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NASA NTRS1977

Diffuse gamma radiation

An examination of the intensity, energy spectrum, and spatial distribution of the diffuse gamma-radiation observed by SAS-2 satellite away from the galactic plane in the energy range above 35 MeV has shown that it consists of two components. One component is generally correlated with galactic latitudes, the atomic hydrogen column density was deduced from 21 cm measurements, and the continuum radio emission, believed to be synchrotron emission. It has an energy spectrum similar to that in the plane and joins smoothly to the intense radiation from the plane. It is therefore presumed to be of galactic origin. The other component is apparently isotropic, at least on a coarse scale, and has a steep energy spectrum. No evidence is found for a cosmic ray halo surrounding the galaxy in the shape of a sphere or oblate spheroid with galactic dimensions. Constraints for a halo model with significantly larger dimensions are set on the basis of an upper limit to the gamma-ray anisotropy.

Fichtel, C. E.↗

DOE OSTI2023

Gamma-ray imaging of inertial confinement fusion implosions reveals remaining ablator carbon distribution

The joint LANL/LLNL nuclear imaging team has acquired the first gamma-ray images of inertial confinement fusion implosions at the National Ignition Facility. The gamma-ray image provides crucial information to help characterize the inertially confined fuel and ablator assembly at stagnation, information that would be difficult to acquire from neutron or x-ray observations. Gamma imaging visualizes both gamma radiation emitted directly in deuterium–tritium (DT) fusion reactions as well as gamma rays produced when DT fusion neutrons scatter inelastically on carbon nuclei in the remaining ablator of the fuel capsule. The resulting image provides valuable information on the position and density of the remaining ablator and potential contamination of the hot spot—a powerful diagnostic window into the capsule assembly during burn.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

NASA NTRS1994

Do gamma-ray bursts originate from an extended Galactic Halo of high-velocity neutron stars?

The gamma-ray burst brightness distribution is inhomogeneous and the distribution on the sky is nearly isotropic. These features argue against an association of gamma-ray bursts with those Galactic objects that are known to exhibit a strong concentration toward the Galactic center or plane. The observed statistical properties indicate a cosmological origin. Circumstantial evidence suggests that neutron stars are involved in the burst phenomenon. Here we consider Population II neutron stars in an extended Galactic Halo (EGH) as an alternative to cosmological scenarios. The Burst and Transient Source Experiment (BATSE) data indicate a small deviation from isotropy near the 2 sigma level of statistical significance. If confirmed for an increasing number of bursts, these anisotropies could rule out cosmological scenarios. On the other hand, EGH models require small anisotropies like those observed by BATSE. We consider simple distribution models to determine the generic properties such halos must have to be consistent with the observations and discuss the implications of the corresponding distance scale on burst models.

Hartmann, Dieter H.↗

NASA NTRS1992

High energy gamma ray observations

Since the trajectories of astrophysical charged particles are bent by magnetic fields and normally curl many times before their detection, their origin may not be inferred from their directions as is the case with photons. Fortunately, charged particles reveal their presence through interactions in many instances leading to high-energy gamma rays. Bremsstrahlung, Compton, synchrotron, and curvature radiation all generally have a monotonically decreasing energy spectra reflecting that of the parent particles, whereas nucleon-nucleon radiation has a maximum at about 70 MeV reflecting the nature of the interaction process. Gamma radiation has been seen coming from neutron stars in pulses with the same period as the radio pulsar. Solar gamma rays also have been seen, as have short bursts of gamma rays whose origin remain a mystery. Galactic diffuse gamma radiation reveals the distribution of cosmic rays in our Galaxy. Beyond our Galaxy, active galaxies are seen in gamma rays implying a huge energy in the form of cosmic rays to be present there. The Optically Violent Variable quasar 3C 279 is particularly astounding. During an active state 3C 279 was seen to be emitting approximately 10 exp 48 erg/s if its radiation is isotropic.

