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1

Calculation of Gamma-ray Exposure Buildup Factors up to 40mfp using the EGS4 Monte Carlo Code with a Particle Splitting  

Microsoft Academic Search

Gamma-ray exposure buildup factors up to 40 mfp have been calculated using the Monte Carlo code EGS4 for water, iron and lead for point isotropic sources. The new algorithm which applies particle-splitting at each preset depth to simulate almost same number of particles from the preset depth is developed in order to obtain reasonable results with EGS4 at deep-penetrations. Comparisons

Hideo HIRAYAMA

1995-01-01

2

A 3D point-kernel multiple scatter model for parallel-beam SPECT based on a gamma-ray buildup factor  

NASA Astrophysics Data System (ADS)

A three-dimensional (3D) point-kernel multiple scatter model for point spread function (PSF) determination in parallel-beam single-photon emission computed tomography (SPECT), based on a dose gamma-ray buildup factor, is proposed. This model embraces nonuniform attenuation in a voxelized object of imaging (patient body) and multiple scattering that is treated as in the point-kernel integration gamma-ray shielding problems. First-order Compton scattering is done by means of the Klein-Nishina formula, but the multiple scattering is accounted for by making use of a dose buildup factor. An asset of the present model is the possibility of generating a complete two-dimensional (2D) PSF that can be used for 3D SPECT reconstruction by means of iterative algorithms. The proposed model is convenient in those situations where more exact techniques are not economical. For the proposed model's testing purpose calculations (for the point source in a nonuniform scattering object for parallel beam collimator geometry), the multiple-order scatter PSF generated by means of the proposed model matched well with those using Monte Carlo (MC) simulations. Discrepancies are observed only at the exponential tails mostly due to the high statistic uncertainty of MC simulations in this area, but not because of the inappropriateness of the model.

Marinkovic, Predrag; Ilic, Radovan; Spaic, Rajko

2007-09-01

3

Modeling of gamma ray energy-absorption buildup factors for thermoluminescent dosimetric materials using multilayer perceptron neural network: A comparative study  

NASA Astrophysics Data System (ADS)

In this work, multilayered perceptron neural networks (MLPNNs) were presented for the computation of the gamma-ray energy absorption buildup factors (BA) of seven thermoluminescent dosimetric (TLD) materials [LiF, BeO, Na2B4O7, CaSO4, Li2B4O7, KMgF3, Ca3(PO4)2] in the energy region 0.015-15 MeV, and for penetration depths up to 10 mfp (mean-free-path). The MLPNNs have been trained by a Levenberg-Marquardt learning algorithm. The developed model is in 99% agreement with the ANSI/ANS-6.4.3 standard data set. Furthermore, the model is fast and does not require tremendous computational efforts. The estimated BA data for TLD materials have been given with penetration depth and incident photon energy as comparative to the results of the interpolation method using the Geometrical Progression (G-P) fitting formula.

Kucuk, Nil; Manohara, S. R.; Hanagodimath, S. M.; Gerward, L.

2013-05-01

4

New Photon Exposure Buildup Factors  

SciTech Connect

A New Monte Carlo code (EBUF) is developed to calculate improved point isotropic photon exposure buildup factors in media. Variance reduction techniques are used to perform calculations up to 60 mean free paths. EBUF accounts for coherent scattering and bound-electron Compton scattering. Bremsstrahlung photons and annihilation gamma rays as well as K and L X-rays are considered. The most recent cross-section data are used. The EBUF exposure buildup factors compare very well with those from the ANS-6.4.3 Working Group (ANS-6.4.3) when the same initial conditions are assumed: no coherent scattering, free-electron Compton scattering, and only K X-ray fluorescence. Next, a detailed physics treatment is used to calculate a representative set of exposure buildup factors in aluminum, iron, lead, water, air, and concrete over a large energy range (20 keV to 10 MeV). The effects of L X-rays are shown for lead at low energy. The EBUF factors are in good agreement with the SN1D code results for low-Z media. Finally, total exposure values from EBUF and ANS-6.4.3 are compared. Quite significant differences are observed because the ANS-6.4.3 calculations do not account for binding effects in Compton scattering, L X-ray fluorescence, and coherent scattering in mixtures.

Chibani, Omar

2001-02-15

5

Lower Limits on Lorentz Factors in Gamma-Ray Bursts  

Microsoft Academic Search

As is well known, the requirement that gamma-ray bursts be optically thin to high-energy photons yields a lower limit on the Lorentz factor (gamma) of the expansion. In this paper, we provide a simple derivation of the lower limit on gamma due to the annihilation of photon pairs and correct the errors in some of the previous calculations of this

Yoram Lithwick; Re'em Sari

2001-01-01

6

Accumulation and dissipation of positive charges induced on a PMMA build-up cap of an ionisation chamber by (60)Co gamma-ray irradiation.  

PubMed

The signal current from an ionisation chamber with a PMMA build-up cap decreases with irradiation time due to electric fields produced by positive charges induced on the cap. In the present study, it was confirmed that the signal current decreases faster for irradiation using narrower (60)Co gamma-ray beams. This is because the number of secondary electrons that are emitted from surrounding materials and penetrate the build-up cap is smaller in a narrower gamma-ray beam, so that fewer positive charges are neutralised. The ionisation chamber was first subjected to continuous gamma-ray irradiation for 24 h, following which it was irradiated with shorter periodic gamma-ray bursts while measuring the current signal. This allowed the coefficients of positive charge accumulation and dissipation to be determined. It was found that the dissipation coefficient has a large constant value during gamma-ray irradiation and decreases asymptotically to a small value after irradiation is stopped. From the coefficients, the minimum signal current was calculated, which is the value when accumulation and dissipation balance each other under continuous irradiation. The time required for the signal current to recover following irradiation was also calculated. PMID:23390147

Morishita, Y; Takata, N

2013-02-06

7

Energy absorption buildup factors for thermoluminescent dosimetric materials and their tissue equivalence  

NASA Astrophysics Data System (ADS)

Gamma ray energy-absorption buildup factors were computed using the five-parameter geometric progression (G-P) fitting formula for seven thermoluminescent dosimetric (TLD) materials in the energy range 0.015-15 MeV, and for penetration depths up to 40 mfp (mean free path). The generated energy-absorption buildup factor data have been studied as a function of penetration depth and incident photon energy. Buildup factors determined in the present work should be useful in radiation dosimetry, diagnostics and therapy. The tissue equivalence of TLD materials is also discussed.

Manohara, S. R.; Hanagodimath, S. M.; Gerward, L.

2010-05-01

8

Gamma -Ray Shielding Effect of Various Building Materials.  

National Technical Information Service (NTIS)

It is necessary to know the gamma -ray attenuation coefficients and the dose buildup factors for various building materials in order to evaluate the gamma -ray shielding factor of the residential houses in a reactor accident. As a matter of fact, however,...

Y. Yamaguchi K. Minami S. Ohtani

1985-01-01

9

Factors influencing in situ gamma-ray measurements  

NASA Astrophysics Data System (ADS)

Introduction In situ passive gamma-ray sensors are very well suitable for mapping physical soil properties. In order to make a qualitative sound soil map, high quality input parameters for calibration are required. This paper will focus on the factors that affect the output of in situ passive gamma-ray sensors, the primary source, soil, not taken into account. Factors The gamma-ray spectrum contains information of naturally occurring nuclides 40K, 238U and 232Th and man-made nuclides like 137Cs, as well as the total count rate. Factors that influence the concentration of these nuclides and the count rate can be classified in 3 categories. These are sensor design, environmental conditions and operational circumstances. Sensor design The main elements of an in situ gamma-ray sensor that influence the outcome and quality of the output are the crystal and the spectrum analysis method. Material and size of the crystal determine the energy resolution. Though widely used, NaI crystals are not the most efficient capturer of gamma radiation. Alternatives are BGO and CsI. BGO has a low peak resolution, which prohibits use in cases where man-made nuclides are subject of interest. The material is expensive and prone to temperature instability. CsI is robust compared to NaI and BGO. The density of CsI is higher than NaI, yielding better efficiency, especially for smaller crystal sizes. More volume results in higher energy efficiency. The reduction of the measured spectral information into concentration of radionuclides is mostly done using the Windows analysis method. In Windows, the activities of the nuclides are found by summing the intensities of the spectrum found in a certain interval surrounding a peak. A major flaw of the Windows method is the limited amount of spectral information that is incorporated into the analysis. Another weakness is the inherent use of ‘stripping factors' to account for contributions of radiation from nuclide A into the peak of nuclide B. This can be overcome using Full Spectrum Analysis (FSA). This method incorporates virtually all data present in the measured gamma spectrum. In FSA, a Chi-squared algorithm is used to fit a set of "Standard Spectra" to the measured spectrum. The uncertainty in the FSA method is at least a factor 2 lower compared to the Windows method. Environmental conditions Environmental conditions can influence the signal output and therefore the quality. In general, the density of the medium through which gamma-radiation travels determines the interaction of the radiation with matter and thus affects the sensor readings. Excluding soil as being the source; water is the most important external factor in this respect. The amount of water in soil will affect the signal. In general, energy loss occurs as water content in soil increases. As a result, the nuclide concentrations will be lower. Monte Carlo simulations show a difference of 16% in nuclide concentration for completely dry and fully saturated sandy soils. Another water related issue is rainfall. With rain radon gas, a product of 238U, will precipitate. This causes spectral noise effects. Snow and fog have the same effect to a minor degree. Another aspect is the openness of soil. From experience we know that the concentration of 40K differs if soil is tilled. Finally, on earth there is always radioactive noise present from the galaxy. The "Standard Spectra" used in the FSA method can take noise and geometric effects into account. Operational circumstances During a survey an operator should be aware of the effects of driving speed and measurement height. In general, a larger crystal has better energy efficiency and is therefore more suitable for high speed. E.g. a 70 x 150 mm CsI crystal provides qualitative satisfactory output for soil mapping up to 10 km/hr. Sample locations, however, are best measured during a longer period (3 to 5 minutes). The measurement height affects the measurement resolution; the lower the sensor, the smaller the measured area. In addition, Monte Carlo simulations show that the m

Loonstra, E. H.; van Egmond, F. M.

2009-04-01

10

New buildup factor data for point kernel calculations  

SciTech Connect

An American Nuclear Society Standards Committee Working Group, identified as ANS-6.4.3, is developing a set of evaluated gamma-ray isotropic point-source buildup factors and attenuation coefficients for a standard reference data base. As a first step, a largely unpublished set of buildup factors calculated with the moments method has been evaluated by recalculating key values with Monte Carlo, integral transport, and discrete ordinates methods. Attention is being given to frequently-neglected processes such as bremsstrahlung and the effect of introducing a tissue phantom behind the shield. The proposed standard contains data for a source energy range from 15 keV to 15 MeV and for approximately 19 elements and 3 mixtures (water, air, and concrete). The data will also be represented as coefficients for the G-P fitting function. The 1985 data base was released as part of the CCC-493B/QAD-CGGP code package available from the Radiation Shielding Information Center (RSIC).

Trubey, D.K.; Harima, Y.

1986-01-01

11

Calculated photon KERMA factors based on the LLNL EGDL (Evaluated Gamma-Ray Data Library) data file  

SciTech Connect

Photon (Gamma-Ray) KERMA factors calculated from the LLNL EGDL (Evaluated Gamma-Ray Data Library) file are tabulated for the elements from Z=1 to Z=30 and for 15 composite materials. The KERMA factors are presented for 191 energy groups over the incident photon energy range from 100 eV to 100 MeV. 3 refs.

Howerton, R.J.

1986-10-10

12

Gamma Rays, Q-Values, and Kerma Factors.  

National Technical Information Service (NTIS)

Formats have been proposed to allow the inclusion of evaluated neutron kerma factors in ENDF/B. The task of preparing evaluated kerma factors is analyzed in this report and is found to present numerous difficulties. Two alternative approaches to kerma-fac...

D. W. Muir

1976-01-01

13

Measurement of k 0 Factors in Prompt Gamma-Ray Neutron Activation Analysis  

Microsoft Academic Search

The guided thermal neutron beam at 100 MW Dhruva research reactor facility of Bhabha Atomic Research Centre (BARC) was used to carry out prompt gamma-ray neutron activation analysis (PGNAA). The prompt k\\u000a0-factors have been determined for the isotopes of the elements H, B, K, Co, Cu, Ca, Ti, Cr, Cd, Ba, Hg and Gd with respect to 1951 keV

R. N. Acharya; K. Sudarshan; A. G. C. Nair; Y. M. Scindia; A. Goswami; A. V. R. Reddy; S. B. Manohar

2001-01-01

14

LORENTZ-FACTOR-ISOTROPIC-LUMINOSITY/ENERGY CORRELATIONS OF GAMMA-RAY BURSTS AND THEIR INTERPRETATION  

SciTech Connect

The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta ({Gamma}{sub 0}) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between {Gamma}{sub 0} and isotropic {gamma}-ray energy: {Gamma}{sub 0}{proportional_to}E{sup 0.25}{sub {gamma},iso,52}. By including more GRBs with updated data and more methods to derive {Gamma}{sub 0}, we confirm this correlation and obtain {Gamma}{sub 0} {approx_equal} 91E{sup 0.29}{sub {gamma},iso,52}. Evaluating the mean isotropic {gamma}-ray luminosities L{sub {gamma},iso} of the GRBs in the same sample, we discover an even tighter correlation {Gamma}{sub 0} {approx_equal} 249L{sup 0.30}{sub {gamma},iso,52}. We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive {Gamma}{sub 0}{proportional_to}L{sup 0.22}{sub {gamma},iso}, which is consistent with the data. This suggests that the central engine of long GRBs is likely a stellar mass black hole surrounded by a hyper-accreting disk.

Lue Jing; Zou Yuanchuan; Lei Weihua; Wu Qingwen; Wang Dingxiong [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Zhang Bing; Lue Houjun [Department of Physics and Astronomy, University of Nevada Las Vegas, 4505 Maryland Parkway, Box 454002, Las Vegas, NV 89154-4002 (United States); Liang Enwei, E-mail: zouyc@hust.edu.cn, E-mail: leiwh@hust.edu.cn, E-mail: zhang@physics.unlv.edu [Department of Physics, Guangxi University, Nanning 530004 (China)

2012-05-20

15

Analysis of 10B by PIGE with factor analytical gamma-ray peak identification.  

PubMed

Studying the biodistribution of boronated compounds for B neutron capture therapy (BNCT) requires the accurate detection of low levels of boron (10B) in biological samples. Proton induced gamma-ray emission analysis (PIGE) of 10B was found to be viable in a study of low density lipoprotein (LDL), in tissue and blood samples. However, the method is sensitive to Na present in the samples and can therefore not be used for accurate measurements of 10B concentrations below 5 ppm in samples containing Na. PIGE can be considered to be an appropriate reference method for chemical B analysis. The factor analytical method presented here is the most objective way to separate Na and B peaks from each other, and the factorizing method can be applied in different forms of spectral analysis. PMID:7581292

Savolainen, S; Räisänen, J; Eteläniemi, V; Abo Ramadan, U A; Kallio, M

1995-09-01

16

FACTORS AFFECTING NITRITE BUILD-UP IN NITRIFYING BIOFILM REACTOR  

Microsoft Academic Search

Nitrite build-up in a nitrifying biofilm reactor for direct denitrification from the nitrite stage was investigated. At least three factors were found to influence the nitrite build-up: (i) the relative specific growth rates of Nitrosomonas to Nitrobacter, ?Ns\\/ ?Nb in the biofilm; (ii) the relative initial ratio between Nitrosomonas and Nitrobacter on the support surface, (Mao)Ns\\/(Mao)Nb; (iii) the level of

Yu Liu; Joo-Hwa Tay

2001-01-01

17

A REVISED LIMIT OF THE LORENTZ FACTORS OF GAMMA-RAY BURSTs WITH TWO EMITTING REGIONS  

SciTech Connect

Fermi observations of GeV emission from gamma-ray bursts (GRBs) have suggested that the Lorentz factor of some GRBs is around a thousand or even higher. At the same time, the same Fermi observations have shown an extended GeV emission indicating that this higher energy emission might be a part of the afterglow and it does not come from the same region as the lower energy prompt emission. If this interpretation is correct then we may have to reconsider the opacity limits on the Lorentz factor which are based on a one-zone model. We describe here a two-zone model in which the GeV photons are emitted in a larger radius than the MeV photons and we calculate the optical depth for pair creation of a GeV photon passing the lower energy photons shell. We find that, as expected, the new two-zone limits on the Lorentz factor are significantly lower. When applied to Fermi bursts the corresponding limits are lower by a factor of five compared to the one-zone model. It is possible that both the MeV and GeV regions have relatively modest Lorentz factors ({approx}200-400). This two-zone limit is significantly softer than the one-zone limit.

Zou Yuanchuan [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Fan Yizhong [Purple Mountain Observatory, Chinese Academy of Science, Nanjing 210008 (China); Piran, Tsvi, E-mail: zouyc@hust.edu.c, E-mail: yzfan@pmo.ac.c, E-mail: tsvi@phys.huji.ac.i [Racah Institute of Physics, The Hebrew University, Jerusalem 91904 (Israel)

2011-01-01

18

Determination of correction factors for borehole natural gamma-ray measurements by Monte Carlo simulations  

Microsoft Academic Search

The analysis of natural gamma-ray spectra measured in boreholes has to take into account borehole parameters such as the presence of casings and borehole diameter. For large, high-efficiency gamma-ray detectors, such as BGO-based systems, which employ full-spectrum data analysis, corresponding corrections were not previously determined. In a joint project of the Nuclear Geophysics Division of the Kernfysisch Versneller Instituut (NGD\\/KVI),

M. Maucec; P. H. G. M. Hendriks; J. Limburg; R. J. de Meijer

2009-01-01

19

Distribution of Gamma-ray Burst Ejecta Energy with Lorentz Factor  

SciTech Connect

The early X-ray afterglow for a significant number of gamma-ray bursts detected by the Swift satellite is observed to have a phase of very slow flux decline with time (F{sub {nu}} {proportional_to} t{sup -{alpha}} with 0.2 {approx}< {alpha} {approx}< 0.8) for 10{sup 2.5} s{approx}< t {approx}< 10{sup 4} s, while the subsequent decline is the usual 1 {approx}< {alpha}{sub 3} {approx}< 1.5 behavior, that was seen in the pre-Swift era. We show that this behavior is a natural consequence of a small spread in the Lorentz factor of the ejecta, by a factor of {approx} 2-4, where the slower ejecta gradually catch-up with the shocked external medium, thus increasing the energy of forward shock and delaying its deceleration. The end of the ''shallow'' flux decay stage marks the beginning of the Blandford-McKee self similar external shock evolution. This suggests that most of the energy in the relativistic outflow is in material with a Lorentz factor of {approx} 30-50.

Granot, Jonathan; /KIPAC, Menlo Park; Kumar, Pawan; /Texas U., Astron. Dept.

2005-10-07

20

Lorentz-factor-Isotropic-luminosity/Energy Correlations of Gamma-Ray Bursts and Their Interpretation  

NASA Astrophysics Data System (ADS)

The bulk Lorentz factor of the gamma-ray burst (GRB) ejecta (?0) is a key parameter to understanding GRB physics. Liang et al. have discovered a correlation between ?0 and isotropic ?-ray energy: ?0vpropE 0.25 ?, iso, 52. By including more GRBs with updated data and more methods to derive ?0, we confirm this correlation and obtain ?0 ~= 91E 0.29 ?, iso, 52. Evaluating the mean isotropic ?-ray luminosities L ?, iso of the GRBs in the same sample, we discover an even tighter correlation ?0 ~= 249L 0.30 ?, iso, 52. We propose an interpretation to this later correlation. Invoking a neutrino-cooled hyperaccretion disk around a stellar mass black hole as the central engine of GRBs, we derive jet luminosity powered by neutrino annihilation and baryon loading from a neutrino-driven wind. Applying beaming correction, we finally derive ?0vpropL 0.22 ?, iso, which is consistent with the data. This suggests that the central engine of long GRBs is likely a stellar mass black hole surrounded by a hyper-accreting disk.

Lü, Jing; Zou, Yuan-Chuan; Lei, Wei-Hua; Zhang, Bing; Wu, Qingwen; Wang, Ding-Xiong; Liang, En-Wei; Lü, Hou-Jun

2012-05-01

21

High sensitivity gamma-ray spectrometry: state of the art and trial application of factor analysis  

Microsoft Academic Search

The remote sensing of terrestrial gamma rays has application in geologic mapping, mineral exploration, reactor site monitoring, location of lost radioactive sources, measurement of the water equivalence of snow, and soil mapping. Although the state of the art is quite good, there is a need to reexamine the use of detectors other than thallium activated sodium iodide detectors (e.g., plastic

Joseph S. Duval

1977-01-01

22

Very High Lorentz Factor Fireballs and Gamma-Ray Burst Spectra  

NASA Astrophysics Data System (ADS)

Collisionless entrainment of the surrounding matter imports the relativistic baryon component in the Gamma-Ray Burst (GRB) fireball frame. We show that half the fireball energy can be transferred from radiation to the comoving hot motions of baryons under the photosphere. The yet baryon-poor fireball can reexpand to a very high Lorentz factor (VHLF) ? ˜ 10^3-10^6 by its own relativistic collisionless pressure beyond the photosphere (so-called collisionless bulk acceleration), leading to internal and external shocks. A simple synchrotron emission from the VHLF internal shocks produces (i) the extra power-law spectral component with variability observed in the Fermi GeV bursts, up to the TeV range for the future Cherenkov Telescope Array (CTA), (ii) the GeV onset delay with a weak luminosity dependence t_{delay} ˜ L^{-1/5}, and (iii) the spectral break of GRB 090926 by the synchrotron cooling break or the maximum synchrotron cutoff limited by the dynami cal time, not by the e^{ą} creation cutoff. The relativistic baryon component could also heat the photospheric thermal photons into the main GRB Band spectrum via pp, p? (Bethe-Heitler and photomeson), and Coulomb thermalization processes. In this hot photosphere-internal-external shock model, we can predict the anticorrelation of ˜TeV neutrinos and GeV ?-rays, which may be detectable using IceCube. The spectral peak and luminosity (Yonetoku) relation is also reproduced if the progenitor stars are nearly identical. We also discuss the steep/shallow decay of early X-ray afterglows and short GRBs.

Ioka, K.

2010-10-01

23

THE BULK LORENTZ FACTORS OF FERMI-LAT GAMMA RAY BURSTS  

SciTech Connect

The Lorentz factor (LF) of gamma-ray burst (GRB) ejecta may be constrained by observations of high-energy (HE) spectral attenuation. The recent Fermi-LAT observations of prompt GeV emission from several bright GRBs have led to conclusions of unexpectedly large LFs, {Gamma}>10{sup 3}. Here we revisit this problem with two main concerns. (1) With a one-zone assumption where all photons are assumed to be generated in the same region (radius) and time, we self-consistently calculate the {gamma}{gamma} optical depth by adopting a target photon spectrum with an HE cutoff. We find that this might be important when the GRB LF is below a few hundreds. (2) Recent Fermi-LAT observations suggest that the bulk MeV-range and HE ({approx}>100 MeV) emission may arise from different regions. We then consider a two-zone case where HE emission is generated in much larger radii than that of the MeV-range emission. We find that the HE emission may mainly be attenuated by the MeV-range emission and that the attenuated HE spectrum does not show an exponential spectral cutoff but a slight steepening. This suggests that there may be no abrupt cutoff due to {gamma}{gamma} attenuation if relaxing the one-zone assumption. By studying the spectra of three bright Fermi-LAT GRBs, 080916C, 090510, and 090902B, we show that bulk LFs of {Gamma} {approx} 600 can be consistent with observations in the two-zone case. Even lower LFs can be obtained in the multi-zone case.

Zhao Xiaohong; Bai Jinming [National Astronomical Observatories/Yunnan Observatory, Chinese Academy of Sciences, P.O. Box 110, 650011 Kunming (China); Li Zhuo, E-mail: zhaoxh@ynao.ac.cn [Department of Astronomy, Peking University, Beijing 100871 (China)

2011-01-10

24

The Bulk Lorentz Factors of Fermi-LAT Gamma Ray Bursts  

NASA Astrophysics Data System (ADS)

The Lorentz factor (LF) of gamma-ray burst (GRB) ejecta may be constrained by observations of high-energy (HE) spectral attenuation. The recent Fermi-LAT observations of prompt GeV emission from several bright GRBs have led to conclusions of unexpectedly large LFs, ?>103. Here we revisit this problem with two main concerns. (1) With a one-zone assumption where all photons are assumed to be generated in the same region (radius) and time, we self-consistently calculate the ?? optical depth by adopting a target photon spectrum with an HE cutoff. We find that this might be important when the GRB LF is below a few hundreds. (2) Recent Fermi-LAT observations suggest that the bulk MeV-range and HE (gsim100 MeV) emission may arise from different regions. We then consider a two-zone case where HE emission is generated in much larger radii than that of the MeV-range emission. We find that the HE emission may mainly be attenuated by the MeV-range emission and that the attenuated HE spectrum does not show an exponential spectral cutoff but a slight steepening. This suggests that there may be no abrupt cutoff due to ?? attenuation if relaxing the one-zone assumption. By studying the spectra of three bright Fermi-LAT GRBs, 080916C, 090510, and 090902B, we show that bulk LFs of ? ~ 600 can be consistent with observations in the two-zone case. Even lower LFs can be obtained in the multi-zone case.

Zhao, Xiao-Hong; Li, Zhuo; Bai, Jin-Ming

2011-01-01

25

The Highest Energy Gamma Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are equally likely to occur from any part of the sky, are detected by satellites about once per day, and emit most of their energy in a few seconds. Consequently, a detector with a large field of view and high duty factor is essential to observe gamma-ray bursts. EGRET was the 1st such detector sensitive enough to detect GeV gamma rays from gamma-ray bursts. While only 4 bursts were detected, these were the brightest bursts, as measured at < 1 MeV, in EGRET's field of view. Therefore, GeV emission may be characteristic of many bursts, and several models even predict emission extending to > TeV energies. Recently, a new TeV gamma-ray observatory, Milagro, has begun observing the Northern hemisphere sky. Milagro has > 1 sr field of view and operates 24 hours/day, 7 days/week. Milagrito, a smaller prototype of Milagro, operated for 15 months and 54 bursts were identified by BATSE, a sub-MeV detector in low Earth orbit, to be within Milagrito's field of view. One of the 54 bursts had marginal evidence of TeV gamma-ray emission. The prospect of observing gamma-ray bursts with Milagro will be discussed.

Dingus, Brenda L.

2000-04-01

26

Observations of the Highest Energy Gamma Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to TeV gamma rays from gamma-ray bursts are beginning operation.

Dingus, Brenda L.

2003-04-01

27

The Highest Energy Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

Gamma-ray bursts are equally likely to occur from any part of the sky, are detected by satellites about once per day, and emit most of their energy in a few seconds. Consequently, a detector with a large field of view and high duty factor is essential to observe gamma-ray bursts. EGRET was the 1st such detector sensitive enough to detect

Brenda L. Dingus

2000-01-01

28

Directional detector of gamma rays  

DOEpatents

A directional detector of gamma rays comprises a strip of an electrical cuctor of high atomic number backed with a strip of a second electrical conductor of low atomic number. These elements are enclosed within an electrical conductor that establishes an electrical ground, maintains a vacuum enclosure and screens out low-energy gamma rays. The detector exhibits a directional sensitivity marked by an increased output in the favored direction by a factor of ten over the output in the unfavored direction.

Cox, Samson A. (Downers Grove, IL); Levert, Francis E. (Chicago, IL)

1979-01-01

29

Observations of the Highest Energy Gamma-Rays from Gamma-Ray Bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2002-01-01

30

Observations of the Highest Energy Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2003-01-01

31

Observations of the highest energy gamma-rays from gamma-ray bursts  

Microsoft Academic Search

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile

Brenda L. Dingus

2001-01-01

32

Stimulating effect of space flight factors on Artemia cysts: comparison with irradiation by gamma rays.  

PubMed

The Artemia cyst, a gastrula in dormant state, is a very suitable material to investigate the individual effects of HZE cosmic particles. Monolayers of Artemia cysts, sandwiched with nuclear emulsions, flew aboard the Soviet biosatellite Cosmos 1129. The space flight stimulated the developmental capacity expressed by higher percentages of emergence, hatching, and alive nauplii at day 4-5. A greater mean life span was reported in Artemias developed from Artemia cysts hit by the cosmic heavy ions. On Earth, Artemia cysts were exposed to 1, 10, 100, 200 and 400 Gy of gamma (gamma) rays. A stimulating effect on developmental capacity was observed for 10 Gy; the mean life span was significantly increased for this dose. These results are discussed in comparison with previous investigations performed on Earth and in space. PMID:3718384

Gaubin, Y; Pianezzi, B; Gasset, G; Plannel, H; Kovalev, E E

1986-06-01

33

Stimulating effect of space flight factors on Artemia cysts: comparison with irradiation by gamma rays  

SciTech Connect

The Artemia cyst, a gastrula in dormant state, is a very suitable material to investigate the individual effects of HZE cosmic particles. Monolayers of Artemia cysts, sandwiched with nuclear emulsions, flew aboard the Soviet biosatellite Cosmos 1129. The space flight stimulated the developmental capacity expressed by higher percentages of emergence, hatching, and alive nauplii at day 4-5. A greater mean life span was reported in Artemias developed from Artemia cysts hit by the cosmic heavy ions. On Earth, Artemia cysts were exposed to 1, 10, 100, 200 and 400 Gy of gamma (gamma) rays. A stimulating effect on developmental capacity was observed for 10 Gy; the mean life span was significantly increased for this dose. These results are discussed in comparison with previous investigations performed on Earth and in space.

Gaubin, Y.; Pianezzi, B.; Gasset, G.; Plannel, H.; Kovalev, E.E.

1986-06-01

34

GRAYSKY-A new gamma-ray skyshine code  

SciTech Connect

This paper describes a new prototype gamma-ray skyshine code GRAYSKY (Gamma-RAY SKYshine) that has been developed at BNFL, as part of an industrially based master of science course, to overcome the problems encountered with SKYSHINEII and RANKERN. GRAYSKY is a point kernel code based on the use of a skyshine response function. The scattering within source or shield materials is accounted for by the use of buildup factors. This is an approximate method of solution but one that has been shown to produce results that are acceptable for dose rate predictions on operating plants. The novel features of GRAYSKY are as follows: 1. The code is fully integrated with a semianalytical point kernel shielding code, currently under development at BNFL, which offers powerful solid-body modeling capabilities. 2. The geometry modeling also allows the skyshine response function to be used in a manner that accounts for the shielding of air-scattered radiation. 3. Skyshine buildup factors calculated using the skyshine response function have been used as well as dose buildup factors.

Witts, D.J.; Twardowski, T.; Watmough, M.H. (British Nuclear Fuels Ltd., Cheshire (United Kingdom))

1993-01-01

35

Observations of the highest energy gamma-rays from gamma-ray bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst. .

Dingus, Brenda L.

2001-04-01

36

Observations of the Highest Energy Gamma-Rays from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

EGRET has extended the highest energy observations of gamma-ray bursts to GeV gamma rays. Such high energies imply the fireball that is radiating the gamma-rays has a bulk Lorentz factor of several hundred. However, EGRET only detected a few gamma-ray bursts. GLAST will likely detect several hundred bursts and may extend the maximum energy to a few 100 GeV. Meanwhile new ground based detectors with sensitivity to gamma-ray bursts are beginning operation, and one recently reported evidence for TeV emission from a burst.

Dingus, Brenda L.

2002-12-01

37

CONSTRAINING THE BULK LORENTZ FACTOR OF GAMMA-RAY BURST OUTFLOW IN THE MAGNETIC-DOMINATED JET MODEL  

SciTech Connect

Recent observations by the Fermi-LAT showed that there are delayed arrivals of GeV photons relative to the onset of MeV photons in some gamma-ray bursts (GRBs). In order to avoid a large optical depth, the minimal value of the Lorentz factor has been estimated to be higher than 1000 in some of the brightest bursts. In this paper, we present a detailed calculation of the time delay between the MeV and GeV photons in the framework of the magnetic-dominated jet model. We find that the time delay strongly depends on the saturated bulk Lorentz factor of the jet. Inspired by this fact, we use this model to calculate the Lorentz factors of the four brightest Fermi bursts. The results indicate that the Lorentz factors are much smaller than those obtained from the 'single-zone' scenario. The short burst GRB 090510 has a minimal Lorentz factor of 385, while the three long bursts, GRB 080916c, GRB 090902b, and GRB 090926, have almost the same Lorentz factors with an average value near 260. Another interesting result is that, for long bursts, GeV photons are emitted after the bulk Lorentz factor saturates. For the short GRB, however, MeV and GeV photons are emitted at the same phase, i.e., either in the expansion phase or in the coasting phase.

Chang Zhe; Lin Hainan; Jiang Yunguo, E-mail: changz@ihep.ac.cn, E-mail: linhn@ihep.ac.cn, E-mail: jiangyg@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, 100049 Beijing (China)

2012-11-10

38

Differences in wedge factor determination in air using a PMMA mini-phantom or a brass build-up cap.  

PubMed

The head scatter dose contribution to the output of a treatment machine has been determined for an open and wedged 60Co gamma-ray beam and for open and wedged x-ray beams of 4, 8, and 16 MV. From those data wedge factor values "in air" have been deduced, expressed as the ratio of the dose to water, measured in air, for the situation with and without wedge, for the same number of monitor units (or treatment time for 60Co). The measurements have been performed using a polymethyl-metacrylate (PMMA) and a graphite-walled ionization chamber inserted in a brass build-up cap and in a PMMA mini-phantom, respectively. Absolute wedge factor values deduced with both detector systems and based on the ratio of ionization chamber readings, differ for the investigated photon beams, up to 3.5% for the 4 MV x-ray beam. The deviations results from the difference in composition between the detector materials and water and can be taken into account by conversion of the ionization chamber readings for both the open and wedged photon beams to the absorbed dose to water. For the brass build-up cap detector system the ratio of the conversion factors for the wedged and open beam changes the ratio of the ionization chamber readings up to about 3.6% for the 4 MV x-ray beam. For the mini-phantom the conversion factors for the wedged and open beam are almost equal for all photon beams. Consequently, for that system wedge factors based on ionization chamber readings or dose values are the same. With respect to the wedge factor variation with field size a somewhat larger increase has been determined for the 60Co and 4 MV photon beam using the brass build-up cap: about 1% for field sizes varying between 5 cm x 5 cm and 15 cm x 15 cm. This effect has to be related to an apparent more pronounced variation of the head scatter dose contribution with field size for the wedged photon beams if the brass build-up cap detection system is used. It can be concluded that determination of wedge factors "in air" under reference irradiation conditions, performed with both the mini-phantom and brass build-up cap yields within 0.5% the same result if the wedge factors are based on a dose to water ratio. However, by using high-Z build-up materials the determination is more complicated because appropriate conversion factors are then required, while similar conversion factors can be ignored if more water equivalent build-up materials such as PMMA are applied. PMID:9434981

Heukelom, S; Lanson, J H; Mijnheer, B J

1997-12-01

39

Gamma ray detector shield  

DOEpatents

A gamma ray detector shield comprised of a rigid, lead, cylindrical-shaped vessel having upper and lower portions with an pneumatically driven, sliding top assembly. Disposed inside the lead shield is a gamma ray scintillation crystal detector. Access to the gamma detector is through the sliding top assembly.

Ohlinger, R.D.; Humphrey, H.W.

1985-08-26

40

Basic foundations of the internal structure of the calibration factor for the gamma-ray log  

NASA Astrophysics Data System (ADS)

The problem of the ?-ray log calibration factor is discussed with relation to the determination of the ore grade and to geochemical applications. The influence of the physical parameters of the formation (bulk density, porosity) and its elemental composition (equivalent atomic number) on the calibration factor is shown. The two calibration factors: “wet” and “dry” are distinguished in order to determine the “dry” ore grade (in mass of radioactive material per unit mass of dry ore) and the “wet” ore grade (in mass of radioactive material per unit mass of ore in the natural geological formation). Primary and scattered photons are taken into account in the study of the calibration factor characteristics. The entire uranium and thorium radioactive families are taken into account, as well as the case when all three major sources of natural rock radioactivity are present: i.e. potassium, uranium and thorium. The influence of borehole conditions (borehole size and presence of drilling fluid or casing in the borehole) on the calibration factors are discussed. As a result the best experimental conditions for the ?-ray tool calibration have been established. The link of the calibration factors with the API ?-ray units are also presented.

Czubek, Jan A.

1995-06-01

41

Gamma ray optics  

SciTech Connect

Via refractive or diffractive scattering one can shape {gamma} ray beams in terms of beam divergence, spot size and monochromaticity. These concepts might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. We will demonstrate the experimental feasibility of gamma ray monochromatization on a ppm level and the creation of a gamma ray beam with nanoradian divergence. The results are obtained using the inpile target position of the High Flux Reactor of the ILL Grenoble and the crystal spectrometer GAMS. Since the refractive index is believed to vanish to zero with 1/E{sup 2}, the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using the crystal spectrometer GAMS, we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E{sup 2} extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.

Jentschel, M.; Guenther, M. M.; Habs, D.; Thirolf, P. G. [Institut Laue-Langevin, F38042 Grenoble (France); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching (Germany); Max-Planck-Institut fuer Quantenoptik, D-85748 Garching, Germany and Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany); Ludwig-Maximilians-Universitaet Muenchen, D-85748 Garching (Germany)

2012-07-09

42

Gamma ray optics  

NASA Astrophysics Data System (ADS)

Via refractive or diffractive scattering one can shape ? ray beams in terms of beam divergence, spot size and monochromaticity. These concepts might be particular important in combination with future highly brilliant gamma ray sources and might push the sensibility of planned experiments by several orders of magnitude. We will demonstrate the experimental feasibility of gamma ray monochromatization on a ppm level and the creation of a gamma ray beam with nanoradian divergence. The results are obtained using the inpile target position of the High Flux Reactor of the ILL Grenoble and the crystal spectrometer GAMS. Since the refractive index is believed to vanish to zero with 1/E2, the concept of refractive optics has never been considered for gamma rays. The combination of refractive optics with monochromator crystals is proposed to be a promising design. Using the crystal spectrometer GAMS, we have measured for the first time the refractive index at energies in the energy range of 180 - 2000 keV. The results indicate a deviation from simple 1/E2 extrapolation of X-ray results towards higher energies. A first interpretation of these new results will be presented. We will discuss the consequences of these results on the construction of refractive optics such as lenses or refracting prisms for gamma rays and their combination with single crystal monochromators.

Jentschel, M.; Günther, M. M.; Habs, D.; Thirolf, P. G.

2012-07-01

43

Gamma ray camera  

DOEpatents

A gamma ray camera is disclosed for detecting rays emanating from a radiation source such as an isotope. The gamma ray camera includes a sensor array formed of a visible light crystal for converting incident gamma rays to a plurality of corresponding visible light photons, and a photosensor array responsive to the visible light photons in order to form an electronic image of the radiation therefrom. The photosensor array is adapted to record an integrated amount of charge proportional to the incident gamma rays closest to it, and includes a transparent metallic layer, photodiode consisting of a p-i-n structure formed on one side of the transparent metallic layer, and comprising an upper p-type layer, an intermediate layer and a lower n-type layer. In the preferred mode, the scintillator crystal is composed essentially of a cesium iodide (CsI) crystal preferably doped with a predetermined amount impurity, and the p-type upper intermediate layers and said n-type layer are essentially composed of hydrogenated amorphous silicon (a-Si:H). The gamma ray camera further includes a collimator interposed between the radiation source and the sensor array, and a readout circuit formed on one side of the photosensor array. 6 figs.

Perez-Mendez, V.

1997-01-21

44

Gamma ray camera  

DOEpatents

A gamma ray camera for detecting rays emanating from a radiation source such as an isotope. The gamma ray camera includes a sensor array formed of a visible light crystal for converting incident gamma rays to a plurality of corresponding visible light photons, and a photosensor array responsive to the visible light photons in order to form an electronic image of the radiation therefrom. The photosensor array is adapted to record an integrated amount of charge proportional to the incident gamma rays closest to it, and includes a transparent metallic layer, photodiode consisting of a p-i-n structure formed on one side of the transparent metallic layer, and comprising an upper p-type layer, an intermediate layer and a lower n-type layer. In the preferred mode, the scintillator crystal is composed essentially of a cesium iodide (CsI) crystal preferably doped with a predetermined amount impurity, and the p-type upper intermediate layers and said n-type layer are essentially composed of hydrogenated amorphous silicon (a-Si:H). The gamma ray camera further includes a collimator interposed between the radiation source and the sensor array, and a readout circuit formed on one side of the photosensor array.

Perez-Mendez, Victor (Berkeley, CA)

1997-01-01

45

Hypernuclear gamma rays  

SciTech Connect

The observation of hypernuclear ..gamma.. rays pprovides a method of determining the spin dependence of the ..lambda..-nucleon interaction with a sensitivity not approachable by other means in the forseeable future. The transitions of primary interest are those between states that differ only in the orientation of the spin of the ..lambda.. particle with respect to the angular momentum of the nuclear core. The effective ..lambda..-nucleon interaction can be specified by a small number of ..gamma..-ray measurements. A program of experiments directed at this goal is in progress at Brookhaven National Laboratory. This paper reviews the status of the subject with emphasis on the recent experiment to measure ground state doublet splittings using germanium ..gamma..-ray detectors.

May, M.

1985-01-01

46

Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts are the brightest transient sources in the gamma-ray sky. Since their discovery in the late 1960s, the investigation of the astrophysical sys- tems in which these phenomena take place, and the physical mechanisms that drive them, has become a vast and prolific area of modern astrophysics. In this work I will briefly describe the most relevant observations of these sources, and the models that describe their nature, emphasizing on the in- vestigations about the progenitor astrophysical systems. FULL TEXT IN SPANISH

Pellizza, L. J.

47

Gamma-ray bursts.  

PubMed

Gamma-ray bursts (GRBs) are bright flashes of gamma rays coming from the cosmos. They occur roughly once per day, typically last for tens of seconds, and are the most luminous events in the universe. More than three decades after their discovery, and after pioneering advances from space and ground experiments, they still remain mysterious. The launch of the Swift and Fermi satellites in 2004 and 2008 brought in a trove of qualitatively new data. In this Review, we survey the interplay between these recent observations and the theoretical models of the prompt GRB emission and the subsequent afterglow. PMID:22923573

Gehrels, Neil; Mészáros, Péter

2012-08-24

48

Gamma Ray Observatory survives  

Microsoft Academic Search

Right now the budgetary position of NASA science projects for fiscal year 1982 is shaky, outside of the Space Shuttle Program. Two scientifically crucial missions being planned are the Gamma Ray Observatory (GRO) and the Venus Orbiting Imaging Radar (VOIR). President Reagan's proposed budgetary cuts have left both programs intact but delayed. For FY 1982, GRO will be able to

Peter M. Bell

1981-01-01

49

Scission gamma rays  

SciTech Connect

Gamma rays probably emitted by the fissioning nucleus {sup 236}U* at the instant of the break of the neck or within the time of about 10{sup -21} s after or before this were discovered in the experiment devoted to searches for the effect of rotation of the fissioning nucleus in the process {sup 235}U(n,{gamma}f) and performed in a polarized beam of cold neutrons from the MEPHISTO Guideline at the FRM II Munich reactor. Detailed investigations revealed that the angular distribution of these gamma rays is compatible with the assumption of the dipole character of the radiation and that their energy spectrum differs substantially from the spectrum of prompt fission gamma rays. In the measured interval 250-600 keV, this spectrum can be described by an exponential function at the exponent value of {alpha} = -5 x 10{sup -3} keV{sup -1}. The mechanism of radiation of such gamma rays is not known at the present time. Theoretical models based on the phenomenon of the electric giant dipole resonance in a strongly deformed fissioning nucleus or in a fission fragment predict harder radiation whose spectrum differs substantially from the spectrum measured in the present study.

Danilyan, G. V., E-mail: danilyan@itep.r [Institute of Theoretical and Experimental Physics (Russian Federation); Klenke, J. [Forschungs-Neutronenquelle Heinz Maier-Leibnitz (FRM II) (Germany); Krakhotin, V. A.; Kuznetsov, V. L.; Novitsky, V. V.; Pavlov, V. S.; Shatalov, P. B. [Institute of Theoretical and Experimental Physics (Russian Federation)

2009-11-15

50

Gamma-ray bursts  

Microsoft Academic Search

Gamma-ray bursts are the most luminous explosions in the Universe, and their origin and mechanism are the focus of intense research and debate. More than three decades after their discovery, and after pioneering breakthroughs from space and ground experiments, their study is entering a new phase with the recently launched Swift satellite. The interplay between these observations and theoretical models

P. Mészáros

2006-01-01

51

Delayed gamma Rays from Fission.  

National Technical Information Service (NTIS)

Studies of delayed gamma rays from fission at early times were conducted using the pulsed beams of neutrons and bremsstrahlung x rays from an electron linear accelerator to produce fissions. Measurements of the energy spectrum of isomeric gamma rays from ...

R. B. Walton R. E. Sund

1965-01-01

52

Gamma-Ray Burst Wallsheet  

NSDL National Science Digital Library

The Gamma-ray Burst Wallsheet was developed to illustrate the properties of light emanating from a gamma-ray burst as seen by three distant satellites, including NASA's Swift. The back of the wallsheet has one of the three activities in the accompanying educator guide (Angling for Gamma-ray Bursts).

