased collectivity and large g -factors ( g ≈ 0.4).

Direction of the angular momentum in the entry state and the crystal ball

In a crystal ball all continuum gamma rays of a cascade from the entry state to a yrast state can in principle be observed. If one assumes a preference for stretched E2 transitions one expects a 'doughnut'-shaped angular distribution where the symmetry axis gives the direction of the entry-state angular momentum approximately. The computer code ICARUS, which simulates gamma -ray cascades after heavy-ion fusion reactions, is extended to include angular distributions. By Monte-Carlo simulation one tests how accurately one can extract the direction of the entry angular momentum as a function of excitation energy and angular momentum of the entry state. For 158Er the mean error varies from 20 degrees -40 degrees depending on excitation energy and angular momentum. The entry-state weighted mean error is 25 degrees .

Measurement of the linear polarization of continuum gamma rays from ( 32S, xn) reactions to prolate and oblate rare-earth nuclei

We describe the techniques and report the results of a measurement of the linear polarization, P γ of continuum γ-rays from Er and Dy nuclei produced in ( 32S, xn) reactions on 130Te and 124Sn targets. For the prolate 156–158Er isotopes we find P γ ≈ 0.35 in the γ-ray energy range if0.3 MeV ≦ E γ ≦ 1.5 MeV, thus confirming the E2 nature of the unresolved yrast cascades in rotational nuclei. In contrast, the rather small polarization P γ ≈ 0.05 for E γ ≦ 1.0 MeV measured for the oblate 151,152Dy isotopes, and the shape of the spectrum of continuum γ-rays suggest a rather direct feeding of the yrast states by statistical cascades. For 1.0 MeV ≦ E γ ≦ 1.5 MeV we find P γ ≈ 0.3 indicating collective rotations of the Dy nuclei at spin I ≧ 40 h z.shtsls; . Measurements of γ-ray angular distributions with a collimated NaI detector support these results. From the reduction of the P γ , and A 2 values of the γ-ray continuum in 156–158Er, compared to those measured for discrete E2 yrast transitions, we obtain estimates for the intensities of the M1 and statistical components in the continuum of these nuclei.