Fichtel, Carl E.↗

NASA NTRS2012

Combined Effects of Gamma Radiation and High Dietary Iron on Peripheral Leukocyte Distribution and Function

Both radiation and increased iron stores can independently increase oxidative damage, resulting in protein, lipid and DNA oxidation. Oxidative stress increases the risk of many health problems including cancer, cataracts, and heart disease. This study, a subset of a larger interdisciplinary investigation of the combined effect of iron overload on sensitivity to radiation injury, monitored immune parameters in the peripheral blood of rats subjected to gamma radiation, high dietary iron or both. Specific immune measures consisted of: (1) peripheral leukocyte distribution, (2) plasma cytokine levels and (3) cytokine production profiles following whole blood mitogenic stimulation

Crucian, Brian E.↗

DOE OSTI2022

Measurements of jet yield and acoplanarity using semi-inclusive $\gamma_{\text{dir}}$+jet and $\pi^{0}$+jet distributions in $p$+$p$ and central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV by STAR

The STAR collaboration presents measurements of semi-inclusive distributions of charged jets recoiling from high transverse energy (E T ) direct photon and π 0 triggers in p+p and central Au+Au collisions at $\sqrt{s_{NN}} = 200$ GeV. Jets are reconstructed from charged particles using the anti-k T algorithm with jet resolution parameters R = 0.2 and 0.5. The large uncorrelated background in central Au+Au collisions is corrected using a mixed-event technique. This enables a jet measurement extending to low transverse momentum and large R with well-controlled systematic uncertainties. We present measurements of the jet R dependence of suppression, intra-jet broadening, and acoplanarity of π 0 +jet and γ dir +jet for trigger E T between 9–20 GeV.

Anderson, Derek↗

DOE OSTI2022

Measurement of Medium-induced Modification of Jet Yield and Acoplanarity Using Semi-inclusive $\gamma _{\mathrm {dir}}+$jet and $\pi ^{0}+$jet Distributions in $p+p$ and Central Au$+$Au Collisions at $\sqrt {s_{NN}} = 200$ GeV by STAR

The STAR Collaboration presents measurements of semi-inclusive distributions of charged jets recoiling from high transverse energy ($E_T$) direct photon and $π^0$ triggers in $p+p$ and central Au+Au collisions at $\sqrt{sNN}$=200 GeV. Jets are reconstructed from charged particles using the anti-$k_T$ algorithm with jet resolution parameters R=0.2 and 0.5. The large uncorrelated background in central Au+Au collisions is corrected using a mixed-event technique. This enables a jet measurement extending to low transverse momentum and large R with well-controlled systematic uncertainties. We present measurements of the jet R dependence of suppression, intra-jet broadening, and acoplanarity of $π^0$+jet and $γ_{dir}$+jet for trigger $E_T (E_{T}^{trig})$ between 9–20 GeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

NASA NTRS1994

Constraints on the luminosity function of gamma-ray bursts detected by BATSE

We have utilized the integral moment analysis technique of Horack & Emslie to extract information on the allowable form of the luminosity function for gamma-ray bursts observed by Burst and Transient Source Experiment (BATSE). Using the general properties of moments, we are able to derive constraints on the range of luminosity from which the gamma-ray bursts must be sampled. These constraints are independent of the form of the radial distribution of the gamma-ray bursts, and depend only on the assumptions that space is Euclidean and that the luminosity function phi(L) is distance independent. For power-law luminosity functions of the form phi(L) = A(sub 0)L(exp -alpha), we find that the range of luminosity from which 80% of the gamma-ray bursts must be sampled cannot exceed approximately 6.5, with a 3 sigma upper limit of 12-15, regardless of the value of alpha.

Horack, J. M.↗

NASA NTRS2011

Evaluation of the Combined Effects of Gamma Radiation and High Dietary Iron on Peripheral Leukocyte Distribution and Function

NASA is concerned with the health risks to astronauts, particularly those risks related to radiation exposure. Both radiation and increased iron stores can independently increase oxidative damage, resulting in protein, lipid and DNA oxidation. Oxidative stress increases the risk of many health problems including cancer, cataracts, and heart disease. This study, a subset of a larger interdisciplinary investigation of the combined effect of iron overload on sensitivity to radiation injury, monitored immune parameters in the peripheral blood of rats subjected to gamma radiation, high dietary iron or both. Specific immune measures consisted of (A) peripheral leukocyte distribution; (B) plasma cytokine levels; (C) cytokine production profiles following whole blood stimulation of either T cells or monocytes.