2005-01-01

53

Gamma ray lines from the galactic center and gamma ray transients  

SciTech Connect

The observations and interpretations of cosmic (nonsolar) gamma ray lines are discussed. The most prominent of these lines is the e(+)e(-) annihilation line which was observed from the Galactic Center and from several gamma ray transients. At the Galactic Center the e(+)e(-) pairs are probably produced by an accreting massive black hole (solar mass of approximately one million) and annihilate within the central light year to produce a line at almost exactly 0.511 MeV. In gamma ray transients the annihilation line is redshifted by factors consistent with neutron star surface redshifts. Other observed transient gamma ray lines appear to be due to cyclotron absorption in the strong magnetic fields of neutron stars, and nuclear deexcitations and neutron capture, which could also occur on or around these objects.

Ramaty, R.; Leiter, D.; Lingenfelter, R.E.

1981-04-01

54

Gamma ray lines from the Galactic Center and gamma ray transients  

NASA Astrophysics Data System (ADS)

The observations and interpretations of cosmic (nonsolar) gamma ray lines are discussed. The most prominent of these lines is the e(+)e(-) annihilation line which was observed from the Galactic Center and from several gamma ray transients. At the Galactic Center the e(+)e(-) pairs are probably produced by an accreting massive black hole (solar mass of approximately one million) and annihilate within the central light year to produce a line at almost exactly 0.511 MeV. In gamma ray transients the annihilation line is redshifted by factors consistent with neutron star surface redshifts. Other observed transient gamma ray lines appear to be due to cyclotron absorption in the strong magnetic fields of neutron stars, and nuclear deexcitations and neutron capture, which could also occur on or around these objects.

Ramaty, R.; Leiter, D.; Lingenfelter, R. E.

1981-04-01

55

Gamma-ray localization of terrestrial gamma-ray flashes.  

PubMed

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with an accuracy of ?5-10° at 50 MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400 km. Considering that our gamma rays reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space. PMID:20867680

Marisaldi, M; Argan, A; Trois, A; Giuliani, A; Tavani, M; Labanti, C; Fuschino, F; Bulgarelli, A; Longo, F; Barbiellini, G; Del Monte, E; Moretti, E; Trifoglio, M; Costa, E; Caraveo, P; Cattaneo, P W; Chen, A; D'Ammando, F; De Paris, G; Di Cocco, G; Di Persio, G; Donnarumma, I; Evangelista, Y; Feroci, M; Ferrari, A; Fiorini, M; Froysland, T; Galli, M; Gianotti, F; Lapshov, I; Lazzarotto, F; Lipari, P; Mereghetti, S; Morselli, A; Pacciani, L; Pellizzoni, A; Perotti, F; Picozza, P; Piano, G; Pilia, M; Prest, M; Pucella, G; Rapisarda, M; Rappoldi, A; Rubini, A; Sabatini, S; Soffitta, P; Striani, E; Vallazza, E; Vercellone, S; Vittorini, V; Zambra, A; Zanello, D; Antonelli, L A; Colafrancesco, S; Cutini, S; Giommi, P; Lucarelli, F; Pittori, C; Santolamazza, P; Verrecchia, F; Salotti, L

2010-09-14

56

Gamma-Ray Localization of Terrestrial Gamma-Ray Flashes  

SciTech Connect

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by the AGILE Mini-Calorimeter. We detect 8 TGFs with gamma-ray photons of energies above 20 MeV localized by the AGILE gamma-ray imager with an accuracy of {approx}5-10 deg. at 50 MeV. Remarkably, all TGF-associated gamma rays are compatible with a terrestrial production site closer to the subsatellite point than 400 km. Considering that our gamma rays reach the AGILE satellite at 540 km altitude with limited scattering or attenuation, our measurements provide the first precise direct localization of TGFs from space.

Marisaldi, M.; Labanti, C.; Fuschino, F.; Bulgarelli, A.; Trifoglio, M.; Di Cocco, G.; Gianotti, F. [INAF-IASF Bologna, Via Gobetti 101, I-40129 Bologna (Italy); Argan, A.; De Paris, G. [INAF, Viale del Parco Mellini 84, Roma (Italy); Trois, A.; Del Monte, E.; Costa, E.; Di Persio, G.; Donnarumma, I.; Evangelista, Y.; Feroci, M.; Lazzarotto, F.; Pacciani, L.; Rubini, A.; Sabatini, S. [INAF-IASF Roma, via del Fosso del Cavaliere 100, I-00133 Roma (Italy)

2010-09-17

57

Gamma-ray luminosity properties of gamma-ray pulsars  

Microsoft Academic Search

Based on a new self-consistent outer gap model, we statistically study luminosity properties of gamma-ray pulsars with ages of <=2× 107 yr in the Galaxy as well as those with ages of <=5× 106 yr in the Gould belt using a Monte Carlo method, where the gamma-ray beaming effect has been included. Generally, the relation between gamma-ray luminosity, Lgamma, and

L. Zhang; Z. X. Han; Z. J. Jiang

2005-01-01

58

Standard reference data for gamma-ray transport in homogeneous media. [PWR; BWR  

SciTech Connect

An American Nuclear Society Standards Committee Working Group, identified as ANS-6.4.3, is developing a set of evaluated gamma-ray isotropic point-source buildup factors and attenuation coefficients for a standard reference data base. As a first step, a largely unpublished set of buildup factors calculated with the moments method is being evaluated by recalculating key values with Monte Carlo, integral transport, and discrete ordinates methods. Attention is being given to frequently neglected processes such as bremsstrahlung and the effect of introducing a tissue phantom behind the shield. The proposed standard will contain data for a source energy range from 15 keV to 15 MeV and for approximately 12 elements and 3 mixtures (water, air, and concrete).

Trubey, D.K.

1983-01-01

59

Extragalactic Gamma-Rays Gamma Ray Bursts and Blazars  

Microsoft Academic Search

The extragalactic gamma-ray sky is dominated by two classes of sources: Gamma-Ray Bursts (GRBs) and radio loud active galactic nuclei whose jets are pointing at us (blazars). We believe that the radiation we receive from them originates from the transformation of bulk relativistic energy into random energy. Although the mechanisms to produce, collimate and accelerate the jets in these sources

Gabriele Ghisellini

2005-01-01

60

Gamma ray energy tracking in GRETINA  

NASA Astrophysics Data System (ADS)

The next generation of stable and exotic beam accelerators will provide physics opportunities to study nuclei farther away from the line of stability. However, these experiments will be more demanding on instrumentation performance. These come from the lower production rate for more exotic beams, worse beam impurities, and large beam velocity from the fragmentation and inverse reactions. Gamma-ray spectroscopy will be one of the most effective tools to study exotic nuclei. However, to fully exploit the physics reach provided by these new facilities, better gamma-ray detector will be needed. In the last 10 years, a new concept, gamma-ray energy tracking array, was developed. Tracking arrays will increase the detection sensitivity by factors of several hundred compared to current arrays used in nuclear physics research. Particularly, the capability of reconstructing the position of the interaction with millimeters resolution is needed to correct the Doppler broadening of gamma rays emitted from high velocity nuclei. GRETINA is a gamma-ray tracking array which uses 28 Ge crystals, each with 36 segments, to cover .5ex1 -.1em/ -.15em.25ex4 of the 4? solid angle. The gamma ray tracking technique requires detailed pulse shape information from each of the segments. These pulses are digitized using 14-bit 100 MHz flash ADCs, and digital signal analysis algorithms implemented in the on-board FPGAs provides energy, time and selection of pulse traces. A digital trigger system, provided flexible trigger functions including a fast trigger output, and also allows complicated trigger decisions to be made up to 20 microseconds. Further analyzed, carried out in a computer cluster, determine the energy, time, and three-dimensional positions of all gamma-ray interactions in the array. This information is then utilized, together with the characteristics of Compton scattering and pair-production processes, to track the scattering sequences of the gamma rays. GRETINA construction is completed in March 2011, and extensive engineering runs were carried out using radioactive sources, and beams from the 88-Inch Cyclotron at LBNL. The data obtained will be used to optimize its performance. Then the first scientific campaign will start in March 2012 at NSCL MSU.

Lee, I. Y.

2011-10-01

61

The Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory Compton) is the second in NASA's series of great Observatories. Launched on 1991 April 5, Compton represents a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made. We describe the capabilities of the four scientific instruments, and the observing program of the first 2 years of the mission. Examples of early discoveries by Compton are enumerated, including the discovery that gamma-ray bursts are isotropic but spatially inhomogeneous in their distribution; the discovery of a new class of high-energy extragalacatic gamma-ray sources, the gamma-ray AGNs; the discovery of emission from SN 1987A in the nuclear line of Co-57; and the mapping of emission from Al-26 in the interstellar medium (ISM) near the Galactic center. Future observations will include deep surveys of selected regions of the sky, long-tem studies of individual objects, correlative studies of objects at gamma-ray and other energies, a Galactic plane survey at intermediate gamma-ray energies, and improved statistics on gamma-ray bursts to search for small anisotropies. After completion of the all-sky survey, a Guest Investigator program is in progress with guest observers' time share increasing from 30% upward for the late mission phases.

Gehrels, N.; Chipman, E.; Kniffen, D.

1994-06-01

62

Delayed gamma Rays from Fission.  

National Technical Information Service (NTIS)

Measurements of the energy spectrum of delayed gamma rays from the neutron fission of PU239 and U235 were performed with a naI detector at a number of time intervals between 2 and 80 microsec. The data showed three new prominent gamma rays with energies o...

R. B. Walton R. E. Sund

1966-01-01

63

The gamma-ray cosmos  

NASA Astrophysics Data System (ADS)

NASA's Compton Observatory spacecraft and the Russian/French Granat satellite have yielded vast new knowledge concerning the gamma-ray universe, which is indicative of the most energetic events in existence. A survey is presently conducted of the state of observational and theoretical understanding of gamma-ray sources in active galaxies and within the Galaxy.

Chupp, Edward L.

1992-12-01

64

Gamma ray astrophysics  

NASA Astrophysics Data System (ADS)

A general review of cosmic energetic gamma particles is given. A discussion on the subject starting with the discovery of the PeV gamma rays by Sammorski and Stamm, passing to the super-nova SN1987A explosion when several groups waited for high energy gamma particles but none has come so far up to the measurements of TeV gamma incoming from the Crab Nebula. The discussion in this paper is a by product of the cosmic ray research done in the Chacaltaya Cosmic Rays Observatory in the past few years. A brief description of the facilities on Mount Chacaltaya (5,200 m above sea level (a.s.l.)) is also given.

Martinic, Nicholas J.

1994-04-01

65

A UNIFORM CORRELATION BETWEEN SYNCHROTRON LUMINOSITY AND DOPPLER FACTOR IN GAMMA-RAY BURSTS AND BLAZARS: A HINT OF SIMILAR INTRINSIC LUMINOSITIES?  

SciTech Connect

We compile 23 gamma-ray bursts (GRBs) and 21 blazars with estimated Doppler factors, and the Doppler factors of GRBs are estimated from their Lorentz factors by assuming their jet viewing angles {theta} {yields} 0{sup 0}. Using the conventional assumption that the prompt emission of GRBs is dominated by the synchrotron radiation, we calculate the synchrotron luminosity of GRBs from their total isotropic energy and burst duration. Intriguingly, we discover a uniform correlation between the synchrotron luminosity and Doppler factor, L{sub syn}{proportional_to}D{sup 3.1}, for GRBs and blazars, which suggests that they may share some similar jet physics. One possible reason is that GRBs and blazars have, more or less, similar intrinsic synchrotron luminosities and both of them are strongly enhanced by the beaming effect. After Doppler and redshift correction, we find that the intrinsic peak energy of the GRBs ranges from 0.1 to 3 keV with a typical value of 1 keV. We further correct the beaming effect for the observed luminosity of GRBs and find that a positive correlation exists between the intrinsic synchrotron luminosity and peak energy for GRBs, which is similar to that of blazars. Our results suggest that both the intrinsic positive correlation and the beaming effect may be responsible for the observed tight correlation between the isotropic energy and the peak energy in GRBs (the so-called Amati relation).

Wu Qingwen; Zou Yuanchuan; Wang Dingxiong [School of Physics, Huazhong University of Science and Technology, Wuhan 430074 (China); Cao Xinwu; Chen Liang, E-mail: qwwu@hust.edu.cn, E-mail: zouyc@hust.edu.cn, E-mail: dxwang@hust.edu.cn, E-mail: cxw@shao.ac.cn, E-mail: chenliangew@hotmail.com [Key Laboratory for Research in Galaxies and Cosmology, Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai 200030 (China)

2011-10-10

66

HIGH-ENERGY GAMMA-RAY AFTERGLOWS FROM LOW-LUMINOSITY GAMMA-RAY BURSTS  

SciTech Connect

The observations of gamma-ray bursts (GRBs) such as 980425, 031203 and 060218, with luminosities much lower than those of other classic bursts, lead to the definition of a new class of GRBs-LL-GRBs. The nature of the outflow responsible for them is not yet clear. Two scenarios have been suggested: one is the conventional relativistic outflow with initial Lorentz factor of order of GAMMA{sub 0} approx> 10 and the other is a trans-relativistic outflow with GAMMA{sub 0} approx = 1-2. Here, we compare the high-energy gamma-ray afterglow emission from these two different models, taking into account both synchrotron self-inverse Compton (SSC) scattering and the external inverse Compton scattering due to photons from the cooling supernova or hypernova envelope (SNIC). We find that the conventional relativistic outflow model predicts a relatively high gamma-ray flux from SSC at early times (<10{sup 4} s for typical parameters) with a rapidly decaying light curve, while in the trans-relativistic outflow model, one would expect a much flatter light curve of high-energy gamma-ray emission at early times, which could be dominated by both the SSC emission and the SNIC emission, depending on the properties of the underlying supernova and the shock parameter epsilon{sub e} and epsilon{sub B}. The Fermi Gamma-ray Space Telescope should be able to distinguish between the two models in the future.

He Haoning; Wang Xiangyu; Yu Yunwei [Department of Astronomy, Nanjing University, Nanjing 210093 (China); Meszaros, Peter [Department of Astronomy and Astrophysics, Pennsylvania State University, University Park, PA 16802 (United States)

2009-12-01

67

Gamma-Ray Localization of Terrestrial Gamma-Ray Flashes  

Microsoft Academic Search

Terrestrial gamma-ray flashes (TGFs) are very short bursts of high-energy photons and electrons originating in Earth's atmosphere. We present here a localization study of TGFs carried out at gamma-ray energies above 20 MeV based on an innovative event selection method. We use the AGILE satellite Silicon Tracker data that for the first time have been correlated with TGFs detected by

M. Marisaldi; C. Labanti; F. Fuschino; A. Bulgarelli; M. Trifoglio; G. Di Cocco; F. Gianotti; A. Argan; G. De Paris; A. Trois; E. Del Monte; E. Costa; G. Di Persio; I. Donnarumma; Y. Evangelista; M. Feroci; F. Lazzarotto; L. Pacciani; A. Rubini; S. Sabatini

2010-01-01

68

Can We Probe the Lorentz Factor of Gamma-ray Bursts from GeV-TeV Spectra Integrated Over Internal Shocks?  

NASA Astrophysics Data System (ADS)

We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that the conventional exponential and/or broken power-law cutoff should be drastically modified to a shallower broken power law in practical observations that integrate emissions from different internal shocks. Since the steepening is tiny for observations, this "smearing" effect can generally reduce the previous estimates of the Lorentz factor of the GRB outflows. We apply our formulation to GRB 080916C, recently detected by the Large Area Telescope detector on the Fermi satellite, and find that the minimum Lorentz factor can be ~600 (or even smaller values), which is below but consistent with the previous result of ~900. Observing the steepening energy (the so-called "pair-break energy") is crucial to diagnosing the Lorentz factor and/or the emission site in future observations, especially current and future Cherenkov telescopes such as MAGIC, VERITAS, and CTA.

Aoi, Junichi; Murase, Kohta; Takahashi, Keitaro; Ioka, Kunihito; Nagataki, Shigehiro

2010-10-01

69

CAN WE PROBE THE LORENTZ FACTOR OF GAMMA-RAY BURSTS FROM GeV-TeV SPECTRA INTEGRATED OVER INTERNAL SHOCKS?  

SciTech Connect

We revisit the high-energy spectral cutoff originating from the electron-positron pair creation in the prompt phase of gamma-ray bursts (GRBs) with numerical and analytical calculations. We show that the conventional exponential and/or broken power-law cutoff should be drastically modified to a shallower broken power law in practical observations that integrate emissions from different internal shocks. Since the steepening is tiny for observations, this 'smearing' effect can generally reduce the previous estimates of the Lorentz factor of the GRB outflows. We apply our formulation to GRB 080916C, recently detected by the Large Area Telescope detector on the Fermi satellite, and find that the minimum Lorentz factor can be {approx}600 (or even smaller values), which is below but consistent with the previous result of {approx}900. Observing the steepening energy (the so-called 'pair-break energy') is crucial to diagnosing the Lorentz factor and/or the emission site in future observations, especially current and future Cherenkov telescopes such as MAGIC, VERITAS, and CTA.

Aoi, Junichi; Nagataki, Shigehiro [YITP, Kyoto University, Kyoto 606-8502 (Japan); Murase, Kohta [Department of Physics, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 (Japan); Takahashi, Keitaro [Department of Physics and Astrophysics, Nagoya University, Nagoya 464-8602 (Japan); Ioka, Kunihito, E-mail: murase.2@mps.ohio-state.ed [KEK - High Energy Accelerator Research Organization, Tsukuba 305-0801 (Japan)

2010-10-10

70

Gamma rays at airplane altitudes  

SciTech Connect

An examination of the gamma ray flux above 1 TeV in the atmosphere is needed to better understand the anomalous showers from point sources. Suggestions are made for future experiments on board airplanes.

Iwai, J.; Koss, T.; Lord, J.; Strausz, S.; Wilkes, J.; Woosley, J. (University of Washington, Seattle, WA 98195 USA (US))

1990-03-20

71

Gamma-ray Burst Cosmology  

Microsoft Academic Search

Gamma-ray bursts (GRBs) are brief flashes of gamma-rays occurring at cosmological distances. GRB was discovered by Vela satellite in 1967. The discovery of afterglows in 1997 made it possible to measure the GRBs' redshifts and confirmed the cosmological origin. GRB cosmology includes utilizing long GRBs as standard candles to constrain the dark energy and cosmological parameters, measuring the high-redshift star

F. Y. Wang

2011-01-01

72

Underground Gamma-Ray Spectrometry  

Microsoft Academic Search

Gamma-ray spectrometry using high purity Ge detectors has made significant advances in recent years because large crystals have become readily available and the importance of very radiopure materials in the construction of detectors has been understood. The combination of these improvements has made it possible to decrease detection limits in special low-background counting systems. Gamma-ray spectrometry systems located underground are

Mikael Hult; Matthias Köhler; Nova Gorica

73

Swift: Gamma-Ray Bursts  

NSDL National Science Digital Library

In the late 1960s, scientists accidentally discovered gamma-ray bursts, intense flashes of energy that typically last no more than a few seconds or minutes. For decades after the discovery of these powerful bursts, they remained one of the greatest mysteries in astronomy. This video segment discusses the Swift satellite mission, launched in 2004 to investigate gamma-ray bursts, and presents some theories as to their origins. The segment is four minutes fourteen seconds in length.

74

Gamma-ray burst afterglows  

Microsoft Academic Search

The discovery of counterparts in X-ray and optical to radio wavelengths has revolutionized the study of gamma-ray bursts, until recently the most enigmatic of astrophysical phenomena. We now know that gamma-ray bursts are the biggest explosions in nature, caused by the ejection of ultrarelativistic matter from a powerful energy source and its subsequent collision with its environment. We have just

Paradijs van J. A; Chryssa Kouveliotou; Ralph A. M. J. Wijers

2000-01-01

75

Supernovae and Gamma Ray Bursts  

Microsoft Academic Search

We review the observational status of the Supernova\\/Gamma-Ray Burst connection. Recent (and less recent) observations of long duration Gamma-ray bursts suggest that a significant fraction of them (but not all) are associated with bright SNe of type Ib\\/c. Current estimates of the SN and GRB rates yield a ratio GRB\\/SNe-Ibc in the range ~ 0.4% - 3%. An analysis of

M. Della Valle

2007-01-01

76

Unveiling the secrets of gamma ray bursts  

Microsoft Academic Search

Gamma Ray Bursts are unpredictable and brief flashes of gamma rays that occur about once a day in random locations in the sky. Since gamma rays do not penetrate the Earth's atmosphere, they are detected by satellites, which automatically trigger ground-based telescopes for follow-up observations at longer wavelengths. In this introduction to Gamma Ray Bursts we review how building a

Andreja Gomboc

2012-01-01

77

Modeling gamma-ray bursts  

NASA Astrophysics Data System (ADS)

Discovered serendipitously in the late 1960s, gamma-ray bursts (GRBs) are huge explosions of energy that happen at cosmological distances. They provide a grand physical playground to those who study them, from relativistic effects such as beaming, jets, shocks and blastwaves to radiation mechanisms such as synchrotron radiation to galatic and stellar populations and history. Through the Swift and Fermi space telescopes dedicated to observing GRBs over a wide range of energies (from keV to GeV), combined with accurate pinpointing that allows ground based follow-up observations in the optical, infrared and radio, a rich tapestry of GRB observations has emerged. The general picture is of a mysterious central engine (CE) probably composed of a black hole or neutron star that ejects relativistic shells of matter into intense magnetic fields. These shells collide and combine, releasing energy in "internal shocks" accounting for the prompt emission and flaring we see and the "external shock" or plowing of the first blastwave into the ambient surrounding medium has well-explained the afterglow radiation. We have developed a shell model code to address the question of how X-ray flares are produced within the framework of the internal shock model. The shell model creates randomized GRB explosions from a central engine with multiple shells and follows those shells as they collide, merge and spread, producing prompt emission and X-ray flares. We have also included a blastwave model, which can constrain X-ray flares and explain the origin of high energy (GeV) emission seen by the Fermi telescope. Evidence suggests that gamma-ray prompt emission and X-ray flares share a common origin and that at least some flares can only be explained by long-lasting central engine activity. We pay special attention to the time history of central engine activity, internal shocks, and observed flares. We calculate the gamma-ray (Swift/BAT band) and X-ray (Swift/XRT band) lightcurves for arbitrary central engine activity and compare the model results with the observational data. We show that the observed X-ray flare phenomenology can be explained within the internal shock model. The number, width and occurring time of flares are then used to diagnose the central engine activity, putting constraints on the energy, ejection time, width and number of ejected shells. We find that the observed X-ray flare time history generally reflects the time history of the central engine, which reactivates multiple times after the prompt emission phase with progressively reduced energy. This shell model code can be used to constrain broadband observations of GRB 090926A, which showed two flares in both the Swift UVOT and XRT bands. Using the prompt emission fluence to constrain the total energy contained in the blastwave, the internal shock model requires that Lorentz factors of the shells causing flares must be less than the Lorentz factor of the blastwave when the shells are ejected. Recent observations of Gamma-Ray Bursts (GRBs) by the Fermi Large Area Telescope (LAT) revealed a power law decay feature of the high energy emission (above 100 MeV), which led to the suggestion that it originates from an external shock. We analyze four GRBs (080916C, 090510, 090902B and 090926A) jointly detected by Fermi LAT and Gamma-ray Burst Monitor (GBM), which have high quality lightcurves in both instrument energy bands. Using the MeV prompt emission (GBM) data, we can record the energy output from the central engine as a function of time. Assuming a constant radiative efficiency, we are able to track energy accumulation in the external shock using our internal/external shell model code and show that the late time lightcurves fit well within the external shock model, but the early time lightcurves are dominated by the internal shock component which has a shallow decay phase due to the initial pile-up of shells onto the blast wave.

Maxham, Amanda

78

GRB 090313 AND THE ORIGIN OF OPTICAL PEAKS IN GAMMA-RAY BURST LIGHT CURVES: IMPLICATIONS FOR LORENTZ FACTORS AND RADIO FLARES  

SciTech Connect

We use a sample of 19 gamma-ray bursts (GRBs) that exhibit single-peaked optical light curves to test the standard fireball model by investigating the relationship between the time of the onset of the afterglow and the temporal rising index. Our sample includes GRBs and X-ray flashes for which we derive a wide range of initial Lorentz factors (40 < {Gamma} < 450). Using plausible model parameters, the typical frequency of the forward shock is expected to lie close to the optical band; within this low typical frequency framework, we use the optical data to constrain {epsilon}{sub e} and show that values derived from the early time light-curve properties are consistent with published typical values derived from other afterglow studies. We produce expected radio light curves by predicting the temporal evolution of the expected radio emission from forward and reverse shock components, including synchrotron self-absorption effects at early time. Although a number of GRBs in this sample do not have published radio measurements, we demonstrate the effectiveness of this method in the case of Swift GRB 090313, for which millimetric and centimetric observations were available, and conclude that future detections of reverse-shock radio flares with new radio facilities such as the EVLA and ALMA will test the low-frequency model and provide constraints on magnetic models.

Melandri, A.; Kobayashi, S.; Mundell, C. G.; Guidorzi, C.; Bersier, D.; Steele, I. A.; Smith, R. J. [Astrophysics Research Institute, Liverpool John Moores University, Twelve Quays House, Egerton Wharf, Birkenhead, CH41 1LD (United Kingdom); De Ugarte Postigo, A. [INAF Osservatorio Astronomico di Brera, via Bianchi 46, 23807 Merate (Saint Lucia) (Italy); Pooley, G. [Mullard Radio Astronomy Observatory, Cavendish Laboratory, Madingley Road, Cambridge CB3 0HE (United Kingdom); Yoshida, M. [Okoyama Astrophysical Observatory, National Astronomical Observatory, Kamogata, Okayama 719-0232 (Japan); Castro-Tirado, A. J.; Gorosabel, J.; Kubanek, P.; Sota, A. [Instituto de AstrofisIca de AndalucIa (CSIC), Glorieta de la Astronomia s/n, E-18080 Granada (Spain); JelInek, M. [Hiroshima Astrophysical Science Center, Hiroshima University 1-3-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8526 (Japan); Gomboc, A. [Faculty of Mathematics and Physics, University of Ljubljana, Jadranska 19, SI-1000 Ljubljana (Slovenia); Bremer, M.; Winters, J. M. [Institut de Radioastronomie Millimetrique, 300 rue de la Piscine, 38406 St. Martin d'Heres (France); De Gregorio-Monsalvo, I.; GarcIa-Appadoo, D., E-mail: axm@astro.livjm.ac.u [European Southern Observatory, Casilla 19001, Santiago 19 (Chile)

2010-11-10

79

An Elementary Treatment of Gamma-Ray Heating and Gamma-Ray Dosage in Inhomogeneous Reactors  

Microsoft Academic Search

An analysis is made of the heat produced by the absorption of gamma rays in a sample placed into a reactor. It is clearly shown that enormous local (space) variations in gamma flux exist in current reactors. An application to the Hanford reactors is treated in some detail. Although the estimates obtained may be good to but a factor of

Primak

1952-01-01

80

Optical observations of Gamma-Ray Bursts  

Microsoft Academic Search

We briefly review the status and recent progress in the field of optical observations of gamma-ray burst afterglows. We will focus on the fundamental observational evidence for the relationship between gamma-ray bursts and the final evolutionary phases of massive stars. In particular, we will address (i) gamma-ray burst host galaxies, (ii) optically dark gamma-ray burst afterglows, (iii) the gamma-ray burst–supernova

J. Hjorth; E. Pian; J. P. U. Fynbo

2004-01-01

81

The Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory (Compton) was launched by the Space Shuttle Atlantis on 5 April 1991. The spacecraft and instruments are in good health and returning exciting results. The mission provides nearly six orders of magnitude in spectral coverage, from 30 keV to 30 GeV, with sensitivity over the entire range an order of magnitude better than that of previous observations. The 16,000 kilogram observatory contains four instruments on a stabilized platform. The mission began normal operations on 16 May 1991 and is now over half-way through a full-sky survey. The mission duration is expected to be from six to ten years. A Science Support Center has been established at Goddard Space Flight Center for the purpose of supporting a vigorous Guest Investigator Program. New scientific results to date include: (1) the establishment of the isotropy, combined with spatial inhomogeneity, of the distribution of gamma-ray bursts in the sky; (2) the discovery of intense high energy (100 MeV) gamma-ray emission from 3C 279 and other quasars and BL Lac objects, making these the most distant and luminous gamma-ray sources ever detected; (3) one of the first images of a gamma-ray burst; (4) the observation of intense nuclear and position-annihilation gamma-ray lines and neutrons from several large solar flares; and (5) the detection of a third gamma-ray pulsar, plus several other transient and pulsing hard X-ray sources.

Gehrels, N.; Chipman, E.; Kniffen, D. A.

1993-01-01

82

Jet simulations and Gamma-ray burst afterglow jet breaks  

Microsoft Academic Search

The conventional derivation of the gamma-ray burst afterglow jet break time\\u000auses only the blast wave fluid Lorentz factor and therefore leads to an\\u000aachromatic break. We show that in general gamma-ray burst afterglow jet breaks\\u000aare chromatic across the self-absorption break. Depending on circumstances, the\\u000aradio jet break may be postponed significantly. Using high-accuracy adaptive\\u000amesh fluid simulations in

H. J. van Eerten; Z. Meliani; R. A. M. J. Wijers; R. Keppens

2010-01-01

83

Jet simulations and gamma-ray burst afterglow jet breaks  

Microsoft Academic Search

The conventional derivation of the gamma-ray burst afterglow jet break time uses only the blast wave fluid Lorentz factor and therefore leads to an achromatic break. We show that in general gamma-ray burst afterglow jet breaks are chromatic across the self-absorption break. Depending on circumstances, the radio jet break may be postponed significantly. Using high-accuracy adaptive mesh fluid simulations in

H. J. van Eerten; Z. Meliani; R. A. M. J. Wijers; R. Keppens

2011-01-01

84

Jet simulations and gamma-ray burst afterglow jet breaks  

Microsoft Academic Search

The conventional derivation of the gamma-ray burst afterglow jet break time uses only the blast wave fluid Lorentz factor and therefore leads to an achromatic break. We show that in general gamma-ray burst afterglow jet breaks are chromatic across the self-absorption break. Depending on circumstances, the radio jet break may be postponed significantly. Using high-accuracy adaptive mesh fluid simulations in

Eerten van H. J; Z. Meliani; R. A. M. J. Wijers; R. Keppens

2012-01-01

85

Effect of Pairing Correlations on Nuclear Gamma-Ray Transitions  

Microsoft Academic Search

Several examples of the effect of pairing correlations on nuclear gamma-ray transitions are presented. It is shown that even if collective coupling exists, gamma-ray transitions of electric multipole type between low-lying quasiparticle states whose free shell-model orbit energies are symmetrically related to the Fermi energy may be extremely retarded. In this work the factor (UiUf-ViVf) which arises from the pairing

Hidetsugu Ikegami; Takeshi Udagawa

1964-01-01

86

Effect of Gamma-Ray Beaming on the Fluxes of Gamma-Ray Pulsars  

Microsoft Academic Search

We study the effect of gamma-ray beaming on gamma-ray emission of the pulsars in a self-sustained outer gap model. In this model, averaged gamma-ray flux is a function of period, magnetic field, magnetic inclination angle and solid angle of gamma-ray beaming for a gamma-ray pulsar. We generate a sample of gamma-ray pulsars with their ages less than 106 years by

Ze-Jun Jiang; Li Zhang

2005-01-01

87

Gamma-ray Imaging Methods  

SciTech Connect

In this document we discuss specific implementations for gamma-ray imaging instruments including the principle of operation and describe systems which have been built and demonstrated as well as systems currently under development. There are several fundamentally different technologies each with specific operational requirements and performance trade offs. We provide an overview of the different gamma-ray imaging techniques and briefly discuss challenges and limitations associated with each modality (in the appendix we give detailed descriptions of specific implementations for many of these technologies). In Section 3 we summarize the performance and operational aspects in tabular form as an aid for comparing technologies and mapping technologies to potential applications.

Vetter, K; Mihailescu, L; Nelson, K; Valentine, J; Wright, D

2006-10-05

88

Analytical expressions for the gate utilization factors of passive multiplicity counters including signal build-up  

SciTech Connect

In the realm of nuclear safeguards, passive neutron multiplicity counting using shift register pulse train analysis to nondestructively quantify Pu in product materials is a familiar and widely applied technique. The approach most commonly taken is to construct a neutron detector consisting of {sup 3}He filled cylindrical proportional counters embedded in a high density polyethylene moderator. Fast neutrons from the item enter the moderator and are quickly slowed down, on timescales of the order of 1-2 {micro}s, creating a thermal population which then persists typically for several 10's {micro}s and is sampled by the {sup 3}He detectors. Because the initial transient is of comparatively short duration it has been traditional to treat it as instantaneous and furthermore to approximate the subsequent capture time distribution as exponential in shape. With these approximations simple expressions for the various Gate Utilization Factors (GUFs) can be obtained. These factors represent the proportion of time correlated events i.e. Doubles and Triples signal present in the pulse train that is detected by the coincidence gate structure chosen (predelay and gate width settings of the multiplicity shift register). More complicated expressions can be derived by generalizing the capture time distribution to multiple time components or harmonics typically present in real systems. When it comes to applying passive neutron multiplicity methods to extremely intense (i.e. high emission rate and highly multiplying) neutron sources there is a drive to use detector types with very fast response characteristics in order to cope with the high rates. In addition to short pulse width, detectors with a short capture time profile are also desirable so that a short coincidence gate width can be set in order to reduce the chance or Accidental coincidence signal. In extreme cases, such as might be realized using boron loaded scintillators, the dieaway time may be so short that the build-up (thermalization transient) within the detector cannot be ignored. Another example where signal build-up might be observed is when a {sup 3}He based system is used to track the evolution of the time correlated signal created by a higher multiplying item within a reflective configuration such as the measurement of a spent fuel assembly. In this work we develop expressions for the GUFs which include signal build-up.

Croft, Stephen [Los Alamos National Laboratory; Evans, Louise G [Los Alamos National Laboratory; Schear, Melissa A [Los Alamos National Laboratory

2010-01-01

89

Upgrade of the JET Gamma-Ray Cameras  

SciTech Connect

The JET gamma-ray camera diagnostics have already provided valuable information on the gamma-ray imaging of fast ion in JET plasmas /1,2/. The applicability of gamma-ray imaging to high performance deuterium and deuterium-tritium JET discharges is strongly dependent on the fulfilment of rather strict requirements for the characterisation of the neutron and gamma-ray radiation fields. These requirements have to be satisfied within very stringent boundary conditions for the design, such as the requirement of minimum impact on the co-existing neutron camera diagnostics. The JET Gamma-Ray Cameras (GRC) upgrade project deals with these issues with particular emphasis on the design of appropriate neutron/gamma-ray filters ('neutron attenuators'). Several design versions have been developed and evaluated for the JET GRC neutron attenuators at the conceptual design level. The main design parameter was the neutron attenuation factor. The two design solutions, that have been finally chosen and developed at the level of scheme design, consist of: a) one quasi-crescent shaped neutron attenuator (for the horizontal camera) and b) two quasi-trapezoid shaped neutron attenuators (for the vertical one). The second design solution has different attenuation lengths: a short version, to be used together with the horizontal attenuator for deuterium discharges, and a long version to be used for high performance deuterium and DT discharges. Various neutron-attenuating materials have been considered (lithium hydride with natural isotopic composition and {sup 6}Li enriched, light and heavy water, polyethylene). Pure light water was finally chosen as the attenuating material for the JET gamma-ray cameras. The neutron attenuators will be steered in and out of the detector line-of-sight by means of an electro-pneumatic steering and control system. The MCNP code was used for neutron and gamma ray transport in order to evaluate the effect of the neutron attenuators on the neutron field of the JET GRC. The modelling was dedicated to the estimation of neutron and (plasma-emitted) gamma-ray attenuation, neutron-induced gamma-ray background and the neutron in-scattering impact on the neutron detectors due to the attenuator in the parking location. A numerical study of the gamma-ray detector (CsI(Tl)) was done by means of the IST Monte Carlo code. It provided preliminary results on the detector efficiency and response function.

Soare, S.; Curuia, M.; Anghel, M.; Constantin, M.; David, E. [Association EURATOM-MEdC, National Institute for Cryogenics and Isotopic Technologies, Rm. Valcea (Romania); Zoita, V.; Craciunescu, T.; Falie, D.; Pantea, A.; Tiseanu, I. [Association EURATOM-MEdC, National Institute for Laser, Plasma and Radiation Physics, Bucharest (Romania); Kiptily, V.; Prior, P.; Edlington, T.; Griph, S.; Krivchenkov, Y.; Loughlin, M.; Popovichev, S.; Riccardo, V.; Syme, B.; Thompson, V. [Association EURATOM-UKAEA/JOC, Culham Science Centre, Abingdon (United Kingdom)] (and others)

2008-03-12

90

Gamma-Ray Emission from Pulsar Outer Magnetospheres  

NASA Astrophysics Data System (ADS)

We investigate a stationary pair production cascade in the outer magnetosphere of an isolated, spinning neutron star. The charge depletion due to global flows of charged particles, causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate gamma-rays via curvature and inverse-Compton processes. Some of such gamma-rays collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen the electric field, which is self-consistently solved together with the energy distribution of particles and gamma-rays at each point along the field lines. By solving the set of Maxwell and Boltzmann equations, we demonstrate that an external injection of charged particles at nearly Goldreich-Julian rate does not quench the gap but shifts its position and that the particle energy distribution cannot be described by a power-law. The injected particles are accelerated in the gap and escape from it with large Lorentz factors. We show that such escaping particles migrating outside of the gap contribute significantly to the gamma-ray luminosity for young pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeV observed for the Vela pulsar can be explained by this component. We also discuss that the luminosity of the gamma-rays emitted by the escaping particles is naturally proportional to the square root of the spin-down luminosity.

Hirotani, Kouichi

2005-06-01

91

Gamma-ray Emission from Outer-gap Accelerator  

NASA Astrophysics Data System (ADS)

We investigate a stationary pair production cascade in the outer magnetosphere of an isolated, spinning neutron star. The charge depletion due to global flows of charged particles, causes a large electric field along the magnetic field lines. Migratory electrons and positrons are accelerated by this field to radiate gamma-rays via curvature and inverse-Compton processes. Some of such gamma-rays collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen the electric field, which is self-consistently solved together with the energy distribution of particles and gamma-rays at each point along the field lines. By solving the set of Maxwell and Boltzmann equations, we demonstrate that an external injection of charged particles at nearly Goldreich-Julian rate does not quench the gap but shifts its position and that the particle energy distribution cannot be described by a power-law. The injected particles are accelerated in the gap and escape from it with large Lorentz factors. We show that such escaping particles migrating outside of the gap contribute significantly to the gamma-ray luminosity for young pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeV observed for the Vela pulsar can be explained by this component. We also discuss that the luminosity of the gamma-rays emitted by the escaping particles is naturally proportional to the square root of the spin-down luminosity.

Hirotani, K.

2003-12-01

92

Gamma-Ray Emission from Pulsar Outer Magnetospheres  

NASA Astrophysics Data System (ADS)

We investigate a stationary pair production cascade in the outer magnetosphere of an isolated, spinning neutron star. The charge depletion due to global flows of charged particles, causes a large electric field along the magnetic field lines. Migratory electrons and/or positrons are accelerated by this field to radiate gamma-rays via curvature and inverse-Compton processes. Some of such gamma-rays collide with the X-rays to materialize as pairs in the gap. The replenished charges partially screen the electric field, which is self-consistently solved together with the energy distribution of particles and gamma-rays at each point along the field lines. By solving the set of Maxwell and Boltzmann equations, we demonstrate that an external injection of charged particles at nearly Goldreich-Julian rate does not quench the gap but shifts its position and that the particle energy distribution cannot be described by a power-law. The injected particles are accelerated in the gap and escape from it with large Lorentz factors. We show that such escaping particles migrating outside of the gap contribute significantly to the gamma-ray luminosity for young pulsars and that the soft gamma-ray spectrum between 100 MeV and 3 GeV observed for the Vela pulsar can be explained by this component. We also discuss that the luminosity of the gamma-rays emitted by the escaping particles is naturally proportional to the square root of the spin-down luminosity.

Hirotani, Kouichi

93

FISSION PRODUCT GAMMA RAY SPECTRA  

Microsoft Academic Search

Uranium-235 fission product gamma spectra were calculated for various ; reactor operating histories. An IBM704 digital computer program was coded to ; compute the gamma energy contributed by each fission product gamma ray and to sum ; these results in energy groups. A representative curve showing the decay of ; various energy groups is presented. Comparisons are made with data

1958-01-01

94

Cosmological gamma-ray bursts  

SciTech Connect

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Gamma-ray bursts are brief events that dominate the emission from all other gamma-ray objects in the sky, flicker for tens of seconds, and then turn off. Their nature remains uncertain despite years of efforts to understand them. One hypothesis is that the bursts arise within our galaxy albeit in an extended halo of neutron stars. Another hypothesis uses the isotropic distribution of gamma-ray bursts to argue that they come from nearly the edge of the universe. If gamma-ray bursts originate from cosmological distances, then the expansion of the universe should cause the dimmer (and presumably further) bursts to last longer. The authors have developed methods for measuring this time stretching, related the time stretching to the distance to the bursts, determined how the detailed physics causes temporal variations, and found the amount of total energy and peak luminosity that the events must be producing.

Fenimore, E.; Epstein, R.; Ho, C.; Intzand, J.

1996-04-01

95

Gamma-Ray Shielding Studies.  

National Technical Information Service (NTIS)

A monoenergetic beam of gamma rays was used to study the deep penetration of 10-MeV gamma radiation in aluminum. Recently a positron annihilation system was developed at General Atomic for the purpose of making shielding measurements in the energy range f...

J. A. Lonergan E. A. Beaver J. Parez D. F. Herring

1967-01-01

96

Periodicities in gamma ray bursts  

SciTech Connect

Gamma ray burst models based on magnetic neutron stars face a problem of account for the scarcity of observed periods. Both this scarcity and the typical period found when any is detected are explained if the neutron stars are accreting in binary systems

Wood, K.S.

1984-05-26

97

Cosmic gamma-ray bursts  

Microsoft Academic Search

The results of the observation of cosmic gamma-ray bursts are discussed and available theoretical models are presented. Emphasis is placed on a cosmological model in which a gamma burst results from a powerful (? 1051–1053 erg) and very short ( ?10 –100 s) energy release which occurs in a compact ( ? 106–107 cm) region and gives rise to a

Konstantin A Postnov

1999-01-01

98

On Gamma-Ray Bursts  

Microsoft Academic Search

We show by example how the uncoding of Gamma-Ray Bursts (GRBs) offers unprecedented possibilities to foster new knowledge in fundamental physics and in astrophysics. After recalling some of the classic work on vacuum polarization in uniform electric fields by Klein, Sauter, Heisenberg, Euler and Schwinger, we summarize some of the efforts to observe these effects in heavy ions and high

Remo Ruffini; M. G. Bernardini; C. L. Bianco; Letizia Caito; Pascal Chardonnet; Christian Cherubini; M. G. Dainotti; Federico Fraschetti; Andrea Geralico; Roberto Guida; Barbara Patricelli; Michael Rotondo; J. A. Rueda Hernandez; Gregory Vereshchagin; She-Sheng Xue

2008-01-01

99

The gamma Rays of Uranium  

Microsoft Academic Search

OUR knowledge of the gamma rays of uranium has until now been confined to their discovery by Rutherford (Phys. Zeit., 1902, 517) and to the observations of Eve (ibid., 1907, 185). The latter directed attention to their extraordinary feebleness and to their relatively low penetrating power. Eve found that uranium gives out only about one-tenth as much gamma radiation as

Frederick Soddy; Alexander S. Russell

1909-01-01

100

Portable compton gamma-ray detection system  

DOEpatents

A Compton scattered gamma-ray detector system. The system comprises a gamma-ray spectrometer and an annular array of individual scintillators. The scintillators are positioned so that they are arrayed around the gamma-ray spectrometer. The annular array of individual scintillators includes a first scintillator. A radiation shield is positioned around the first scintillator. A multi-channel analyzer is operatively connected to the gamma-ray spectrometer and the annular array of individual scintillators.

Rowland, Mark S. (Alamo, CA); Oldaker, Mark E. (Pleasanton, CA)

2008-03-04

101

Low-level gamma-ray spectrometry  

Microsoft Academic Search

Low-level gamma-ray spectrometry generally equates to high-sensitivity gamma-ray spectrometry that can be attained by background reduction, selective signal identification, or some combination of both. Various methods for selectively identifying gamma-ray events and for reducing the background in gamma ray spectrometers are given. The relative magnitude of each effect on overall sensitivity and the relative 'cost' for implementing them are given

R L Brodzinski

1991-01-01

102

High energy gamma ray balloon instrument  

Microsoft Academic Search

The High Energy Gamma Ray Balloon Instrument was built in part to verify certain subsystems' performance for the Energetic Gamma Ray Experiment Telescope (EGRET) instrument, the high energy telescope to be carried on the Gamma Ray Observatory. This paper describes the instrument, the performance of some subsystems, and some relevant results.

D. J. Thompson; R. G. Baker; D. L. Bertsch; J. R. Chesney; S. M. Derdeyn; C. H. Ehrmann; C. E. Fichtel; S. D. Hunter; J. S. Jacques; N. A. Laubenthal

1985-01-01

103

Faint Radio Sources and Gamma Ray Bursts  

Microsoft Academic Search

We calculate the number density of faint radio sources that are expected in radio source surveys due to the isotropic emission of Gamma Ray Burst sources. The calculation assumes the beamed supernovae model for gamma ray burst sources detected in gamma rays, x-rays, optical and radio wavelengths. Since the radio wavelength emission is expected to be more isotropically radiated, the

G. I. Langston; A. H. Minter; T. M. Freismuth

2002-01-01

104

Monte Carlo calibration of the SMM gamma ray spectrometer for high energy gamma rays and neutrons  

Microsoft Academic Search

The Gamma Ray Spectrometer (GRS) on the Solar Maximum Mission spacecraft was primarily designed and calibrated for nuclear gamma ray line measurements, but also has a high energy mode which allows the detection of gamma rays at energies above 10 MeV and solar neutrons above 20 MeV. The GRS response has been extrapolated until now for high energy gamma rays

J. F. Cooper; C. Reppin; D. J. Forrest; E. L. Chupp; G. H. Share; R. L. Kinzer

1985-01-01

105

Energy absorption buildup factors of human organs and tissues at energies and penetration depths relevant for radiotherapy and diagnostics.  

PubMed

Energy absorption geometric progression (GP) fitting parameters and the corresponding buildup factors have been computed for human organs and tissues, such as adipose tissue, blood (whole), cortical bone, brain (grey/white matter), breast tissue, eye lens, lung tissue, skeletal muscle, ovary, testis, soft tissue, and soft tissue (4-component), for the photon energy range 0.015-15 MeV and for penetration depths up to 40 mfp (mean free path). The chemical composition of human organs and tissues is seen to influence the energy absorption buildup factors. It is also found that the buildup factor of human organs and tissues changes significantly with the change of incident photon energy and effective atomic number, Z(eff). These changes are due to the dominance of different photon interaction processes in different energy regions and different chemical compositions of human organs and tissues. With the proper knowledge of buildup factors of human organs and tissues, energy absorption in the human body can be carefully controlled. The present results will help in estimating safe dose levels for radiotherapy patients and also useful in diagnostics and dosimetry. The tissue-equivalent materials for skeletal muscle, adipose tissue, cortical bone, and lung tissue are also discussed. It is observed that water and MS20 are good tissue equivalent materials for skeletal muscle in the extended energy range. PMID:22089011

Manohara, S R; Hanagodimath, S M; Gerward, L

2011-11-15

106

High-energy Gamma-ray Afterglows from Low-luminosity Gamma-ray Bursts  

Microsoft Academic Search

The observations of gamma-ray bursts (GRBs) such as 980425, 031203 and 060218, with luminosities much lower than those of other classic bursts, lead to the definition of a new class of GRBs---LL-GRBs. The nature of the outflow responsible for them is not yet clear. Two scenarios have been suggested: one is the conventional relativistic outflow with initial Lorentz factor of

Hao-Ning He; Xiang-Yu Wang; Yun-Wei Yu; Peter Mészáros

2009-01-01

107

RHESSI as Gamma Ray Burst Polarimeter  

NASA Astrophysics Data System (ADS)

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) was designed to measure hard X-rays and ?-rays from solar flares. With its big detection area and thin side shielding it also proved to be well suited for studying Gamma Ray Bursts (GRB). Polarization analysis is feasible as well, due to a big modulation factor (MF), though serious constraints on the minimum detectable polarization (MDP) come from detection efficiency of double scattered photons. More constraints are given by background of accidental and real coincidences.

Hajdas, W.; Wigger, C.; Zehnder, A.

2005-07-01

108

Gamma rays and matter-antimatter asymmetry.  

NASA Astrophysics Data System (ADS)

It is commonly asserted that although there is a marked asymmetry of matter and antimatter on all scales up to and including clusters of galaxies, on the supercluster scale there could indeed be symmetry, the ensuing annihilation gamma rays being of lower intensity than those observed. The authors argue here that this is not so after making a detailed examination of the manner in which such a supercluster, antisupercluster geometry could be present and allowing for factors which appear not to have been previously considered.

Dudarewicz, A.; Wolfendale, A. W.

109

Determination of the gamma-ray spectrum in a strong neutron\\/gamma-ray mixed field  

Microsoft Academic Search

The knowledge of gamma-ray spectrum highly affects the accuracy of the correspondingly derived gamma-ray dose and the correctness of calculated neutron dose in the neutron\\/gamma-ray mixed field dosimetry when using the paired ionization chambers technique. It is of our interest to develop a method to determine the gamma-ray spectrum in a strong neutron\\/gamma-ray mixed field. The current type detector, Mg(Ar)

Yuan-Hao Liu; Yi-Chun Lin; Sander Nievaart; Wen-Tsae Chou; Hong-Ming Liu; Shiang-Huei Jiang

2011-01-01

110

High-energy gamma rays from the intense 1993 January 31 gamma-ray burst  

Microsoft Academic Search

The intense gamma-ray burst of 1993 January 31 was detected by the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Observatory. Sixteen gamma rays above 30 MeV were imaged in the telescope when only 0.04 gamma rays were expected by chance. Two of these gamma rays have energies of approximately 1 GeV, and the five bin spectrum of the

M. Sommer; D. L. Bertsch; B. L. Dingus; C. E. Fichtel; G. J. Fishman; A. K. Harding; R. C. Hartman; S. D. Hunter; K. Hurley; G. Kanbach; D. A. Kniffen; C. Kouveliotou; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; P. L. Nolan; E. Schneid; P. Sreekumar; D. J. Thompson

1994-01-01

111

Feasibility study of gamma-ray medical radiography.  

PubMed

This research explores the feasibility of using gamma-ray radiography in medical imaging. We will show that gamma-ray medical radiography has the potential to provide alternative diagnostic medical information to X-ray radiography. Approximately one Ci Am-241 radioactive source which emits mono-energetic 59.5 keV gamma rays was used. Several factors that influence the feasibility of this study were tested. They were the radiation source uniformity, image uniformity, and image quality parameters such as contrast, noise, and spatial resolution. In addition, several gamma-ray and X-ray images were acquired using humanoid phantoms. These images were recorded on computed radiography image receptors and displayed on a standard monitor. Visual assessments of these images were then conducted. The Am-241 radioactive source provided relatively uniform radiation exposure and images. Image noise and image contrast were mainly dependent on the exposure time and source size, whereas spatial resolution was dependent on source size and magnification factor. The gamma-ray humanoid phantom images were of lower quality than the X-ray images mainly due to the low radioactivity used and not enough exposure time. Nevertheless, the gamma-ray images displayed most of the main structures contained in the humanoid phantoms. Higher exposure rates and thus lower exposure times were estimated for different pure Am-241 source sizes that are hypothesized to provide high quality images similar to X-ray images. For instance, a 10mm source size of pure Am-241 with 7s exposure time should produce images similar in contrast and noise to X-ray images. This research paves the way for the production and usage of a highly radioactive Am-241 source with the potential to lead to the feasibility of acceptable quality medical gamma-ray radiography. PMID:23208227

Alyassin, Abdalmajeid M; Maqsoud, Hamza A; Mashat, Ahmad M; Al-Mohr, Al-Sayed; Abdulwajid, Subhan

2012-11-09

112

Probing the gamma-ray sky  

NASA Astrophysics Data System (ADS)

The observational results of the NASA's Compton Gamma Ray Observatory (GRO) are reviewed with attention given to the results from solar flares and gamma-ray bursts. The observatory is described emphasizing the Burst and Transient Source Experiment, the Oriented Scintillation Spectrometer Experiment, and the Energetic Gamma Ray Experiment Telescope. Increases in gamma-ray emission are noted in solar observations, and the pulsar in the Crab nebula was studied extensively. More gamma-ray pulsars were observed, and a total of 261 gamma-ray bursts are recorded as a result of the GRO observations. A gamma-ray galaxy was discovered by the GRO instruments, and the source - 3C 279 - is estimated to be 7 billion light years from earth. The GRO is shown to be of use in the characterization of astronomical phenomena that cannot be observed from earth.

Hurley, Kevin

1992-12-01

113

Design and performance of the GAMMA-400 gamma-ray telescope for dark matter searches  

NASA Astrophysics Data System (ADS)

The GAMMA-400 gamma-ray telescope is designed to measure the fluxes of gamma-rays and cosmic-ray electrons + positrons, which can be produced by annihilation or decay of the dark matter particles, as well as to survey the celestial sphere in order to study point and extended sources of gamma-rays, measure energy spectra of Galactic and extragalactic diffuse gamma-ray emission, gamma-ray bursts, and gamma-ray emission from the Sun. GAMMA-400 covers the energy range from 100 MeV to 3000 GeV. Its angular resolution is ~0.01° (E? > 100 GeV), the energy resolution ~1% (E? > 10 GeV), and the proton rejection factor ~106. GAMMA-400 will be installed on the Russian space platform Navigator. The beginning of observations is planned for 2018.

Galper, A. M.; Adriani, O.; Aptekar, R. L.; Arkhangelskaja, I. V.; Arkhangelskiy, A. I.; Boezio, M.; Bonvicini, V.; Boyarchuk, K. A.; Fradkin, M. I.; Gusakov, Yu. V.; Kaplin, V. A.; Kachanov, V. A.; Kheymits, M. D.; Leonov, A. A.; Longo, F.; Mazets, E. P.; Maestro, P.; Marrocchesi, P.; Mereminskiy, I. A.; Mikhailov, V. V.; Moiseev, A. A.; Mocchiutti, E.; Mori, N.; Moskalenko, I. V.; Naumov, P. Yu.; Papini, P.; Picozza, P.; Rodin, V. G.; Runtso, M. F.; Sparvoli, R.; Spillantini, P.; Suchkov, S. I.; Tavani, M.; Topchiev, N. P.; Vacchi, A.; Vannuccini, E.; Yurkin, Yu. T.; Zampa, N.; Zverev, V. G.; Zirakashvili, V. N.

2013-02-01

114

THE ORIGIN OF GAMMA RAYS FROM GLOBULAR CLUSTERS  

SciTech Connect

Fermi has detected gamma-ray emission from eight globular clusters (GCs). It is commonly believed that the energy sources of these gamma rays are millisecond pulsars (MSPs) inside GCs. Also it has been standard to explain the spectra of most Fermi Large Area Telescope pulsars including MSPs resulting from the curvature radiation (CR) of relativistic electrons/positrons inside the pulsar magnetosphere. Therefore, gamma rays from GCs are expected to be the collection of CR from all MSPs inside the clusters. However, the angular resolution is not high enough to pinpoint the nature of the emission. In this paper, we calculate the gamma rays produced by the inverse Compton (IC) scattering between relativistic electrons/positrons in the pulsar wind of MSPs in the GCs and background soft photons including cosmic microwave/relic photons, background star lights in the clusters, the galactic infrared photons, and the galactic star lights. We show that the gamma-ray spectrum from 47 Tucanae can be explained equally well by upward scattering of either the relic photons, the galactic infrared photons, or the galactic star lights, whereas the gamma-ray spectra from the other seven GCs are best fitted by the upward scattering of either the galactic infrared photons or the galactic star lights. We also find that the observed gamma-ray luminosity is correlated better with the combined factor of the encounter rate and the background soft photon energy density. Therefore, the IC scattering may also contribute to the observed gamma-ray emission from GCs detected by Fermi in addition to the standard CR process. Furthermore, we find that the emission region of high-energy photons from GCs produced by the IC scattering is substantially larger than the cores of GCs with a radius >10 pc. The diffuse radio and X-rays emitted from GCs can also be produced by the synchrotron radiation and IC scattering, respectively. We suggest that future observations including radio, X-rays, and gamma rays with energy higher than 10 GeV and better angular resolution can provide better constraints for the models.

Cheng, K. S. [Department of Physics, University of Hong Kong, Pokfulam Road (Hong Kong); Chernyshov, D. O. [Moscow Institute of Physics and Technology, Institutskii lane, 141700 Moscow Region, Dolgoprudnii (Russian Federation); Dogiel, V. A. [I. E. Tamm Theoretical Physics Division of P. N. Lebedev Institute, Leninskii pr, 53, 119991 Moscow (Russian Federation); Hui, C. Y. [Department of Astronomy and Space Science, Chungnam National University, Daejeon (Korea, Republic of); Kong, A. K. H. [Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu, Taiwan (China)

2010-11-10

115

Investigation of human teeth with respect to the photon interaction, energy absorption and buildup factor  

NASA Astrophysics Data System (ADS)

The effective atomic numbers and electron densities of human teeth have been calculated for total photon interaction (Z,Ne) and photon energy absorption (Z,ZNe) in the energy region 1 keV-20 MeV. Besides, the energy absorption (EABF) and exposure (EBF) buildup factors have been calculated for these samples by using the geometric progression fitting approximation in the energy region 0.015-15 MeV up to 40 mfp (mean free path). Wherever possible the results were compared with experiment. Effective atomic numbers (Z) of human teeth were calculated using different methods. Discrepancies were noted in Z between the direct and interpolation methods in the low and high energy regions where absorption processes dominate while good agreement was observed in intermediate energy region where Compton scattering dominates. Significant variations up to 22% were observed between Z and Z in the energy region 30-150 keV which is the used energy range in dental cone beam computed tomography (CBCT) X-ray machines. The Zeff values of human teeth were found to relatively vary within 1% if different laser treatments are applied. In this variation, the Er:YAG laser treated samples were found to be less effected than Nd:YAG laser treated ones when compared with control group. Relative differences between EABF and EBF were found to be significantly high in the energy region 60 keV-1 MeV even though they have similar variations with respect to the different parameters viz. photon energy, penetration depth.

Kurudirek, Murat; Topcuoglu, Sinan

2011-05-01

116

Recommended standards for gamma ray intensities  

NASA Astrophysics Data System (ADS)

Gamma ray data are used in more and more areas of application, and so over the years the demand for recommended gamma ray energies and intensities has increased. This paper proposes a list of gamma rays whose intensity is sufficiently well-known and they can be used for the calibration of gamma ray spectrometers and other applications; it is based on studies carried out by an international group of evaluators: the Decay Data Evaluation Project. One goal of this paper is to gather this set of data together in order to facilitate and generalize their use. In the first part, a brief description of the methodology followed throughout the evaluations is given, different methods of gamma ray intensity evaluation are presented, some typical examples of evaluations are shown; in the second part, the list of chosen nuclides is given along with their applications, and finally a list of recommended gamma ray intensities is presented.

Bé, Marie-Martine; Chechev, Valery P.

2013-11-01

117

Advanced gamma ray technology for scanning cargo containers.  

PubMed

The shipping industry is striving to increase security for cargo containers without significantly impeding traffic. Three Science Applications International Corporation (SAIC) development programs are supporting this effort. SAIC's ICIS system combines SAIC's VACIS gamma ray imaging, radiation scanning, OCR, elemental analysis and other technologies to scan containers for nuclear materials and other hazards in normal terminal traffic. SAIC's enhanced gamma ray detector improves VACIS image resolution by a factor of three. And SAIC's EmptyView software analyzes VACIS images to automatically verify empty containers. PMID:15996470

Orphan, Victor J; Muenchau, Ernie; Gormley, Jerry; Richardson, Rex

2005-06-29

118

Radon emanation and soil moisture effects on airborne gamma-ray measurements  

NASA Astrophysics Data System (ADS)

A theoretical model is developed to explain variations in airborne gamma-ray measurements over a calibration range near Ottawa, Ontario. The gamma-ray flux from potassium and the thorium decay series showed an expected decrease with increasing soil moisture. However, the gamma-ray flux from the uranium decay series was highest in the spring when the ground was water-saturated and even covered with snow. These results are explained through the build-up of radon and its associated gamma-ray-emitting decay products in the clay soil of the calibration range with increasing soil moisture. Similar results were found from airborne measurements over other clay soils. However, measurements over sandy soils showed that the count rates from all three radio elements increased with decreasing soil moisture. This difference between soil types was attributed to the lower radon emanation of the more coarse-grained sandy soils compared to finer-grained clay soils. The theoretical and experimental results demonstrate that any estimate of the natural gamma-ray field caused by radium in the ground must take into consideration the radon emanation coefficient of the soil. The radon diffusion coefficient of the soil must also be considered since it depends strongly on soil moisture. This has significant implications for the assessment of outdoor radiation doses using laboratory analyses of soil samples and the use of ground and airborne gamma-ray measurements for radon potential mapping.

Grasty, Robert L.

1997-09-01

119

GRETINA: A gamma ray energy tracking array  

Microsoft Academic Search

A gamma-ray energy tracking array (GRETA) is a new concept for the detection of gamma radiation. In such an array, the individual interactions of all the gamma rays are identified by their energies and positions. Then, using tracking algorithms based on the properties of gamma ray interactions, the scattering sequences are reconstructed. GRETA will give high peak efficiency, peak-to-background ratio,

I. Y. Lee; R. M. Clark; M. Cromaz; M. A. Deleplanque; M. Descovich; R. M. Diamond; P. Fallon; A. O. Macchiavelli; F. S. Stephens; D. Ward

2004-01-01

120

The physics of gamma-ray bursts  

Microsoft Academic Search

Gamma-ray bursts (GRB's), short and intense pulses of low-energy gamma rays, have fascinated astronomers and astrophysicists since their unexpected discovery in the late sixties. During the last decade, several space missions---BATSE (Burst and Transient Source Experiment) on the Compton Gamma-Ray Observatory, BeppoSAX and now HETE II (High-Energy Transient Explorer)---together with ground-based optical, infrared, and radio observatories have revolutionized our understanding

Tsvi Piran

2004-01-01

121

The Supernovae\\/Gamma-Ray Burst Connection  

Microsoft Academic Search

The correlation of SN 1998bw and GRB 980425 shows that some supernovae produce gamma-ray bursts. SN 1998bw resembled previous Type Ic supernovae in terms of its spectral evolution and finite polarization. A check of correlations between the Asiago supernova catalog and the BATSE catalog of gamma-ray bursts suggests that a correlation of gamma-ray bursts with Type Ic supernovae cannot be

J. C. Wheeler; L. Wang; P. Hoflich

1998-01-01

122

In situ gamma-ray spectrometry for the measurement of uranium in surface soils  

Microsoft Academic Search

The application of the technique of in situ gamma-ray spectrometry to the measurement of uranium isotopes in surface soils is described. A basic review of the in situ methodology using high resolution germanium gamma-ray spectrometers is given and specifics on calculated fluences, dose rates in air, and calibration factors are provided for relevant uranium isotopes and their progeny. The influence

K. M. Miller; P. Shebell; G. A. Klemic

1994-01-01

123

Non-association of a celestial gamma ray source with the new Milky Way satellite galaxy  

Microsoft Academic Search

The newly discovered satellite galaxy located in the Milky Way galactic anti-center region is discussed along with the possibility that a nearby gamma ray source is associated with it. The factors which led to the conclusion that the gamma ray excess is not associated with the galaxy are considered.

R. C. Lamb; D. J. Thompson; C. E. Fichtel

1975-01-01

124

Gamma-ray irradiated polymer optical waveguides  

SciTech Connect

Optical waveguides fabricated by gamma-ray irradiation on polymer through a gold mask are presented. The gamma-ray induced index change is found almost linearly dependent on the dose of the irradiation. And the measured propagation losses are low enough for practical application. Due to the high penetrability of gamma ray, uniform refractive index change in depth can be easily achieved. Moreover, due to large-area printing, the uniformity of waveguide made by gamma-ray irradiation is much better than that by e-beam direct writing.

Lai, C.-C.; Wei, T.-Y.; Chang, C.-Y.; Wang, W.-S.; Wei, Y.-Y. [Graduate Institute of Photonics and Optoelectronics and Department of Electrical Engineering, National Taiwan University, No. 1, Roosevelt Road Sec. 4, Taipei 10617, Taiwan (China); Nuclear Science and Technology Development Center, National Tsing-Hua University, No. 101, Sec. 2, Kuang-Fu Road, Hsin-Chu 30043, Taiwan (China)

2008-01-14

125

Using Gamma Rays as Intergalactic Magnetometers  

NASA Astrophysics Data System (ADS)

Gamma rays from distant blazars interact with the extragalactic background light, creating electron-positron pairs, and reducing the amount of gamma-rays seen by ground-based atmospheric Cherenkov telescopes. These pairs can Compton-scatter the cosmic microwave background, creating a gamma-ray signature observable by the Fermi Large Area Telesope (LAT). The signature is also dependent on the intergalactic magnetic field (IGMF), since it can deflect the pairs from our line of sight, reducing the gamma-ray emission. We present preliminary constraints on the IGMF using Fermi-LAT and Cherenkov telescope observations, ruling out both very large and very small values of the IGMF strength.

Finke, Justin; Reyes, L. C.; Georganopoulos, M.; Fermi-LAT Collaboration

2013-04-01

126

Low-level gamma-ray spectrometry  

SciTech Connect

Low-level gamma-ray spectrometry generally equates to high-sensitivity gamma-ray spectrometry that can be attained by background reduction, selective signal identification, or some combination of both. Various methods for selectively identifying gamma-ray events and for reducing the background in gamma-ray spectrometers are given. The relative magnitude of each effect on overall sensitivity and the relative cost'' for implementing them are given so that a cost/benefit comparison can be made and a sufficiently sensitive spectrometer system can be designed for any application without going to excessive or unnecessary expense. 10 refs., 8 figs.

Brodzinski, R.L.

1990-10-01

127

Gamma rays from compact binary systems  

NASA Astrophysics Data System (ADS)

Some of the very high energy (VHE) gamma-ray sources detected with the modern generation of Cherenkov telescopes have been identified with previously known X-ray binary systems. These detections demonstrate the richness of non-thermal phenomena in compact galactic objects containing relativistic outflows or winds produced near black holes and neutron stars. Recently, the well-known microquasar Cygnus X-3 seems to be associated with a gamma-ray source detected with AGILE. Here I summarise the main observational results on gamma-ray emission from X-ray binaries, as well as some of the proposed scenarios to explain the production of VHE gamma-rays.

Paredes, Josep M.

2008-12-01

128

Gamma ray bursts inner engines  

NASA Astrophysics Data System (ADS)

Long gamma ray bursts (GRBs) are brief durations of intense, highly variable gamma radiation coming from point like sources in the Universe. GRBs have been seen in connection with Type 1c supernovae. Their isotropical equivalent energy released in gamma rays is in some cases above 10 54 erg, but the engine creating this energy is unknown. In this thesis several models for the engine are explored. It is shown that cannonballs can in principle form from hyperaccreting disks, however the cannonball model requires almost all supernovae to create cannonballs, and our finding then implies that a hyperaccreting disk is a natural consequence in most supernovae, a notion which remains to be confirmed. General relativistic magnetohydrodynamic simulations of the collapsar model have been performed. Within our setup we found that the duration of the collapsar is too short to explain GRBs, and the energy output is not sufficient. Also the supernova connection could not be explained. I find that the more likely candidate for the GRB engine is an accreting quark star. A quark star has a maximum mass, if the mass increases above this the star will collapse to a black hole. This allows for a two stage engine that might be able to explain features observed in GRBs.

Staff, Jan Erling

129

Gamma-ray burst models.  

PubMed

I consider various possibilities for making gamma-ray bursts, particularly from close binaries. In addition to the much-studied neutron star+neutron star and black hole+neutron star cases usually considered good candidates for short-duration bursts, there are also other possibilities. In particular, neutron star+massive white dwarf has several desirable features. These systems are likely to produce long-duration gamma-ray bursts (GRBs), in some cases definitely without an accompanying supernova, as observed recently. This class of burst would have a strong correlation with star formation and occur close to the host galaxy. However, rare members of the class need not be near star-forming regions and could have any type of host galaxy. Thus, a long-duration burst far from any star-forming region would also be a signature of this class. Estimates based on the existence of a known progenitor suggest that this type of GRB may be quite common, in agreement with the fact that the absence of a supernova can only be established in nearby bursts. PMID:17293332

King, Andrew

2007-05-15

130

The spectrum of gamma-ray burst: a clue  

Microsoft Academic Search

In this work, we numerically calculate the thermal radiation efficiency of the baryonic outflow. The possible outflow acceleration in the transparent stage, which lowers thermal radiation efficiency, has been taken into account. In the standard internal shock model for the prompt emission, the fast shells should move with a typical Lorentz factor ~5 Gammai otherwise the gamma-ray burst (GRB) efficiency

Yi-Zhong Fan

2010-01-01

131

PHOTOGRAPHIC METHOD IN X AND $gamma$ RAY DOSIMETRY  

Microsoft Academic Search

An analysis was made of x and gamma radiation dosimetry by ; photographic emulsion blackening. Experiments were made for determining the ; dependence and relation of direction and saturation factors. A method is ; suggested for photofilm calibration with Co⁜° gamma rays, which can be ; aecomplished under any working conditions. The discrimination and correlation of ; x and gamma

F. Behounek; J. Klumpar; J. Koci; P. Jirousek

1957-01-01

132

Gamma rays from the interactions of reactor fast neutrons ordered by increasing gamma-ray energy  

Microsoft Academic Search

Radioactive material handled in nuclear safeguards often emits both gamma rays and neutrons. The gamma rays emitted by the radioactive isotopes are listed in several compilations, which can be used for identification and quantitative analysis of the radioactive isotopes present. Some of the neutrons are moderated and undergo thermal capture. The capture gamma rays are also listed in several compilations

1982-01-01

133

Vegetation Density Determinations by Gamma Ray Absorption.  

National Technical Information Service (NTIS)

A method of non-destructive determination of vegetation density in place is presented. This method utilizes a gamma ray absorption technique. The 122 keV gamma rays from Cobalt-57 were used for this work. The determinations are made using the principle of...

C. M. Cialella J. G. Dante

1971-01-01

134

The science of gamma-ray spectroscopy  

Microsoft Academic Search

The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. Nevertheless, there is a wide agreement that high amounts of radioactive nuclei are produced during these events, that are expected to be strong gamma-ray emitters. In this paper we investigate the use of gamma-rays as a diagnostic tool. For this purpose we have performed a complete

J. Isern; E. Bravo; A. Hirschmann

2006-01-01

135

A review of gamma ray bursts  

Microsoft Academic Search

Gamma-ray bursts have continued to puzzle astronomers since their discovery thirty years ago. The sources and emission mechanisms are still uncertain. The instruments on the Compton Gamma Ray Observatory, most notably BATSE, have produced a revolution in our understanding of bursts. BATSE found that the burst spatial distribution was isotropic but inhomogeneous, a result inconsistent with any disk population of

Charles Meegan; Kevin Hurley; Alanna Connors; Brenda Dingus; Steven Matz

1997-01-01

136

On The Origin of Gamma Ray Bursts  

Microsoft Academic Search

We propose that repeated photoexcitation\\/ionization of high Z atoms of highly relativistic flows by star light in dense stellar regions followed by emission of decay\\/recombination photons, which are beamed and boosted to gamma ray energies in the observer frame, produce gamma ray bursts (GRBs). We show that this overlooked mechanism, which is able to convert efficiently baryonic kinetic energy release

Nir J. Shaviv; Arnon Dar

1996-01-01

137

Gamma ray observation with emulsion hybrid telescope  

Microsoft Academic Search

A new gamma ray observation project with balloon borne emulsion chambers is presented. A new technique based on the accelerator emulsion experiments was implemented for studying high energy stellar objects with cosmic gamma rays. This paper provides the aim and concept of this project as well as some results of test experiments.

S. Aoki; K. Kodam; J. Kawada; N. Nonaka; A. Suzuki; T. Hara; Y. Watanabe; H. Rokujyo; A. Ariga; M. Kazuyama; H. Kubota; M. Komatsu; T. Sako; O. Sato; Y. Taira; S. Takahashi; N. Naganawa; T. Nakano; M. Nakamura; K. Niwa; Y. Nonoyama; K. Hamada; T. Fukuda; T. Furukawa; K. Hoshino; M. Miyanishi; S. Miyamoto; K. Morishima; T. Yoshioka; J. Yoshida; A. Iyono; Y. Sato; I. Tezuka

2009-01-01

138

The Supernova-Gamma-Ray Burst Connection  

Microsoft Academic Search

SN 1998bw and its corresponding relativistically expanding radio source are coincident with the gamma -ray burst source GRB 980425. We searched for other possible supernova- gamma -ray burst associations among 101 recent Type Ia and 17 Type Ib\\/c supernovae (SNe) for which the dates of optical maximum are relatively well known. We show that Type Ia SNe can be excluded

Lifan Wang; J. Craig Wheeler

1998-01-01

139

Supernova and Gamma-Ray Burst Remnants  

Microsoft Academic Search

The connection between Supernovae and Gamma-Ray Bursts has provided insights to extend our understanding of both these phenomena beyond what was known from studying them separately. A unique window into the connections between the progenitors and mechanisms of supernova and gamma-ray burst explosions is provided by their remnants. This meeting brings together experts of the remnants of both Supernovae and

Roger Chevalier; Una Hwang; Martin Laming

2006-01-01

140

Very high-energy gamma rays from gamma-ray bursts.  

PubMed

Very high-energy (VHE) gamma-ray astronomy has undergone a transformation in the last few years, with telescopes of unprecedented sensitivity having greatly expanded the source catalogue. Such progress makes the detection of a gamma-ray burst at the highest energies much more likely than previously. This paper describes the facilities currently operating and their chances for detecting gamma-ray bursts, and reviews predictions for VHE gamma-ray emission from gamma-ray bursts. Results to date are summarized. PMID:17293337

Chadwick, Paula M

2007-05-15

141

The GLAST Gamma-Ray Telescope Mission  

SciTech Connect

The Gamma-ray Large Area Space Telescope, GLAST, is an orbital mission under construction to measure the cosmic gamma-ray flux in the energy range 20 MeV to >300 GeV, with supporting measurements for gamma-ray bursts from 10 keV to 25 MeV. With its launch in 2007, GLAST will open a new and important window on a wide variety of high energy phenomena, including black holes and active galactic nuclei; gamma-ray bursts; the origin of cosmic rays and supernova remnants; and searches for hypothetical new phenomena such as supersymmetric dark-matter annihilations, Lorentz-invariance violation, and exotic relics from the Big Bang. In addition to a short review of the science opportunities, this talk will describe the high-energy gamma-ray telescope and its components and review the mission status.

Johnson, Robert P. [Institute for Particle Physics, University of California, Santa Cruz, CA 95065 (United States)

2006-07-11

142

Simulations for a proposed gamma-ray space telescope using MEGAlib  

NASA Astrophysics Data System (ADS)

Gamma-Ray Imaging, Polarimetry and Spectroscopy (GRIPS) is a proposed space mission for gamma-ray astrophysics. It will be capable of imaging gamma-rays via Compton scattering and pair production in the energy range from ~200 keV up to ~50MeV. GRIPS will address fundamental astrophysical questions through observations of energetic gamma-ray phenomena such as gamma-ray bursts, blazars and supernovae in this unique energy window. The Medium-Energy Gamma-ray Astronomy library (MEGAlib) is an open-source object-oriented software library designed to simulate and analyse data from low-to-medium-energy gamma-ray telescopes, especially Compton telescopes such as GRIPS. The library comprises all necessary data analysis steps from initial simulations through to event reconstruction and image reconstruction. Simulations are being carried out to optimize the sensitivity of GRIPS to gamma-ray sources using MEGAlib and the results are presented here. GRIPS will offer an improvement in sensitivity in its operational energy range by a factor of ~40 compared with previous missions.

Foley, Suzanne; Zoglauer, Andreas; Greiner, Jochen; Kanbach, Gottfried

2012-09-01

143

Search for Gamma-rays from Lightest Kaluza-Klein ParticleDark Matter with GLAST  

SciTech Connect

The Gamma-Ray Large Area Space Telescope (GLAST), scheduled to be launched in 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT), GLAST main instrument, has a wide field of view (> 2 sr), a large effective area and a 20 MeV-300 GeV energy range. It provides excellent high-energy gamma-ray observations for Dark-Matter searches. Here we study the possibility to detect gamma-rays coming from Lightest Kaluza-Klein Particle (LKP) annihilations in the context of the minimal Universal Extra Dimensions (UED) models. We perform the analysis for different LKP masses and for a Galactic Center (GC) Navarro, Frenk and White (NFW) halo model modified by a boost factor parameter. Finally we give an estimate of the background to obtain the expected total gamma-ray flux and the corresponding expected GLAST sensitivity.

Nuss, E.; Cohen-Tanugi, J.; Lionetto, A.; /Montpellier U. /SLAC /Rome U.,Tor Vergata

2006-05-16

144

Exposure buildup factors for bakelite, perspex and magnox-A12 up to 40 m.f.p. using the interpolation method  

Microsoft Academic Search

The Geometric Progression (G-P) fitting parameters have been computed with respect to the equivalent atomic number for the composite materials of bakelite and perspex by the interpolation method. These parameters are then used to generate the exposure buildup factors up to 40 m.f.p. in the energy range of 0.015-15.0 MeV for these materials. The behaviour of buildup factors is shown

G. S. Brar; Apjit Kaur Sandhu; Makhan Singh; Gurmel S. Mudahar

1994-01-01

145

Exposure buildup factors for bakelite, perspex and magnox-A12 up to 40 m.f.p. using the interpolation method  

NASA Astrophysics Data System (ADS)

The Geometric Progression (G-P) fitting parameters have been computed with respect to the equivalent atomic number for the composite materials of bakelite and perspex by the interpolation method. These parameters are then used to generate the exposure buildup factors up to 40 m.f.p. in the energy range of 0.015-15.0 MeV for these materials. The behaviour of buildup factors is shown in the form of plots as a function of penetration depth.

Brar, G. S.; Sandhu, Apjit Kaur; Singh, Makhan; Mudahar, Gurmel S.

1994-11-01

146

DARK MATTER IN THE CLASSICAL DWARF SPHEROIDAL GALAXIES: A ROBUST CONSTRAINT ON THE ASTROPHYSICAL FACTOR FOR {gamma}-RAY FLUX CALCULATIONS  

SciTech Connect

We present a new analysis of the relative detectability of dark matter annihilation in the Milky Way's eight 'classical' dwarf spheroidal (dSph) satellite galaxies. Ours is similar to previous analyses in that we use Markov-Chain Monte Carlo techniques to fit dark matter halo parameters to empirical velocity dispersion profiles via the spherical Jeans equation, but more general in the sense that we do not adopt priors derived from cosmological simulations. We show that even without strong constraints on the shapes of dSph dark matter density profiles (we require only that the inner profile satisfies -liM{sub r {yields} 0} dln {rho}/dln r {<=} 1), we obtain a robust and accurate constraint on the astrophysical component of a prospective dark matter annihilation signal, provided that the integration angle is approximately twice the projected half-light radius of the dSph divided by distance to the observer, {alpha}{sub int} {approx} 2r{sub h} /d. Using this integration angle, which represents a compromise between maximizing prospective flux and minimizing uncertainty in the dSph's dark matter distribution, we calculate the relative detectability of the classical dSphs by ground- and space-based {gamma}-ray observatories.

Walker, M. G. [Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom); Combet, C.; Hinton, J. A.; Maurin, D.; Wilkinson, M. I., E-mail: mwalker@cfa.harvard.edu, E-mail: dmaurin@lspc.in2p3.fr [Department of Physics and Astronomy, University of Leicester, Leicester, LE1 7RH (United Kingdom)

2011-06-01

147

Gamma-Ray Burst Physics with Glast  

NASA Astrophysics Data System (ADS)

The Gamma-ray Large Area Space Telescope (GLAST) is an international space mission that will study the cosmos in the energy range 10 keV-300 GeV, the upper end of which is one of the last poorly observed region of the celestial electromagnetic spectrum. The ancestor of the GLAST/LAT was the Energetic Gamma Ray Experiment Telescope (EGRET) detector, which flew onboard the Compton Gamma Ray Observatory (CGRO). The amount of information and the step forward that the high energy astrophysics made thanks to its 9 years of observations are impressive. Nevertheless, EGRET uncovered the tip of the iceberg, raising many questions, and it is in the light of EGRET's results that the great potential of the next generation gamma-ray telescope can be appreciated. GLAST will have an imaging gamma-ray telescope, the Large Area Telescope (LAT) vastly more capable than instruments flown previously, as well as a secondary instrument, the GLAST Bursts Monitor, or GBM, to augment the study of gamma-ray bursts. Gamma-Ray Bursts (GRBs) science is one of the most exciting challenges for the GLAST mission, exploring the high energy emission of one of the most intense phenomena in the sky, shading light on various problems: from the acceleration of particles to the emission processes, to more exotic physics like Quantum Gravity effect. In this paper we report the work done so far in the simulation development as well as the study of the LAT sensitivity to GRB.

Omodei, N.

2006-04-01

148

Gamma-Ray Burst Physics with GLAST  

SciTech Connect

The Gamma-ray Large Area Space Telescope (GLAST) is an international space mission that will study the cosmos in the energy range 10 keV-300 GeV, the upper end of which is one of the last poorly observed region of the celestial electromagnetic spectrum. The ancestor of the GLAST/LAT was the Energetic Gamma Ray Experiment Telescope (EGRET) detector, which flew onboard the Compton Gamma Ray Observatory (CGRO). The amount of information and the step forward that the high energy astrophysics made thanks to its 9 years of observations are impressive. Nevertheless, EGRET uncovered the tip of the iceberg, raising many questions, and it is in the light of EGRET's results that the great potential of the next generation gamma-ray telescope can be appreciated. GLAST will have an imaging gamma-ray telescope, the Large Area Telescope (LAT) vastly more capable than instruments own previously, as well as a secondary instrument, the GLAST Bursts Monitor, or GBM, to augment the study of gamma-ray bursts. Gamma-Ray Bursts (GRBs) science is one of the most exciting challenges for the GLAST mission, exploring the high energy emission of one of the most intense phenomena in the sky, shading light on various problems: from the acceleration of particles to the emission processes, to more exotic physics like Quantum Gravity effect. In this paper we report the work done so far in the simulation development as well as the study of the LAT sensitivity to GRB.

Omodei, N.; /INFN, Pisa

2006-10-06

149

How to Make a Gamma-ray  

NASA Video Gallery

Animation showing a proton traveling near the speed of light striking a slower-moving proton. The protons survive the collision, but their interaction creates an unstable particle, a pion, with only 14 percent of the proton's mass. In 10 millionths of a billionth of a second, the pion decays into a pair of gamma-ray photons. Years of data collected by NASA's Fermi Gamma-Ray Space Telescope reveal that the shattered remains of a supernova first observed in 1572 shine in high-energy gamma-rays.

Holly Zell

2011-12-12

150

Detecting Axionlike Particles with Gamma Ray Telescopes  

SciTech Connect

We propose that axionlike particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to a detectable signature in the spectra of high-energy gamma-ray sources. This occurs as a result of gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the 'Hillas criterion', such as jets of active galactic nuclei or hot spots of radio galaxies. The discovery of such an effect is possible by GLAST in the 1-100 GeV range and by ground-based gamma-ray telescopes in the TeV range.

Hooper, Dan; Serpico, Pasquale D. [Center for Particle Astrophysics, Fermi National Accelerator Laboratory, Batavia, Illinois 60510-0500 (United States)

2007-12-07

151

Detecting axionlike particles with gamma ray telescopes.  

PubMed

We propose that axionlike particles (ALPs) with a two-photon vertex, consistent with all astrophysical and laboratory bounds, may lead to a detectable signature in the spectra of high-energy gamma-ray sources. This occurs as a result of gamma rays being converted into ALPs in the magnetic fields of efficient astrophysical accelerators according to the "Hillas criterion", such as jets of active galactic nuclei or hot spots of radio galaxies. The discovery of such an effect is possible by GLAST in the 1-100 GeV range and by ground-based gamma-ray telescopes in the TeV range. PMID:18233353

Hooper, Dan; Serpico, Pasquale D

2007-12-06

152

Are 0. 1%-accurate gamma-ray assays possible for /sup 235/U solutions  

SciTech Connect

The factors influencing the accuracy of passive gamma-ray assay of uniform, homogeneous solution samples have been studied in some detail, particularly for the assay of /sup 235/U in uranium solutions. Factors considered are the overall long-term electronic stability, the information losses caused by the rate-related electronic processes of pulse pileup and dead-time, and the self-attenuation of gamma rays within the samples. Both experimental and computational studies indicate that gamma-ray assay procedures for solution samples of moderate size (from approx. 10 to perhaps a few hundred milliliters) are now capable of accuracies approaching 0.1% in many practical cases.

Parker, J.L.

1983-01-01

153

The MILAGRO Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

MILAGRO will be the first water-\\v{C}erenkov detector specifically built to study extensive air showers. It is being built in an existing man-made pond 60m x 80m by 8m, located in the Jemez mountains near Los Alamos, NM. Unlike conventional air shower detectors, which sample less than 1% of the particles which reach detector level, MILAGRO will be totally sensitive to the electrons, photons, hadrons, and muons in the air shower. The energy threshold of the MILAGRO detector is comparable to atmospheric \\v{C}erenkov detectors, however it has several advantages over these optical detectors. MILAGRO is operational 24 hours a day in all weather conditions and it has an open aperture which allows it to view the entire northern sky every day. These capabilities allow for a systematic all-sky survey to be done for the first time at VHE energies. MILAGRO will measure the Crab spectrum with high significance. In addition, it will detect and measure the spectra from AGN's such as MRK 421. MILAGRO will be the first VHE detector capable of recording Gamma Ray Bursts at energies above 250 GeV. MILAGRO will search for point sources of VHE gamma radiation, both steady and episodic. The scientific merits of this detector together with its design and current status will be discussed.

Shoup, A.; Barwick, S.; Chumney, P.; Yodh, G. B.; Chang, C. Y.; Chen, M. L.; Dion, C.; Goodman, J. A.; Berley, D.; Haines, T. J.; Hoffman, C. M.; Nagle, D. E.; Sandberg, V. D.; Sanders, G.; Schaller, S.; White, D. H.; Schmidt, D. M.; Sinnis, C.; Cavalli-Sforza, M.; Coyne, D.; Dorfan, D.; Kelley, L.; Klein, S.; Schnee, R.; Williams, D. A.; Yang, T.; Mincer, A. I.; Nemethy, P.; Bauer, D.; Caldwell, D.; Lu, A.; Yellin, S.; O'Neill, T. J.; Tumer, O. T.; Zych, A.; Freedman, S. J.; Fujikawa, B. K.; Ellsworth, R. W.; Biller, S.; Dingus, B. L.; Ahulwalia, H. S.

1994-12-01

154

Gamma-ray Emission from HMXBs  

NASA Astrophysics Data System (ADS)

During the last ten years, high-mass X-ray binaries (HMXB) have consolidated their status of gamma-ray sources. Even before the first EGRET detection candidates, HMXB seemed to be interesting sources to look for gamma rays, and study the processes giving rise to such an energetic photons. Presently, there is already a well established population of gamma-ray emittings HMXB found or confirmed by the current GeV and TeV instruments. These objects have turned out to be very efficient as accelerators, and also channelling the available energy budget into relativistic particles. Their emission is strongly variable and typically periodical, with a low-energy counterpart that is intimately related to the processes at the highest energies. In this talk, I will review the main processes associated to the production of gamma-rays in high-mass X-ray binaries.

Bosch-Ramon, Valenti

2012-07-01

155

Gamma Ray Bursts from Magnetospheric Plasma Oscillations.  

National Technical Information Service (NTIS)

Neutron star Magnetospheric Plasma Oscillations (MPO), can account for the energetics, decay time scale, and spectra of typical Gamma Ray Bursts (GRBs). The soft photon source is likely to be due to backwarming of the reprocessing boundary by the incipien...

F. Melia

1989-01-01

156

Neutron Detection Gamma Ray Sensitivity Criteria  

SciTech Connect

The shortage of 3He has triggered the search for effective alternative neutron detection technologies for national security and safeguards applications. Any new detection technology must satisfy two basic criteria: (1) it must meet a neutron detection efficiency requirement, and (2) it must be insensitive to gamma-ray interference at a prescribed level, while still meeting the neutron detection requirement. It is the purpose of this paper to define measureable gamma ray sensitivity criteria for neutron detectors. Quantitative requirements are specified for: intrinsic gamma ray detection efficiency and gamma ray absolute rejection. The ratio GARRn is defined, and it is proposed that the requirement for neutron detection be 0.9 < GARRn < 1.1 at a 10 mR/h exposure rate. An example of results from a 3He based neutron detector are provided showing that this technology can meet the stated requirements. Results from tests of some alternative technologies are also reported.

Kouzes, Richard T.; Ely, James H.; Lintereur, Azaree T.; Mace, Emily K.; Stephens, Daniel L.; Woodring, Mitchell L.

2011-10-21

157

Gamma-Ray Pulsar Studies With GLAST  

SciTech Connect

Some pulsars have their maximum observable energy output in the gamma-ray band, offering the possibility of using these high-energy photons as probes of the particle acceleration and interaction processes in pulsar magnetospheres. After an extended hiatus between satellite missions, the recently-launched AGILE mission and the upcoming Gamma-ray Large Area Space Telescope (GLAST) Large Area Telescope (LAT) will allow gamma-ray tests of the theoretical models developed based on past discoveries. With its greatly improved sensitivity, better angular resolution, and larger energy reach than older instruments, GLAST LAT should detect dozens to hundreds of new gamma-ray pulsars and measure luminosities, light curves, and phase-resolved spectra with unprecedented resolution. It will also have the potential to find radio-quiet pulsars like Geminga, using blind search techniques. Cooperation with radio and X-ray pulsar astronomers is an important aspect of the LAT team's planning for pulsar studies.