Crucian, Brian E.↗

NASA NTRS1985

Nuclear cascades in electromagnetic showers produced by primary gamma-quanta in the atmosphere

Distributions were calculated for the number of electrons N sub e, number of muons with the energy above 5 GeV N sub mu and the energy of hadron component E sub h in electromagnetic showers, produced by primary gamma-quanta with energies theta approx. equals 30 deg and observed at the mountain level 700 g/square centimeters. The mean number of nuclear interactions of photos with the energy above 5 GeV is about 0.3 per each TeV of the primary energy and nuclear cascades take out in average about 2% of the total shower energy. The mean number of 5 GeV muons for the electromagnetic shower is (2 to 5)% from the number of muons in cosmic ray showers with the same number of electrons at the observation level. similar value for the total energy of hadron component is also (2 to 5)%. N sub mu and N sub e values as well as E sub h and n sub e don't correlate at the fixed primary energy E sug gamma (o). Between N sub mu and E sub h there is a positive correlation at the given E sub gamma.

Danilova, T. V.↗

DOE OSTI2022

Constraining dark matter microphysics with the annihilation signal from subhalos

In the cold dark matter scenario, galactic dark matter halos are populated with a large number of smaller subhalos. Previous work has shown that dark matter annihilations in subhalos can generate a distinctive, non-Poisson signal in the gamma-ray photon counts probability distribution function (PDF). Here we show that the gamma-ray PDF also carries information about the velocity dependence of the dark matter annihilation cross section. After calculating the PDF assuming s-wave and Sommerfeld-enhanced annihilation, we perform a mock data analysis to illustrate how current and future observations can constrain the microphysics of the dark matter annihilation. We find that, with current Fermi data, and assuming a dark matter annihilation cross section roughly at the limit of current bounds from annihilation in dwarf spheroidal galaxies, one can potentially distinguish the non-Poissonian fluctuations expected from dark matter annihilation in subhalos from Poisson sources, as well as from dark matter models with an incorrect velocity-dependence. Here we explore how robust these results are to assumptions about the modeling of the galactic gamma-ray background, but further work is needed to determine the impact of realistic astrophysical source populations on our results. We also point out a four-parameter degeneracy between the velocity dependence of the dark matter annihilation, the minimum subhalo mass, the power law index of the subhalo mass function, and the normalization of the dark matter signal. This degeneracy can be broken with priors from N-body simulations or from observational constraints on the subhalo mass function.

79 ASTRONOMY AND ASTROPHYSICS↗

NASA NTRS1992

Gravitational lensing, time delay, and gamma-ray bursts

The probability distributions of time delay in gravitational lensing by point masses and isolated galaxies (modeled as singular isothermal spheres) are studied. For point lenses (all with the same mass) the probability distribution is broad, and with a peak at delta(t) of about 50 S; for singular isothermal spheres, the probability distribution is a rapidly decreasing function with increasing time delay, with a median delta(t) equals about 1/h month, and its behavior depends sensitively on the luminosity function of galaxies. The present simplified calculation is particularly relevant to the gamma-ray bursts if they are of cosmological origin. The frequency of 'recurrent' bursts due to gravitational lensing by galaxies is probably between 0.05 and 0.4 percent. Gravitational lensing can be used as a test of the cosmological origin of gamma-ray bursts.

Mao, Shude↗

NASA NTRS1982

Eutectic equilibria in the quaternary system Fe-Cr-Mn-C

The constitution of the quaternary system, Fe-Cr-Mn-C and to a lesser extent of the quinary system, Fe-Cr-Mn-Al-C were examined for in situ composite alloy candidates. Multivariant eutectic compositions were determined from phase equilibria studies wherein M7C3 carbides (approximately 30% by volume) formed from the melt within gamma iron. An extended field of the hexagonal carbide, (Cr, Fe, Mn)7 C3, was found without undergoing transformation to the orthorhombic structure. Increasing stability for this carbide was found for higher ratios of Cr/Fe(+) Cr + Mn. Aluminum additions promoted a ferritic matrix while manganese favored the desired gamma austenitic matrix. In coexistence with the matrix phase, chromium enters preferentially the carbide phase while manganese distributes equally between the gamma matrix and the M7C3 carbide. The composition and lattice parameters of the carbide and matrix phases were determined to establish their respective stabilities.