Thompson, D.J.; /NASA, Goddard

2011-11-23

158

GRAPE - The Gamma Ray Polarimeter Experiment  

NASA Astrophysics Data System (ADS)

We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), has been successfully demonstrated in the lab using partially polarized gamma-ray sources and using fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model was flown on a high altitude balloon flight to demonstrate the design and to collect background data. We are currently working on the development of a much larger balloon payload that would provide a significant level of sensitivity for gamma-ray bursts on a long-duration balloon flight and, if flown near solar max, would also provide significant sensitivity for solar flare polarization measurements. We shall review the history, status and future potential of the GRAPE project and summarize the potential for making polarization measurements of gamma-ray bursts and solar flares.

McConnell, Mark L.; Bloser, P. F.; Legere, J.; Ryan, J. M.; Connor, T.

2009-01-01

159

Do Gamma-ray Burst Sources Repeat.  

National Technical Information Service (NTIS)

The demonstration of repeated gamma-ray bursts from an individual source would severely constrain burst source models. Recent reports of evidence for repetition in the first BATSE burst catalog have generated renewed interest in this issue. Here, we analy...

C. A. Meegan D. H. Hartmann J. J. Brainerd M. Briggs W. S. Paciesas

1994-01-01

160

Gamma-ray emission from thermonuclear supernovae  

SciTech Connect

The explosion mechanism associated with thermonuclear supernovae (SNIa) is still a matter of debate. Nevertheless, there is a wide agreement that high amounts of radioactive nuclei are produced during these events and that they are expected to be strong {gamma}-ray emitters. In this paper we investigate the use of this {gamma}-rays as a diagnostic tool. For this purpose we have performed a complete study of the {gamma}-ray spectra associated with all the different scenarios currently proposed: detonation, deflagration, delayed detonation, and pulsating delayed detonation. Our study shows that the {gamma}-ray emission from SNIa is, effectively, a promising tool but that has to be carefully used since it can lead to misinterpretations. We also show that 3D effects can be relevant in some circumstances and that they can provide important information about the exploding system and the thermonuclear burning front mechanism if high resolution spectra could be obtained.

Isern, J. [Institut de Ciencies de l'Espai (CSIC - IEEC), Campus UAB, Torre C5-parells 2n, 08193 Bellaterra (Spain); Institut d'Estudis Espacials de Catalunya (Spain); Bravo, E.; Hirschmann, A. [Departament de Fisica i Enginyeria Nuclear UPC (Spain); Diagonal 647, 08028 Barcelona (Spain); Institut d'Estudis Espacials de Catalunya (Spain)

2007-08-21

161

Radio counterparts of gamma-ray pulsars  

NASA Astrophysics Data System (ADS)

Observations of pulsars with the Large Area Telescope (LAT) on the Fermi satellite have revolutionized our view of the gamma-ray pulsar population. For the first time, a large number of young gamma-ray pulsars have been discovered in blind searches of the LAT data. More generally, the LAT has discovered many new gamma-ray sources whose properties suggest that they are powered by unknown pulsars. Radio observations of gamma-ray sources have been key to the success of pulsar studies with the LAT. For example, radio observations of LAT-discovered pulsars provide constraints on the relative beaming fractions, which are crucial for pulsar population studies. Also, radio searches of LAT sources with no known counterparts have been very efficient, with the discovery of over forty millisecond pulsars. I review radio follow-up studies of LAT-discovered pulsars and unidentified sources, and discuss some of the implications of the results.

Guillemot, L.

2013-03-01

162

Thermal neutron capture gamma-rays  

SciTech Connect

The energy and intensity of gamma rays as seen in thermal neutron capture are presented. Only those (n,..cap alpha..), E = thermal, reactions for which the residual nucleus mass number is greater than or equal to 45 are included. These correspond to evaluations published in Nuclear Data Sheets. The publication source data are contained in the Evaluated Nuclear Structure Data File (ENSDF). The data presented here do not involve any additional evaluation. Appendix I lists all the residual nuclides for which the data are included here. Appendix II gives a cumulated index to A-chain evaluations including the year of publication. The capture gamma ray data are given in two tables - the Table 1 is the list of all gamma rays seen in (n,..gamma..) reaction given in the order of increasing energy; the Table II lists the gamma rays according to the nuclide.

Tuli, J.K.

1983-01-01

163

Gamma-ray Burst Predictions for the Fermi Gamma Ray Space Telescope  

Microsoft Academic Search

Results of a phenomenological model to estimate the gamma-ray burst (GRB) detection rate by the Fermi Gamma-Ray Space Telescope are reported. This estimate is based on the Burst and Transient Source Experiment (BATSE) 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV-5 GeV with Energetic Gamma-Ray Experiment Telescope (EGRET) and at 20 keV-2 MeV with BATSE,

Truong Le; Charles D. Dermer

2009-01-01

164

Low-State Gamma-Ray Emission from Blazars and the Gamma-Ray Background  

Microsoft Academic Search

We examine the contribution of flat spectrum radio sources (FSRSs), or blazars, to the diffuse gamma-ray background (DGRB), prompted by the association of the extragalactic gamma -ray sources detected by the EGRET instrument aboard the Compton Gamma Ray Observatory (CGRO) with this class of objects by using their well-studied log N--log S distribution. The basic assumption of our study are

Demosthenes Kazanas; Eric Perlman

1997-01-01

165

Gamma-Ray Library and Uncertainty Analysis: Passively Emitted Gamma Rays Used in Safeguards Technology  

Microsoft Academic Search

Non-destructive gamma-ray analysis is a fundamental part of nuclear safeguards, including nuclear energy safeguards technology. Developing safeguards capabilities for nuclear energy will certainly benefit from the advanced use of gamma-ray spectroscopy as well as the ability to model various reactor scenarios. There is currently a wide variety of nuclear data that could be used in computer modeling and gamma-ray spectroscopy

2009-01-01

166

Fermi Gamma-ray Space Telescope Observations of Gamma-ray Pulsars  

Microsoft Academic Search

The Large Area Telescope on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST), with its large field of view and effective area, combined with its excellent timing capabilities, is poised to revolutionize the field of gamma-ray astrophysics. The large improvement in sensitivity over EGRET is expected to result in the discovery of many new gamma-ray pulsars, which in turn

P. M. Saz Parkinson

2009-01-01

167

Pair-Signatures and High-Energy Gamma-Ray Emission from Gamma-Ray Bursts  

Microsoft Academic Search

We discuss high-energy gamma-ray emission from gamma-ray bursts (GRBs). When such high-energy gamma rays are expected, e+\\/- pairs may play an important role both inside and outside the source. e+\\/- pair-signatures inside the source (the pair-annihilation bump and the cutoff due to the pair-creation process) are useful for diagnosing the fireball of GRBs. The recipes for diagnoses are largely model-independent

Kohta Murase; Kunihito Ioka; Shigehiro Nagataki

2008-01-01

168

Constraints on the Luminosity Function of Gamma-Ray Bursts from the Gamma Ray Background  

Microsoft Academic Search

The width of the gamma-ray burst (GRB) luminosity function is presently not well constrained. A wide luminosity function might be expected were GRBs associated with supernovae, for example. The possibility that a large number of undetected GRBs might make a contribution to the diffuse soft gamma-ray background is investigated. If gamma-ray bursts (GRBs) create supernova-like remnants, the width of the

H. Che

1999-01-01

169

Solar Two Gamma-Ray Observatory  

Microsoft Academic Search

The field of high energy gamma-ray astronomy grew tremendously in the last decade due to the launch of the EGRET detector on the Compton Gamma-Ray Observatory in 1991 and the proliferation of ground-based air ?herenkov telescopes (ACTs) such as the Whipple 10 meter reflector. Interestingly, the ground-based telescopes only see 4–5 of the over 170 objects detected by EGRET. A

T. Tümer; D. Bhattacharya; U. Mohideen; R. Rieben; V. Souchkov; H. Tom; J. Zweerink

1999-01-01

170

GRI: the gamma-ray imager mission  

NASA Astrophysics Data System (ADS)

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are the major science themes that are addressed in the gamma-ray regime. With the INTEGRAL observatory, ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques hav paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow to study particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Knödlseder, Jürgen

2006-07-01

171

The Gamma-Ray Imager GRI  

NASA Astrophysics Data System (ADS)

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are the major science themes that are addressed in the gamma-ray regime. With the INTEGRAL observatory, ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction and multilayer coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow to study particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Wunderer, Cornelia B.; GRI Collaboration

2006-09-01

172

Gamma-Ray Burst Physics with GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Space Telescope (GLAST), scheduled to be launched in late of 2007, is the next generation satellite for high-energy gamma-ray astronomy. The Large Area Telescope (LAT), the main instrument of GLAST, will survey the sky in the energy range between 20 MeV to more than 300 GeV, shedding light on many issues left open by its highly

Nicola Omodei

2007-01-01

173

A General Gamma-Ray Source Catalog  

NASA Astrophysics Data System (ADS)

The past several years have seen unprecedented growth in the field of gamma-ray astronomy. Highly successful missions such as the Compton Gamma-Ray Observatory (CGRO) have led to both a great increase in the number of detected gamma-ray sources and a more fundamental understanding of the basic physical processes involved for those sources. New ground-based observatories, the Rossi X-Ray Timing Explorer (RXTE), and the SIGMA instrument aboard the GRANAT spacecraft have all contributed to this explosion. Detailed observations of active galaxies, pulsars, accreting binaries, and diffuse emission have had a tremendous impact on our view of the universe. Given that new experiments that will provide a similar increase in source numbers are several years away, it is a good time to take inventory of the state of gamma-ray astronomy. To this end, we have developed a general gamma-ray point-source catalog containing 309 objects that summarize the field. Gamma-ray astronomy, as we define it, includes photon energies from 50 keV to about 1 TeV. While many catalogs concentrate on a single type of astronomical object and/or a very restricted energy range, the nature of this catalog is somewhat different. The large variety of objects and the many orders of magnitude in energy space covered by gamma-ray astronomy presents an organizational challenge. We focus on two main types of information: a general listing of the basic characteristics of each source, and detailed tables of a representative sample of high-energy observations. We also summarize the gamma-ray instruments whose observations are included in the catalog.

Macomb, D. J.; Gehrels, N.

1999-02-01

174

Gamma-Ray Bursts: the Four Crises  

Microsoft Academic Search

We discuss some open problems concerning the origin and the emission\\u000amechanism of gamma-ray bursts (GRBs) in light of recent developments. If GRBs\\u000aoriginate at extragalactic distances, we are facing four crises: (1) an energy\\u000acrisis, models have to account for more than 10^{53} ergs of energy emitted in\\u000athe gamma-ray energy band; (2) a spectral crisis, emission models have

Marco Tavani

1998-01-01

175

Gamma-Ray Bursts: the Four Crises  

Microsoft Academic Search

We discuss some open problems concerning the origin and the emission mechanism of gamma-ray bursts (GRBs) in light of recent developments. If GRBs originate at extragalactic distances, we are facing four crises: (1) an energy crisis, models have to account for more than 10^{53} ergs of energy emitted in the gamma-ray energy band; (2) a spectral crisis, emission models have

M. Tavani

1999-01-01

176

Swift's 500th Gamma Ray Burst  

NASA Video Gallery

On April 13, 2010, NASA's Swift Gamma-ray Burst Explorer satellite discovered its 500th burst. Swift's main job is to quickly localize each gamma-ray burst (GRB), report its position so that others can immediately conduct follow-up observations, and then study the burst using its X-ray and Ultraviolet/Optical telescopes. Some notable bursts are identified in the video.

Katherine Lewis

2010-04-19

177

Swift gamma-ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well a using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

Neil A. Gehrels

2000-01-01

178

Gamma Ray Bursts Cook Book I: Formulation  

Microsoft Academic Search

Since the suggestion of relativistic shocks as the origin of gamma-ray bursts\\u000a(GRBs) in early 90's, the mathematical formulation of this process has stayed\\u000aat phenomenological level. One of the reasons for the slow development of\\u000atheoretical works in this domain has been the simple power-law behaviour of the\\u000aafterglows hours or days after the prompt gamma-ray emission. Nowadays with

Houri Ziaeepour

2008-01-01

179

Swift: A gamma ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

2001-01-01

180

Classification of Swift's gamma-ray bursts  

Microsoft Academic Search

Context. Two classes of gamma-ray bursts have been identified in the BATSE catalogs characterized by durations shorter and longer than about 2 s. There are, however, some indications for the existence of a third class. Swift satellite detectors have different spectral sensitivity than pre-Swift ones for gamma-ray bursts. Therefore we reanalyze the durations and their distribution and also the classi-

I. Horváth; L. G. Balázs; Z. Bagoly; P. Veres

2008-01-01

181

First Gamma Ray Burst Observations with Swift  

Microsoft Academic Search

Swift is a NASA Explorer mission that was launched on November 20, 2004. It is a multiwavelength observatory for transient astronomy. The goals of the mission are to determine the origin of gamma-ray bursts and their afterglows and use bursts to probe the early Universe. A wide-field gamma-ray camera will detect more than a hundred GRBs per year to 3

Neil Gehrels

2005-01-01

182

The swift gamma-ray burst MIDEX  

Microsoft Academic Search

Swift is a first of its kind multiwavelength transient observatory for gamma-ray burst astronomy. It has the optimum capabilities for the next breakthroughs in determining the origin of gamma-ray bursts and their afterglows as well as using bursts to probe the early Universe. Swift will also perform the first sensitive hard X-ray survey of the sky. The mission is being

Neil Gehrels

2000-01-01

183

Gamma-ray bursts and Swift  

Microsoft Academic Search

Discovered by accident using satellites monitoring the nuclear test-ban treaty, gamma-ray bursts (GRBs) are the most powerful explosive events in the Universe. Several GRBs per day occur randomly on the sky, typically lasting a few seconds as a gamma-ray source. This abrupt burst is followed by emission across the entire electromagnetic spectrum which can last for several weeks or more.

Paul O'Brien; Julian Osborne; Keith Mason

2005-01-01

184

GeV gamma-ray sources  

NASA Astrophysics Data System (ADS)

We report on the preliminary extension of our work on cataloging the GeV sky to approximately 7 years of CGRO/EGRET observations with special emphasis on a search for transient sources. The search method and significance levels are presented. Our initial results on 13 possible transients indicate that 3 may be new gamma-ray sources. Sixteen new steady GeV sources are also detected, 3 of which have never been reported as gamma-ray sources. .

Lamb, R. C.; Macomb, D. J.

2000-06-01

185

Mining Gamma-Ray Burst Data  

Microsoft Academic Search

Gamma-ray bursts provide what is probably one of the messiest of all astrophysical data sets. Burst class properties are indistinct,\\u000a as overlapping characteristics of individual bursts are convolved with effects of instrumental and sampling biases. Despite\\u000a these complexities, data mining techniques have allowed new insights to be made about gamma-ray burst data. We demonstrate\\u000a how data mining techniques have simultaneously

Jon Hakkila; Richard J. Roiger; David J. Haglin; Robert S. Mallozzi; Geoffrey N. Pendleton; Charles A. Meegan

186

GRI: The Gamma-Ray Imager mission  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe While at lower wavebands the observed emission is generally dominated by thermal processes the gamma-ray sky provides us with a view on the non-thermal Universe Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood and nuclear

Jürgen Knödlseder

2006-01-01

187

The Gamma-Ray Imager GRI  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear

Cornelia B. Wunderer

2008-01-01

188

The Gamma-Ray Imager GRI  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear

Cornelia B. Wunderer

2006-01-01

189

Gamma-Ray Bursts from Minijets  

Microsoft Academic Search

Striking similarities exist between high-energy gamma-ray emission from active galactic nuclei (AGNs) and gamma-ray bursts (GRBs). They suggest that GRBs are generated by inverse Compton scattering from highly relativistic electrons in transient jets. Such jets may be produced along the axis of an accretion disk formed around stellar black holes (BHs) or neutron stars (NSs) in BH-NS and NS-NS mergers

Nir J. Shaviv; Arnon Dar

1995-01-01

190

Cataclysmic Variables and Gamma-Ray Sources  

NASA Astrophysics Data System (ADS)

The cataclysmic variables are associated with high energy events and probably many of them could be potential gamma-ray sources. Up to now Fermi-LAT detected 3 gamma-ray transients, which belong to CVs and related objects: V407 Cyg, N Sco 2012 and N Mon 2012 = V959 Mon. We present the first multicolour observations of the slow classical nova V959 Mon.

Pavlenko, E.; Malanushenko, V.; Shugarov, S.; Chochol, D.

2013-07-01

191

Observing Gamma-ray Bursts with GLAST  

Microsoft Academic Search

The Gamma-ray Large Area Telescope (GLAST) is a satellite-based observatory to study the high-energy gamma-ray sky. The Large Area Telescope, the main instrument, is a pair-conversion telescope which will survey the sky in the energy range 20 MeV to greater than 300 GeV. The LAT's wide field of view (>2; sr), large effective area and low deadtime combine to provide

Julie E. McEnery

2007-01-01

192

Gamma-ray Albedo of the Moon  

SciTech Connect

We use the GEANT4 Monte Carlo framework to calculate the gamma-ray albedo of the Moon due to interactions of cosmic ray (CR) nuclei with moon rock. Our calculation of the albedo spectrum agrees with the EGRET data. We show that the spectrum of gamma-rays from the Moon is very steep with an effective cutoff around 3 GeV (600 MeV for the inner part of the Moon disc). Since it is the only (almost) black spot in the gamma-ray sky, it provides a unique opportunity for calibration of gamma-ray telescopes, such as the forthcoming Gamma Ray Large Area Space Telescope (GLAST). The albedo flux depends on the incident CR spectrum which changes over the solar cycle. Therefore, it is possible to monitor the CR spectrum using the albedo gamma-ray flux. Simultaneous measurements of CR proton and helium spectra by the Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics (PAMELA), and observations of the albedo -rays by the GLAST Large Area Telescope (LAT), can be used to test the model predictions and will enable the GLAST LAT to monitor the CR spectrum near the Earth beyond the lifetime of PAMELA.

Moskalenko, Igor V.; Porter, Troy A.

2007-06-14

193

Observing cosmic nuclei in gamma rays  

NASA Astrophysics Data System (ADS)

Nucleosynthesis events in cosmic objects create new nuclei, admixtures of radioactive isotopes being part of the matter ejected into interstellar space by these events. Gamma rays are emitted in radioactive decays, and can be measured with space-based gamma-ray telescopes. Four mission years of INTEGRAL have led to discoveries of new sources and to detailed astronomical refinements of already-known gamma-ray line emission. As part of the main science objectives of INTEGRAL's spectrometer SPI, diffuse emission from annihilation of positrons has presented a new puzzle, as the Galactic distribution of their presumed sources does not agree with the gamma-ray image. Recent massive-star nucleosynthesis is traced throughout the Galaxy with radioactivites seen in 26Al and now also 60Fe gamma rays; precision line spectroscopy now reveals Doppler shifts for the 26Al line, separately for different parts of the Galaxy. This provides new insights into the dynamics of hot interstellar gas. The processes generating new atomic nuclei in stars and supernovae are reflected in the abundances of the ejected radioactivities. For individual supernovae, measurements of 44Ti with its 85 year decay time probes the symmetry of the supernova interior. Since such gamma-ray measurements probe the generation of new nuclei in cosmic sites through a radiation process which is independent of environmental parameters such as temperature or ionization, it will remain worthwhile to further develop instrumentation in this window to the nuclear-physics universe.

Diehl, Roland

2008-01-01

194

Gamma-ray bursts afterglows in magnetized stellar winds  

NASA Astrophysics Data System (ADS)

Recent analytical and numerical work argue that successful relativistic Fermi acceleration requires a weak magnetization of the unshocked plasma, all the more so at high Lorentz factors. The present Letter tests this conclusion by computing the afterglow of a gamma-ray burst outflow propagating in a magnetized stellar wind using 'ab initio' principles regarding the microphysics of relativistic Fermi acceleration. It is shown that in magnetized environments, one expects a drop-out in the X-ray band on subday scales as the synchrotron emission of the shock-heated electrons exits the frequency band. At later times, Fermi acceleration becomes operative when the blast Lorentz factor drops below a certain critical value, leading to the recovery of the standard afterglow light curve. Interestingly, the observed drop-out bears resemblance with the fast decay found in gamma-ray bursts early X-ray afterglows.

Lemoine, Martin; Pelletier, Guy

2011-11-01

195

Overall Evolution of Jetted Gamma-ray Burst Ejecta  

Microsoft Academic Search

Whether gamma-ray bursts are highly beamed or not is a very difficult but\\u000aimportant problem that we are confronted with. Some theorists suggest that\\u000abeaming effect usually leads to a sharp break in the afterglow light curve\\u000aduring the ultra-relativistic phase, with the breaking point determined by\\u000a$\\\\gamma = 1 \\/ \\\\theta_0$, where $\\\\gamma$ is the Lorentz factor of the

Y. F. Huang; L. J. Gou; Z. G. Dai; T. Lu

1999-01-01

196

Unsteady outflow models for cosmological gamma-ray bursts  

Microsoft Academic Search

The 'event' that triggers a gamma-ray burst cannot last for more than a few seconds. This is, however, long compared with the dynamical timescale of a compact stellar-mass object (approximately 10 (exp-3) s). Energy is assumed to be released as an outflow with high mean Lorentz factor Gamma. But a compact stellar-mass collapse or merger is, realistically, likely to generate

M. J. Rees; P. Meszaros

1994-01-01

197

GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy  

Microsoft Academic Search

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better\\u000a by a factor of 40 or more compared to the previous missions in this energy range (COMPTEL, INTEGRAL; see Fig. 1). These gamma-ray observations will be complemented by observations in the soft X-ray and (near-)infrared region with the\\u000a corresponding telescopes

Jochen Greiner; Karl Mannheim; Felix Aharonian; Marco Ajello; Lajos G. Balasz; Guido Barbiellini; Ronaldo Bellazzini; Shawn Bishop; Gennady S. Bisnovatij-Kogan; Steven Boggs; Andrej Bykov; Guido Dicocco; Roland Diehl; Dominik Elsässer; Suzanne Foley; Claes Fransson; Neil Gehrels; Lorraine Hanlon; Dieter Hartmann; Wim Hermsen; Wolfgang Hillebrandt; Rene Hudec; Anatoli Iyudin; Jordi Jose; Matthias Kadler; Gottfried Kanbach; Wlodek Klamra; Jürgen Kiener; Sylvio Klose; Ingo Kreykenbohm; Lucien M. Kuiper; Nikos Kylafis; Claudio Labanti; Karlheinz Langanke; Norbert Langer; Stefan Larsson; Bruno Leibundgut; Uwe Laux; Francesco Longo; Kei’ichi Maeda; Radoslaw Marcinkowski; Martino Marisaldi; Brian McBreen; Sheila McBreen; Attila Meszaros; Ken’ichi Nomoto; Mark Pearce; Asaf Peer; Elena Pian; Nikolas Prantzos; Georg Raffelt; Olaf Reimer; Wolfgang Rhode; Felix Ryde; Christian Schmidt; Joe Silk; Boris M. Shustov; Andrew Strong; Nial Tanvir; Friedrich-Karl Thielemann; Omar Tibolla; David Tierney; Joachim Trümper; Dmitry A. Varshalovich; Jörn Wilms; Grzegorz Wrochna; Andrzej Zdziarski; Andreas Zoglauer

2011-01-01

198

Prompt gamma rays from thermal-neutron capture  

Microsoft Academic Search

A catalog of ..gamma..-rays emitted following thermal-neutron capture in natural elements is presented. In Table I, ..gamma..-rays are arranged in order of increasing energy. Each line contains the ..gamma..-ray energy, intensity, element identification, thermal-neutron radiative-capture cross section, and the energies and intensities of two of the more abundant ..gamma..-rays associated with that element. In Table II, ..gamma..-rays are arranged by

M. A. Lone; R. A. Leavitt; D. A. Harrison

1981-01-01

199

The Supernovae Associated with Gamma-Ray Bursts  

Microsoft Academic Search

Supernovae were long suspected as possible progenitors of gamma-ray bursts. The arguments relied on circumstantial evidence. Several recent gamma-ray bursts, notably GRB 030329, have provided direct, spectroscopic evidence that supernovae and gamma-ray bursts are related. The supernovae associated with gamma-ray bursts are all of Type Ic, implying a compact progenitor, which has implications for gamma-ray burst models. Other peculiar Type

T. Matheson

2005-01-01

200

The Gamma-Ray Imager GRI  

NASA Astrophysics Data System (ADS)

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear reactions are synthesizing the basic constituents of our world. Cosmic accelerators and cosmic explosions are major science themes that are addressed in the gamma-ray regime. ESA's INTEGRAL observatory currently provides the astronomical community with a unique tool to investigate the sky up to MeV energies and hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes have been discovered. NASA's GLAST mission will similarly take the next step in surveying the high-energy ( GeV) sky, and NuSTAR will pioneer focusing observations at hard X-ray energies (to 80 keV). There will be clearly a growing need to perform deeper, more focused investigations of gamma-ray sources in the 100-keV to MeV regime. Recent technological advances in the domain of gamma-ray focusing using Laue diffraction and multilayer-coated mirror techniques have paved the way towards a gamma-ray mission, providing major improvements compared to past missions regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow the study of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Wunderer, Cornelia B.; GRI Collaboration

2008-03-01

201

The 1979 March 5 gamma-ray transient: Was it a classic gamma-ray burst?  

Microsoft Academic Search

The 1979 March 5 gamma-ray transient has long been thought to be fundamentally different from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the KONUS experiment, the unusual characteristics of the March 5 transient were detectable primarily because it was extremely bright.

E. E. Fenimore; R. W. Klebesadel; J. G. Laros

1996-01-01

202

The 1979 March 5 Gamma-Ray Transient: Was It a Classic Gamma-Ray Burst?  

Microsoft Academic Search

The 1979 March 5 gamma-ray transient has long been thought to be fundamentally different from the classic gamma-ray bursts (GRBs). It had recurrences, pulsations, and a soft spectral component unlike classic GRBs. With the exception of the soft component reported from the KONUS experiment, the unusual characteristics of the March 5 transient were detectable primarily because it was extremely bright.

E. E. Fenimore; R. W. Klebesadel; J. G. Laros

1996-01-01

203

Monte Carlo simulation of x-ray buildup factors of lead and its applications in shielding of diagnostic x-ray facilities  

SciTech Connect

X-ray buildup factors of lead in broad beam geometry for energies from 15 to 150 keV are determined using the general purpose Monte Carlo N-particle radiation transport computer code (MCNP4C). The obtained buildup factors data are fitted to a modified three parameter Archer et al. model for ease in calculating the broad beam transmission with computer at any tube potentials/filters combinations in diagnostic energies range. An example for their use to compute the broad beam transmission at 70, 100, 120, and 140 kVp is given. The calculated broad beam transmission is compared to data derived from literature, presenting good agreement. Therefore, the combination of the buildup factors data as determined and a mathematical model to generate x-ray spectra provide a computationally based solution to broad beam transmission for lead barriers in shielding x-ray facilities.

Kharrati, Hedi; Agrebi, Amel; Karaoui, Mohamed-Karim [Ecole Superieure des Sciences et Techniques de la Sante de Monastir, Avenue Avicenne 5000 Monastir (Tunisia); Faculte des Sciences de Monastir (Tunisia)

2007-04-15

204

Searching for Gamma-ray Pulsars using the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope  

Microsoft Academic Search

The Large Area Telescope (LAT) on the recently launched Fermi Gamma-ray Space Telescope (formerly GLAST) has greatly increased the sensitivity to astrophysical gamma-ray sources over previous gamma-ray telescope missions such as the Energetic Gamma Ray Experiment Telescope (EGRET) on the Compton Gamma-Ray Observatory (CGRO). The LAT has a much larger effective area and field of view, helping to increase the

Michael Dormody

2009-01-01

205

Gamma-Ray Bursts and Particle Acceleration  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts (GRBs) are possible sources of ultra-high-energy cosmic rays (UHE-CRs). To test the GRB origin of UHECRs, it is essential to search for characteristic, proton-induced signatures of secondary radiation. In this paper we present our recent results of Monte Carlo simulations that model the broadband prompt emission of GRBs including various processes associated with electrons and protons accelerated to high energies. The most notable effect of accelerated protons on the high-energy spectra is the synchrotron emission from secondary electron-positron pairs injected by photomeson interactions. Secondary photons tend to make the spectra flat, so a spectral flattening in the GeV-TeV bands may serve as a signature of UHECR acceleration. In some cases, the proton-induced photons overwhelm the photon field, resulting in a spectral peak due to inverse Compton emission from secondary pairs located around 107 eV. We can expect to detect synchrotron photons from protons or muons. Observations with GLAST or with atmospheric Cerenkov telescopes can provide useful estimates of the bulk Lorents factor and can constrain the proton acceleration efficiency.

Asano, Katsuaki

2008-08-01

206

Sensitivity of HAWC to gamma ray bursts  

NASA Astrophysics Data System (ADS)

HAWC is a ground based very high-energy gamma ray detector under construction in Mexico at an altitude of 4100 m a.s.l. Higher altitude, improved design and a larger physical size used to reject CR background, make HAWC 10-20 times more sensitive than its predecessor Milagro. HAWC's large field of view, ~2sr, and over 90% duty cycle make it ideal to search for GRBs. We review the sensitivity of HAWC to GRBs with two independent data acquisition systems. We show that some of the brightest GRBs observed by Fermi LAT (e.g. GRB 090510) could result in >5 ? observation by HAWC. The observations (or limits) of GRBs by HAWC will provide information on the high-energy spectra of GRBs. The high-energy spectra will teach us about extra galactic background light, the Lorentz boost factor of the jets tha power GRBs and/or particle acceleration models of GRBs. Finally we present limits on > 10 GeV emission from GRB 111016B, recently studied with HAWC's engineering array VAMOS.

Taboada, Ignacio; HAWC Collaboration

2012-12-01

207

Gamma-Ray Bursts and Particle Acceleration  

SciTech Connect

Gamma-ray bursts (GRBs) are possible sources of ultra-high-energy cosmic rays (UHE-CRs). To test the GRB origin of UHECRs, it is essential to search for characteristic, proton-induced signatures of secondary radiation. In this paper we present our recent results of Monte Carlo simulations that model the broadband prompt emission of GRBs including various processes associated with electrons and protons accelerated to high energies. The most notable effect of accelerated protons on the high-energy spectra is the synchrotron emission from secondary electron-positron pairs injected by photomeson interactions. Secondary photons tend to make the spectra flat, so a spectral flattening in the GeV-TeV bands may serve as a signature of UHECR acceleration. In some cases, the proton-induced photons overwhelm the photon field, resulting in a spectral peak due to inverse Compton emission from secondary pairs located around 10{sup 7} eV. We can expect to detect synchrotron photons from protons or muons. Observations with GLAST or with atmospheric Cerenkov telescopes can provide useful estimates of the bulk Lorents factor and can constrain the proton acceleration efficiency.

Asano, Katsuaki [Interactive Research Center for Science, Graduate School of Science, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo 152-8550 (Japan)

2008-08-28

208

A general scheme for modelling gamma-ray burst prompt emission  

Microsoft Academic Search

We describe a general method for modelling gamma-ray burst (GRB) prompt emission, and determine the range of magnetic field strength, electron energy, Lorentz factor of the source and the distance of the source from the central explosion that is needed to account for the prompt gamma-ray emission of a typical long-duration burst. We find that for the burst to be

Pawan Kumar; Erin McMahon; UT Austin

2008-01-01

209

Connection Between Energy-dependent Lags And Peak Luminosity In Gamma-ray Bursts  

Microsoft Academic Search

We suggest a connection between the pulse paradigm at gamma-ray energies and\\u000athe recently demonstrated luminosity distribution in gamma-ray bursts: the\\u000aspectral evolution timescale of pulse structures is anticorrelated with peak\\u000aluminosity, and with quantities which might be expected to reflect the bulk\\u000arelativistic Lorentz factor, such as spectral hardness ratio. We establish this\\u000arelationship in two important burst samples

J. P. Norris; G. F. Marani; J. T. Bonnell

1999-01-01

210

Andromeda: a mission to determine the gamma-ray burst distance scale  

Microsoft Academic Search

Andromeda is a wide-field, imaging, hard x-ray\\/soft gamma-ray instrument capable of detecting gamma-ray bursts (GRBs) a factor approximately 20 times fainter than GRO\\/BATSE. During one-year of a two-year mission, it could determine whether GRBs are Galactic or cosmological in origin by searching for an excess of bursts towards the nearby Andromeda galaxy (M31). As a pointed, imaging instrument with sensitivity

Fiona A. Harrison; Walter R. Cook; Thomas A. Prince; Stephen M. Schindler; Charles J. Hailey; Stephen E. Thorsett

1995-01-01

211

The measurement of gamma ray induced heating in a mixed neutron and gamma ray environment  

SciTech Connect

The problem of measuring the gamma heating in a mixed DT neutron and gamma ray environment was explored. A new detector technique was developed to make this measurement. Gamma heating measurements were made in a low-Z assembly irradiated with 14-Mev neutrons and (n, n{prime}) gammas produced by a Texas Nuclear Model 9400 neutron generator. Heating measurements were made in the mid-line of the lattice using a proportional counter operating in the Continuously-varied Bias-voltage Acquisition mode. The neutron-induced signal was separated from the gamma-induced signal by exploiting the signal rise-time differences inherent to radiations of different linear energy transfer coefficient, which are observable in a proportional counter. The operating limits of this measurement technique were explored by varying the counter position in the low-Z lattice, hence changing the irradiation spectrum observed. The experiment was modelled numerically to help interpret the measured results. The transport of neutrons and gamma rays in the assembly was modelled using the one- dimensional radiation transport code ANISN/PC. The cross-section set used for these calculations was derived from the ENDF/B-V library using the code MC{sup 2}-2 for the case of DT neutrons slowing down in a low-Z material. The calculated neutron and gamma spectra in the slab and the relevant mass-stopping powers were used to construct weighting factors which relate the energy deposition in the counter fill-gas to that in the counter wall and in the surrounding material. The gamma energy deposition at various positions in the lattice is estimated by applying these weighting factors to the measured gamma energy deposition in the counter at those locations.

Chiu, H.K.

1991-10-01

212

GRI: The Gamma-Ray Imager mission  

NASA Astrophysics Data System (ADS)

With the INTEGRAL observatory ESA has provided a unique tool to the astronomical community revealing hundreds of sources, new classes of objects, extraordinary views of antimatter annihilation in our Galaxy, and fingerprints of recent nucleosynthesis processes. While INTEGRAL provides the global overview over the soft gamma-ray sky, there is a growing need to perform deeper, more focused investigations of gamma-ray sources. In soft X-rays a comparable step was taken going from the Einstein and the EXOSAT satellites to the Chandra and XMM/Newton observatories. Technological advances in the past years in the domain of gamma-ray focusing using Laue diffraction have paved the way towards a new gamma-ray mission, providing major improvements regarding sensitivity and angular resolution. Such a future Gamma-Ray Imager will allow studies of particle acceleration processes and explosion physics in unprecedented detail, providing essential clues on the innermost nature of the most violent and most energetic processes in the Universe.

Knödlseder, Jürgen

213

Luminosity Evolution of Gamma-Ray Pulsars  

NASA Astrophysics Data System (ADS)

We investigate the electrodynamic structure of a pulsar outer-magnetospheric particle accelerator and the resulting gamma-ray emission. By considering the condition for the accelerator to be self-sustained, we derive how the trans-magnetic-field thickness of the accelerator evolves with the pulsar age. It is found that the thickness is small but increases steadily if the neutron-star envelope is contaminated by sufficient light elements. For such a light element envelope, the gamma-ray luminosity of the accelerator is kept approximately constant as a function of age in the initial 10,000 yr, forming the lower bound of the observed distribution of the gamma-ray luminosity of rotation-powered pulsars. If the envelope consists of only heavy elements, on the other hand, the thickness is greater, but it increases less rapidly than a light element envelope. For such a heavy element envelope, the gamma-ray luminosity decreases relatively rapidly, forming the upper bound of the observed distribution. The gamma-ray luminosity of a general pulsar resides between these two extreme cases, reflecting the envelope composition and the magnetic inclination angle with respect to the rotation axis. The cutoff energy of the primary curvature emission is regulated below several GeV even for young pulsars because the gap thickness, and hence the acceleration electric field, is suppressed by the polarization of the produced pairs.

Hirotani, Kouichi

2013-04-01

214

Inverse compton scattering gamma ray source  

NASA Astrophysics Data System (ADS)

Special Nuclear Materials (SNM) (e.g. U-235, Pu-239) can be detected by active interrogation with gamma rays (>6 MeV) through photofission. For long-range detection (˜1 km), an intense beam of gamma rays (˜1014 per second) is required in order to produce measurable number of neutrons. The production of such fluxes of gamma rays, and in the pulse formats useful for detection, presents many technical challenges, and requires novel approaches to the accelerator and laser technology. RadiaBeam is currently designing a gamma ray source based on Inverse Compton Scattering (ICS) from a high-energy electron beam. To achieve this, improvements in photoinjector, linac, final focus, and laser system are planned. These enhanced sub-systems build on parallel work being performed at RadiaBeam, UCLA, and elsewhere. A high-repetition rate photoinjector, a high-gradient S-band linac, and a laser pulse recirculator will be used. The proposed system will be a transportable source of high-flux, high-energy quasi-monochromatic gamma rays for active interrogation of special nuclear materials.

Boucher, S.; Frigola, P.; Murokh, A.; Ruelas, M.; Jovanovic, I.; Rosenzweig, J. B.; Travish, G.

2009-09-01

215

Gamma-ray Emission in GPS Quasars  

NASA Astrophysics Data System (ADS)

In this paper, it is argued that the relativistic jets in gigahertz peaked spectrum (GPS) quasars are oriented at small angle to the line of sight and are powerful gamma-ray sources. Besides luminous hard gamma-ray emission, most of them may have significant soft gamma-ray and X-ray emission due to infrared photons from very dense and dusty nuclear interstellar media in GPS quasars, which is consistent with ASCA X-ray observations. Because Compton cooling in GPS quasars is stronger than in flat spectrum radio quasars (FSRQs), synchrotron emission in GPS quasars may less dominate over thermal emission of the accretion disk and hot dust than in FSRQs, hence most GPS quasars show low optical polarization and small variability. We suggest that it is the significant radio emission of electron/positron pairs produced by the interaction of gamma-rays with the dense gas and dust grains in GPS quasars that makes GPS quasars show steep radio spectra, low radio polarization, and relatively faint VLBI/VLBA cores. The gamma-ray emission in GPS quasars can be tested by the observation of the INTEGRAL and GLAST in the near future.

Bai, Jin-Ming

2005-06-01

216

Fermi Observations of High-Energy Gamma-Ray Emission from GRB 080916C  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gamma-ray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass.

Abdo, A. A.; Ackermann, M.; Arimoto, M.; Asano, K.; Atwood, W. B.; Axelsson, M.; Baldini, L.; Ballet, J.; Band, D. L.; Barbiellini, G.; Baring, M. G.; Bastieri, D.; Battelino, M.; Baughman, B. M.; Bechtol, K.; Bellardi, F.; Bellazzini, R.; Berenji, B.; Bhat, P. N.; Bissaldi, E.; Blandford, R. D.; Bloom, E. D.; Bogaert, G.; Bogart, J. R.; Bonamente, E.; Bonnell, J.; Borgland, A. W.; Bouvier, A.; Bregeon, J.; Brez, A.; Briggs, M. S.; Brigida, M.; Bruel, P.; Burnett, T. H.; Burrows, D.; Busetto, G.; Caliandro, G. A.; Cameron, R. A.; Caraveo, P. A.; Casandjian, J. M.; Ceccanti, M.; Cecchi, C.; Celotti, A.; Charles, E.; Chekhtman, A.; Cheung, C. C.; Chiang, J.; Ciprini, S.; Claus, R.; Cohen-Tanugi, J.; Cominsky, L. R.; Connaughton, V.; Conrad, J.; Costamante, L.; Cutini, S.; DeKlotz, M.; Dermer, C. D.; de Angelis, A.; de Palma, F.; Digel, S. W.; Dingus, B. L.; do Couto e Silva, E.; Drell, P. S.; Dubois, R.; Dumora, D.; Edmonds, Y.; Evans, P. A.; Fabiani, D.; Farnier, C.; Favuzzi, C.; Finke, J.; Fishman, G.; Focke, W. B.; Frailis, M.; Fukazawa, Y.; Funk, S.; Fusco, P.; Gargano, F.; Gasparrini, D.; Gehrels, N.; Germani, S.; Giebels, B.; Giglietto, N.; Giommi, P.; Giordano, F.; Glanzman, T.; Godfrey, G.; Goldstein, A.; Granot, J.; Greiner, J.; Grenier, I. A.; Grondin, M.-H.; Grove, J. E.; Guillemot, L.; Guiriec, S.; Haller, G.; Hanabata, Y.; Harding, A. K.; Hayashida, M.; Hays, E.; Morata, J. A. Hernando; Hoover, A.; Hughes, R. E.; Jóhannesson, G.; Johnson, A. S.; Johnson, R. P.; Johnson, T. J.; Johnson, W. N.; Kamae, T.; Katagiri, H.; Kataoka, J.; Kavelaars, A.; Kawai, N.; Kelly, H.; Kennea, J.; Kerr, M.; Kippen, R. M.; Knödlseder, J.; Kocevski, D.; Kocian, M. L.; Komin, N.; Kouveliotou, C.; Kuehn, F.; Kuss, M.; Lande, J.; Landriu, D.; Larsson, S.; Latronico, L.; Lavalley, C.; Lee, B.; Lee, S.-H.; Lemoine-Goumard, M.; Lichti, G. G.; Longo, F.; Loparco, F.; Lott, B.; Lovellette, M. N.; Lubrano, P.; Madejski, G. M.; Makeev, A.; Marangelli, B.; Mazziotta, M. N.; McBreen, S.; McEnery, J. E.; McGlynn, S.; Meegan, C.; Mészáros, P.; Meurer, C.; Michelson, P. F.; Minuti, M.; Mirizzi, N.; Mitthumsiri, W.; Mizuno, T.; Moiseev, A. A.; Monte, C.; Monzani, M. E.; Moretti, E.; Morselli, A.; Moskalenko, I. V.; Murgia, S.; Nakamori, T.; Nelson, D.; Nolan, P. L.; Norris, J. P.; Nuss, E.; Ohno, M.; Ohsugi, T.; Okumura, A.; Omodei, N.; Orlando, E.; Ormes, J. F.; Ozaki, M.; Paciesas, W. S.; Paneque, D.; Panetta, J. H.; Parent, D.; Pelassa, V.; Pepe, M.; Perri, M.; Pesce-Rollins, M.; Petrosian, V.; Pinchera, M.; Piron, F.; Porter, T. A.; Preece, R.; Rainň, S.; Ramirez-Ruiz, E.; Rando, R.; Rapposelli, E.; Razzano, M.; Razzaque, S.; Rea, N.; Reimer, A.; Reimer, O.; Reposeur, T.; Reyes, L. C.; Ritz, S.; Rochester, L. S.; Rodriguez, A. Y.; Roth, M.; Ryde, F.; Sadrozinski, H. F.-W.; Sanchez, D.; Sander, A.; Parkinson, P. M. Saz; Scargle, J. D.; Schalk, T. L.; Segal, K. N.; Sgrň, C.; Shimokawabe, T.; Siskind, E. J.; Smith, D. A.; Smith, P. D.; Spandre, G.; Spinelli, P.; Stamatikos, M.; Starck, J.-L.; Stecker, F. W.; Steinle, H.; Stephens, T. E.; Strickman, M. S.; Suson, D. J.; Tagliaferri, G.; Tajima, H.; Takahashi, H.; Takahashi, T.; Tanaka, T.; Tenze, A.; Thayer, J. B.; Thayer, J. G.; Thompson, D. J.; Tibaldo, L.; Torres, D. F.; Tosti, G.; Tramacere, A.; Turri, M.; Tuvi, S.; Usher, T. L.; van der Horst, A. J.; Vigiani, L.; Vilchez, N.; Vitale, V.; von Kienlin, A.; Waite, A. P.; Williams, D. A.; Wilson-Hodge, C.; Winer, B. L.; Wood, K. S.; Wu, X. F.; Yamazaki, R.; Ylinen, T.; Ziegler, M.; Fermi LAT Collaboration; Fermi GBM Collaboration

2009-03-01

217

Inter-pulse high-resolution gamma-ray spectra using a 14 MeV pulsed neutron generator  

USGS Publications Warehouse

A neutron generator pulsed at 100 s-1 was suspended in an artificial borehole containing a 7.7 metric ton mixture of sand, aragonite, magnetite, sulfur, and salt. Two Ge(HP) gamma-ray detectors were used: one in a borehole sonde, and one at the outside wall of the sample tank opposite the neutron generator target. Gamma-ray spectra were collected by the outside detector during each of 10 discrete time windows during the 10 ms period following the onset of gamma-ray build-up after each neutron burst. The sample was measured first when dry and then when saturated with water. In the dry sample, gamma rays due to inelastic neutron scattering, neutron capture, and decay were counted during the first (150 ??s) time window. Subsequently only capture and decay gamma rays were observed. In the wet sample, only neutron capture and decay gamma rays were observed. Neutron capture gamma rays dominated the spectrum during the period from 150 to 400 ??s after the neutron burst in both samples, but decreased with time much more rapidly in the wet sample. A signal-to-noise-ratio (S/N) analysis indicates that optimum conditions for neutron capture analysis occurred in the 350-800 ??s window. A poor S/N in the first 100-150 ??s is due to a large background continuum during the first time interval. Time gating can be used to enhance gamma-ray spectra, depending on the nuclides in the target material and the reactions needed to produce them, and should improve the sensitivity of in situ well logging. ?? 1984.

Evans, L. G.; Trombka, J. I.; Jensen, D. H.; Stephenson, W. A.; Hoover, R. A.; Mikesell, J. L.; Tanner, A. B.; Senftle, F. E.

1984-01-01

218

Continuum Background in Space-Borne Gamma-Ray Detectors  

NASA Astrophysics Data System (ADS)

The background measured with space-borne gamma-ray spectrometers (GRS) in the 100 keV-10 MeV energy region consists of both discrete lines and continuum. The discrete lines originate in the decay of radioactive species. The continuum originates from a number of different processes and can be an important factor in the detection, for example, of weak gamma-ray lines from a planetary surface. Measurements of the gamma-ray background have been made during the cruise portion of a number of planetary missions. The three missions described here are the Apollo 15 and 16 missions each of which carried a 7 cm x 7 cm NaI scintillation detector, the Mars Observer (MO) mission which used a 5.5 cm X 5.5 cm high-purity germanium (HPGe) detector, and the Near Earth Rendezvous Asteroid (NEAR) mission that has a 2.54 cm x 7.6 cm NaI detector. A comparison of the intensity and spectral shape of these background spectra can be useful to help understand how these backgrounds vary with spacecraft size, detector position, and detector size. The use of shields to reduce the background components on these three missions is a test of the effectiveness of different shield designs.

Evans, Larry G.; Trombka, Jacob I.; Starr, Richard; Boyton, William V.; Bailey, S.

219

Integrated neutron/gamma-ray portal monitors for nuclear safeguards  

NASA Astrophysics Data System (ADS)

Radiation monitoring is one nuclear-safeguards measure used to protect against the theft of special nuclear materials (SNM) by pedestrians departing from SNM access areas. The integrated neutron/gamma-ray portal monitor is an ideal radiation monitor for the task when the SNM is plutonium. It achieves high sensitivity for detecting both bare and shielded plutonium by combining two types of radiation detector. One type is a neutron-chamber detector, comprising a large, hollow, neutron moderator that contains a single thermal-neutron proportional counter. The entrance wall of each chamber is thin to admit slow neutrons from plutonium contained in a moderating shield, while the other walls are thick to moderate fast neutrons from bare or lead-shielded plutonium so that they can be detected. The other type of detector is a plastic scintillator that is primarily for detecting gamma rays from small amounts of unshielded plutonium. The two types of detector are easily integrated by making scintillators part of the thick back wall of each neutron chamber or by inserting them into each chamber void. We compared the influence of the two methods of integration on detecting neutrons and gamma rays, and we examined the effectiveness of other design factors and the methods for signal detection as well.

Fehlau, Paul E.

1994-08-01

220

Neutron and Gamma-ray Measurements  

SciTech Connect

Due to high neutron and gamma-ray yields and large size plasmas many future fusion reactor plasma parameters such as fusion power, fusion power density, ion temperature, fuel mixture, fast ion energy and spatial distributions can be well measured by various fusion product diagnostics. Neutron diagnostics provide information on fusion reaction rate, which indicates how close is the plasma to the ultimate goal of nuclear fusion and fusion power distribution in the plasma core, which is crucial for optimization of plasma breakeven and burn. Depending on the plasma conditions neutron and gamma-ray diagnostics can provide important information, namely about dynamics of fast ion energy and spatial distributions during neutral beam injection, ion cyclotron heating and generated by fast ions MHD instabilities. The influence of the fast particle population on the 2-D neutron source profile was clearly demonstrated in JET experiments. 2-D neutron and gamma-ray source measurements could be important for driven plasma heating profile optimization in fusion reactors. To meat the measurement requirements in ITER the planned set of neutron and gamma ray diagnostics includes radial and vertical neutron and gamma cameras, neutron flux monitors, neutron activation systems and neutron spectrometers. The necessity of using massive radiation shielding strongly influences the diagnostic designs in fusion reactor, determines angular fields of view of neutron and gamma-ray cameras and spectrometers and gives rise to unavoidable difficulties in the absolute calibration. The development, testing in existing tokomaks and a possible engineering integration of neuron and gamma-ray diagnostic systems into ITER are presented.

Krasilnikov, Anatoly V. [RRC 'Kurchatov Institute', Academician Kurchatov squarel, Moscow, 123182 (Russian Federation); SRC RF TRINITI, Troitsk, 142190 (Russian Federation); Sasao, Mamiko [Tohoku University, Sendai (Japan); Kaschuck, Yuri A. [SRC RF TRINITI, Troitsk, 142190 (Russian Federation); Kiptily, Vasily G.; Popovichev, Sergey V. [UKAEA, Abingdon (United Kingdom); Nishitani, Takeo [Japan Atomic Energy Agency, Tokai (Japan); Bertalot, Luciano [ITER Organization, Cadarach (France)

2008-03-12

221

Neutron and Gamma-ray Measurements  

NASA Astrophysics Data System (ADS)

Due to high neutron and gamma-ray yields and large size plasmas many future fusion reactor plasma parameters such as fusion power, fusion power density, ion temperature, fuel mixture, fast ion energy and spatial distributions can be well measured by various fusion product diagnostics. Neutron diagnostics provide information on fusion reaction rate, which indicates how close is the plasma to the ultimate goal of nuclear fusion and fusion power distribution in the plasma core, which is crucial for optimization of plasma breakeven and burn. Depending on the plasma conditions neutron and gamma-ray diagnostics can provide important information, namely about dynamics of fast ion energy and spatial distributions during neutral beam injection, ion cyclotron heating and generated by fast ions MHD instabilities. The influence of the fast particle population on the 2-D neutron source profile was clearly demonstrated in JET experiments. 2-D neutron and gamma-ray source measurements could be important for driven plasma heating profile optimization in fusion reactors. To meat the measurement requirements in ITER the planned set of neutron and gamma ray diagnostics includes radial and vertical neutron and gamma cameras, neutron flux monitors, neutron activation systems and neutron spectrometers. The necessity of using massive radiation shielding strongly influences the diagnostic designs in fusion reactor, determines angular fields of view of neutron and gamma-ray cameras and spectrometers and gives rise to unavoidable difficulties in the absolute calibration. The development, testing in existing tokomaks and a possible engineering integration of neuron and gamma-ray diagnostic systems into ITER are presented.

Krasilnikov, Anatoly V.; Sasao, Mamiko; Kaschuck, Yuri A.; Kiptily, Vasily G.; Nishitani, Takeo; Popovichev, Sergey V.; Bertalot, Luciano

2008-03-01

222

Emission region of gamma ray bursts  

SciTech Connect

Within the last few years the rapid accumulation of gamma ray burst spectral data, especially those of KONUS and SMM, has made the confrontation between theories of the gamma ray emission mechanisms and observations much more urgent and challenging. At present the most viable model seems to be some combination of inverse Comptonization and synchrotron emission. In this paper we limit the acceptable parameter space of the emission region by taking into account the maximum set of observational constraints. We then apply these to two specific scenarios: surface emission versus magnetospheric emission and consider some observable predictions based on these scenarios.

Liang, E.P.

1985-05-01

223

Photospheric Emission from Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

In spite of extensive research over the past decades, a complete physical picture of the origin of the prompt gamma-ray burst emission is still lacking. During recent years, evidence has been accumulating that the jet photosphere plays an important role. In this paper we summarize the lessons learned from Fermi observations regarding the behavior of the photosphere and discuss why photospheric emission does not necessarily appear as blackbody radiation. We concentrate on two strong and important bursts, GRB 090902B and GRB 110721A, which serve as examples of the standard appearance photospheric emission may have in gamma-ray burst spectra.

Axelsson, M.

2013-07-01

224

Gamma ray sources using imperfect relativistic mirrors  

SciTech Connect

The collective backscattering of intense laser radiation by energetic electron beams is considered. Exact solutions for the radiation field are obtained, for arbitrary electron pulse shapes and laser intensities. The electron beams act as imperfect nonlinear mirrors on the incident laser radiation. This collective backscattering process can lead to the development of new sources of ultrashort pulse radiation in the gamma-ray domain. Numerical examples show that, for plausible experimental conditions, intense pulses of gamma rays, due to the double Doppler shift of the harmonics of the incident laser radiation, can be produced using the available technology, with durations less than one attosecond.

Mendonca, J. T. [GoLP and CFIF, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049-001 Lisboa (Portugal); Serbeto, A. [Instituto de Fisica, Universidade Federal Fluminense, 24210-340 Rio de Janeiro (Brazil)

2008-11-15

225

FERMI GAMMA-RAY HAZE VIA DARK MATTER AND MILLISECOND PULSARS  

SciTech Connect

We study possible astrophysical and dark matter (DM) explanations for the Fermi gamma-ray haze in the Milky Way halo. As representatives of various DM models, we consider DM particles annihilating into W {sup +} W {sup -}, b b-bar , and e {sup +} e {sup -}. In the first two cases, the prompt gamma-ray emission from DM annihilations is significant or even dominant at E > 10 GeV, while inverse Compton scattering (ICS) from annihilating DM products is insignificant. For the e {sup +} e {sup -} annihilation mode, we require a boost factor of order 100 to get significant contribution to the gamma-ray haze from ICS photons. Possible astrophysical sources of high-energy particles at high latitudes include type Ia supernovae (SNe) and millisecond pulsars (MSPs). Based on our current understanding of Ia SNe rates, they do not contribute significantly to gamma-ray flux in the halo of the Milky Way. As the MSP population in the stellar halo of the Milky Way is not well constrained, MSPs may be a viable source of gamma-rays at high latitudes provided that there are {approx}(2-6) x 10{sup 4} of MSPs in the Milky Way stellar halo. In this case, pulsed gamma-ray emission from MSPs can contribute to gamma rays around few GeV, while the ICS photons from MSP electrons and positrons may be significant at all energies in the gamma-ray haze. The plausibility of such a population of MSPs is discussed. Consistency with the Wilkinson Microwave Anisotropy Probe (WMAP) microwave haze requires that either a significant fraction of MSP spin-down energy is converted into e {sup +} e {sup -} flux or the DM annihilates predominantly into leptons with a boost factor of order 100.

Malyshev, Dmitry; Cholis, Ilias; Gelfand, Joseph D., E-mail: dm137@nyu.ed, E-mail: ijc219@nyu.ed, E-mail: jg168@astro.physics.nyu.ed [CCPP, 4 Washington Place, Meyer Hall of Physics, NYU, New York, NY 10003 (United States)

2010-10-20

226

TeV gamma ray opacity in PKS 2155-304  

NASA Astrophysics Data System (ADS)

Context. Recently observed rapid time variability in the gamma ray emission from the blazar PKS 2155-304 indicates that either the site of gamma ray emission is close to the black hole or the jet has a very high Lorentz factor. Consideration of the opacity of gamma rays close to the black hole provides additional information related to these two possibilities. Aims: We investigate the TeV gamma ray opacity resulting from pair production on soft photons radiated by the black hole accretion disk, considering situations where the radiation produced by the disk is close to that predicted by the Shakura-Sunyaev model and situations where the disk radiation is much less. Methods: We utilise expressions for the pair opacity of very high energy gamma rays developed by Gould and Schréder and Donea and Protheroe and use expressions for the disk radiation field produced by an accretion disk external to a Poynting flux dominated jet. A lower level of disk emission is modelled by using the spectrum corresponding to a lower accretion rate. We also consider changes in the shape of the gamma ray sepctrum as a flare emerges from the optically thick region. Results: If the gravitational power resulting from accretion is dissipated by radiation in the region of the disk external to the jet, then TeV gamma rays are opaque out to of order 40 gravitational radii ?6 × 1015 cm from the black hole. However, the opacity is considerably reduced if the disk radiates a negligible amount of gravitational power as would be the case if there is a significant disk wind external to the jet. In either case the absence of spectral changes during observed flares excludes scenarios in which the TeV gamma rays are emitted even in regions of modest pair opacity.

Bicknell, G. V.; Wagner, S. J.

2011-02-01

227

HYPERNUCLEAR STRUCTURE FROM GAMMA-RAY SPECTROSCOPY.  

SciTech Connect

The energies of p-shell hypernuclear {gamma} rays obtained from recent experiments using the Hyperball at BNL and KEK are used to constrain the YN interaction which enters into shell-model calculations which include both {Lambda} and {Sigma} configurations.

MILLENER,D.J.

2003-10-14

228

Nature of Cosmic gamma Ray Bursts.  

National Technical Information Service (NTIS)

The nature of cosmic gamma ray burst is studied. The sources of the observed gamma bursts are supposed to be presented by the two populations of galactic objects, namely: the old neutron stars concentrated in the galactic disk; and the old degenerated dwa...

N. I. Shakura N. N. Shakura

1990-01-01

229

Gamma ray activity of neodymium samples  

NASA Astrophysics Data System (ADS)

The gamma ray activity of three samples of natural neodymium has been measured and the concentration of radioactive elements from uranium and thorium chains as well as that from radioactive isotopes of lantanium and lutetium has been quantitatively determined. All the samples show significant contaminations up to p.p.m.

Arpesella, C.; Bellotti, E.; Miramonti, L.; Sverzellati, P. P.

1996-02-01

230

Gamma ray activity of neodymium samples  

Microsoft Academic Search

The gamma ray activity of three samples of natural neodymium has been measured and the concentration of radioactive elements from uranium and thorium chains as well as that from radioactive isotopes of lantanium and lutetium has been quantitatively determined. All the samples show significant contaminations up to p.p.m.

C. Arpesella; E. Bellotti; L. Miramonti; P. P. Sverzellati

1996-01-01

231

Prompt Signals of Gamma Ray Bursts.  

National Technical Information Service (NTIS)

We introduce a new model of gamma ray burst (GRB) that explains its observed prompt signals, namely, its primary thermal spectrum and high energy tail. This mechanism can be applied to either assumption of GRB pro-genitor: coalescence of compact objects o...

P. Chen

2001-01-01

232

Glass as a gamma Ray Dosemeter.  

National Technical Information Service (NTIS)

The advantages of glass as a gamma -rays dosemeter are studied. Experiments have shown that ordinary microscope object glass can be used as a dosemeter, which dose range for linear response extends from about 10 exp 4 -10 exp 6 rads. Heat treatment of the...

Sutrisno Puspodikoro

1978-01-01

233

Gamma-ray Burst Educator Guide  

NSDL National Science Digital Library

This guide accompanies an educational wallsheet that uses Gamma-ray Bursts as an engagement to teach selected topics in physical science and mathematics. It features four curriculum enhancement activities, background information, assessment information, student worksheets, extension and transfer activities, and detailed information about the physical science and mathematics content standards for grades 9-12.

2004-01-01

234

Gamma-ray Burst Science with GLAST  

SciTech Connect

The recent observations of Gamma-ray bursts (GRBs) with Swift have provided unprecedented information about nature of GRBs. The launch of GLAST in late 2007 will unveil the final spectral regime of GRB prompt emission and afterglows. Here we briefly review various theoretical suggestions of producing high energy photons from GRB fireballs, and discuss what observatons are expected from the GLAST observatory.

Zhang Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States)

2007-07-12

235

Cosmological aspects of gamma ray bursts  

Microsoft Academic Search

Gamma-ray burst observations provide a great opportunity for cosmography in high redshift. Some tight correlations between different physical properties of GRBs are discovered and used for cosmography. However, data selection, assumptions, systematic uncertainty and some other issues affect most of them. Most importantly, until the physical origin of a relation is understood, one should be cautious to employ the relation

Razieh Behkam

2010-01-01

236

Hypernuclear Structure from Gamma-Ray Spectroscopy.  

National Technical Information Service (NTIS)

The energies of p-shell hypernuclear(gamma) rays obtained from recent experiments using the Hyperball at BNL and KEK are used to constrain the YN interaction which enters into shell-model calculations which include both(Lambda) and(Sigma) configurations.

D. J. Millener

2004-01-01

237

Supernovae, hypernovae and gamma ray bursts  

Microsoft Academic Search

Recent observations suggest that gamma ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in core collapse supernova explosions (SNe). The result of the event, probably, is not just a compact object plus a spherical ejecta: within a day, a fraction of the parent star falls back to produce a thick accretion disk around the compact

Arnon Dar

2001-01-01

238

Developments in Mercuric Iodide gamma Ray Imaging.  

National Technical Information Service (NTIS)

A mercuric iodide gamma-ray imaging array and camera system previously described has been characterized for spatial and energy resolution. Based on this data, a new camera is being developed to more fully exploit the potential of the array. Characterizati...

B. E. Patt A. G. Beyerle R. C. Dolin C. Ortale

1987-01-01

239

Gamma-ray Astrophysics with AGILE  

SciTech Connect

AGILE will explore the gamma-ray Universe with a very innovative instrument combining for the first time a gamma-ray imager and a hard X-ray imager. AGILE will be operational in spring 2007 and it will provide crucial data for the study of Active Galactic Nuclei, Gamma-Ray Bursts, unidentified gamma-ray sources. Galactic compact objects, supernova remnants, TeV sources, and fundamental physics by microsecond timing. The AGILE instrument is designed to simultaneously detect and image photons in the 30 MeV - 50 GeV and 15 - 45 keV energy bands with excellent imaging and timing capabilities, and a large field of view covering {approx} 1/5 of the entire sky at energies above 30 MeV. A CsI calorimeter is capable of GRB triggering in the energy band 0.3-50 MeV AGILE is now (March 2007) undergoing launcher integration and testing. The PLSV launch is planned in spring 2007. AGILE is then foreseen to be fully operational during the summer of 2007.

Longo, Francesco [Department of Physics, University of Trieste (Italy)]|[INFN, Section of Trieste (Italy); Tavani, M.; Barbiellini, G.; Argan, A.; Basset, M.; Boffelli, F.; Bulgarelli, A.; Caraveo, P.; Cattaneo, P.; Chen, A.; Costa, E.; Del Monte, E.; Di Cocco, G.; Di Persio, G.; Donnarumma, I.; Feroci, M.; Fiorini, M.; Foggetta, L.; Froysland, T.; Frutti, M. (and others)

2007-07-12

240

Gamma Ray Burst Detectives (Elementary School)  

NSDL National Science Digital Library

This interactive resource invites students to join NASA to find the source of gamma ray bursts, the single biggest explosions in the Universe since the Big Bang. The web site features an animation, information on three possible star sources, and a check yes or no for each star with feedback.

Wpsu

2010-04-29

241

Accretion Models of Gamma-Ray Bursts  

Microsoft Academic Search

Many models of gamma-ray bursts (GRBs) involve accretion onto a compact object, usually a black hole, at a mass accretion rate on the order of a fraction of a solar mass per second. If the accretion disk is larger than a few tens or hundreds of Schwarzschild radii, the accretion will proceed via a convection-dominated accretion flow (CDAF) in which

Ramesh Narayan; Tsvi Piran; Pawan Kumar

2001-01-01

242

Positron Annihilation in gamma-Ray Bursts.  

National Technical Information Service (NTIS)

Emission features appear at energies of 350 to 450 keV in the spectra of a number of gamma ray burst sources. These features were interpreted as electron-positron annihilation lines, redshifted by the gravitational field near the surface of a neutron star...

A. K. Harding

1990-01-01

243

Gamma-Ray Burst Environments and Progenitors  

Microsoft Academic Search

Likely progenitors for gamma-ray bursts (GRBs) are the mergers of compact objects or the explosions of massive stars. These two cases have distinctive environments for the GRB afterglow: the compact object explosions occur in the interstellar medium (ISM) and those of massive stars occur in the preburst stellar wind. We calculate the expected afterglow for a burst in a Wolf-Rayet

Roger A. Chevalier; Zhi-Yun Li

1999-01-01

244

Gamma-Ray Bursts The Second Revolution  

Microsoft Academic Search

Gamma-ray bursts GRBs are among the most mysterious astronomical phenomenon ever discovered. Unlike most astronomical discoveries which were explained within weeks or months after their initial discovery, GRBs remain a puzzle for more than thirty years. During the last decade our understanding of GRBs has undergone two major revolutions. First, BATSE discovered that GRBs are distributed isotropically over the sky

Tsvi Piran

1998-01-01

245

Three Types of Gamma-Ray Bursts  

Microsoft Academic Search

A multivariate analysis of gamma-ray burst (GRB) bulk properties is presented to discriminate between distinct classes of GRBs. Several variables representing burst duration, fluence, and spectral hardness are considered. Two multivariate clustering procedures are used on a sample of 797 bursts from the Third BATSE Catalog, a nonparametric average linkage hierarchical agglomerative clustering procedure validated with Wilks' Lambda^* and other

Soma Mukherjee; Eric D. Feigelson; Gutti Jogesh Babu; Fionn Murtagh; Chris Fraley; Adrian Raftery

1998-01-01

246

Theories of Gamma-Ray Bursts  

Microsoft Academic Search

The gamma ray burst phenomenon is reviewed from a theoretical point of view, with emphasis on the fireball shock scenario of the prompt emission and the longer wavelength afterglow. Recent progress and issues are discussed, including spectral-temporal evolution, localizations, jets, spectral lines, environmental and cosmological aspects, as well as some prospects for future experiments in both electromagnetic and nonelectromagnetic channels.

P. Mészáros

2002-01-01

247

Supernovae and gamma-ray bursts†  

Microsoft Academic Search

The observed properties of Supernovae (SNe) and Cosmic Gamma-ray Bursts (GRBs) are briefly summarized. Measurement of SNe distances in cosmology gives important results. It is explained how the acceleration of expansion of Universe was established using SNe. I point out which features of gaseous Supernova Remnants and GRBs (and their afterglows) are common and what is different in those events.

Sergei Blinnikov

2006-01-01

248

The Cosmic Gamma-Ray Bursts  

Microsoft Academic Search

Cosmic gamma-ray bursts are one of the great frontiers of astrophysics today. They are a playground of relativists and observers alike. They may teach us about the death of stars and the birth of black holes, the physics in extreme conditions, and help us probe star formation in the distant and obscured universe. In this review we summarise some of

S. G. Djorgovski; D. A. Frail; S. R. Kulkarni; R. Sari; J. S. Bloom; T. J. Galama; F. A. Harrison; P. A. Price; D. Fox; D. E. Reichart; S. Yost; E. Berger; A. Diercks; R. Goodrich; F. Chaffee

2002-01-01

249

Balloon borne X and gamma ray experiments  

Microsoft Academic Search

A brief history of X and gamma ray astronomy is presented, in order to show the scientific interest in this field of research, and to define the type of work needed for further progress. A general description of the experimental apparatus is given, with a summary of typical detectors and their characteristics. Following this is a discussion of the numerous

K. Hurley

1975-01-01

250

The Supernova Gamma-Ray Burst Connection  

Microsoft Academic Search

There is now clear evidence for Type I supernovae happening in coincidence with two long soft gamma-ray bursts (GRBs) and compelling observations that suggest this may be a common occurrence. At the same time, it is clear that only a small fraction, 1%, of supernovae make GRBs. Why do some stars die one way, and others, another? I will argue

S. E. Woosley

2005-01-01

251

The Supernova Gamma-Ray Burst Connection  

Microsoft Academic Search

This program brought together scientists in both Supernovae and Gamma-Ray Bursts to merge the current progress of both disciplines. We used this combined knowledge to address a range of SN\\/GRB questions such as: Do all long duration GRBs have an underlying SN?, What is special about SNe associated with GRBs?, Where do XRFs, which share several attributes with GRBs, fit

Christopher L. Fryer; Shrinivas R. Kulkarni; Ken'ichi Nomoto; Philip Pinto

2006-01-01

252

Study of gamma-ray strength functions  

SciTech Connect

The use of gamma-ray strength function systematics to calculate neutron capture cross sections and capture gamma-ray spectra is discussed. The ratio of the average capture width, GAMMA/sub ..gamma../-bar, to the average level spacing, D/sub obs/, both at the neutron separation energy, can be derived from such systematics with much less uncertainty than from separate systematics for values of GAMMA/sub ..gamma../-bar and D/sub obs/. In particular, the E1 gamma-ray strength function is defined in terms of the giant dipole resonance (GDR). The GDR line shape is modeled with the usual Lorentzian function and also with a new energy-dependent, Breit-Wigner (EDBW) function. This latter form is further parameterized in terms of two overlapping resonances, even for nuclei where photonuclear measurements do not resolve two peaks. In the mass ranges studied, such modeling is successful for all nuclei away from the N = 50 closed neutron shell. Near the N = 50 shell, a one-peak EDBW appears to be more appropriate. Examples of calculated neutron capture excitation functions and capture gamma-ray spectra using the EDBW form are given for target nuclei in the mass-90 region and also in the Ta-Au mass region. 20 figures.

Gardner, D.G.; Gardner, M.A.; Dietrich, F.S.

1980-08-07

253

First RHESSI terrestrial gamma ray flash catalog  

Microsoft Academic Search

We present a summary of data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) terrestrial gamma ray flash (TGF) catalog. We describe the RHESSI search algorithm and discuss its limitations due to its design emphasis on cleanliness rather than completeness. This search algorithm has identified 820 TGFs between March of 2002 and February of 2008. Radiation damage to

B. W. Grefenstette; D. M. Smith; B. J. Hazelton; L. I. Lopez

2009-01-01

254

A low-background gamma-ray assay laboratory for activation analysis  

NASA Astrophysics Data System (ADS)

The sources of background in a gamma-ray detector were experimentally determined in underground and surface counting rooms, and an optimized shield was constructed at NIST. The optimum thickness of lead was 10-15 cm, with a greater thickness giving an increased background due to the buildup of tertiary cosmic-ray particles. Neither cadmium, tin, copper nor plastic (hydrocarbon or fluorocarbon) was desirable as a shield liner, since all these increased the background continuum or introduced characteristic peaks into the background spectrum. Two broad peaks in the background result from inelastic scattering of cosmic-ray neutrons (0.02 cm-2 s-1) in germanium. These neutrons also excite the lower nuclear levels of lead and structural iron to produce additional gamma-ray peaks in the spectrum. The influence of the 20 MW NIST reactor, located 60 m from the detector, was undetectable. Comparisons among detectors and locations clearly separate cosmic from environmental components of the background.

Lindstrom, Richard M.; Lindstrom, David J.; Slaback, Lester A.; Langland, John K.

1990-12-01

255

Heterogeneity in Short Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

We analyze the Swift/BAT sample of short gamma-ray bursts, using an objective Bayesian Block procedure to extract temporal descriptors of the bursts' initial pulse complexes (IPCs). The sample is comprised of 12 and 41 bursts with and without extended emission (EE) components, respectively. IPCs of non-EE bursts are dominated by single pulse structures, while EE bursts tend to have two or more pulse structures. The medians of characteristic timescales—durations, pulse structure widths, and peak intervals—for EE bursts are factors of ~2-3 longer than for non-EE bursts. A trend previously reported by Hakkila and colleagues unifying long and short bursts—the anti-correlation of pulse intensity and width—continues in the two short burst groups, with non-EE bursts extending to more intense, narrower pulses. In addition, we find that preceding and succeeding pulse intensities are anti-correlated with pulse interval. We also examine the short burst X-ray afterglows as observed by the Swift/X-Ray Telescope (XRT). The median flux of the initial XRT detections for EE bursts (~6×10-10 erg cm-2 s-1) is gsim20× brighter than for non-EE bursts, and the median X-ray afterglow duration for EE bursts (~60,000 s) is ~30× longer than for non-EE bursts. The tendency for EE bursts toward longer prompt-emission timescales and higher initial X-ray afterglow fluxes implies larger energy injections powering the afterglows. The longer-lasting X-ray afterglows of EE bursts may suggest that a significant fraction explode into denser environments than non-EE bursts, or that the sometimes-dominant EE component efficiently powers the afterglow. Combined, these results favor different progenitors for EE and non-EE short bursts.

Norris, Jay P.; Gehrels, Neil; Scargle, Jeffrey D.

2011-07-01

256

HETEROGENEITY IN SHORT GAMMA-RAY BURSTS  

SciTech Connect

We analyze the Swift/BAT sample of short gamma-ray bursts, using an objective Bayesian Block procedure to extract temporal descriptors of the bursts' initial pulse complexes (IPCs). The sample is comprised of 12 and 41 bursts with and without extended emission (EE) components, respectively. IPCs of non-EE bursts are dominated by single pulse structures, while EE bursts tend to have two or more pulse structures. The medians of characteristic timescales-durations, pulse structure widths, and peak intervals-for EE bursts are factors of {approx}2-3 longer than for non-EE bursts. A trend previously reported by Hakkila and colleagues unifying long and short bursts-the anti-correlation of pulse intensity and width-continues in the two short burst groups, with non-EE bursts extending to more intense, narrower pulses. In addition, we find that preceding and succeeding pulse intensities are anti-correlated with pulse interval. We also examine the short burst X-ray afterglows as observed by the Swift/X-Ray Telescope (XRT). The median flux of the initial XRT detections for EE bursts ({approx}6x10{sup -10} erg cm{sup -2} s{sup -1}) is {approx}>20x brighter than for non-EE bursts, and the median X-ray afterglow duration for EE bursts ({approx}60,000 s) is {approx}30x longer than for non-EE bursts. The tendency for EE bursts toward longer prompt-emission timescales and higher initial X-ray afterglow fluxes implies larger energy injections powering the afterglows. The longer-lasting X-ray afterglows of EE bursts may suggest that a significant fraction explode into denser environments than non-EE bursts, or that the sometimes-dominant EE component efficiently powers the afterglow. Combined, these results favor different progenitors for EE and non-EE short bursts.

Norris, Jay P. [Physics and Astronomy Department, University of Denver, Denver, CO 80208 (United States); Gehrels, Neil [Astroparticle Physics Laboratory, NASA/Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Scargle, Jeffrey D. [Space Science and Astrobiology Division, NASA/Ames Research Center, Moffett Field, CA 94035-1000 (United States)

2011-07-01

257

Gamma Ray Telescope Senses High-Energy Radiation  

NSDL National Science Digital Library

This video from NASA describes the GLAST satellite, which is equipped with a gamma-ray telescope, and shares some background about the kinds of extreme universal phenomena indicated by the presence of gamma rays.

Wnet

2011-11-02

258

Observations of cosmic gamma ray sources and their contribution to the diffuse gamma ray background  

NASA Astrophysics Data System (ADS)

The objective is to study soft gamma ray emission in the 0.1 to 10 MeV energy band for selected active galactic nuclei and explore how much they contribute to the total diffuse gamma ray background. A series of imaging observations of extragalactic objects in the low energy gamma-ray region were carried out by the Coded Aperture Directional Gamma-ray Telescope (DGT). The DGT was successfully flown at stratospheric balloon altitudes, and observations were made of the Crab, NGC 1275, MKN 421, and NGC 4151. The measured Crab spectrum is consistent with a featureless power-law of the form. Significant emission was detected up to 500 keV from the Seyfert galaxy, NGC 4151. To increase the total sky exposure the extragalactic field images were analyzed, including the 3C 273 region, obtained by the DGT.

Bhattacharya, Debadarshi

259

Muon Detection of TEV Gamma Rays from Gamma-Ray Bursts  

Microsoft Academic Search

Because of the limited size of the satellite-borne instruments, it has not been possible to observe the flux of gamma-ray bursts (GRBs) beyond GeV energy. We here show that it is possible to detect the GRB radiation of TeV energy and above by detecting the muon secondaries produced when the gamma rays shower in Earth's atmosphere. Observation is made possible

J. Alvarez-Muńiz; F. Halzen

1999-01-01

260

Gamma-ray Emission from the gamma-ray-loud BL Lac Objects  

Microsoft Academic Search

Using the HST observation data of BL Lac objects by Urry et al. and gamma-ray observation data, we find that there is a correlation between Fgamma and Fnuclei for gamma-ray-loud BL Lac objects (correlation coefficients: gamma=0.63, p=4.0 × 10-2), but no correlation between Fgamma and FOhost, where FOnuclei and FOhost are the fluxes of nuclei and host galaxy in V-band.

Guang-Zhong Xie; Ben-Zhong Dai; En-Wei Liang; Zhao-Hua Xie

2001-01-01

261

Gamma-Ray Lenses for Astrophysics—and the Gamma-Ray Imager Mission GRI  

Microsoft Academic Search

Observations of the gamma-ray sky reveal the most powerful sources and the most violent events in the Universe. While at lower wavebands the observed emission is generally dominated by thermal processes, the gamma-ray sky provides us with a view on the non-thermal Universe. Here particles are accelerated to extreme relativistic energies by mechanisms which are still poorly understood, and nuclear

Cornelia B. Wunderer; Peter v. Ballmoos; Nicolas Barriere; Angela Bazzano; Steven E. Boggs; Finn Christensen; Filippo Frontera; Margarida Hernanz; Jürgen Knodlseder; Andreas Zoglauer

2009-01-01

262

Medium-Energy Gamma-Ray Astrophysics with the 3DTI Gamma-Ray Telescope  

Microsoft Academic Search

Gamma-ray observations in the medium energy range (0.50-50.0 MeV) are central to unfolding many outstanding questions in astrophysics. The challenges of medium-energy gamma-ray observations, however, are the low photon statistics and large backgrounds. We review these questions, address the telescope technology requirements, and describe our development of the 3-Dimensional Track Imaging (3-DTI) Compton telescope and its performance for a new

Stanley D. Hunter; Robert G. Baker; Louis M. Barbier; Peter F. Bloser; LaVida Cooper; John F. Krizmanic; Jason T. Link; Mark L. McConnell; Georgia A. de Nolfo; James M. Ryan; Satpal Singh; Seunghee Son

2006-01-01

263

The Prompt Gamma-Ray and Afterglow Energies of Short-Duration Gamma-Ray Bursts  

Microsoft Academic Search

I present an analysis of the gamma-ray and afterglow energies of a complete sample of 16 short-duration GRBs with prompt X-ray follow-up. I find that 80% of the bursts exhibit a linear correlation between their gamma-ray fluence and the afterglow X-ray flux normalized to t=1 day, a proxy for the kinetic energy of the blast wave (FX,1~F1.01+\\/-0.27gamma). An even tighter

E. Berger

2007-01-01

264

A Balloon-Borne Gamma-Ray Polarimeter for Gamma-Ray Bursts  

Microsoft Academic Search

We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), was successfully demonstrated with partially polarized gamma-ray sources in the lab and fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model flew on a

M. L. McConnell; C. M. Bancroft; P. F. Bloser; T. P. Connor; J. S. Legere; J. R. Macri; J. M. Ryan

2009-01-01

265

Absorption of gamma-rays in the 5 March 1979 gamma-ray burst source  

Microsoft Academic Search

Absorption of gamma-rays above the source of their burst on March 5, 1979 is considered, in order to measure their distance. The results of a spherical model of the gamma-ray burst shows that unless the photons were collimated during the burst, the gamma-gamma optical thickness above an isotropically emitting burst source would be as high as 10 to the 5th

A. A. Zdziarski

1984-01-01

266

The Gamma-ray Large Area Space Telescope and Gamma-Ray Bursts  

Microsoft Academic Search

The Gamma-ray Large Area Telescope (GLAST) is a satellite-based observatory to study the high energy gamma-ray sky. The main instrument on GLAST, the Large Area Telescope (LAT) is a pair-conversion telescope that will survey the sky from 20 MeV to greater than 300 GeV With the GLAST launch in 2007, the LAT will open a new and important window on

Julie McEnery

2006-01-01

267

Light Curves of Swift Gamma-Ray Bursts  

Microsoft Academic Search

Recent observations from the Swift gamma-ray burst mission indicate that a fraction of gamma-ray bursts are characterized by a canonical behavior of the X-ray afterglows. We present an effective theory that allows us to account for X-ray light curves of both (short\\/long) gamma-ray bursts and X-ray-rich flashes. We propose that gamma-ray bursts originate from massive magnetic-powered pulsars.

Paolo Cea; Via G. Amendola

2007-01-01

268

Gamma-Ray Observatory - The next great observatory in space  

Microsoft Academic Search

The Gamma-Ray Observatory (GRO) which is part of NASA's Great Observatories space program is presented. The GRO is equipped with the Burst and Transient Source Experiment (which detects low-energy gamma-ray photons from 20 keV to 600 keV and locates sources of gamma-ray bursts), the Oriented Scintillation Spectrometer Experiment (which detects celestial gamma rays from 100 keV to 10 MeV and

Valerie Neal; Gerald Fishman; Donald Kniffen

1990-01-01

269

Wide energy range gamma-ray calibration source  

Microsoft Academic Search

Calibration source with monoenergetic gamma-ray lines in wide energy range designed for gamma-ray detector energetic calibration and testing has been built. Gamma-rays are obtained from thermal neutron capture, which is a suitable and cost efficient way how to provide discrete gamma-ray lines with energies above 3 MeV with reasonable intensity. With appropriate and interchangeable targets the source can generate different

M Kroupa; C Granja; Z Janout; M Kralik; F Krejci; A Owens; S Pospisil; F Quarati; J Solc; M Vobecky

2011-01-01

270

Cygnus X-3 and EGRET Gamma-Ray Observations  

Microsoft Academic Search

0!rQ1The Energetic Gamma Ray Experiment Telescope (EGRET) aboard the Compton Gamma Ray Observatory observed the Cygnus region in 14 different viewing periods during 1991 May to 1994 July. We present here our results on unpulsed and pulsed emissions of gamma rays at E > 50 MeV from Cyg X-3. While we detect a gamma-ray source consistent with the position of

M. Mori; D. L. Bertsch; B. L. Dingus; J. A. Esposito; C. E. Fichtel; S. D. Hunter; G. Kanbach; D. A. Kniffen; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; R. Mukherjee; P. L. Nolan; P. V. Ramanamurthy; E. Schneid; P. Sreekumar; D. J. Thompson

1997-01-01

271

Advanced gamma-ray astronomy telescope experiment: AGATE  

Microsoft Academic Search

In order to continue the achievements in high energy (10 MeV - 100 GeV) gamma-ray astronomy made with the Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on the Compton Gamma Ray Observatory (CGRO), a 'next generation' high energy gamma- ray telescope with a large increase in sensitivity coupled with improved angular resolution will be required. This 'next generation' telescope is envisioned

Brenda L. Dingus; D. L. Bertsch; Rajani Cuddapah; Carl E. Fichtel; Stanley D. Hunter; D. J. Thompson

1993-01-01

272

Observations of GRB 990123 by the Compton Gamma Ray Observatory  

Microsoft Academic Search

GRB 990123 was the first burst from which simultaneous optical, X-ray, and gamma-ray emission was detected; its afterglow has been followed by an extensive set of radio, optical, and X-ray observations. We have studied the gamma-ray burst itself as observed by the Compton Gamma Ray Observatory detectors. We find that gamma-ray fluxes are not correlated with the simultaneous optical observations

M. S. Briggs; D. L. Band; R. M. Kippen; R. D. Preece; C. Kouveliotou; J. van Paradijs; G. H. Share; R. J. Murphy; S. M. Matz; A. Connors; C. Winkler; M. L. McConnell; J. M. Ryan; O. R. Williams; C. A. Young; B. Dingus; J. R. Catelli; R. A. M. J. Wijers

1999-01-01

273

A high energy gamma ray survey of Cygnus and Cassiopeia  

Microsoft Academic Search

A gamma-ray telescope was used to search for celestial sources at energies above several hundred MeV. Upper limits for the gamma ray emission of six strong X-ray sources are given. The atmospheric generation rate of secondary gamma rays was also determined. The gamma ray detector is a large balloon-borne gas Cherenkov detector which has been previously described. It has a

M. F. Campbell

1974-01-01

274

DS02 fluence spectra for neutrons and gamma rays at Hiroshima and Nagasaki with fluence-to-kerma coefficients and transmission factors for sample measurements  

Microsoft Academic Search

Fluence spectra at several ground distances in Hiroshima and Nagasaki are provided along with associated fluence-to-kerma\\u000a coefficients from the Dosimetry System 2002 (DS02). Also included are transmission factors for calculating expected responses\\u000a of in situ sample measurements of neutron activation products such as 32P,36Cl,39Ar,41Ca, 60Co,63Ni,152Eu,  and 154Eu. The free-in-air (FIA) fluences calculated in 2002 are available for 240 angles, 69 energy

Stephen D. Egbert; George D. Kerr; Harry M. Cullings

2007-01-01

275

Very High Energy Gamma Ray Extension of GRO Observations.  

National Technical Information Service (NTIS)

This has been an exiciting year for high energy gamma-ray astronomy, both from space and from ground-based observatories. It has been a particularly active period for the Whipple Observatory gamma-ray group. In phase 1 of the Compton Gamma Ray Observatory...

T. C. Weekes

1992-01-01

276

GLAST and Ground-Based gamma-ray Astronomy.  

National Technical Information Service (NTIS)

The launch of the Gamma-ray Large Area Space Telescope (GLAST) in 2007 will open the possibility of combined studies of astrophysical sources with existing ground-based VHE gamma ray experiments such as H.E.S.S., VERITAS and MAGIC. Ground-based gamma ray ...

B. Giebels F. Longo J. E. Carson J. E. McEnery S. Funk

2007-01-01

277

Imaging and background in low-energy gamma ray astronomy  

Microsoft Academic Search

The current status of low energy gamma ray astronomy is reviewed and the conclusion drawn that the next generation of low energy gamma ray telescopes will require high sensitivity, good timing, and spectral resolution. High angular resolution imaging capability is also considered essential. The imaging of low energy gamma rays is hampered by the difficulties encountered in developing high resolution

Fan Lei

1989-01-01

278

The University of Durham Mark 6 Gamma Ray Telescope  

Microsoft Academic Search

The design, construction and operation of the University of Durham ground-based gamma ray telescope is discussed. The telescope has been designed to detect gamma rays in the = 200 GeV region and to achieve good discrimination between gamma ray and hadron initiated showers in the higher energy region (? 300 GeV). The telescope was commissioned in 1995 and a description

P. Armstrong; P. M. Chadwick; P. J. Cottle; J. E. Dickinson; M. R. Dickinson; N. A. Dipper; W. Hogg; J. Holder; T. R. Kendall; T. J. L. McComb; C. M. Moore; K. J. Orford; S. M. Rayner; I. D. Roberts; M. D. Roberts; M. Robertshaw; S. E. Shaw; K. Tindale; S. P. Tummey; K. E. Turver

1999-01-01

279

The University of Durham Mark 6 Gamma Ray Telescope  

Microsoft Academic Search

The design, construction and operation of the University of Durham ground-based gamma ray telescope is discussed. The telescope has been designed to detect gamma rays in the >= 150 GeV region and to achieve good discrimination between gamma ray and hadron initiated showers using conventional imaging and novel fluctuation measures. The telescope was commissioned in 1995 and a description of

P. M. Chadwick; M. R. Dickinson; N. A. Dipper; J. Holder; T. R. Kendall; T. J. L. McComb; K. J. Orford; S. M. Rayner; I. D. Roberts; S. E. Shaw; K. E. Turver; J. E. Dickinson; M. D. Roberts; S. P. Tummey

1997-01-01

280

Gamma-ray burst data from DMSP satellites.  

National Technical Information Service (NTIS)

A number of gamma-ray bursts have been detected by means of gamma-ray detectors aboard three Air Force Defense Meteorological Satellite Program (DMSP) satellites, in polar orbits at 800 km altitude. The gamma-ray data have a 2-second resolving time, and a...

J. Terrell R. W. Klebesadel P. Lee J. W. Griffee

1991-01-01

281

Very High-Energy Gamma-Ray Sources.  

ERIC Educational Resources Information Center

|Discusses topics related to high-energy, gamma-ray astronomy (including cosmic radiation, gamma-ray detectors, high-energy gamma-ray sources, and others). Also considers motivation for the development of this field, the principal results to date, and future prospects. (JN)|

Weekes, Trevor C.

1986-01-01

282

New Gamma-ray flaring activity from NRAO 676  

NASA Astrophysics Data System (ADS)

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed a renewed gamma-ray flaring activity from a gamma-ray source not included in any of the Fermi LAT catalogs.

Cutini, Sara

2012-10-01

283

Intrinsic germanium gamma-ray data from the New American Petroleum Institute spectral gamma-ray calibration models  

Microsoft Academic Search

High-resolution gamma-ray spectra have been recorded at the new American Petroleum Institute (API) spectral gamma-ray logging calibration center with a US Department of Energy passive spectral gamma-ray logging unit. These measurements were completed before gamma-ray source concentrations were assigned to the calibration model zones. Analyses of spectra gathered from five of the calibration zones yielded linear relationships between: (1) tentative

C. J. Koizumi; W. H. Ulbricht; J. R. Brodeur

1991-01-01

284

A search for gamma-ray bursts and pulsars, and the application of Kalman filters to gamma-ray reconstruction  

Microsoft Academic Search

High-energy gamma-ray astronomy was revolutionized in 1991 with the launch of the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma-Ray Observatory. In addition to unprecedented instrument effective area and a narrow point-spread function, EGRET provided photon time-tagging to an absolute accuracy of 100 mus. The opportunity to analyze high-quality gamma-ray data requires sophisticated statistical and analytic tools. Part

Brian Butler Jones

1999-01-01

285

A Search for Gamma-Ray Bursts and Pulsars, and the Application of Kalman Filters to Gamma-Ray Reconstruction  

Microsoft Academic Search

Part I describes the analysis of periodic and transient signals in EGRET data. A method to search for the transient flux from gamma-ray bursts independent of triggers from other gamma-ray instruments is developed. Several known gamma-ray bursts were independently detected, and there is evidence for a previously unknown gamma-ray burst candidate. Statistical methods using maximum likelihood and Bayesian inference are

Brian Jones

2002-01-01

286

Detection of high-energy gamma rays from quasar PKS 0528 + 134 by EGRET on the Compton Gamma Ray Observatory  

Microsoft Academic Search

The first several pointing directions of the Compton Gamma Ray Observatory, launched on 1991 April 5, were toward the Galactic anticenter. In addition to the known gamma-ray sources, Crab and Geminga, high-energy gamma-ray emission was observed from the quasar PKS 0528 + 134 by the Energetic Gamma Ray Experiment Telescope (EGRET). A redshift measurement, reported here, of 2.07 confirms the

S. D. Hunter; D. L. Bertsch; B. L. Dingus; C. E. Fichtel; R. C. Hartman; G. Kanbach; D. A. Kniffen; P. W. Kwok; Y. C. Lin; J. R. Mattox; H. A. Mayer-Hasselwander; P. F. Michelson; P. Moller; C. von Montigny; P. L. Nolan; K. Pinkau; H.-D. Radecke; H. Rothermel; P. Shaver; E. Schneid; M. Sommer; P. Sreekumar; D. J. Thompson

1993-01-01

287

Search on extraterrestrial gamma-ray lines from Southern Hemisphere sources with high energy resolution gamma-ray telescopes  

Microsoft Academic Search

The scope of the GEL 1 and 2 balloon-borne gamma ray telescope experiments is described. The gamma ray spectrometer to be used on GEL 1 is described. It is designed to study the nature of the Galactic center positron annihilation 511 KeV line. The telescope effect is achieved through the aperture angle formed by the gamma ray spectrometer anticoincidence crystals.