Nowotny, H.↗

NASA NTRS1982

Comments on the gamma-ray burst catalog of Mazets et al. /1981a/

A correlation has been discovered between the Venera spacecraft locations and the gamma-ray burst positions reported in the KONUS catalog (Mazets et al., 1981a). The reason for the correlation is not clear, but it could be due to spatial selection effects and/or large localization errors for weak or soft bursts. Whatever the cause, it seems likely that this systematic bias might significantly affect catalog results pertaining to gamma burst locations, intensity distributions, and spectra. For example, it can explain why the KONUS galactic latitude distribution is peaked significantly south of the galactic equator. Apparent discrepanices between the KONUS and Los Alamos gamma burst data bases are noted.

Laros, J. G.↗

NASA NTRS1994

Is a data set distributed as a power law? A test, with application to gamma-ray burst brightnesses

We present a method to determine whether an observed sample of data is drawn from a parent distribution that is pure power law. The method starts from a class of statistics which have zero expectation value under the null hypothesis, H(sub 0), that the distribution is a pure power law: F(x) varies as x(exp -alpha). We study one simple member of the class, named the `bending statistic' B, in detail. It is most effective for detection a type of deviation from a power law where the power-law slope varies slowly and monotonically as a function of x. Our estimator of B has a distribution under H(sub 0) that depends only on the size of the sample, not on the parameters of the parent population, and is approximated well by a normal distribution even for modest sample sizes. The bending statistic can therefore be used to test a set of numbers is drawn from any power-law parent population. Since many measurable quantities in astrophysics have distriibutions that are approximately power laws, and since deviations from the ideal power law often provide interesting information about the object of study (e.g., a `bend' or `break' in a luminosity function, a line in an X- or gamma-ray spectrum), we believe that a test of this type will be useful in many different contexts. In the present paper, we apply our test to various subsamples of gamma-ray burst brightness from the first-year Burst and Transient Source Experiment (BATSE) catalog and show that we can only marginally detect the expected steepening of the log (N (greater than C(sub max))) - log (C(sub max)) distribution.

Wijers, Ralph A. M. J.↗

NASA NTRS1975

Selected Theoretical Studies Group contributions to the 14th International Cosmic Ray conference

The galactic distribution of H2 was studied through gamma radiation and through X-ray, optical, and infrared absorption measurements from SAS-2 and other sources. A comparison of the latitude distribution of gamma-ray intensity with reddening data shows reddening data to give the best estimate of interstellar gas in the solar vicinity. The distribution of galactic cosmic ray nucleons was determined and appears to be identical to the supernova remnant distribution. Interactions between ultrahigh energy cosmic-ray nuclei and intergalactic photon radiation fields were calculated, using the Monte Carlo method.

Source record↗

NASA NTRS1983

X-ray studies of BL Lacertae objects with the Einstein Observatory - Confrontation with the synchrotron self-Compton predictions

X-ray flux densities measured with the Einstein Observatory are presented for a set of LB Lac objects with available VLBI angular sizes. The static, single-component synchrotron self-Compton formalism is used to predict the X-ray flux densities. Ratios of 10 to the -6th to the 10 to the -8th are found for the observed to predicted flux densities and it is concluded that such a model, at least in its simplest form, does not explain the X-ray emission from these objects as a class. The hypothesis that the compact source is in relativistic motion allows a simple resolution of the discrepancy. The results agree qualitatively with a broad distribution of bulk Lorentz factors Gamma with a fairly low typical value of Gamma approximately equal to and with a quasi-isotropic distribution of the direction of ejection relative to our line of sight.

Madejski, G. M.↗

NASA NTRS1994

On the nature of gamma-ray burst time dilations

The recent discovery that faint gamma-ray bursts are stretched in time relative to bright ones has been interpreted as support for cosmological distances: faint bursts have their durations redshifted relative to bright ones. It was pointed out, however, that the relative time stretching can also be produced by an intrinsic correlation bewteen duration and luminosity of gamma-ray bursts in a nearby, bounded distribution. While both models can explain the average amount of time stretching, we find a difference between them in the way the duration distribution of faint bursts deviates from that of bright ones, assuming the luminosity function of gamma-ray bursts is independent of distance. This allows us to distinguish between these two broad classes of model on the basis of the duration distributions of gamma-ray bursts, leading perhaps to an unambiguous determination of the distance scale of gamma-ray bursts. We apply our proposed test to the second Burst and Transient Source Experiment (BATSE) catalog and conclude, with some caution, that the data favor a cosmological interpretation of the time dilation.

Wijers, Ralph A. M. J.↗