J. M. Dacosta; J. O. D. Jardim; F. Gonzalez-Blanco; D. J. R. Nordemann; I. M. Martin; S. L. G. Dutra; F. Albernhe; G. Vedrenne; D. Boclet; P. Durouchoux

1981-01-01

288

KINEMATIC ORIGIN OF CORRELATIONS BETWEEN GAMMA-RAY BURST OBSERVABLES  

SciTech Connect

Recently, several new correlations between gamma-ray burst (GRB) observables have been discovered. Like previously well-established correlations, they challenge GRB models. Here, we show that in the cannonball (CB) model of GRBs, the newly discovered correlations have the same simple kinematic origin as those discovered earlier. They all result from the strong dependence of the observed radiations on the Lorentz and Doppler factors of the jet of highly relativistic plasmoids (CBs) that produces the observed radiations by interaction with the medium through which it propagates.

Dado, Shlomo; Dar, Arnon, E-mail: dado@phep3.technion.ac.il, E-mail: arnon@physics.technion.ac.il [Physics Department, Technion, Haifa 32000 (Israel)

2012-04-20

289

Analysis of gamma ray burst spectra with cyclotron lines  

SciTech Connect

Motivated by the recent developments in the cyclotron resonance upscattering of soft photons or CUSP model of Gamma Ray Burst (GRB) continuum spectra, we revisit a select database of GRBs with credible cyclotron absorption features. We measure the break energy of the continuum, the slope below the break and deduce the soft photon energy or the electron beam Lorentz factor cutoff. We study the correlation (or lack of) between various parameters in the context of the CUSP model. One surprise result is that there appears to be marginal correlation between the break energy and the spectral index below the break. 20 refs., 8 figs., 2 tabs.

Kargatis, V. (Rice Univ., Houston, TX (USA). Dept. of Space Physics and Astronomy); Liang, E.P. (Lawrence Livermore National Lab., CA (USA))

1990-09-26

290

Mercuric iodide room temperature gamma-ray detectors  

SciTech Connect

High resolution mercuric iodide room temperature gamma-ray detectors have excellent potential as an essential component of space instruments to be used for high energy astrophysics. Mercuric iodide detectors are being developed both as photodetectors used in combination with scintillation crystals to detect gamma-rays, and as direct gamma-ray detectors. These detectors are highly radiation damage resistant. The list of applications includes gamma-ray burst detection, gamma-ray line astronomy, solar flare studies, and elemental analysis. 3 refs.

Patt, B.E.; Markakis, J.M.; Gerrish, V.M. (EG and G Energy Measurements, Inc., Goleta, CA (USA)); Haymes, R.C. (National Aeronautics and Space Administration, Washington, DC (USA). Astrophysics Div.); Trombka, J.I. (National Aeronautics and Space Administration, Greenbelt, MD (USA). Goddard Space Flight Center)

1989-01-01

291

Balloon-borne gamma-ray telescope with nuclear emulsion  

Microsoft Academic Search

We are planning to observe cosmic gamma-ray in the energy range 10MeV to 100GeV by balloon-borne gamma-ray telescope with nuclear emulsion. Nuclear emulsion is a precise tracker. By detecting starting point of electron pair, gamma-ray direction can be determined precisely (1.4mrad@1-2GeV). This is much better than Fermi Gamma-ray Space Telescope launched June 2008. Now we are developing the gamma-ray telescope

Satoru Takahashi; Shigeki Aoki; Tsutomu Fukuda; Kaname Hamada; Toshio Hara; Atsushi Iyono; Jiro Kawada; Masashi Kazuyama; Koichi Kodama; Masahiro Komatsu; Shinichiro Koshiba; Hirotaka Kubota; Seigo Miyamoto; Motoaki Miyanishi; Kunihiro Mor-Ishima; Naotaka Naganawa; Tatsuhiro Naka; Mitsuhiro Nakamura; Toshiyuki Nakano; Kimio Niwa; Yoshiaki Nonoyama; Keita Ozaki; Hiroki Rokujo; Takashi Sako; Os-Amu Sato; Yoshihiro Sato; Kazuya Suzuki; Atsumu Suzuki; Ikuo Tezuka; Junya Yoshida; Teppei Yoshioka

2010-01-01

292

Balloon-borne gamma-ray telescope with nuclear emulsion  

NASA Astrophysics Data System (ADS)

We are planning to observe cosmic gamma-ray in the energy range 10MeV to 100GeV by balloon-borne gamma-ray telescope with nuclear emulsion. Nuclear emulsion is a precise tracker. By detecting starting point of electron pair, gamma-ray direction can be determined precisely (1.4mrad@1-2GeV). This is much better than Fermi Gamma-ray Space Telescope launched June 2008. Now we are developing the gamma-ray telescope with nuclear emulsion and are planning to observe by balloon flight. Overview and status of our telescope is introduced in this presentation.

Takahashi, Satoru; Aoki, Shigeki; Fukuda, Tsutomu; Hamada, Kaname; Hara, Toshio; Iyono, Atsushi; Kawada, Jiro; Kazuyama, Masashi; Kodama, Koichi; Komatsu, Masahiro; Koshiba, Shinichiro; Kubota, Hirotaka; Miyamoto, Seigo; Miyanishi, Motoaki; Mor-Ishima, Kunihiro; Naganawa, Naotaka; Naka, Tatsuhiro; Nakamura, Mitsuhiro; Nakano, Toshiyuki; Niwa, Kimio; Nonoyama, Yoshiaki; Ozaki, Keita; Rokujo, Hiroki; Sako, Takashi; Sato, Os-Amu; Sato, Yoshihiro; Suzuki, Kazuya; Suzuki, Atsumu; Takahashi, Satoru; Tezuka, Ikuo; Yoshida, Junya; Yoshioka, Teppei

293

The Calculation of Solar Gamma-rays by TALYS  

NASA Astrophysics Data System (ADS)

Solar gamma-ray lines, produced from nuclear reactions of accelerated particles interacting with solar atmosphere ambient medium, are the most direct diagnosis about the acceleration and transport of electrons and ions in solar flares. Analysis of gamma-ray line spectrum in solar flare has provided information about composition, spectrum and angular distribution of the accelerated ions, as well as elemental abundance of the ambient solar atmosphere. A new gamma-ray calculation program was developed by using an efficient nuclear code - TALYS. The theory of gamma-ray production in solar flares is treated in detail. In addition, the characteristics of gamma-ray spectrum are also presented.

Chen, W.; Gan, W. Q.

2011-05-01

294

The Calculation of Solar Gamma-Rays by TALYS  

NASA Astrophysics Data System (ADS)

Solar gamma-ray lines, produced from nuclear reactions of accelerated particles interacting with the solar atmospheric medium, are the most direct diagnosis for the acceleration and transportation of energetic electrons and ions in solar flares. Much information about composition, spectrum, and angular distribution of the accelerated ions, as well as the elemental abundances of the ambient solar atmosphere can be derived from solar gamma-ray line spectra. A new gamma-ray calculation program has been developed by using an efficient nuclear code - TALYS. The theory of gamma-ray production in solar flares is treated in detail. The characteristics of gamma-ray spectrum are also presented.

Chen, Wei; Gan, Wei-Qun

2012-01-01

295

Real time gamma-ray signature identifier  

SciTech Connect

A real time gamma-ray signature/source identification method and system using principal components analysis (PCA) for transforming and substantially reducing one or more comprehensive spectral libraries of nuclear materials types and configurations into a corresponding concise representation/signature(s) representing and indexing each individual predetermined spectrum in principal component (PC) space, wherein an unknown gamma-ray signature may be compared against the representative signature to find a match or at least characterize the unknown signature from among all the entries in the library with a single regression or simple projection into the PC space, so as to substantially reduce processing time and computing resources and enable real-time characterization and/or identification.

Rowland, Mark (Alamo, CA); Gosnell, Tom B. (Moraga, CA); Ham, Cheryl (Livermore, CA); Perkins, Dwight (Livermore, CA); Wong, James (Dublin, CA)

2012-05-15

296

Gamma-Ray Burst Progenitors: Merger Model  

NASA Astrophysics Data System (ADS)

The mergers of neutron stars and black holes remain a viable model for gamma-ray burst central engines, at least for the class of short bursts: their time scales, occurrence rates and energy output seem to be consistent with observations. We will present results of our latest simulations showing how the orbit of a neutron star around a black hole shrinks due to gravitational radiation, how the neutron star's matter gets accreted by the black hole, and how the tidal forces of the black hole finally shred the neutron star into a thick disk. In this process, huge amounts of energy are radiated away by gravitational waves and by neutrinos emitted from the hot disk. The neutrino luminosities are so large that an appreciable fraction (some few percent!) of neutrinos annihilate with antineutrinos creating the clean fireball necessary to power gamma-ray bursts.

Ruffert, Maximilian

2002-04-01

297

Gamma-ray multiplicity measurements using STEFF  

NASA Astrophysics Data System (ADS)

An ongoing investigation into the angular momentum generated during the fission of 252Cf is currently under way using the SpecTrometer for Exotic Fission Fragments (STEFF). Measurements have been made of the fold distribution (measured multiplicity) with STEFF. These have been compared to a Monte-carlo simulation to determine a value for the average angular momentum Jrms = 6hslash which is comparable to previous measurements [1]. Measurements of the gamma-ray multiplicity were performed whilst gating on different fragment mass regions. The result was compared with a sum of the lowest 2+ energies from both fragment and complementary in the mass gate. The results support the view that gamma-ray multiplicity is largely determined by the decay of the nucleus through near yrast transitions that follow the statistical decay.

Pollitt, A. J.; Smith, A. G.; Tsekhanovich, I.; Dare, J. A.

2012-09-01

298

SUB-LUMINOUS {gamma}-RAY PULSARS  

SciTech Connect

Most pulsars observed by the Fermi Large Area Telescope have {gamma}-ray luminosities scaling with spin-down power E-dot as L{sub {gamma}}{approx}(E-dot x 10{sup 33} erg s{sup -1}){sup 1/2}. However, there exist one detection and several upper limits an order of magnitude or more fainter than this trend. We describe these 'sub-luminous' {gamma}-ray pulsars and discuss the case for this being an orientation effect. Of the 12 known young radio pulsars with E-dot >10{sup 34} erg s{sup -1} and d {<=} 2 kpc several are substantially sub-luminous. The limited available geometrical constraints favor aligned geometries for these pulsars, although no one case for alignment is compelling. In this scenario GeV emission detected from such sub-luminous pulsars can be due to a lower altitude, lower-power accelerator gap.

Romani, R. W.; Kerr, M.; Craig, H. A. [Department of Physics, Stanford University, Stanford, CA 94305 (United States); Johnston, S. [Australia Telescope National Facility, CSIRO, Epping, NSW 1710 (Australia); Cognard, I. [Laboratoire de Physique et Chimie de l'Environnement, LPCE UMR 6115 CNRS, 45071 Orleans Cedex 02 (France); Smith, D. A., E-mail: rwr@astro.stanford.edu [Centre d'Etudes Nucleaires de Bordeaux Gradignan, Universite Bordeaux 1, CNRS/IN2p3, 33175 Gradignan (France)

2011-09-01

299

Gamma-Ray Burst:. Discoveries with Swift  

NASA Astrophysics Data System (ADS)

Gamma Ray Bursts (GRBs) are bright, brief flashes of high energy photons and are the most powerful explosions since the Big Bang, with typical energies up to around 1051 ergs. Their outbursts persist for durations ranging from milliseconds to tens of seconds or more. In these brief moments the explosions radiate more energy than the Sun will release in its entire 10 billion year lifetime. They come in two classes: long (ż2 s), softspectrum bursts and short, hard events. Current theories attribute these phenomena to the final collapse of a massive star, or the coalescence of a binary system induced by gravity wave emission. New results from Swift and related programmes offer fresh understanding of the physics of gamma-ray bursts and of the local environments and host galaxies of burst progenitors. Bursts found at very high red-shifts are new tools for exploring the intergalactic medium, the first stars and the earliest stages of galaxy formation.

Wells, Alan

2007-11-01

300

Neutron-driven gamma-ray laser  

DOEpatents

A lasing cylinder emits laser radiation at a gamma-ray wavelength of 0.87 .ANG. when subjected to an intense neutron flux of about 400 eV neutrons. A 250 .ANG. thick layer of Be is provided between two layers of 100 .ANG. thick layer of .sup.57 Co and these layers are supported on a foil substrate. The coated foil is coiled to form the lasing cylinder. Under the neutron flux .sup.57 Co becomes .sup.58 Co by neutron absorption. The .sup.58 Co then decays to .sup.57 Fe by 1.6 MeV proton emission. .sup.57 Fe then transitions by mesne decay to a population inversion for lasing action at 14.4 keV. Recoil from the proton emission separates the .sup.57 Fe from the .sup.57 Co and into the Be, where Mossbauer emission occurs at a gamma-ray wavelength.

Bowman, Charles D. (Los Alamos, NM)

1990-01-01

301

Neutron-driven gamma-ray laser  

DOEpatents

A lasing cylinder emits laser radiation at a gamma-ray wavelength of 0.87 {angstrom} when subjected to an intense neutron flux of about 400 eV neutrons. A 250 {angstrom} thick layer of Be is provided between two layers of 100 {angstrom} thick layer of {sup 57}Co and these layers are supported on a foil substrate. The coated foil is coiled to form the lasing cylinder. Under the neutron flux {sup 57}Co becomes {sup 58}Co by neutron absorption. The {sup 58}Co then decays to {sup 57}Fe by 1.6 MeV proton emission. {sup 57}Fe then transitions by mesne decay to a population inversion for lasing action at 14.4 keV. Recoil from the proton emission separates the {sup 57}Fe from the {sup 57}Co and into the Be, where Mossbauer emission occurs at a gamma-ray wavelength.

Bowman, C.D.

1989-03-28

302

SuperAGILE and Gamma Ray Bursts  

SciTech Connect

The solid-state hard X-ray imager of AGILE gamma-ray mission -- SuperAGILE -- has a six arcmin on-axis angular resolution in the 15-45 keV range, a field of view in excess of 1 steradian. The instrument is very light: 5 kg only. It is equipped with an on-board self triggering logic, image deconvolution, and it is able to transmit the coordinates of a GRB to the ground in real-time through the ORBCOMM constellation of satellites. Photon by photon Scientific Data are sent to the Malindi ground station at every contact. In this paper we review the performance of the SuperAGILE experiment (scheduled for a launch in the middle of 2006), after its first onground calibrations, and show the perspectives for Gamma Ray Bursts.

Pacciani, Luigi; Costa, Enrico; Del Monte, Ettore; Donnarumma, Immacolata; Evangelista, Yuri; Feroci, Marco; Frutti, Massimo; Lazzarotto, Francesco; Lapshov, Igor; Rubini, Alda; Soffitta, Paolo; Tavani, Marco [IASF-INAF Rome (Italy); Barbiellini, Guido [INFN Trieste (Italy); Mastropietro, Marcello [CNR Montelibretti (Italy); Morelli, Ennio [IASF-INAF-Bologna (Italy); Rapisarda, Massimo [ENEA Frascati (Italy)

2006-05-19

303

The Compton Gamma Ray Observatory: mission status.  

NASA Astrophysics Data System (ADS)

The Arthur Holly Compton Gamma Ray Observatory (Compton) is the second in NASA's series of Great Observatories. Compton has now been operating for over two and a half years, and has given a dramatic increase in capability over previous gamma-ray missions. The spacecraft and scientific instruments are all in good health, and many significant discoveries have already been made and continue to be made. The authors describe the capabilities of the four scientific instruments and the observing programs for the first three years of the mission. During Phases 2 and 3 of the mission a Guest Investigator program has been in progress with the Guest Observers' time share increasing from 30% to over 50% for the later mission phases.

Gehrels, N.; Chipman, E.; Kniffen, D. A.

304

Cosmic-Rays and Gamma Ray Bursts  

NASA Astrophysics Data System (ADS)

Cosmic-rays are subatomic particles of energies ranging between a few eV to hundreds of TeV. These particles register a power-law spectrum, and it seems that most of them originate from astrophysical galactic and extragalactic sources. The shock acceleration in superalfvenic astrophysical plasmas, is believed to be the main mechanism responsible for the production of the non-thermal cosmic-rays. Especially, the importance of the very high energy cosmic-ray acceleration, with its consequent gamma-ray radiation and neutrino production in the shocks of the relativistic jets of Gamma Ray Bursts, is a favourable theme of study. I will discuss the cosmic-ray shock acceleration mechanism particularly focusing on simulation studies of cosmic-ray acceleration occurring in the relativistic shocks of GRB jets.

Meli, A.

2013-07-01

305

Gamma ray bursts: a 1983 overview  

SciTech Connect

Gamma ray burst observations are reviewed with mention of new gamma-ray and optical transient measurements and with discussions of the controversial, contradictory and unresolved issues that have recently emerged: burst spectra appear to fluctuate in time as rapidly as they are measured, implying that any one spectrum may be incorrect. Energy spectra can be obligingly fitted to practically any desired shape, implying, in effect, that no objective spectral resolution exists at all. Burst fluxes and temporal quantities, including the total event energy, are characterized very differently with differing instruments, implying that even elementary knowledge of their properties is instrumentally subjective. Finally, the log N-log S determinations are deficient in the weak bursts, while there is no detection of a source direction anisotropy, implying that Ptolemy was right or that burst source distance estimates are basically guesswork. These issues may remain unsolved until vastly improved instruments are flown.

Cline, T.L.

1983-10-01

306

Plasma Instabilities in Gamma-Ray Bursts  

SciTech Connect

Magnetic fields are important in a variety of astrophysical scenarios, ranging from possible creation mechanisms of cosmological magnetic fields through relativistic jets such as that from Active Galactic Nuclei and gamma-ray bursts to local phenomena in the solar system. Here, the outstanding importance of plasma instabilities to astrophysics is illustrated by applying the so-called neutral point method to gamma-ray bursts (GRBs), which are assumed to have a homogeneous background magnetic field. It is shown how magnetic turbulence, which is a prerequisite for the creation of dissipation and, subsequently, radiation, is created by the highly relativistic particles in the GRB jet. Using the fact that different particle compositions lead to different instability conditions, conclusions can be drawn about the particle composition of the jet, showing that it is more likely of baryonic nature.

Tautz, Robert C. [Institut fuer Theoretische Physik, Lehrstuhl IV: Weltraum-und Astrophysik, Ruhr-Universitaet Bochum, D-44780 Bochum (Germany)

2008-12-24

307

Gamma-ray polarimetry with Compton Telescope  

NASA Astrophysics Data System (ADS)

Compton telescope is a promising technology to achieve very high sensitivity in the soft gamma-ray band (0.1-10 MeV) by utilizing Compton kinematics. Compton kinematics also enables polarization measurement which will open new windows to study gamma-ray production mechanism in the universe. CdTe and Si semiconductor technologies are key technologies to realize the Compton telescope in which their high energy resolution is crucial for high angular resolution and background rejection capability. We have assembled a prototype module using a double-sided silicon strip detector and CdTe pixel detectors. In this paper, we present expected polarization performance of a proposed mission (NeXT/SGD). We also report results from polarization measurements using polarized synchrotron light and validation of EGS4 MC simulation.

Tajima, Hiroyasu; Madejski, Grzegorz; Mitani, Takefumi; Tanaka, Takaaki; Nakamura, Hidehito; Nakazawa, Kazuhiro; Takahashi, Tadayuki; Fukazawa, Yasushi; Kamae, Tuneyoshi; Kokubun, Motohide; Marlow, Daniel; Nomachi, Masaharu; do Couto e Silva, Eduardo

2004-10-01

308

THE REMARKABLE {gamma}-RAY ACTIVITY IN THE GRAVITATIONALLY LENSED BLAZAR PKS 1830-211  

SciTech Connect

We report the extraordinary {gamma}-ray activity (E > 100 MeV) of the gravitationally lensed blazar PKS 1830-211 (z = 2.507) detected by AGILE between 2010 October and November. On October 14, the source experienced a factor of {approx}12 flux increase with respect to its average value and remained brightest at this flux level ({approx}500 x 10{sup -8} photons cm{sup -2} s{sup -1}) for about four days. The one-month {gamma}-ray light curve across the flare showed a mean flux F(E > 100 MeV) = 200 x 10{sup -8} photons cm{sup -2} s{sup -1}, which resulted in a factor of four enhancement with respect to the average value. Following the {gamma}-ray flare, the source was observed in near-IR (NIR)-optical energy bands at the Cerro Tololo Inter-American Observatory and in X-Rays by Swift/X-Ray Telescope and INTEGRAL/IBIS. The main result of these multifrequency observations is that the large variability observed in {gamma}-rays does not have a significant counterpart at lower frequencies: no variation greater than a factor of {approx}1.5 appeared in the NIR and X-Ray energy bands. PKS 1830-211 is then a good '{gamma}-ray only flaring' blazar showing substantial variability only above 10-100 MeV. We discuss the theoretical implications of our findings.

Donnarumma, I.; De Rosa, A.; Vittorini, V.; Tavani, M.; Striani, E.; Pacciani, L. [INAF/IASF-Roma, Via del Fosso del Cavaliere 100, I-00133 Roma (Italy); Miller, H. R.; Eggen, J.; Maune, J. [Department of Physics and Astronomy Georgia State University, GA 30303-3083 (United States); Popovic, L. C. [Astronomical Observatory, Volgina 7, 11160, Belgrade 74 (Serbia); Simic, S. [Isaac Newton Institute of Chile, Yugoslavia Branch, Belgrade (Serbia); Kuulkers, E. [European Space Astronomy Centre, SRE-O, Villanueva de la Canada, Madrid (Spain); Vercellone, S. [INAF/IASF Palermo Via Ugo La Malfa 153, 90146 Palermo (Italy); Pucella, G. [ENEA-Frascati, Via E. Fermi 45, I-00044 Frascati, Roma (Italy); Verrecchia, F.; Pittori, C.; Giommi, P. [ASI-ASDC, Via G. Galilei, I-00044 Frascati, Roma (Italy); Barbiellini, G. [Dipartimento di Fisica and INFN Trieste, Via Valerio 2, I-34127 Trieste (Italy); Bulgarelli, A. [INAF/IASF-Bologna, Via Gobetti 101, I-40129 Bologna (Italy); Cattaneo, P. W., E-mail: immacolata.donnarumma@iasf-roma.inaf.it [INFN-Pavia, Via Bassi 6, I-27100 Pavia (Italy)

2011-08-01

309

GAMANAL. Interpretation of Gamma-Ray Spectra  

Microsoft Academic Search

GAMANAL provides a complete qualitative and quantitative analysis of mixtures of radioactive species such as fission products by computer interpretation of high-resolution gamma-ray spectra. The program first determines and removes the background or Compton continuum under the peaks in a spectrum to locate the peak regions. This is done by examining the pulse-height spectrum data for background and peak regions

Gunnink

1986-01-01

310

Gamma Ray Bursts, Swift and REM  

Microsoft Academic Search

Relevant information about the physics of Gamma Ray Bursts (GRBs) is hidden in the first phases of the afterglow, i.e. in the multi-wavelength (X-ray to Radio) emission soon after the explosion. Optical and NIR afterglow are particularly important since they allow to measure the redshift of the source and possibly to discover the host galaxies. We present in these pages

G. Chincarini; F. M. Zerbi

2003-01-01

311

Supernova, Hypernova and Gamma Ray Bursts  

Microsoft Academic Search

Recent observations suggest that gamma ray bursts (GRBs) and their afterglows\\u000aare produced by highly relativistic jets emitted in core collapse supernova\\u000aexplosions (SNe). The result of the event, probably, is not just a compact\\u000aobject plus a spherical ejecta: within days, a fraction of the parent star\\u000afalls back to produce a thick accretion disk around the compact object.

Arnon Dar

2001-01-01

312

Gamma ray bursts and cosmic ray origin  

Microsoft Academic Search

This paper presents the theoretical basis of the fireball\\/blast wave model, and some implications of recent results on GRB source models and cosmic-ray production from GRBs. BATSE observations of the prompt gamma-ray luminous phase, and Beppo-SAX and long wavelength afterglow observations of GRBs are briefly summarized. Derivation of spectral and temporal indices of an adiabatic blast wave decelerating in a

C. D. Dermer

2001-01-01

313

Gamma Ray Bursts and Cosmic Ray Origin  

Microsoft Academic Search

This paper presents the theoretical basis of the fireball\\/blast wave model, and some implications of recent results on GRB source models and cosmic-ray production from GRBs. BATSE observations of the prompt gamma-ray luminous phase, and Beppo-SAX and long wavelength afterglow observations of GRBs are briefly summarized. Derivation of spectral and temporal indices of an adiabatic blast wave decelerating in a

C. D. Dermer

2002-01-01

314

Fermi Detects Solar Flare's Gamma Rays  

NASA Video Gallery

During a powerful solar blast in March, NASA's Fermi Gamma-ray Space Telescope detected the highest-energy light ever associated with an eruption on the sun. The discovery heralds Fermi's new role as a solar observatory, a powerful new tool for understanding solar outbursts during the sun's maximum period of activity. Credit: NASA's Goddard Space Flight Center > Related story > Download high-res video

gsfcvideo

2012-06-12

315

Time resolved gamma-ray spectrometry  

Microsoft Academic Search

A new approach is proposed for the measurement of the time-dependent processes in gamma-ray spectrometry. During data acquisition,\\u000a the energy and the detection time of each event are recorded and the data are later analyzed off-line. This separation of\\u000a acquisition and data handling extends the possibilities of the analysis. A series of demonstration experiments was performed\\u000a to show the feasibility

L. Szentmiklósi; T. Belgya; G. L. Molnár; Zs. Révay

2007-01-01

316

Linssi : Database for gamma-ray spectrometry  

Microsoft Academic Search

Linssi is a Structured Query Language (SQL) database for HPGe gamma-ray spectrometry. It covers the whole production chain from\\u000a sample preparation to final analysis results. Static or mobile sampling and measurement and multiple sample types are supported.\\u000a In addition, each sample can be split or combined any number of times. A sample may be measured multiple times and each measurement

P. A. Aarnio; J. J. Ala-Heikkilä; A. Isolankila; A. Kuusi; M. Moring; M. Nikkinen; T. Siiskonen; H. Toivonen; K. Ungar; W. Zhang

2008-01-01

317

Pulsar kicks and gamma-ray burst  

Microsoft Academic Search

Aims:We use the supernova-GRB (gamma-ray burst) association and assume that the GRB asymmetric explosions produce pulsars in order to test the consistency of distributions of modeled and observed pulsar-kick velocities. Methods: The deduced distribution of kick velocity from the model of GRB and the observed kick distribution of radio pulsars are checked by a K-S test. Results: These two distributions

X. H. Cui; H. G. Wang; R. X. Xu; G. J. Qiao

2007-01-01

318

Pulsar's kicks and Gamma-ray bursts  

Microsoft Academic Search

The consistence of the distributions of pulsar's kick velocities from the\\u000amodel of GRB and from the pulsar observations is tested based on the\\u000asupernova-GRB ($\\\\gamma$-ray burst) association and under the assumption that\\u000athe GRB asymmetric explosions produce pulsars. The deduced distribution of kick\\u000avelocity from the model of GRB and the observed kick distribution of radio\\u000apulsars are checked

X. H. Cui; H. G. Wang; R. X. Xu; G. J. Qiao

2007-01-01

319

Gamma-Ray Bursts and Particle Acceleration  

Microsoft Academic Search

Gamma-ray bursts (GRBs) are possible sources of ultra-high-energy cosmic rays (UHE-CRs). To test the GRB origin of UHECRs, it is essential to search for characteristic, proton-induced signatures of secondary radiation. In this paper we present our recent results of Monte Carlo simulations that model the broadband prompt emission of GRBs including various processes associated with electrons and protons accelerated to

Katsuaki Asano; Katsuaki

2008-01-01

320

The Swift Gamma-Ray Burst Mission  

Microsoft Academic Search

The Swift mission, scheduled for launch in 2004, is a multiwavelength observatory for gamma-ray burst (GRB) astronomy. It is a first-of-its-kind autonomous rapid-slewing satellite for transient astronomy and pioneers the way for future rapid-reaction and multiwavelength missions. It will be far more powerful than any previous GRB mission, observing more than 100 bursts yr-1 and performing detailed X-ray and UV\\/optical

N. Gehrels; G. Chincarini; P. Giommi; K. O. Mason; J. A. Nousek; A. A. Wells; N. E. White; S. D. Barthelmy; D. N. Burrows; L. R. Cominsky; K. C. Hurley; F. E. Marshall; P. Mészáros; P. W. A. Roming; L. Angelini; L. M. Barbier; T. Belloni; S. Campana; P. A. Caraveo; M. M. Chester; O. Citterio; T. L. Cline; M. S. Cropper; J. R. Cummings; A. J. Dean; E. D. Feigelson; E. E. Fenimore; D. A. Frail; A. S. Fruchter; G. P. Garmire; K. Gendreau; G. Ghisellini; J. Greiner; J. E. Hill; S. D. Hunsberger; H. A. Krimm; S. R. Kulkarni; P. Kumar; F. Lebrun; N. M. Lloyd-Ronning; C. B. Markwardt; B. J. Mattson; R. F. Mushotzky; J. P. Norris; J. Osborne; B. Paczynski; D. M. Palmer; H.-S. Park; A. M. Parsons; J. Paul; M. J. Rees; C. S. Reynolds; J. E. Rhoads; T. P. Sasseen; B. E. Schaefer; A. T. Short; A. P. Smale; I. A. Smith; L. Stella; G. Tagliaferri; T. Takahashi; M. Tashiro; L. K. Townsley; J. Tueller; M. J. L. Turner; M. Vietri; W. Voges; M. J. Ward; R. Willingale; F. M. Zerbi; W. W. Zhang

2004-01-01

321

Kinetics of proposed gamma-ray lasers  

SciTech Connect

Gamma-ray lasers, although proposed for many years, remain undeveloped because pumping can destroy conditions essential for gain. We review many of the solutions (viz, narrowed-line, explosive neutron pump, two-stage pump, two-step pump) proposed so far, with emphasis on kinetics. The most promising approach requires fast interlevel transfer from a separated isomer to initiate a superradiant Borrmann mode in a solid host. However, suitable nuclear transitions and nondestructive transfer mechanisms have yet to be identified.

Baldwin, G.C.

1985-01-01

322

A portable gamma ray spectrometer/computer  

SciTech Connect

A state-of-the-art portable gamma ray spectrometer has been developed commercially. The instrument is available with NaI or hand-held Germanium detectors and can collect and analyze up to 4K channels of PHA or MCS spectra. An integral LCD provides graphic and character readout. Dual microprocessors are operated in a tightly-coupled multi-programming environment providing unique operator interface capability.

Roberts, H.

1984-02-01

323

Nuclear gamma Rays Following K- Capture  

Microsoft Academic Search

It is suggested that the study of the nuclear deexcitation gamma rays emitted following K- capture may help clarify the nature of the capture mechanism. We consider capture in 208Pb and 16O. Capture rates to the various proton or neutron single-hole states in 207Pb, 207Tl, 15O, and 15N are estimated, and the consequences of capture to the isomeric states in

S. D. Bloom; M. S. Weiss; C. M. Shakin

1972-01-01

324

Status of the Milagro Gamma Ray Observatory  

Microsoft Academic Search

The Milagro Gamma Ray Observatory is the world's first large-area water Cherenkov detector capable of continuously monitoring the sky at TeV energies. Located in the mountains of northern New Mexico, Milagro will perform an all sky survey of the Northern Hemisphere at energies between 250 GeV and 50 TeV. With ą a high duty-cycle, large detector area, and wide field-of-view

Joseph McCullough; W. Benbow; D. Berley; M.-L. Chen; D. G. Coyne; R. S. Delay; B. L. Dingus; D. E. Dorfan; R. W. Ellsworth; D. Evans; A. Falcone; L. Fleysher; R. Fleysher; G. Gisler; J. A. Goodman; T. J. Haines; C. M. Hoffman; S. Hugenberger; L. A. Kelley; I. Leonor; J. Macri; M. McConnell; J. E. McEnery; R. S. Miller; A. I. Mincer; M. F. Morales; P. Nemethy; J. M. Ryan; M. Schneider; B. Shen; A. Shoup; G. Sinnis; A. J. Smith; G. W. Sullivan; T. N. Thompson; O. T. Tumer; K. Wang; M. O. Wascko; S. Westerhoff; D. A. Williams; T. Yang; G. B. Yodh

1999-01-01

325

Short-hard gamma-ray bursts  

Microsoft Academic Search

Two types of gamma-ray bursts (GRBs) are observed: short-duration hard spectrum GRBs and long-duration soft spectrum GRBs. For many years long GRBs were the focus of intense research while the lack of observational data limited the study of short-hard GRBs (SHBs). In 2005 a breakthrough occurred following the first detections of SHB afterglows, longer wavelength emission that follows the burst

Ehud Nakar

2007-01-01

326

The Cosmic Gamma-Ray Bursts  

Microsoft Academic Search

Cosmic gamma-ray bursts are one of the great frontiers of astrophysics today.\\u000aThey are a playground of relativists and observers alike. They may teach us\\u000aabout the death of stars and the birth of black holes, the physics in extreme\\u000aconditions, and help us probe star formation in the distant and obscured\\u000auniverse. In this review we summarise some of

S. G. Djorgovski; D. A. Frail; S. R. Kulkarni; R. Sari; J. S. Bloom; T. J. Galama; F. A. Harrison; P. A. Price; D. Fox; D. E. REICHART; S. Yost; E. Berger; A. Diercks; R. Goodrich; F. Chaffee

2001-01-01

327

Gamma Ray Bursts and Cosmic Ray Origin  

Microsoft Academic Search

This paper presents the theoretical basis of the fireball\\/blast wave model,\\u000aand some implications of recent results on GRB source models and cosmic-ray\\u000aproduction from GRBs. BATSE observations of the prompt gamma-ray luminous\\u000aphase, and Beppo-SAX and long wavelength afterglow observations of GRBs are\\u000abriefly summarized. Derivation of spectral and temporal indices of an adiabatic\\u000ablast wave decelerating in a

C. D. Dermer

2002-01-01

328

Gamma-ray spectroscopy: An historical perspective  

Microsoft Academic Search

The possibility of MeV-range gamma-rays from extraterrestrial sources had been speculated on by cosmic-ray physicists since the late 1940's. The first definitive detection occurred with balloon-borne cosmic-ray instrumentation during a class 2 solar flare in March 1958, apparently associated with the acceleration of a nonthermal particle population. Following this detection, physicists were motivated to develop instrumentation specific for observation of

Laurence E. Peterson

1988-01-01

329

Gamma-ray spectroscopy: An historical perspective  

Microsoft Academic Search

The possibility of MeV-range gamma-rays from extraterrestrial sources had been speculated on by cosmic-ray physicists since the late 1940’s. The first definitive detection occurred with balloon-borne cosmic-ray instrumentation during a class 2 solar flare in March 1958, apparently associated with the acceleration of a nonthermal particle population. Following this detection, physicists were motivated to develop instrumentation specific for observation of

Laurence E. Peterson

1988-01-01

330

The Supernova Gamma-Ray Burst Connection  

Microsoft Academic Search

Observations show that at least some gamma-ray bursts (GRBs) happen simultaneously with core-collapse supernovae (SNe), thus linking by a common thread nature's two grandest explosions. We review here the growing evidence for and theoretical implications of this association, and conclude that most long-duration soft-spectrum GRBs are accompanied by massive stellar explosions (GRB-SNe). The kinetic energy and luminosity of well-studied GRB-SNe

S. E. Woosley; J. S. Bloom

2006-01-01

331

Spectral variations in gamma-ray bursts  

Microsoft Academic Search

We report the initial results of an analysis of 19 gamma-ray burst energy spectra recorded by the Venera-13 and 14 SIGNE experiments. The complete data-base includes some 150 events, with 5 channel energy spectra taken in the 50-700 keV range with 0.5 s time resolution, for 64 s. The observed spectra of each event analyzed were fitted with a power

K. Hurley; V. Kargatis; E. Liang; C. Barat; E. Eveno; M. Niel; V. Sh. Dolidze; A. A. Kozlenkov; I. G. Mitrofanov; A. S. Pozanenko

1991-01-01

332

Gamma-rays from massive protostars  

Microsoft Academic Search

Massive protostars have associated bipolar outflows with velocities of\\u000ahundreds of km\\/s. Such outflows produce strong shocks when interact with the\\u000aambient medium leading to regions of non-thermal radio emission. Under certain\\u000aconditions, the population of relativistic particles accelerated at the\\u000aterminal shocks of the protostellar jets can produce significant gamma-ray\\u000aemission. We estimate the conditions necessary for high-energy emission

Gustavo E. Romero; Anabella T. Araudo; Valenti Bosch-Ramon; Josep M. Paredes

2009-01-01

333

Gamma-Rays from Massive Protostars  

Microsoft Academic Search

Massive protostars have associated bipolar outflows with velocities of hundreds of km s-1. Such outflows produce strong shocks when interact with the ambient medium leading to regions of non-thermal radio emission. Under certain conditions, the population of relativistic particles accelerated at the terminal shocks of the protostellar jets can produce significant gamma-ray emission. We estimate the conditions necessary for high-energy

G. E. Romero; A. T. Araudo; V. Bosch-Ramon; J. M. Paredes

2010-01-01

334

The Blackholic energy: long and short Gamma-Ray Bursts (New perspectives in physics and astrophysics from the theoretical understanding of Gamma-Ray Bursts, II)  

Microsoft Academic Search

We outline the confluence of three novel theoretical fields in our modeling of Gamma-Ray Bursts (GRBs): 1) the ultrarelativistic regime of a shock front expanding with a Lorentz gamma factor ~ 300; 2) the quantum vacuum polarization process leading to an electron-positron plasma originating the shock front; and 3) the general relativistic process of energy extraction from a black hole

Remo Ruffini; Maria Grazia Bernardini; Carlo Luciano Bianco; Pascal Chardonnet; Federico Fraschetti; Vahe Gurzadyan; Luca Vitagliano; She-Sheng Xue

2005-01-01

335

Opacity Build-up in Impulsive Relativistic Sources  

SciTech Connect

Opacity effects in relativistic sources of high-energy gamma-rays, such as gamma-ray bursts (GRBs) or Blazars, can probe the Lorentz factor of the outflow as well as the distance of the emission site from the source, and thus help constrain the composition of the outflow (protons, pairs, magnetic field) and the emission mechanism. Most previous works consider the opacity in steady state. Here we study the effects of the time dependence of the opacity to pair production ({gamma}{gamma} {yields} e{sup +}e{sup -}) in an impulsive relativistic source, which may be relevant for the prompt gamma-ray emission in GRBs or flares in Blazars. We present a simple, yet rich, semi-analytic model for the time and energy dependence of the optical depth, {tau}{gamma}{gamma}, in which a thin spherical shell expands ultra-relativistically and emits isotropically in its own rest frame over a finite range of radii, R{sub 0} {le} R {le} R{sub 0}+{Delta}R. This is particularly relevant for GRB internal shocks. We find that in an impulsive source ({Delta}R {approx}< R{sub 0}), while the instantaneous spectrum (which is typically hard to measure due to poor photon statistics) has an exponential cutoff above the photon energy {var_epsilon}1(T) where t{gamma}{gamma}({var_epsilon}1) = 1, the time integrated spectrum (which is easier to measure) has a power-law high-energy tail above the photon energy {var_epsilon}1* {approx} {var_epsilon}1({Delta}T) where {Delta}T is the duration of the emission episode. Furthermore, photons with energies {var_epsilon} > {var_epsilon}1* are expected to arrive mainly near the onset of the spike in the light curve or flare, which corresponds to the short emission episode. This arises since in such impulsive sources it takes time to build-up the (target) photon field, and thus the optical depth {tau}{gamma}{gamma}({var_epsilon}) initially increases with time and {var_epsilon}1(T) correspondingly decreases with time, so that photons of energy {var_epsilon} > {var_epsilon}1* are able to escape the source mainly very early on while {var_epsilon}1(T) > {var_epsilon}. As the source approaches a quasi-steady state ({Delta}R >> R0), the time integrated spectrum develops an exponential cutoff, while the power-law tail becomes increasingly suppressed.

Granot, Jonathan; Cohen-Tanugi, Johann; Silva, Eduardo do Couto e

2007-09-28

336

Radio search for gamma-ray pulsar counterparts  

NASA Astrophysics Data System (ADS)

The Fermi gamma-ray satellite, launched in June 2008 is already returning remarkable results. In particular, it has discovered a large number of gamma-ray pulsars without any known radio counterpart (where only 1 was known prior to launch) and has detected unknown sources of gamma-ray radiation in the galactic plane with arcmin positional accuracy. Here we request time to (a) search the gamma-ray pulsars for radio pulsations using very deep integrations at 1.4 GHz and (b) search the unidentified galactic plane sources for radio pulsars. Detecting (or not) pulsars in the former case will help to distinguish between models of gamma-ray emission in pulsars. Detection of radio pulsars in the latter case will enable a search for gamma-ray pulsations to be made and/or determine other causes (such as pulsar wind nebulae) for the gamma-ray emission.

Keith, Michael; Johnston, Simon; Romani, Roger W.; Thompson, David J.; Weltevrede, Patrick; Michelson, Peter

2009-04-01

337

Physical constraints on models of gamma-ray bursters  

SciTech Connect

This report deals with the constraints that can be placed on models of gamma-ray burst sources based on only the well-established observational facts and physical principles. The premise is developed that the very hard x-ray and gamma-ray continua spectra are well-established aspects of gamma-ray bursts. Recent theoretical work on gamma-ray bursts are summarized with emphasis on the geometrical properties of the models. Constraints on the source models which are implied by the x-ray and gamma-ray spectra are described. The allowed ranges for the luminosity and characteristic dimension for gamma-ray burst sources are shown. Some of the deductions and inferences about the nature of the gamma-ray burst sources are summarized. 67 refs., 3 figs.

Epstein, R.I.

1985-01-01

338

Solar Two Gamma-Ray Observatory  

NASA Astrophysics Data System (ADS)

The field of high energy gamma-ray astronomy grew tremendously in the last decade due to the launch of the EGRET detector on the Compton Gamma-Ray Observatory in 1991 and the proliferation of ground-based air ?herenkov telescopes (ACTs) such as the Whipple 10 meter reflector. Interestingly, the ground-based telescopes only see 4-5 of the over 170 objects detected by EGRET. A simple extrapolation of the EGRET objects' energy spectra up to the energies which the ACTs are sensitive suggests that many of them should have been detected. The key to resolving this lack of detections is to observe these sources in the previously unobserved 20-250 GeV energy range. The Solar Two Observatory collaboration is developing a secondary optics system on the central tower of the world's largest solar energy pilot plant, Solar Two, to observe gamma-ray sources in this energy range. The progress in building the secondary optics system to be used to image ˜64 heliostats at Solar Two located in Barstow, California, is presented. We hope to design and build this detector over the next 2 years.

Tümer, T.; Bhattacharya, D.; Mohideen, U.; Rieben, R.; Souchkov, V.; Tom, H.; Zweerink, J.

1999-06-01

339

Afterglow Radiation from Gamma Ray Bursts  

SciTech Connect

Gamma-ray bursts (GRB) are huge fluxes of gamma rays that appear randomly in the sky about once a day. It is now commonly accepted that GRBs are caused by a stellar object shooting off a powerful plasma jet along its rotation axis. After the initial outburst of gamma rays, a lower intensity radiation remains, called the afterglow. Using the data from a hydrodynamical numerical simulation that models the dynamics of the jet, we calculated the expected light curve of the afterglow radiation that would be observed on earth. We calculated the light curve and spectrum and compared them to the light curves and spectra predicted by two analytical models of the expansion of the jet (which are based on the Blandford and McKee solution of a relativistic isotropic expansion; see Sari's model [1] and Granot's model [2]). We found that the light curve did not decay as fast as predicted by Sari; the predictions by Granot were largely corroborated. Some results, however, did not match Granot's predictions, and more research is needed to explain these discrepancies.

Desmond, Hugh; /Leuven U. /SLAC

2006-08-28

340

Thermonuclear model for. gamma. -ray bursts  

SciTech Connect

The production of ..gamma..-ray bursts by thermonuclear explosions on strongly magnetized nuetron stars is examined. For a neutron star with a magnetic field strength of several times 10/sup 12/ gauss, accretion at approx.10/sup -13/ M/sub sun/ yr/sup -1/ is focused onto kilometer sized regions. The accreted material is confined above the surface by the magnetic field and by a combination of magnetic and crustal stresses below the surface. Stable hydrogen burning leads to a critical helium mass that, depending upon model parameters, explodes either by convective deflagration or detonation, liberating 10/sup 38/--10/sup 40/ ergs km/sup -2/ of thermonuclear energy. Multibillion degree plasma pushed above the surface by the explosion has ..beta..>1 and therefore expands and stresses the magnetic field. Hard emission comes both from the magnetically confined photosphere and from relativistic electrons accelerated by magnetic field recombination. The hard ..gamma..-ray outburst of several seconds is followed by an enduring, softer emission of X-rays, lasting from several minutes to an hour, as the subsurface ashes of the thermonuclear explosion cool. Gamma-ray bursters, at a typical distance of several hundred parsecs, should recur on a time scale of months (low energy) to centuries (high energy). Special attention is given to the spectracular event of 1979 March 5.

Woosley, S.E.; Wallace, R.K.

1982-07-15

341

Gamma Ray Burst All-Sky Spectrometer  

NASA Astrophysics Data System (ADS)

The Gamma Ray Burst All-Sky Spectrometer Experiment (GASE) is designed to detect radio emission from gamma ray bursts (GRB's). Radio emission from GRB's could help us better understand the plasma physics of the blast and might also help us measure dark energy. GASE uses short-baseline interferometry with eight dipole antennas located at the MIT Haystack Observatory. These antennas measure the radiofrequency sky at 30 MHz over a 4 MHz bandwidth and are able to collect information from the entire sky. Since the entire sky is surveyed, radio frequency interference occurring at the horizon can be eliminated as a transient source. Along with the SWIFT satellite and the Gamma Ray Burst Coordinate system, we will be able measure blast time, duration and position. We are currently designing techniques to calibrate and image the full sky in radio. In addition to locating and measuring GRB's, GASE may be able to measure dark energy due to the dispersion by the IGM. The pulse of radio emission is delayed as it travels through the intergalactic plasma, with longer wavelengths taking longer to arrive than shorter wavelengths. With the known free electron density (?m) we will use the dispersion measure to calculate the line of sight distance to the GRB and compare to the observed redshift to measure dark energy.

Steger, Arielle

2011-05-01

342

Gamma rays as an indicator of nucleosynthesis  

NASA Astrophysics Data System (ADS)

In 1957 the collaboration of E. M. Burbidge, G. R. Burbidge, W. A. Fowler, and F. Hoyle, and the work by A. G. W. Cameron, laid the foundations for understanding the origin of the elements in terms of a few basic processes and astrophysical environments. Half a century after this pioneering work, there is considerable observational evidence for the basic notions of element synthesis during the big-bang, followed by hydrostatic and explosive stellar nucleosynthesis ever since the first population of stars re-illuminated the Universe, and through particle interactions in the turbulent interstellar medium. In 1969 D. D. Clayton, S. A. Colgate, and G. J. Fishman proposed to search for gamma-ray lines from the decay of 56-Ni, freshly synthesized in supernovae. Evidence for these lines was obtained for SN 1987A, and three decades after this pivotal supernova we have ample gamma-ray line evidence for ongoing nucleosynthesis in the Milky Way from surveys for individual sources and unresolved, integrated diffuse emission from an ensemble of such sources. We review the observational evidence for gamma ray lines from various species, and discuss the astrophysical implications of detections and a few puzzles suggested by lack of detections. We reflect on historic developments, assess the accomplishments, and present an outlook on the future of this branch of nuclear astrophysics.

Hartmann, Dieter H.

2007-04-01

343

GAMMA-RAY VARIABILITY FROM WIND CLUMPING IN HIGH-MASS X-RAY BINARIES WITH JETS  

SciTech Connect

In the subclass of high-mass X-ray binaries known as 'microquasars', relativistic hadrons in the jets launched by the compact object can interact with cold protons from the star's radiatively driven wind, producing pions that then quickly decay into gamma rays. Since the resulting gamma-ray emissivity depends on the target density, the detection of rapid variability in microquasars with Gamma-Ray Large Area Space Telescope and the new generation of Cherenkov imaging arrays could be used to probe the clumped structure of the stellar wind. We show here that the fluctuation in gamma rays can be modeled using a 'porosity length' formalism, usually applied to characterize clumping effects. In particular, for a porosity length defined by h {identical_to} l/f, i.e., as the ratio of the characteristic size l of clumps to their volume filling factor f, we find that the relative fluctuation in gamma-ray emission in a binary with orbital separation a scales as {radical}(h/{pi}a) in the 'thin-jet' limit, and is reduced by a factor 1/{radical}(1 +{phi}a/2l) for a jet with a finite opening angle {phi}. For a thin jet and quite moderate porosity length h {approx} 0.03a, this implies a ca. 10% variation in the gamma-ray emission. Moreover, the illumination of individual large clumps might result in isolated flares, as has been recently observed in some massive gamma-ray binaries.

Owocki, S. P.; Townsend, R. H. D. [Bartol Research Institute, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States); Romero, G. E.; Araudo, A. T. [Inst. Argentino de RadioastronomIa (CCT La Plata, CONICET), C.C.5, 1894 Villa Elisa, Buenos Aires (Argentina)

2009-05-01

344

A link between prompt optical and prompt gamma-ray emission in gamma-ray bursts.  

PubMed

The prompt optical emission that arrives with the gamma-rays from a cosmic gamma-ray burst (GRB) is a signature of the engine powering the burst, the properties of the ultra-relativistic ejecta of the explosion, and the ejecta's interactions with the surroundings. Until now, only GRB 990123 had been detected at optical wavelengths during the burst phase. Its prompt optical emission was variable and uncorrelated with the prompt gamma-ray emission, suggesting that the optical emission was generated by a reverse shock arising from the ejecta's collision with surrounding material. Here we report prompt optical emission from GRB 041219a. It is variable and correlated with the prompt gamma-rays, indicating a common origin for the optical light and the gamma-rays. Within the context of the standard fireball model of GRBs, we attribute this new optical component to internal shocks driven into the burst ejecta by variations of the inner engine. The correlated optical emission is a direct probe of the jet isolated from the medium. The timing of the uncorrelated optical emission is strongly dependent on the nature of the medium. PMID:15889084

Vestrand, W T; Wozniak, P R; Wren, J A; Fenimore, E E; Sakamoto, T; White, R R; Casperson, D; Davis, H; Evans, S; Galassi, M; McGowan, K E; Schier, J A; Asa, J W; Barthelmy, S D; Cummings, J R; Gehrels, N; Hullinger, D; Krimm, H A; Markwardt, C B; McLean, K; Palmer, D; Parsons, A; Tueller, J

2005-05-12

345

Jet simulations and gamma-ray burst afterglow jet breaks  

NASA Astrophysics Data System (ADS)

The conventional derivation of the gamma-ray burst afterglow jet break time uses only the blast wave fluid Lorentz factor and therefore leads to an achromatic break. We show that in general gamma-ray burst afterglow jet breaks are chromatic across the self-absorption break. Depending on circumstances, the radio jet break may be postponed significantly. Using high-accuracy adaptive mesh fluid simulations in one dimension, coupled to a detailed synchrotron radiation code, we demonstrate that this is true even for the standard fireball model and hard-edged jets. We confirm these effects with a simulation in two dimensions. The frequency dependence of the jet break is a result of the angle dependence of the emission, the changing optical depth in the self-absorbed regime and the shape of the synchrotron spectrum in general. In the optically thin case the conventional analysis systematically overestimates the jet break time, leading to inferred opening angles that are underestimated by a factor of ˜1.3 and explosion energies that are underestimated by a factor of ˜1.7, for explosions in a homogeneous environment. The methods presented in this paper can be applied to adaptive mesh simulations of arbitrary relativistic fluid flows. All analysis presented here makes the usual assumption of an on-axis observer.

van Eerten, H. J.; Meliani, Z.; Wijers, R. A. M. J.; Keppens, R.

2011-01-01

346

GRIPS - Gamma-Ray Imaging, Polarimetry and Spectroscopy  

NASA Astrophysics Data System (ADS)

We propose to perform a continuously scanning all-sky survey from 200 keV to 80 MeV achieving a sensitivity which is better by a factor of 40 or more compared to the previous missions in this energy range (COMPTEL, INTEGRAL; see Fig. 1). These gamma-ray observations will be complemented by observations in the soft X-ray and (near-)infrared region with the corresponding telescopes placed on a separate satellite. The Gamma-Ray Imaging, Polarimetry and Spectroscopy (" GRIPS") mission with its three instruments Gamma-Ray Monitor (GRM), X-Ray Monitor (XRM) and InfraRed Telescope (IRT) addresses fundamental questions in ESA's Cosmic Vision plan. Among the major themes of the strategic plan, GRIPS has its focus on the evolving, violent Universe, exploring a unique energy window. We propose to investigate ?-ray bursts and blazars, the mechanisms behind supernova explosions, nucleosynthesis and spallation, the enigmatic origin of positrons in our Galaxy, and the nature of radiation processes and particle acceleration in extreme cosmic sources including pulsars and magnetars. The natural energy scale for these non-thermal processes is of the order of MeV. Although they can be partially and indirectly studied using other methods, only the proposed GRIPS measurements will provide direct access to their primary photons. GRIPS will be a driver for the study of transient sources in the era of neutrino and gravitational wave observatories such as IceCUBE and LISA, establishing a new type of diagnostics in relativistic and nuclear astrophysics. This will support extrapolations to investigate star formation, galaxy evolution, and black hole formation at high redshifts.

Greiner, Jochen; Mannheim, Karl; Aharonian, Felix; Ajello, Marco; Balasz, Lajos G.; Barbiellini, Guido; Bellazzini, Ronaldo; Bishop, Shawn; Bisnovatij-Kogan, Gennady S.; Boggs, Steven; Bykov, Andrej; DiCocco, Guido; Diehl, Roland; Elsässer, Dominik; Foley, Suzanne; Fransson, Claes; Gehrels, Neil; Hanlon, Lorraine; Hartmann, Dieter; Hermsen, Wim; Hillebrandt, Wolfgang; Hudec, Rene; Iyudin, Anatoli; Jose, Jordi; Kadler, Matthias; Kanbach, Gottfried; Klamra, Wlodek; Kiener, Jürgen; Klose, Sylvio; Kreykenbohm, Ingo; Kuiper, Lucien M.; Kylafis, Nikos; Labanti, Claudio; Langanke, Karlheinz; Langer, Norbert; Larsson, Stefan; Leibundgut, Bruno; Laux, Uwe; Longo, Francesco; Maeda, Kei'ichi; Marcinkowski, Radoslaw; Marisaldi, Martino; McBreen, Brian; McBreen, Sheila; Meszaros, Attila; Nomoto, Ken'ichi; Pearce, Mark; Peer, Asaf; Pian, Elena; Prantzos, Nikolas; Raffelt, Georg; Reimer, Olaf; Rhode, Wolfgang; Ryde, Felix; Schmidt, Christian; Silk, Joe; Shustov, Boris M.; Strong, Andrew; Tanvir, Nial; Thielemann, Friedrich-Karl; Tibolla, Omar; Tierney, David; Trümper, Joachim; Varshalovich, Dmitry A.; Wilms, Jörn; Wrochna, Grzegorz; Zdziarski, Andrzej; Zoglauer, Andreas

2012-10-01

347

Soft Gamma-Ray Repeaters and Magnetars  

NASA Astrophysics Data System (ADS)

The history and observational properties of the soft gamma repeaters are reviewed in this Chapter. Over the past decades, we have gone from viewing these objects as a special class of cosmic gamma-ray burst, to seeing them as one manifestation of magnetars. There is now a solid body of multiwavelength observations, as well as some more controversial properties. There are still a number of fundamental unanswered questions, which will require better theory, more sensitive observations, and many years to answer. The story of the soft gamma repeaters (SGRs) begins in 1979. On January 7th, a short duration, soft spectrum burst was observed from the direction of the Galactic center [28]. At that time, relatively little was known about cosmic gamma-ray bursts (GRBs), but their energy spectra, as observed up to that point, were clearly “hard,” containing photons up to hundreds of keV and beyond. On the other hand, it was clear that the spectrum of the January 7 event was much softer than that of a GRB, i.e., with little emission beyond 100 keV. The event was called “a gamma-ray burst without the gamma-rays.” Several months later, the most intense gamma-ray transient which had been observed up to that time, the March 5, 1979 burst, was detected. This event had a hard spectrum and a long duration, with a pulsating tail, and it was localized to the N49 supernova remnant in the Large Magellanic Cloud [3,7]. At the distance of the LMC, the intensity of this burst was >103 times the Eddington luminosity. And in the days that followed, smaller bursts were detected from the source [31]. Many theories were proposed to explain this event, which was generally thought to be an unusual GRB. Several weeks later, another repeating source was discovered when it emitted three short duration, soft spectrum bursts in 3 days [32]. Finally, between July and December 1987, yet another repeater was discovered [2]. This object turned out to be the same as the one which had been detected on January 7, 1979. The source was named SGR1806-20, with SGR standing both for the constellation (Sagittarius) and for Soft Gamma Repeater, to distinguish it from the GRBs.

Hurley, Kevin

348

CdZnTe gamma ray spectrometer for orbital gamma ray spectroscopy.  

SciTech Connect

We present the design and analysis of a new gamma ray spectrometer for planetary science that uses an array of CdZnTe detectors to achieve the detection efficiency needed for orbital measurements. The use of CdZnTe will provide significantly improved pulse height resolution relative to scintillation-based detectors, with commensurate improvement in the accuracy of elemental abundances determined by gamma ray and neutron spectroscopy. The spectrometer can be flown either on the instrument deck of the spacecraft or on a boom. For deck-mounted systems, a BGO anticoincidence shield is included in the design to suppress the response of the CdZnTe detector to gamma rays that originate in the spacecraft. The BGO shield also serves as a backup spectrometer, providing heritage from earlier planetary science missions and reducing the risk associated with the implementation of new technology.

Prettyman, T. H. (Thomas H.); Feldman, W. C. (William C.); Fuller, K. R. (Kenneth R.); Storms, S. A. (Steven A.); Soldner, S. A.; Lawrence, David J. (David Jeffery),; Browne, M. C. (Michael C.); Moss, C. E. (Calvin E.)

2001-01-01

349

A Balloon-Borne Gamma-Ray Polarimeter for Gamma-Ray Bursts  

NASA Astrophysics Data System (ADS)

We have developed a design for a hard X-ray polarimeter operating in the energy range from 50 to 500 keV. This modular design, known as GRAPE (Gamma-Ray Polarimeter Experiment), was successfully demonstrated with partially polarized gamma-ray sources in the lab and fully polarized photon beams at Argonne National Laboratory. In June of 2007, a GRAPE engineering model flew on a high altitude balloon flight which demonstrated the design and collected background data. A much larger payload is currently under development that will provide a significant level of sensitivity for gamma-ray bursts on a long-duration balloon flight. The first balloon flight of the full GRAPE instrument is currently scheduled to take place in the Fall of 2011 from Ft. Sumner, NM.

McConnell, M. L.; Bancroft, C. M.; Bloser, P. F.; Connor, T. P.; Legere, J. S.; Macri, J. R.; Ryan, J. M.

2009-05-01

350

E1 and E2S factors of C12(alpha,gamma0)O16 from gamma-ray angular distributions with a 4 pi-detector array  

Microsoft Academic Search

A new experiment to determine the thermonuclear cross section of the C12(alpha,gamma)O16 reaction has been performed in regular kinematics using an intense alpha-particle beam of up to 340 muA from the Stuttgart DYNAMITRON. For the first time, a 4pi-germanium-detector setup has been used to measure the angular distribution of the gamma rays at all angles simultaneously. It consisted of an

M. Assunçăo; M. Fey; A. Lefebvre-Schuhl; J. Kiener; V. Tatischeff; J. W. Hammer; C. Beck; C. Boukari-Pelissie; A. Coc; J. J. Correia; S. Courtin; F. Fleurot; E. Galanopoulos; C. Grama; F. Haas; F. Hammache; F. Hannachi; S. Harissopulos; A. Korichi; R. Kunz; D. Ledu; A. Lopez-Martens; D. Malcherek; R. Meunier; Th. Paradellis; M. Rousseau; N. Rowley; G. Staudt; S. Szilner; J. P. Thibaud; J. L. Weil

2006-01-01

351

Gamma-Ray Burst Central Engines: Black Hole Versus Magnetar  

NASA Astrophysics Data System (ADS)

Discovered over forty years ago, Gamma-Ray Bursts (GRBs) remain a forefront topic in modern astrophysics. Perhaps the most fundamental question associated with GRBs is the nature of the astrophysical agent (or agents) that ultimately powers them: the central engine. In this review, I focus on the possible central engines of long-duration GRBs, and the constraints that present observations place on these models. Long GRBs are definitively associated with the deaths of massive stars, but whether the central engine is an accreting black hole or a rapidly-spinning, highly-magnetized neutron star (a “proto-magnetar”) remains unsettled. This distinction has been brought into particular focus by recent MHD simulations of the core-collapse of massive, rotating “collapsar progenitors,” which suggest that powerful magneto-centrifugal outflows from the proto-neutron star may stave off black hole formation entirely. Although both black hole and magnetar GRB models remain viable, I argue that the magnetar model is more mature in the sense that it provides quantitative explanations for the durations, energies, Lorentz factors, and collimation of long GRB outflows. Given these virtues, one promising strategy to break the present stalemate is to further develop the magnetar model until inescapable (and falsifiable) predictions emerge. This course of action signals a renewed challenge to translate time-dependent jet properties (power, magnetization, and Lorentz factor) into observables (gamma-ray light curves and spectra).

Metzger, B. D.

2010-10-01

352

Implications of the VHE {gamma}-Ray Detection of 3C279  

SciTech Connect

We present simultaneous optical (BVRI) and X-ray (RXTE PCA) data on the quasar 3C279 from the day of the recent VHE detection by MAGIC and discuss the implications of the snap-shot spectral energy distribution (SED) for leptonic jet models of blazars. A one-zone synchrotron-self-Compton origin of the SED up to VHE {gamma}-rays can be ruled out. The VHE emission could, in principle, be interpreted as Compton upscattering of external radiation (e.g., from the broad-line regions) in a one-zone leptonic model. However, such an interpretation would require either an unusually low magnetic field of B{approx}0.03 G, or (in order to achieve approximate equipartition between magnetic field at B{approx}0.25 G and relativistic electrons) an unrealistically high Doppler factor of {gamma}{approx}140. In addition, such a model fails to reproduce the observed X-ray flux. We therefore conclude that a simple one-zone, homogeneous leptonic jet model is not able to plausibly reproduce the SED of 3C279 including the recently detected VHE {gamma}-ray emission. This as well as the lag of correlated variability in the optical with the VHE {gamma}-ray emission suggests a multi-zone model in which the optical emission is produced in a different region than the VHE {gamma}-ray emission. Alternatively, also a hadronic origin of the VHE {gamma}-rays seems plausible.

Boettcher, M. [Astrophysical Institute, Department of Physics and Astronomy, Ohio University, Athens, OH 45701 (United States)

2008-12-24

353

A STATISTICAL MODEL FOR THE {gamma}-RAY VARIABILITY OF THE CRAB NEBULA  

SciTech Connect

A statistical scenario is proposed to explain the {gamma}-ray variability and flares of the Crab Nebula, which were observed recently by the Fermi/LAT. In this scenario electrons are accelerated in a series of knots, whose sizes follow a power-law distribution. These knots presumably move outward from the pulsar and have a distribution in the Doppler boost factor. The maximal electron energy is assumed to be proportional to the size of the knot. Fluctuations at the highest energy end of the overall electron distribution will result in variable {gamma}-ray emission via the synchrotron process in the {approx}100 MeV range. Since highly boosted larger knots are rarer than smaller knots, the model predicts that the variability of the synchrotron emission increases with the photon energy. We realize such a scenario with a Monte Carlo simulation and find that the model can reproduce both the two {gamma}-ray flares over a period of {approx}1 year and the monthly scale {gamma}-ray flux fluctuations as observed by the Fermi/LAT. The observed {gamma}-ray spectra in both the steady and flaring states are also well reproduced.

Yuan Qiang; Yin Pengfei; Bi Xiaojun [Key Laboratory of Particle Astrophysics, Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Wu Xuefeng; Zhang Bing [Department of Physics and Astronomy, University of Nevada Las Vegas, Las Vegas, NV 89154 (United States); Liu Siming [Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210008 (China)

2011-04-01

354

Common Gamma-ray Glows above Thunderclouds  

NASA Astrophysics Data System (ADS)

Gamma-ray glows are continuous, long duration gamma- and x-ray emission seen coming from thunderclouds. The Airborne for Energetic Lightning Emissions (ADELE) observed 12 gamma-ray glows during its summer 2009 flight campaign over the areas of Colorado and Florida in the United States. For these glows we shall present their spectra, relationship to lightning activity and how their duration and size changes as a function of distance. Gamma-ray glows follow the relativistic runaway electron avalanche (RREA) spectrum and have been previously measured from the ground and inside the cloud. ADELE measured most glows as it flew above the screening layer of the cloud. During the brightest glow on August 21, 2009, we can show that we are flying directly into a downward facing relativistic runaway avalanche, indicative of flying between the upper positive and negative screening layer of the cloud. In order to explain the brightness of this glow, RREA with an electric field approaching the limit for relativistic feedback must be occurring. Using all 12 glows, we show that lightning activity diminishes during the onset of the glow. Using this along with the fact that glows occur as the field approaches the level necessary for feedback, we attempt to distinguish between two possibilities: that glows are evidence that RREA with feedback, rather than lightning, is sometimes the primary channel for discharging the cloud, or else that the overall discharging is still controlled by lightning, with glows simply appearing during times when a subsidence of lightning allows the field to rise above the threshold for RREA.

Kelley, Nicole; Smith, David; Dwyer, Joseph; Hazelton, Bryna; Grefenstette, Brian; Lowell, Alex; Splitt, Michael; Lazarus, Steven; Rassoul, Hamid

2013-04-01

355

Crab Nebula Gamma-ray Flares as Relativistic Reconnection Minijets  

NASA Astrophysics Data System (ADS)

We present an analytic statistical model of relativistic magnetic reconnection outflows (``minijets") that can describe the Crab Nebula gamma-ray light curve, including the multiple ? week-long flares observed by the AGILE and Fermi/LAT satellites. We argue that the flares' unusually short duration, high luminosity, and high photon energies suggest the flare emission regions are moving toward Earth at bulk relativistic speeds, consistent with reconnection minijets. We show that electrostatic acceleration in the reconnecting region can efficiently accelerate particles up to the radiation reaction limit to produce a mono-energetic synchrotron spectral energy distribution. The statistics of observed minijet high energy fluxes and timescales are assumed to be strongly influenced by their Doppler factors. For statistically independent minijets, we find analytical expressions for all of the moments of the high energy nebular light curve (time average, variance, skewness, etc.). The short timescale variability of the nebula displays a power spectrum with index -2. In the limit of a low reconnection event rate, the observed flare high energy flux distribution follows a power-law of index $\\sim -1$, implying that the flare high energy flux average is dominated by bright rare flares. Thus, we provide a simple minijet statistical model of the Crab Nebula light curve that can be directly compared with gamma-ray observations.

Clausen-Brown, Eric Ryan; Lyutikov, M.

2012-01-01

356

Gamma ray spectroscopy and timing using LSO and PIN photodiodes  

SciTech Connect

The high density, high light output, and short decay time of LSO (lutetium orthosilicate, Lu{sub 2}SiO{sub 5}:Ce) make it an attractive scintillator for gamma ray spectroscopy. The low cost, small size, high quantum efficiency, and ruggedness of silicon photodiodes make them attractive photodetectors for this same application, although their high noise (compared to a photomultiplier tube) reduces their appeal. In this work the authors measure the gamma ray energy resolution, timing accuracy, and conversion factor from gamma energy to number of electron-hole pairs produced with a 3 x 3 x 22 mm{sup 3} LSO scintillator crystal read out with a 3 x 3 mm{sup 2} silicon PIN photodiode. When the detector is excited with 511 keV photons, a photopeak centered at 4,910 e{sup {minus}} with 149 keV fwhm is observed and a timing signal with 25 ns fwhm jitter is produced. While these performance measures are inferior to those obtained with photomultiplier tubes, they are acceptable for some applications.

Moses, W.W.; Derenzo, S.E. [Lawrence Berkeley Lab., CA (United States); Melcher, C.L.; Manente, R.A. [Schlumberger-Doll Research, Ridgefield, CT (United States)

1995-08-01

357

Observational evidence of dissipative photospheres in gamma-ray bursts  

NASA Astrophysics Data System (ADS)

The emission from a gamma-ray burst (GRB) photosphere can give rise to a variety of spectral shapes. The spectrum can retain the shape of a Planck function or it can be broadened and have the shape of a Band function. This fact is best illustrated by studying GRB090902B. The main gamma-ray spectral component is initially close to a Planck function, which can only be explained by emission from the jet photosphere. Later, the same component evolves into a broader Band function. This burst thus provides observational evidence that the photosphere can give rise to a non-thermal spectrum. We show that such a broadening is most naturally explained by subphotospheric dissipation in the jet. The broadening mainly depends on the strength and location of the dissipation, the magnetic field strength and the relation between the energy densities of thermal photons and electrons. We suggest that the evolution in spectral shape observed in GRB090902B is due to a decrease in the bulk Lorentz factor of the flow, leading to the main dissipation becoming subphotospheric. Such a change in the flow parameters can also explain the correlation observed between the peak energy of the spectrum and low-energy power-law slope, ?, a correlation commonly observed in GRBs. We conclude that photospheric emission could indeed be a ubiquitous feature during the prompt phase in GRBs and play a decisive role in creating the diverse spectral shapes and spectral evolutions that are observed.

Ryde, Felix; Pe'Er, Asaf; Nymark, Tanja; Axelsson, Magnus; Moretti, Elena; Lundman, Christoffer; Battelino, Milan; Bissaldi, Elisabetta; Chiang, James; Jackson, Miranda S.; Larsson, Stefan; Longo, Francesco; McGlynn, Sinead; Omodei, Nicola

2011-08-01

358

Simulation of prompt gamma-ray emission during proton radiotherapy.  

PubMed

The measurement of prompt gamma rays emitted from proton-induced nuclear reactions has been proposed as a method to verify in vivo the range of a clinical proton radiotherapy beam. A good understanding of the prompt gamma-ray emission during proton therapy is key to develop a clinically feasible technique, as it can facilitate accurate simulations and uncertainty analysis of gamma detector designs. Also, the gamma production cross-sections may be incorporated as prior knowledge in the reconstruction of the proton range from the measurements. In this work, we performed simulations of proton-induced nuclear reactions with the main elements of human tissue, carbon-12, oxygen-16 and nitrogen-14, using the nuclear reaction models of the GEANT4 and MCNP6 Monte Carlo codes and the dedicated nuclear reaction codes TALYS and EMPIRE. For each code, we made an effort to optimize the input parameters and model selection. The results of the models were compared to available experimental data of discrete gamma line cross-sections. Overall, the dedicated nuclear reaction codes reproduced the experimental data more consistently, while the Monte Carlo codes showed larger discrepancies for a number of gamma lines. The model differences lead to a variation of the total gamma production near the end of the proton range by a factor of about 2. These results indicate a need for additional theoretical and experimental study of proton-induced gamma emission in human tissue. PMID:22864267

Verburg, Joost M; Shih, Helen A; Seco, Joao

2012-08-03

359

Fermi observations of high-energy gamma-ray emission from GRB 080916C.  

PubMed

Gamma-ray bursts (GRBs) are highly energetic explosions signaling the death of massive stars in distant galaxies. The Gamma-ray Burst Monitor and Large Area Telescope onboard the Fermi Observatory together record GRBs over a broad energy range spanning about 7 decades of gammaray energy. In September 2008, Fermi observed the exceptionally luminous GRB 080916C, with the largest apparent energy release yet measured. The high-energy gamma rays are observed to start later and persist longer than the lower energy photons. A simple spectral form fits the entire GRB spectrum, providing strong constraints on emission models. The known distance of the burst enables placing lower limits on the bulk Lorentz factor of the outflow and on the quantum gravity mass. PMID:19228997

Abdo, A A; Ackermann, M; Arimoto, M; Asano, K; Atwood, W B; Axelsson, M; Baldini, L; Ballet, J; Band, D L; Barbiellini, G; Baring, M G; Bastieri, D; Battelino, M; Baughman, B M; Bechtol, K; Bellardi, F; Bellazzini, R; Berenji, B; Bhat, P N; Bissaldi, E; Blandford, R D; Bloom, E D; Bogaert, G; Bogart, J R; Bonamente, E; Bonnell, J; Borgland, A W; Bouvier, A; Bregeon, J; Brez, A; Briggs, M S; Brigida, M; Bruel, P; Burnett, T H; Burrows, D; Busetto, G; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Ceccanti, M; Cecchi, C; Celotti, A; Charles, E; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Cominsky, L R; Connaughton, V; Conrad, J; Costamante, L; Cutini, S; Deklotz, M; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; Dingus, B L; do Couto E Silva, E; Drell, P S; Dubois, R; Dumora, D; Edmonds, Y; Evans, P A; Fabiani, D; Farnier, C; Favuzzi, C; Finke, J; Fishman, G; Focke, W B; Frailis, M; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Germani, S; Giebels, B; Giglietto, N; Giommi, P; Giordano, F; Glanzman, T; Godfrey, G; Goldstein, A; Granot, J; Greiner, J; Grenier, I A; Grondin, M-H; Grove, J E; Guillemot, L; Guiriec, S; Haller, G; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hernando Morat, J A; Hoover, A; Hughes, R E; Jóhannesson, G; Johnson, A S; Johnson, R P; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kavelaars, A; Kawai, N; Kelly, H; Kennea, J; Kerr, M; Kippen, R M; Knödlseder, J; Kocevski, D; Kocian, M L; Komin, N; Kouveliotou, C; Kuehn, F; Kuss, M; Lande, J; Landriu, D; Larsson, S; Latronico, L; Lavalley, C; Lee, B; Lee, S-H; Lemoine-Goumard, M; Lichti, G G; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Marangelli, B; Mazziotta, M N; McBreen, S; McEnery, J E; McGlynn, S; Meegan, C; Mészáros, P; Meurer, C; Michelson, P F; Minuti, M; Mirizzi, N; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Moretti, E; Morselli, A; Moskalenko, I V; Murgia, S; Nakamori, T; Nelson, D; Nolan, P L; Norris, J P; Nuss, E; Ohno, M; Ohsugi, T; Okumura, A; Omodei, N; Orlando, E; Ormes, J F; Ozaki, M; Paciesas, W S; Paneque, D; Panetta, J H; Parent, D; Pelassa, V; Pepe, M; Perri, M; Pesce-Rollins, M; Petrosian, V; Pinchera, M; Piron, F; Porter, T A; Preece, R; Rainň, S; Ramirez-Ruiz, E; Rando, R; Rapposelli, E; Razzano, M; Razzaque, S; Rea, N; Reimer, A; Reimer, O; Reposeur, T; Reyes, L C; Ritz, S; Rochester, L S; Rodriguez, A Y; Roth, M; Ryde, F; Sadrozinski, H F-W; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Schalk, T L; Segal, K N; Sgrň, C; Shimokawabe, T; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Stamatikos, M; Starck, J-L; Stecker, F W; Steinle, H; Stephens, T E; Strickman, M S; Suson, D J; Tagliaferri, G; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Tenze, A; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Turri, M; Tuvi, S; Usher, T L; van der Horst, A J; Vigiani, L; Vilchez, N; Vitale, V; von Kienlin, A; Waite, A P; Williams, D A; Wilson-Hodge, C; Winer, B L; Wood, K S; Wu, X F; Yamazaki, R; Ylinen, T; Ziegler, M

2009-02-19

360

High-spin gamma-ray spectroscopy  

SciTech Connect

Nuclei can carry angular momentum by single-particle alignments and by collective motion, as has been well illustrated in discrete-line spectroscopy. From continuum ..gamma..-ray studies in still higher spin regions, it appears that these modes both continue. In favorable cases in rare-earth nuclei, particle alignments from the valence shell separate from proton alignments from the next higher shell. A new generation of Compton-suppressed Ge detector arrays will greatly enhance high-spin studies, both continuum and discrete-line. 17 references.

Diamond, R.M.

1984-03-01

361

Gamma Ray Bursts: an Enigma Being Unraveled  

SciTech Connect

The best astrophysical accelerators are quasars and the 'progenitors' of GRBs which, after decades of observations and scores of theories, we still do not understand. But, I shall argue, we now know quite well where GRBs come from, and we understand how their 'beams' behave, as they make short pulses of gamma rays and long-duration X-ray, optical and radio 'afterglows'. I shall argue that our understanding of these phenomena, based on the 'Cannonball Model', is unusually simple, precise and successful. The 'sociology' of GRBs is interesting per se and, in this sense, the avatars of the Cannonball Model in confronting the generally accepted 'fireball models' are also quite revealing.

De Rujula, Alvaro (Boston University and CERN)

2003-05-14

362

Gamma Ray Bursts In Their Historic Context  

NASA Astrophysics Data System (ADS)

Gamma ray bursts remained essentially non-understood or misunderstood from their 1973 discovery (not, I will claim, ``serendipitous'') to the first, 1997, redshift. This is by no means a record. The poster explored some of the examples of longer-standing puzzles and the after-dinner talk some of the details of the GRB case. The most striking feature of the GRB history is probably the unanimity with which ``all we, like sheep, went astray,'' which followed the epoch of ``we have turned everyone to his own way.'' Some of the reasons for this, the range of hypotheses, and how GRBs were presented to the astronomical and larger communities are discussed.

Trimble, Virginia

2004-09-01

363

Gamma Rays from Heavy Neutralino Dark Matter  

SciTech Connect

We consider the gamma-ray spectrum from neutralino dark matter annihilations and show that internal bremsstrahlung of W pair final states gives a previously neglected source of photons at energies near the mass of the neutralino. For masses larger than about 1 TeV, and for present day detector resolutions, this results in a characteristic signal that may dominate not only over the continuous spectrum from W fragmentation, but also over the {gamma}{gamma} and {gamma}Z line signals which are known to give large rates for heavy neutralinos. Observational prospects thus seem promising.

Bergstroem, Lars; Bringmann, Torsten; Eriksson, Martin; Gustafsson, Michael [Department of Physics, Stockholm University, AlbaNova University Center, SE - 106 91 Stockholm (Sweden)

2005-12-09

364

PRECURSORS OF SHORT GAMMA-RAY BURSTS  

SciTech Connect

We carried out a systematic search of precursors on the sample of short gamma-ray bursts (GRBs) observed by Swift. We found that {approx}8%-10% of short GRBs display such early episodes of emission. One burst (GRB 090510) shows two precursor events, the former {approx}13 s and the latter {approx}0.5 s before the GRB. We did not find any substantial difference between the precursor and the main GRB emission, and between short GRBs with and without precursors. We discuss possible mechanisms to reproduce the observed precursor emission within the scenario of compact object mergers. The implications of our results on quantum gravity constraints are also discussed.

Troja, E.; Gehrels, N. [NASA, Goddard Space Flight Center, Greenbelt, MD 20771 (United States); Rosswog, S. [School of Engineering and Science, Jacobs University Bremen, Campus Ring 1, 28759 Bremen (Germany)

2010-11-10

365

Material recognition using fission gamma rays  

NASA Astrophysics Data System (ADS)

Material recognition is studied by measuring the transmission spectrum of 252Cf fission gamma rays in the energy range E?=0.1-5.5 MeV for 0.1-MeV-wide energy bins through a number of elementary samples. Each transmitted spectrum is compared with a library of reference spectra for different elements providing the possibility of material identification. In case of elemental samples with known thickness, this procedure allows the identification of the sample Z with uncertainty typically lower than 3 Z-units over a wide range of elements. Applications to composite materials are also reported.

Viesti, G.; Sajo-Bohus, L.; Fabris, D.; Lunardon, M.; Moretto, S.; Nebbia, G.; Pesente, S.

2009-07-01

366

Fermi gamma-ray imaging of a radio galaxy.  

PubMed

The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from the giant radio lobes of the radio galaxy Centaurus A. The resolved gamma-ray image shows the lobes clearly separated from the central active source. In contrast to all other active galaxies detected so far in high-energy gamma-rays, the lobe flux constitutes a considerable portion (greater than one-half) of the total source emission. The gamma-ray emission from the lobes is interpreted as inverse Compton-scattered relic radiation from the cosmic microwave background, with additional contribution at higher energies from the infrared-to-optical extragalactic background light. These measurements provide gamma-ray constraints on the magnetic field and particle energy content in radio galaxy lobes, as well as a promising method to probe the cosmic relic photon fields. PMID:20360067

Abdo, A A; Ackermann, M; Ajello, M; Atwood, W B; Baldini, L; Ballet, J; Barbiellini, G; Bastieri, D; Baughman, B M; Bechtol, K; Bellazzini, R; Berenji, B; Blandford, R D; Bloom, E D; Bonamente, E; Borgland, A W; Bregeon, J; Brez, A; Brigida, M; Bruel, P; Burnett, T H; Buson, S; Caliandro, G A; Cameron, R A; Caraveo, P A; Casandjian, J M; Cavazzuti, E; Cecchi, C; Celik, O; Chekhtman, A; Cheung, C C; Chiang, J; Ciprini, S; Claus, R; Cohen-Tanugi, J; Colafrancesco, S; Cominsky, L R; Conrad, J; Costamante, L; Cutini, S; Davis, D S; Dermer, C D; de Angelis, A; de Palma, F; Digel, S W; do Couto e Silva, E; Drell, P S; Dubois, R; Dumora, D; Farnier, C; Favuzzi, C; Fegan, S J; Finke, J; Focke, W B; Fortin, P; Fukazawa, Y; Funk, S; Fusco, P; Gargano, F; Gasparrini, D; Gehrels, N; Georganopoulos, M; Germani, S; Giebels, B; Giglietto, N; Giordano, F; Giroletti, M; Glanzman, T; Godfrey, G; Grenier, I A; Grove, J E; Guillemot, L; Guiriec, S; Hanabata, Y; Harding, A K; Hayashida, M; Hays, E; Hughes, R E; Jackson, M S; Jóhannesson, G; Johnson, A S; Johnson, T J; Johnson, W N; Kamae, T; Katagiri, H; Kataoka, J; Kawai, N; Kerr, M; Knödlseder, J; Kocian, M L; Kuss, M; Lande, J; Latronico, L; Lemoine-Goumard, M; Longo, F; Loparco, F; Lott, B; Lovellette, M N; Lubrano, P; Madejski, G M; Makeev, A; Mazziotta, M N; McConville, W; McEnery, J E; Meurer, C; Michelson, P F; Mitthumsiri, W; Mizuno, T; Moiseev, A A; Monte, C; Monzani, M E; Morselli, A; Moskalenko, I V; Murgia, S; Nolan, P L; Norris, J P; Nuss, E; Ohsugi, T; Omodei, N; Orlando, E; Ormes, J F; Paneque, D; Parent, D; Pelassa, V; Pepe, M; Pesce-Rollins, M; Piron, F; Porter, T A; Rainň, S; Rando, R; Razzano, M; Razzaque, S; Reimer, A; Reimer, O; Reposeur, T; Ritz, S; Rochester, L S; Rodriguez, A Y; Romani, R W; Roth, M; Ryde, F; Sadrozinski, H F-W; Sambruna, R; Sanchez, D; Sander, A; Saz Parkinson, P M; Scargle, J D; Sgrň, C; Siskind, E J; Smith, D A; Smith, P D; Spandre, G; Spinelli, P; Starck, J-L; Stawarz, ?; Strickman, M S; Suson, D J; Tajima, H; Takahashi, H; Takahashi, T; Tanaka, T; Thayer, J B; Thayer, J G; Thompson, D J; Tibaldo, L; Torres, D F; Tosti, G; Tramacere, A; Uchiyama, Y; Usher, T L; Vasileiou, V; Vilchez, N; Vitale, V; Waite, A P; Wallace, E; Wang, P; Winer, B L; Wood, K S; Ylinen, T; Ziegler, M; Hardcastle, M J; Kazanas, D

2010-04-01

367

Superluminal blazars and the extragalactic gamma ray background.  

NASA Astrophysics Data System (ADS)

The detection of a few dozen extragalactic gamma ray blazars of extremely high luminosity by the EGRET instrument on board the Compton Gamma Ray Observatory appears to suggest that blazars make the overwhelming contribution to the cosmic gamma ray background in the energy range 100 MeV - 10 GeV. The authors point out that the superluminal effect which boosts and beams the gamma ray emission in the jets of blazars will flatten the source count in the low flux part. Consequently, the unresolved blazars would not be expected to make much contribution to the gamma ray background. From their direct modelling of the source count, they conclude that the contribution of the unresolved blazars to the gamma ray background is only 10% of the latest estimate of the EGRET data. The implication for the cosmological evolution of the blazars is discussed.

Xinyu, Chi; Young, E. C. M.

1997-07-01

368

Superluminal blazars and the extragalactic gamma ray background  

NASA Astrophysics Data System (ADS)

The detection of a few dozen extragalactic gamma ray blazars of extremely high luminosity by the EGRET instrument on board the Compton Gamma Ray Observatory appears to suggest that blazars make the overwhelming contribution to the cosmic gamma ray background in the energy range 100 MeV - 10 GeV. In this paper we point out that the superluminal effect which boosts and beams the gamma ray emission in the jets of blazars will flatten the source count in the low flux part. Consequently, the unresolved blazars would not be expected to make much contribution to the gamma ray background. From our direct modelling of the source count, we conclude that the contribution of the unresolved blazars to the gamma ray background is only 10% of the latest estimate of the EGRET data. The implication for the cosmological evolution of the blazars is discussed.

Chi, Xinyu; Young, Enoch C. M.

1997-07-01

369

Colorado School of Mines fusion gamma ray diagnostic project  

NASA Astrophysics Data System (ADS)

The purpose of our fusion gamma ray project continues to be the development of fusion gamma ray spectrometry as a diagnostic of high temperature fusion plasmas. The three broad areas in support of this purpose are: measurement of gamma ray producing reactions at low energies; development of gamma ray spectrometers capable of measuring the gamma ray yields from current and proposed fusion plasma devices; and determination of appropriate plasma parameters from measured fusion gamma ray yields at present fusion plasma devices. This report summarizes the progress made in these three areas. The recently completed measurement of the radiative capture of protons by the nuclei Li-6, Li-7, Be-9, and B-11 is summarized. Preliminary results of the investigation of the radiative capture of deuterons by Li-6 and B-10 as well as additional data taken on the reaction D(d,gamma)He-4 at very low energies are also presented.

Cecil, F. E.

1991-02-01

370

Multiwavelength observations of Gamma-Ray Bright Blazars  

NASA Astrophysics Data System (ADS)

We have investigated total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. The blazars with faster apparent speeds, 3C 273, 3C 279, PKS 1510-089, and 3C 66A, exhibit stronger variability of the gamma-ray emission with higher flux density. Only blazars with faster apparent speeds show simultaneous optical and gamma-ray brightness variations during the flares. Our results are consisted with models in which the gamma-ray emission arises in high-relativistic jets.

Morozova, D. A.; Troitskiy, I. S.

2012-05-01

371

Massive Binaries as VHE Gamma-ray Sources  

NASA Astrophysics Data System (ADS)

Recent progress in gamma-ray astronomy has established Very High Energy (VHE) gamma-ray binaries as a new class of gamma-ray sources. All of them are massive binaries consisting of an OB star and a compact object. The next generation observing fascilities, such as the Cherenkov Telescope Array, will detect many more massive binaries as VHE gamma-ray sources. Studying VHE gamma-ray binaries is important not only to understand physics at work in individual systems, but also to construct a unified dynamical model for the interaction and the origin of high-energy emission in this class of objects. In this talk, we discuss the interaction between the stellar wind and/or circumstellar disk and the compact object, based on 3-D hydrodynamic simulations of a few VHE gamma-ray binaries.

Okazaki, Atsuo

2013-06-01

372

Gamma-ray burst data from DMSP satellites  

SciTech Connect

A number of gamma-ray bursts have been detected by means of gamma-ray detectors aboard three Air Force Defense Meteorological Satellite Program (DMSP) satellites, in polar orbits at 800 km altitude. The gamma-ray data have a 2-second resolving time, and are usually telemetered in 5 energy bins in the range 50--1000 keV. Although it is not possible to detect gamma-ray bursts when the DMSP satellites are passing through the radiation belt or the South Atlantic Anomaly, or when the source is obscured by the Earth, a number of gamma-ray bursts have been detected by two or even three of the satellites. The DMSP data may be of considerable, assistance in evaluating time histories, locations, and spectra of gamma-ray bursts.

Terrell, J.; Klebesadel, R.W.; Lee, P. [Los Alamos National Lab., NM (United States); Griffee, J.W. [Sandia National Labs., Albuquerque, NM (United States)

1991-12-31

373

Gamma-ray burst data from DMSP satellites  

SciTech Connect

A number of gamma-ray bursts have been detected by means of gamma-ray detectors aboard three Air Force Defense Meteorological Satellite Program (DMSP) satellites, in polar orbits at 800 km altitude. The gamma-ray data have a 2-second resolving time, and are usually telemetered in 5 energy bins in the range 50--1000 keV. Although it is not possible to detect gamma-ray bursts when the DMSP satellites are passing through the radiation belt or the South Atlantic Anomaly, or when the source is obscured by the Earth, a number of gamma-ray bursts have been detected by two or even three of the satellites. The DMSP data may be of considerable, assistance in evaluating time histories, locations, and spectra of gamma-ray bursts.

Terrell, J.; Klebesadel, R.W.; Lee, P. (Los Alamos National Lab., NM (United States)); Griffee, J.W. (Sandia National Labs., Albuquerque, NM (United States))

1991-01-01

374

Natural gamma-ray spectrometry as a tool for radiation dose and radon hazard modelling.  

PubMed

We reviewed the calibration procedures of gamma-ray spectrometry with particular emphasis to factors that affect accuracy, detection limits and background radiation in field measurements for dosimetric and radon potential mapping. Gamma-ray spectra were acquired in western Liguria (Italy). The energy windows investigated are centred on the photopeaks of (214)Bi (1.76 MeV), (208)Tl (2.62 MeV) and (40)K (1.46 MeV). The inferred absorbed dose rate and the radon flux are estimated to be lower than 60 nGy h(-1) and 22 Bq m(-2)h(-1), respectively. PMID:19249218

Verdoya, M; Chiozzi, P; De Felice, P; Pasquale, V; Bochiolo, M; Genovesi, I

2009-01-24

375

Fermi LAT observations of increasing gamma-ray activity of blazar 3C279  

NASA Astrophysics Data System (ADS)

The Large Area Telescope (LAT), one of the two instruments on the Fermi Gamma-ray Space Telescope, has observed over 27th and 28th September 2010, a sharp increase in gamma-ray activity from the blazar 3C279. Preliminary analysis indicates that the source rapidly reached a daily flux (E>100MeV) of (3.9+/-1.4) x10^-6 ph cm^-2 s^-1 on the 27th (errors are statistical only), more than a factor of 4 greater than reported in the Fermi-LAT 1st year catalog.

Cannon, A.

2010-09-01

376

Elastic scattering of gamma rays and X-rays  

NASA Astrophysics Data System (ADS)

Studies of elastic gamma ray scattering were pursued independently by the groups of Prof. Ghose and the author for several decades in spite of somewhat meagre support. Several techniques for such studies developed by the two groups and some of the results obtained in the energy range from tens of keV to about 1.5 MeV are described briefly. The theoretical background necessary for understanding these results is also outlined. The results showed the importance of Modified Relativistic Form Factor (MRFF) approximation in the explanation of atomic Rayleigh scattering cross sections in the small angle regime and the necessity for an inclusion of real Delbrück scattering amplitudes at large scattering angles. Dispersion corrections to form factor amplitudes or the so-called anomalous scattering factors are shown to be needed at photon energies close to electron binding energy thresholds. A few promising future extensions of such studies are indicated at the end.

Kane, P. P.

2005-12-01

377

The ``Supercritical Pile'' Model for Gamma-Ray Bursts: Getting the nuFnu Peak at 1 MeV  

Microsoft Academic Search

We propose that the internal energy of the gamma-ray burst (GRB) blast waves, thought to be stored in the form of relativistic protons comoving with the blast wave, is converted explosively (i.e., on light crossing timescales) into relativistic electrons of the same Lorentz factor, which are responsible for the production of observed prompt gamma-ray emission of the burst. This conversion

Demosthenes Kazanas; Markos Georganopoulos; Apostolos Mastichiadis

2002-01-01

378

VLBI Observations of Southern EGRET Identifications. II. VLBA Observations and the Importance of Jet Bending in Gamma-Ray Sources  

Microsoft Academic Search

We present VLBI images of six southern hemisphere radio sources that have been identified by EGRET as sources of greater-than-100 MeV gamma-ray emission, PKS 0521-365, PKS 1127-145, PKS 1622-253, PKS 1622-297, PKS 1730-130, and PKS 1908-201. We quantitatively investigate the suggestion of von Montigny et al. that jet bending may be a significant factor affecting the gamma-ray identification of radio-loud

S. J. Tingay; D. W. Murphy; P. G. Edwards

1998-01-01

379

How to Tell a Jet from a Balloon: A Proposed Test for Beaming in Gamma Ray Bursts  

Microsoft Academic Search

If gamma ray bursts are highly collimated, the energy requirements of each\\u000aevent may be reduced by several (~ 4-6) orders of magnitude, and the event rate\\u000aincreased correspondingly. Extreme conditions in gamma ray bursters lead to\\u000ahighly relativistic motions (bulk Lorentz factors Gamma > 100). This results in\\u000astrong forward beaming of the emitted radiation in the observer's rest

James E. Rhoads

1997-01-01

380

How to Tell a Jet from a Balloon: A Proposed Test for Beaming in Gamma-Ray Bursts  

Microsoft Academic Search

If gamma-ray bursts are highly collimated, radiating into only a small fraction of the sky, the energy requirements of each event may be reduced by several (~4--6) orders of magnitude, and the event rate is increased correspondingly. Extreme conditions in gamma-ray bursters lead to highly relativistic motions (bulk Lorentz factors of Gamma >~ 100). This results in strong forward beaming

James E. Rhoads

1997-01-01

381

Soft gamma-ray polarimetry using a Laue lens telescope: The Gamma Ray Imager  

Microsoft Academic Search

The Gamma Ray Imager (GRI) mission is a concept that was elaborated by a large international consortium and proposed to ESA in the framework of the Cosmic Vision first announcement of opportunity in 2007. The aim was simple: to beat the instrumental background in order to get a sensitivity improvement of at least one order of magnitude with respect to

Nicolas Barričre; Lorenzo Natalucci; Pietro Ubertini

382

The Cannonball Model of Gamma Ray Bursts: Spectral and Temporal Properties of the Gamma Rays  

Microsoft Academic Search

Recent observations suggest that gamma ray bursts (GRBs) and their afterglows are produced by highly relativistic jets emitted in supernova explosions. We have proposed that the result of the event is not just a compact object plus the ejecta: within days, a fraction of the parent star falls back to produce a thick accretion disk. The subsequent accretion generates jets

Arnon Dar; Alvaro De Rújula

2000-01-01

383

Improved Gamma-Ray Flux Monitoring at the High Intensity Gamma-Ray Source (HIGS)  

NASA Astrophysics Data System (ADS)

An improved gamma-ray beam flux monitor has been built for use at the High Intensity Gamma-Ray Source at the Duke University Free Electron Laser Laboratories. It is important to know precisely the gamma-ray flux of this beam. It is also important to limit beam attenuation to a minimum while making an accurate flux measurement. The improvements from a more accurate gamma-ray intensity monitor will allow for more precise cross-section measurements and will be valuable to many of the experiments conducted at HIGS. The detector consists of a thin scintillator optically coupled to two photomultiplier tubes, a thin foil, and then another thin scintillator attached to two photomultiplier tubes. The front scintillator is used to veto counts from charged particles emitted upstream in the beam-line. The preliminary tests of the monitor show very promising results and after slight adjustments and calibrations, the detector will be ready to acquire accurate beam intensity measurements while contributing very little to beam attenuation.

Reynolds, Robert

2002-10-01

384

The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope  

SciTech Connect

The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008. In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

Grenier, Isabelle (University Paris Diderot and CEA Saclay, France)

2009-04-01

385

The Animated Gamma-ray Sky Revealed by the Fermi Gamma-ray Space Telescope  

ScienceCinema

The Fermi Gamma-ray Space Telescope has been observing the sky in gamma-rays since August 2008. In addition to breakthrough capabilities in energy coverage (20 MeV-300 GeV) and angular resolution, the wide field of view of the Large Area Telescope enables observations of 20% of the sky at any instant, and of the whole sky every three hours. It has revealed a very animated sky with bright gamma-ray bursts flashing and vanishing in minutes, powerful active galactic nuclei flaring over hours and days, many pulsars twinkling in the Milky Way, and X-ray binaries shimmering along their orbit. Most of these variable sources had not been seen by the Fermi predecessor, EGRET, and the wealth of new data already brings important clues to the origin of the high-energy emission and particles powered by the compact objects. The telescope also brings crisp images of the bright gamma-ray emission produced by cosmic-ray interactions in the interstellar medium, thus allowing to measure the cosmic nuclei and electron spectra across the Galaxy, to weigh interstellar clouds, in particular in the dark-gas phase. The telescope sensitivity at high energy will soon provide useful constraints on dark-matter annihilations in a variety of environments. I will review the current results and future prospects of the Fermi mission.

386

Propagation of gamma-rays at cosmological redshifts  

Microsoft Academic Search

We discuss absorption and reprocessing of gamma-rays at cosmological redshifts. We consider Compton scattering and pair production by gamma-rays on the cosmic baryonic matter, and photon-photon scattering and photon-photon pair production by gamma-rays and Compton scattering of relativistic pairs on the cosmic blackbody background. We point out the cosmological importance of photon-photon scattering (a process not previously considered in astrophysics).

Andrzej A. Zdziarski; Roland Svensson

1989-01-01

387

X-rays and gamma-rays at cosmological distances  

Microsoft Academic Search

Recent work on absorption and reprocessing of gamma-rays at cosmological redshifts as well as the current status of this field of research are discussed. The authors consider Compton scattering and pair production by gamma-rays on cosmic baryonic matter, and photon-photon scattering and photon-photon pair production by gamma-rays and Compton scattering of relativistic pairs on the cosmic blackbody background. The region

A. A. Zdziarski; R. Svensson

1990-01-01

388

Gamma ray polarimetry using a position sensitive germanium detector  

Microsoft Academic Search

Imaging gamma-ray detectors make sensitive polarimeters in the Compton energy regime by measuring the scatter direction of gamma rays. The principle is to capitalize on the angular dependence of the Compton scattering cross section to polarized gamma rays and measure the distribution of scatter directions within the detector. This technique is effective in a double-sided germanium detector between roughly 50keV

R. A Kroeger; W. N Johnson; J. D Kurfess; B. F Phlips

1999-01-01

389

Neutron-Capture gamma Rays from Various Elements  

Microsoft Academic Search

Neutron-capture gamma-ray spectra have been measured in the energy range 0.3 to 3 Mev by means of a two-crystal Compton scintillation spectrometer. The efficiency of the instrument as a function of energy was determined experimentally. The uniqueness of the 2.23-Mev gamma ray following capture of a neutron by hydrogen has been confirmed, and this gamma ray was used as a

T. H. Braid

1956-01-01

390

The nature of the outflow in gamma-ray bursts  

Microsoft Academic Search

The Swift satellite has enabled us to follow the evolution of gamma-ray burst (GRB) fireballs from the prompt gamma-ray emission to the afterglow phase. The early-time X-ray and optical data for GRBs obtained by telescopes aboard the Swift satellite show that the source for prompt gamma-ray emission, the emission that heralds these bursts, is short lived, and is distinct from

P. Kumar; E. McMahon; A. Panaitescu; R. Willingale; P. O'Brien; D. Burrows; J. Cummings; N. Gehrels; S. Holland; S. B. Pandey; D. vanden Berk; S. Zane

2007-01-01

391

Gamma Ray Bursts: Explaining the Universe's Biggest Bangs  

NSDL National Science Digital Library

This radio broadcast discusses research into gamma ray bursts, the largest explosions in the universe. Topics include the SWIFT satellite mission and discoveries; the immense energy output of a gamma ray burst, and the causes of long and short gamma ray bursts (long bursts caused by core collapse into a black hole, and the short bursts from binary stellar system mergers, such as a neutron star colliding with a black hole). The broadcast is 28 minutes and 50 seconds in length.

392

Analysis of fissionable material using delayed gamma rays from photofission  

Microsoft Academic Search

The energetic gamma-ray spectra from the fission products of photofission have been investigated to determine whether photofission can identify heavily shielded fissionable material. Target samples of natural thorium, 93% enriched 235U, natural uranium, and 93% enriched 239Pu were irradiated with bremsstrahlung gamma rays produced by 10-MeV electrons from a small linear accelerator. The gamma-ray spectra for each of the four

C. L. Hollas; D. A. Close; C. E. Moss

1987-01-01

393

The Solar Maximum Mission Atlas of Gamma?Ray Flares  

Microsoft Academic Search

We present a compilation of data for all 258 gamma-ray —ares detected above 300 keV by the Gamma Ray Spectrometer (GRS) aboard the Solar Maximum Mission satellite. This gamma-ray —are sample was collected during the period from 1980 February to 1989 November; covering the latter half of the 21st solar sunspot cycle and the onset of the 22d solar sunspot

W. Thomas Vestrand; Gerald H. Share; Ronald J. Murphy; David J. Forrest; Erich Rieger; Edward L. Chupp; Gottfried Kanbach

1999-01-01

394

VHE gamma rays from PSR B1706-44  

Microsoft Academic Search

Observations made with the University of Durham Mark 6 atmospheric Cerenkov telescope confirm that PSR B1706-44 is a VHE gamma-ray emitter. The gamma-ray flux has been measured at 250 GeV, and suggests a spectral slope that is consistent with extrapolation from the sub-10 GeV region. There is no indication from our dataset that the VHE gamma-rays are pulsed, in contrast

P. M. Chadwick; M. R. Dickinson; N. A. Dipper; J. Holder; T. R. Kendall; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; I. D. Roberts; S. E. Shaw; K. E. Turver

1997-01-01

395

The Uuniversity of Durham Mark 6 Gamma Ray Telescope  

Microsoft Academic Search

The design, construction and operation of the University of Durham\\u000aground-based gamma ray telescope is discussed. The telescope has been designed\\u000ato detect gamma rays in the < 200 GeV region and to achieve good discrimination\\u000abetween gamma ray and hadron initiated showers in the higher energy region (>\\u000a300 GeV). The telescope was commissioned in 1995 and a description

P. Armstrong; P. M. Chadwick; P. J. Cottle; J. E. Dickinson; M. R. Dickinson; N. A. Dipper; S. E. Hilton; W. Hogg; J. Holder; T. R. Kendall; T. J. L. McComb; C. M. Moore; K. J. Orford; S. M. Rayner; I. D. Roberts; M. D. Roberts; M. Robertshaw; S. E. Shaw; K. Tindale; S. P. Tummey; K. E. Turver

1998-01-01

396

Iron and cadmium capture gamma-ray photofission measurements  

Microsoft Academic Search

Photofission measurements have been made in ²³⁸U, ²³²Th, and ²³⁡Np in iron and cadmium capture gamma-ray spectra in cylindrical neutron-driven gamma-ray sources in the thermal column of the National Bureau of Standards (NBS) Reactor. The gamma-ray source strength was measured with neutron activation foils and by direct counting of activations produced in the metal cylinders. Photofission measurements were made with

T. G. Williamson; G. P. Lamaze; D. M. Gilliam; C. M. Eisenhauer

1990-01-01

397

Fermi Discovery of Gamma-ray Emission from NGC 1275  

Microsoft Academic Search

We report the discovery of high-energy (E > 100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at the center of the Perseus cluster of galaxies, based on observations made with the Large Area Telescope (LAT) of the Fermi Gamma-ray Space Telescope. The positional center of the gamma-ray source is only ≈3' away from the NGC 1275

Aous A. Abdo; M. Ackermann; M. Ajello; K. Asano; L. Baldini; J. Ballet; Guido Barbiellini; Denis Bastieri; B. M. Baughman; K. Bechtol; R. Bellazzini; R. D. Blandford; Elliott D. Bloom; E. Bonamente; A. W. Borgland; J. Bregeon; A. Brez; M. Brigida; P. Bruel; Thompson H. Burnett; G. A. Caliandro; R. A. Cameron; P. A. Caraveo; J. M. Casandjian; E. Cavazzuti; C. Cecchi; A. Celotti; A. Chekhtman; C. C. Cheung; J. Chiang; S. Ciprini; R. Claus; J. Cohen-Tanugi; S. Colafrancesco; L. R. Cominsky; J. Conrad; L. Costamante; C. D. Dermer; A. de Angelis; F. de Palma; S. W. Digel; D. Donato; E. do Couto e Silva; P. S. Drell; R. Dubois; D. Dumora; C. Farnier; C. Favuzzi; J. Finke; W. B. Focke; M. Frailis; Y. Fukazawa; S. Funk; P. Fusco; F. Gargano; M. Georganopoulos; S. Germani; B. Giebels; N. Giglietto; F. Giordano; T. Glanzman; I. A. Grenier; M.-H. Grondin; J. E. Grove; L. Guillemot; S. Guiriec; Y. Hanabata; A. K. Harding; R. C. Hartman; M. Hayashida; E. Hays; R. E. Hughes; G. Jóhannesson; A. S. Johnson; R. P. Johnson; W. N. Johnson; M. Kadler; T. Kamae; Y. Kanai; H. Katagiri; J. Kataoka; N. Kawai; M. Kerr; J. Knödlseder; F. Kuehn; M. Kuss; L. Latronico; M. Lemoine-Goumard; F. Longo; F. Loparco; B. Lott; M. N. Lovellette; P. Lubrano; G. M. Madejski; A. Makeev; M. N. Mazziotta; J. E. McEnery; C. Meurer; P. F. Michelson; W. Mitthumsiri; T. Mizuno; A. A. Moiseev; C. Monte; M. E. Monzani; A. Morselli; I. V. Moskalenko; S. Murgia; T. Nakamori; P. L. Nolan; J. P. Norris; E. Nuss; T. Ohsugi; N. Omodei; E. Orlando; J. F. Ormes; D. Paneque; J. H. Panetta; D. Parent; M. Pepe; M. Pesce-Rollins; F. Piron; T. A. Porter; S. Rainň; M. Razzano; A. Reimer; O. Reimer; T. Reposeur; S. Ritz; A. Y. Rodriguez; R. W. Romani; F. Ryde; H. F.-W. Sadrozinski; R. Sambruna; D. Sanchez; A. Sander; R. Sato; P. M. Saz Parkinson; C. Sgrň; D. A. Smith; P. D. Smith; G. Spandre; P. Spinelli; J.-L. Starck; M. S. Strickman; A. W. Strong; D. J. Suson; H. Tajima; H. Takahashi; T. Takahashi; T. Tanaka; G. B. Taylor; J. G. Thayer; D. J. Thompson; D. F. Torres; G. Tosti; Y. Uchiyama; T. L. Usher; N. Vilchez; V. Vitale; A. P. Waite; K. S. Wood; T. Ylinen; M. Ziegler; H. D. Aller; M. F. Aller; K. I. Kellermann; Y. Y. Kovalev; Yu. A. Kovalev; M. L. Lister; A. B. Pushkarev

2009-01-01

398

Pulsar searches: From radio to gamma-rays  

Microsoft Academic Search

We report the results of four different pulsar searches, covering radio, X-ray, and gamma-ray wavelengths. These searches targeted pulsars in virtually all of their guises: young and old, long-period and short-period, accretion-powered and rotation-powered. Ten new pulsars were discovered. There are very few known gamma-ray pulsars, all of which were found by folding gamma-ray data with a pulse period known

Adam M. Chandler

2003-01-01

399

EGRET Observations of the Extragalactic Gamma-Ray Emission  

Microsoft Academic Search

The all-sky survey in high-energy gamma rays (E > 30 MeV) carried out by EGRET aboard the Compton Gamma Ray Observatory provides a unique opportunity to examine in detail the diffuse gamma-ray emission. The observed diffuse emission has a Galactic component arising from cosmic-ray interactions with the local interstellar gas and radiation, as well as an almost uniformly distributed component

P. Sreekumar; D. L. Bertsch; B. L. Dingus; J. A. Esposito; C. E. Fichtel; R. C. Hartman; S. D. Hunter; G. Kanbach; D. A. Kniffen; Y. C. Lin; H. A. Mayer-Hasselwander; P. F. Michelson; C. von Montigny; A. Muecke; R. Mukherjee; P. L. Nolan; M. Pohl; O. Reimer; E. Schneid; J. G. Stacy; F. W. Stecker; D. J. Thompson; T. D. Willis

1998-01-01

400

Multiwavelength Study of Gamma-Ray Bright Blazars  

Microsoft Academic Search

We investigate total intensity radio images of 6 gamma-ray bright blazars (BL Lac, 3C 279, 3C 273, W Com, PKS 1510-089, and 3C 66A) and their optical and gamma-ray light curves to study connections between gamma-ray and optical brightness variations and changes in the parsec-scale radio structure. We use high-resolution maps obtained by the BU group at 43 GHz with

Daria Morozova; V. M. Larionov; V. A. Hagen-Thorn; S. G. Jorstad; A. P. Marscher; I. S. Troitskii

2011-01-01

401

Nucleonic gamma-ray production in pulsar wind nebulae  

Microsoft Academic Search

Observations of the inner radian of the Galactic disk at very high energy (VHE) gamma-rays have revealed at least 16 new sources.\\u000a Besides shell type super-nova remnants, pulsar wind nebulae (PWN) appear to be a dominant source population in the catalogue\\u000a of VHE gamma-ray sources. Except for the Crab nebula, the newly discovered PWN are resolved at VHE gamma-rays to

D. Horns; F. Aharonian; A. I. D. Hoffmann; A. Santangelo

2007-01-01

402

Simultaneous detection of gamma-ray bundles and air showers  

Microsoft Academic Search

An air shower (EAS) observation system was used with an emulsion chamber, and the correlation between gamma-ray bundles and EAS was studied. It was found that nearly 100% of gamma-ray bundles are accompanied by EAS and about 90% of large EAS with sizes larger than 10 to the 6th power have gamma-ray bundles in their cores. In this experiment a

S. Dake; Y. Hatano; K. Jitsuno; M. Hazama; Y. Nakanishi; K. Nishikawa; M. Sakata; Y. Yamamoto

1979-01-01

403

Evidence for supersymmetric dark matter annihilations into gamma rays  

Microsoft Academic Search

The astrophysical gamma-ray energy spectra measured by balloon-borne emulsion detectors and the Whipple imaging atmospheric Cerenkov telescope are shown to offer possible evidence for the existence of a monoenergetic gamma-ray flux excess over the background centered at 3.5+\\/-0.3 TeV, indicating the annihilation or decay of relic dark matter weakly interacting massive particles. The observed gamma-ray flux is compatible with the

Steven C. Strausz

1997-01-01

404

Probable optical counterpart of a Gamma-ray burster  

Microsoft Academic Search

Sixteen million seconds, or over a half year, of optical monitoring of three Gamma-ray burst positions using the Harvard College Observatory collection of archival plates are described. The probable optical counterpart of the November 19, 1978 Gamma-ray burster has been discovered on a blue emulsion plate exposed in 1928. Optical searches indicate that the absolute magnitude of the Gamma-ray burst

B. E. Schaefer

1981-01-01

405

Prototype TIGRE Compton gamma-ray balloon-borne telescope  

Microsoft Academic Search

A prototype balloon-borne telescope is being constructed for gamma-ray observations in the MeV energy range. The Tracking and Imaging Gamma-Ray Experiment (TIGRE) uses multi-layers of thin silicon detectors to track and measure the energy losses of Compton recoil electrons. When combined with the direction and energy of the Compton scattered gamma-ray a unique incident direction for each photon event is

D. Bhattacharya; T. J. O'Neill; A. Akyüz; J. Samimi; A. D. Zych

2004-01-01

406

Energy spectrum of diffuse component of cosmic soft gamma rays  

Microsoft Academic Search

The new measurements reported take into account gamma rays in the energy range from 0.1 to 4 MeV. A balloon-borne telescope was used in the investigation. The new data are compared with earlier results. The energy spectrum of soft gamma rays is presented in a graph. The approach used in the determination of gamma ray intensity is discussed along with

Y. Fukada; S. Hayakawa; I. Kasahara; F. Makino; Y. Tanakay; B. V. Sreekantan

1975-01-01

407

Wolf-Rayet Stars and Cosmic Gamma-ray Bursts  

Microsoft Academic Search

The observational properties of cosmic gamma-ray bursts and of Wolf-Rayet (WR) stars and their CO cores at the end of their evolution are analyzed. WR stars do not have hydrogen envelopes, facilitating the transformation of the energy of collapse into observable gamma rays. Of the ≈90 well-localized gamma-ray bursts, 21 have optical identifications, of which 16 have measured redshifts (z=0.4

K. A. Postnov; A. M. Cherepashchuk

2001-01-01

408

Supernovae and Gamma-ray Bursts: Flashy and Somber Explosions  

Microsoft Academic Search

We review the observational status of the Supernova\\/Gamma-Ray Burst connection. Several lines of evidence suggest that long duration Gamma-ray Bursts are associated with bright SNe-Ic. However recent observations of GRB 060614 puzzle this scenario, pointing out the existence of long-duration Gamma-ray Burst not accompanied by a bright supernova. An analysis of the association GRB 060218\\/SN 2006aj and X081009\\/SN 2008D finds

Massimo Della Valle

2009-01-01

409

Nuclear criticality as a contributor to gamma ray burst events  

NASA Astrophysics Data System (ADS)

Most gamma ray bursts are able to be explained using supernovae related phenomenon. Some measured results still lack compelling explanations and a contributory cause from nuclear criticality is proposed. This is shown to have general properties consistent with various known gamma ray burst properties. The galactic origin of fast rise exponential decay gamma ray bursts is considered a strong candidate for these types of events.

Hayes, Robert B.

2013-05-01

410

Estimation methods for semiconductor gamma-ray detectors  

Microsoft Academic Search

Gamma-ray detectors based on high-density semiconductors, such as cadmium zinc telluride, are being developed for applications in nuclear medicine, astronomy and the monitoring of nuclear weapons material. In contrast to the more commonly used scintillators, which convert gamma-ray energy into light, semiconductors directly convert the energy of a gamma ray into electrical current. This direct conversion often leads to the

Daniel George Marks

2000-01-01

411

Experiment on gamma-ray generation and application  

NASA Astrophysics Data System (ADS)

An experimental setup of gamma-ray generation through laser Compton scattering has been built on the NewSUBARU storage ring. The aim is to study nuclear transmutation, which is regarded as the first stage to explore the feasibility of developing a nuclear waste disposal system based on the concept of irradiating long-lived fission products by laser Compton scattering gamma ray. In this paper, the gamma-ray generation facility is presented, and some experimental results such as gamma-ray energy spectrum, intensity distribution, and the coupling efficiency of nuclear transmutation, are given. The experimental data is in good agreement with the analytic calculation or simulation analysis.

Li, D.; Imasaki, K.; Aoki, M.; Miyamoto, S.; Amano, S.; Aoki, K.; Hosono, K.; Mochizuki, T.

2004-08-01

412

Fermi Large Area Telescope Bright Gamma-ray Source List  

SciTech Connect

Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope (Fermi) began a sky survey in August. The Large Area Telescope (LAT) on Fermi in three months produced a deeper and better resolved map of the {gamma}-ray sky than any previous space mission. We present here initial results for energies above 100 MeV for the 205 most significant (statistical significance greater than {approx}10{sigma}) {gamma}-ray sources in these data. These are the best characterized and best localized point-like (i.e., spatially unresolved) {gamma}-ray sources in the early mission data.

Abdo, Aous A.; /Naval Research Lab, Wash., D.C.; Ackermann, M.; /KIPAC, Menlo Park /SLAC; Ajello, M.; /KIPAC, Menlo Park /SLAC; Atwood, W.B.; /UC, Santa Cruz; Axelsson, M.; /Stockholm U., OKC /Stockholm U.; Baldini, L.; /INFN, Pisa; Ballet, J.; /DAPNIA, Saclay; Band, D.L.; /NASA, Goddard /NASA, Goddard; Barbiellini, Guido; /INFN, Trieste /Trieste U.; Bastieri, Denis; /INFN, Padua /Padua U.; Bechtol, K.; /KIPAC, Menlo Park /SLAC; Bellazzini, R.; /INFN, Pisa; Berenji, B.; /KIPAC, Menlo Park /SLAC; Bignami, G.F.; /Pavia U.; Bloom, Elliott D.; /KIPAC, Menlo Park /SLAC; Bonamente, E.; /INFN, Perugia /Perugia U.; Borgland, A.W.; /KIPAC, Menlo Park /SLAC; Bregeon, J.; /INFN, Pisa; Brigida, M.; /Bari U. /INFN, Bari; Bruel, P.; /Ecole Polytechnique; Burnett, Thompson H.; /Washington U., Seattle /Bari U. /INFN, Bari /KIPAC, Menlo Park /SLAC /IASF, Milan /IASF, Milan /DAPNIA, Saclay /ASDC, Frascati /INFN, Perugia /Perugia U. /KIPAC, Menlo Park /SLAC /George Mason U. /Naval Research Lab, Wash., D.C. /NASA, Goddard /KIPAC, Menlo Park /SLAC /INFN, Perugia /Perugia U. /KIPAC, Menlo Park /SLAC /Montpellier U. /Sonoma State U. /Stockholm U., OKC /Royal Inst. Tech., Stockholm /Stockholm U. /KIPAC, Menlo Park /SLAC /ASDC, Frascati /NASA, Goddard /Maryland U. /Naval Research Lab, Wash., D.C. /INFN, Trieste /Pavia U. /Bari U. /INFN, Bari /KIPAC, Menlo Park /SLAC /UC, Santa Cruz /KIPAC, Menlo Park /SLAC /KIPAC, Menlo Park /SLAC /KIPAC, Menlo Park /SLAC /Montpellier U. /Bari U. /INFN, Bari /Ecole Polytechnique /NASA, Goddard; /more authors..

2009-05-15

413

Measurement of Disintegration Rates and Absolute {gamma}-ray Intensities  

SciTech Connect

The majority of practical radioactive materials decay by modes that include {gamma}-ray emission. For questions of 'how much' or 'how pure', one must know the absolute intensities of the major radiations. We are using liquid scintillation counting (LSC) to measurements of disintegration rates, coupled with {gamma}-ray spectroscopy to measure absolute {gamma}-ray emission probabilities. Described is a study of the 227Th chain yielding absolute {gamma}-ray intensities with {approx}0.5% accuracy and information on LSC efficiencies.

DeVries, Daniel J.; Griffin, Henry C. [Department of Chemistry, University of Michigan, Ann Arbor, MI 48109 (United States)

2006-03-13

414

Nonrelativistic phase in gamma-ray burst afterglows  

Microsoft Academic Search

The discovery of multiband afterglows definitely shows that most $\\\\gamma$-ray\\u000abursts are of cosmological origin. $\\\\gamma$-ray bursts are found to be one of\\u000athe most violent explosive phenomena in the Universe, in which astonishing\\u000aultra-relativistic motions are involved. In this article, the multiband\\u000aobservational characteristics of $\\\\gamma$-ray bursts and their afterglows are\\u000abriefly reviewed. The standard model of $\\\\gamma$-ray bursts,

HUANG Yongfeng; T. Lu; K. S. Cheng

2007-01-01

415

X-ray echoes from gamma-ray bursts  

SciTech Connect

The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed. 35 refs.

Dermer, C.D.; Hurley, K.C.; Hartmann, D.H. (California Univ., Berkeley (USA) Lawrence Livermore National Laboratory, CA (USA))

1991-03-01

416

Inelastic cross sections from gamma-ray measurements  

SciTech Connect

Measurements of gamma rays following neutron induced reactions have been studied with the Germanium Array for Neutron-induced Excitations (GEANIE) at the Los Alamos Neutron Science Center (LANSCE) for many years. Gamma-ray excitation functions and coincidence studies provide insight into nuclear reaction mechanisms as well as expanding our knowledge of energy levels and gamma-rays. Samples studied with Ge detectors at LANSCE range from Be to Pu. Fe, Cr and Ti have been considered for use as reference cross sections. An overview of the measurements and efforts to create a reliable neutron-induced gamma-ray reference cross section will be presented.

Nelson, Ronald Owen [Los Alamos National Laboratory

2010-12-06

417

GRIPS-Gamma-Ray burst Investigation via Polarimetry and Spectroscopy  

SciTech Connect

The primary scientific goal of the GRIPS mission [1] is to revolutionize our understanding of the early universe using {gamma}-ray bursts. We propose a new generation gamma-ray observatory capable of unprecedented spectroscopy over a wide range of {gamma}-ray energies (200 keV-50 MeV) and of polarimetry (200-1000 keV). Secondary goals achievable by this mission include direct measurements of supernova interiors through {gamma}-rays from radioactive decays, nuclear astrophysics with massive stars and novae, and studies of particle acceleration near compact stars, interstellar shocks, and clusters of galaxies.

Greiner, J. [MPE Garching, Giessenbachstr. 1, 85740 Garching (Germany)

2008-05-22

418

GAMMA-RAY BURST PREDICTIONS FOR THE FERMI GAMMA RAY SPACE TELESCOPE  

SciTech Connect

Results of a phenomenological model to estimate the gamma-ray burst (GRB) detection rate by the Fermi Gamma-Ray Space Telescope are reported. This estimate is based on the Burst and Transient Source Experiment (BATSE) 4B GRB fluence distribution, the mean ratio of fluences measured at 100 MeV-5 GeV with Energetic Gamma-Ray Experiment Telescope (EGRET) and at 20 keV-2 MeV with BATSE, and the mean EGRET GRB spectrum for the five EGRET spark-chamber GRBs. For a 10% fluence ratio and a number spectral index {alpha}{sub 1} = -2 at 100 MeV- 5 GeV energies, we estimate a rate of {approx}20 and 4 GRBs yr{sup -1} in the Fermi Large Area Telescope field of view (FOV) with at least five photons with energy E>100 MeV and E>1 GeV, respectively. We also estimate {approx}1.5 GRBs yr{sup -1} in the Fermi FOV where at least one photon with energy E>10 GeV is detected. For these parameters, we estimate {approx}1-2 GRBs yr{sup -1} detected with the Fermi telescope with more than 100 {gamma}-rays with E {approx}> 100 MeV. Comparison predictions for {alpha}{sub 1} = -2.2, different fluence ratios, and the AGILE {gamma}-ray satellite are made. Searches for different classes of GRBs using a diagram plotting 100 MeV-10 GeV fluence versus 20 keV- 20 MeV fluence is considered as a way to search for separate classes of GRBs and, specifically, spectral differences between the short-hard and long-duration GRB classes, and for hard components in GRBs.

Le, Truong; Dermer, Charles D. [Space Science Division, Code 7653, Naval Research Laboratory, Washington, DC 20375 (United States)], E-mail: tle@ssd5.nrl.navy.mil, E-mail: charles.dermer@nrl.navy.mil

2009-08-01

419

Very high energy gamma ray astrophysics  

SciTech Connect

The second reflector (project GRANITE) is on schedule. At present (January 1992) it and the 10 m reflector are obtaining stereoscopic views of gamma-ray air showers from the Crab Nebula which verify the expected performance of the twin reflector telescopes. With the additional improvements of the upgrade (a pending DOE proposal) the twin reflectors should reach a limiting intensity of 1% that of the Crab. The astonishing early results from the EGRET detector aboard the Compton Gamma Ray Observatory indicate that distant quasars (powered by supermassive black holes) are active at GeV energies. The Whipple instruments are poised to see if such behavior continues above 100 GeV, as well as perform sensitive observations of previously reported GeV (Geminga) and TeV (Hercules X-1, etc.) sources. In addition to observing sources and identifying their location in the sky to one arcminute, experiments are planned to search for WIMPS in the mass range 0.1 to 1 TeV, and to determine the abundance of anti-protons in the cosmic rays. The successful performance of the stereoscopic reflectors demonstrates the feasibility of the concept of arrays of Cherenkov receivers. Design studies for a much larger array (CASITA) are just beginning.

Lamb, R.C.; Lewis, D.A.

1992-02-01

420

Development of gamma ray imaging cameras  

NASA Astrophysics Data System (ADS)

In January 1990, the Department of Energy initiated this project with the objective to develop the technology for general purpose, portable gamma ray imaging cameras useful to the nuclear industry. The ultimate goal of this R&D initiative is to develop the analog to the color television camera where the camera would respond to gamma rays instead of visible photons. The two-dimensional real-time image would be displayed and indicate the geometric location of the radiation relative to the camera's orientation, while the brightness and 'color' would indicate the intensity and energy of the radiation and, hence, identify the emitting isotope. There is a strong motivation for developing such a device for applications within the nuclear industry, for both high- and low-level waste repositories, for environmental restoration problems, and for space and fusion applications. At present, there are no general purpose radiation cameras capable of producing spectral images for such practical applications. At the time of this writing, work on this project has been underway for almost 18 months. Substantial progress has been made in the project's two primary areas: mechanically-collimated (MCC) and electronically-collimated camera (ECC) designs. We present developments covering the mechanically-collimated design, and then discuss the efforts on the electronically-collimated camera. The renewal proposal addresses the continuing R&D efforts for the third year effort.

Wehe, D. K.; Knoll, G. F.

1992-05-01

421

Gamma ray bursts triggered by turbulent reconnection  

NASA Astrophysics Data System (ADS)

Understanding of the nature of gamma-ray bursts (GRBs) is one of the challenging problem facing the astrophysics community. Magnetic reconnection plays a crucial roles in the physics of GRBs, particularly, for those highly magnetized ones. Similar process can happen, as those on solar surface. I shall present our model of GRBs based on turbulent reconnection process. Turbulence fluctuations accumulates through shell collisions and triggers a bursty reconnection event once the turbulence reaches the critical condition, resulting in a runway release of the stored magnetic field energy. Particles are accelerated either directly in the reconnection zone, or stochastically in the turbulent regions, which radiate synchrotron photons that power the observed gamma rays. Within this model, the observed GRB variability timescales could have two components, one slow component associated with the central engine time history, and another fast component associated with relativistic magnetic turbulence in the emission region. The model may be applied to the GRBs that have time-resolved, featureless Band-function spectra.

Yan, Huirong

2012-07-01

422

Development of gamma ray imaging cameras  

SciTech Connect

In January 1990, the Department of Energy initiated this project with the objective to develop the technology for general purpose, portable gamma ray imaging cameras useful to the nuclear industry. The ultimate goal of this R D initiative is to develop the analog to the color television camera where the camera would respond to gamma rays instead of visible photons. The two-dimensional real-time image would be displayed would indicate the geometric location of the radiation relative to the camera's orientation, while the brightness and color'' would indicate the intensity and energy of the radiation (and hence identify the emitting isotope). There is a strong motivation for developing such a device for applications within the nuclear industry, for both high- and low-level waste repositories, for environmental restoration problems, and for space and fusion applications. At present, there are no general purpose radiation cameras capable of producing spectral images for such practical applications. At the time of this writing, work on this project has been underway for almost 18 months. Substantial progress has been made in the project's two primary areas: mechanically-collimated (MCC) and electronically-collimated camera (ECC) designs. We present developments covering the mechanically-collimated design, and then discuss the efforts on the electronically-collimated camera. The renewal proposal addresses the continuing R D efforts for the third year effort. 8 refs.

Wehe, D.K.; Knoll, G.F.

1992-05-28

423

Population III Gamma-Ray Burst  

NASA Astrophysics Data System (ADS)

Gamma-ray bursts (GRBs) are unique probes of the first generation (Pop III) stars. We show that a relativistic gamma-ray burst (GRB) jet can potentially pierce the envelope of a very massive Pop III star even if the Pop III star has a supergiant hydrogen envelope without mass loss, thanks to the long-lived powerful accretion of the envelope itself. While the Pop III GRB is estimated to be energetic (E ?,iso ~ 1055 erg), the supergiant envelope hides the initial bright phase in the cocoon component, leading to a GRB with a long duration ~1000 (1 + z) s and an ordinary isotropic luminosity ~ 1052 erg s-1 (~ 10-9 erg cm-2 s-1 at redshift z ~ 20), although these quantities are found to be sensitive to the core and envelope mass. We also show that Pop III.2 GRBs (which are primordial but affected by radiation from other stars) occur >100 times more frequently than Pop III.1 GRBs, and thus should be suitable targets for future X-ray and radio missions. The radio transient surveys are already constraining the Pop III GRB rate and promising in the future.

Ioka, Kunihito; Suwa, Yudai; Nagakura, Hiroki; de Souza, Rafael S.; Yoshida, Naoki

2012-09-01

424

PULSAR OUTER-GAP ELECTRODYNAMICS: HARDENING OF SPECTRAL SHAPE IN THE TRAILING PEAK IN THE GAMMA-RAY LIGHT CURVE  

SciTech Connect

The spectral characteristics of the pulsed gamma-ray emission from outer-magnetospheric particle accelerators are investigated. Either positrons or electrons are accelerated outward by the magnetic-field-aligned electric field to emit gamma rays via the curvature process. Since the particles move along relatively straight paths in the trailing side of a rotating magnetosphere, they attain higher Lorentz factors to emit more energetic gamma rays than those in the leading side. It is first demonstrated that the cutoff energy of the curvature radiation evolves with the rotation phase owing to the variation of the curvature radii of the particle paths and maximizes at a slightly later phase of the trailing peak in the gamma-ray light curve.

Hirotani, Kouichi, E-mail: hirotani@tiara.sinica.edu.tw [TIARA, Department of Physics, National Tsing Hua University, 101, Sec. 2, Kuang Fu Rd., Hsinchu 30013, Taiwan (China)

2011-06-01

425

Gamma ray and pi0 production from hydrogen and complex nuclei by 270-375 MeV gamma rays  

Microsoft Academic Search

Measurements are reported on the differential cross section for secondary gamma ray production on hydrogen and nuclear targets at 90° in the laboratory through the interactions of primary gamma rays in the energy range 270-375 MeV. A difference method using bremsstrahlung beams at different end point energies was employed. The gamma ray detector was a high resolution Nal(Tl) spectrometer and

B. L. Beron; E. B. Hughes

1973-01-01

426

The Gamma Ray Large Area Space Telescope:. AN Astro-Particle Mission to Explore the High Energy Gamma Ray Sky  

Microsoft Academic Search

The Gamma Ray Large Area Space Telescope (GLAST) is a space mission that will detect photons from the gamma ray sky, in the rich yet poorly explored high energy band between 20MeV and 1TeV. Main instrument on board is the Large Area Telescope (LAT), a gamma-ray pair-conversion telescope, that will measure direction and energy of incoming photons by means of

R. Bellazzini; G. Spandre

2003-01-01

427

Can Galactic Gamma-Ray Background be due to Superposition of gamma-Rays from Millisecond Pulsars?  

Microsoft Academic Search

A diffuse background of high energy gamma-rays has been observe in the Galaxy by space probes such as COS B. We make here an attempt to understand this background in terms of the gamma radiation from millisecond pulsars. Because of their large rotational velocities millisecond pulsars could br strong sources of gamma-rays. We calculate the integrated flux of gamma-rays from

V. B. Bhatia; S. Mishra; N. Panchapakesan

1998-01-01

428

The Gamma-Ray Imaging Spectrometer (GRIS): A new balloon-borne experiment for gamma-ray line astronomy  

Microsoft Academic Search

High resolution gamma-ray spectroscopy is a relatively new field that holds great promise for further understanding of high energy astrophysical processes. When the high resolution gamma-ray spectrometer (GRSE) was removed from the GRO payload, a balloon program was initiated to permit continued development and improvement of instrumentation in this field, as well as continued scientific observations. The Gamma-Ray Imaging Spectrometer

B. J. Teegarden; T. L. Cline; N. Gehrels; G. Porreca; J. Tueller; M. Leventhal; A. F. Huters; C. J. MacCallum; P. D. Stang

1985-01-01

429

Guest Investigator Studies with the Compton Gamma Ray Observatory  

NASA Astrophysics Data System (ADS)

The cumulative all-sky survey by the Compton Gamma Ray Observatory (CGRO), composed of data acquired during the first three years of the mission, included a number of regions of very limited exposure. The most glaring deficiency in coverage was toward the region of the South Galactic Pole (SGP), which received significantly less exposure than other directions- by a factor of at least 2 to 3. Furthermore, nearly all of the SGP exposure was accumulated during the first year of the mission. Since blazars are known to be time-variable, and of unknown duty cycle, a pointing of the CCRO in that direction was considered highly desirable, and long overdue. In addition, data gathered from a pointing toward the SGP and its comparison with comprehensive data available for the North Galactic Pole would be extremely valuable to investigators studying the extragalactic diffuse emission. The reasons outlined above prompted our initiation of a Cycle 4 campaign to systematically search with EGRET and COMPTEL for gamma-ray emission from sources near the South Galactic Pole. The Cycle 4 SGP campaign consisted of tnvo 14-day observations separated in in time by approximately 10 months. The temporal separation of the observations was requested to allow a test for possible variations in the detected sources. Our primary targets were 38 FSRQs which lie within 30 degrees of the SGP, and which satisfy the basic criteria for candidate gamma-ray AGNs,flat-spectrum radio sources, many of which exhibit blazar-type properties). These targets were selected from the standard references, and from the available on-line databases (e.g., the NASA Extragalactic Database, NED), as the most promising AGN targets in the vicinity of the SGP. A 30 radius from the SGP was chosen as the boundary of our survey, since the selected targets would then fall within the most sensitive portion of the fields of view of EGRET and COMPTEL (i.e., within a 30 zenith angle), for a CGRO pointing directed exactly at the SGP. Our South Galactic Pole Survey yielded a number of exciting results. The EGRET data were analyzed using the maximum likelihood techniques to estimate the intensity, spectrum, and position of gamma-ray sources in the field of view. Our analysis revealed four sources at energies greater than 100 MeV with likelihood ratios corresponding to greater than 30 detections (Vestrand et al. 1996). One of the sources is associated with the well known gamma-ray blazar PKS 0208-512, but the other three were previously unknown. Among the new detections was PKS 2155-304 which is often considered a prototype of the x-ray selected BL Lacs. PKS 2155-304, which was also detected at hard x-ray energies by CGRO/OSSE, is one of the brightest BL Lac objects in the sky at optical through x-ray energies and has a history of rapid, strong multiwavelength variability. As such, it has been the subject of intensive, contemporaneous, multiwavelength monitoring covering radio frequencies to x-ray energies.

Vestrand, W. T.

1998-09-01

430

Empirical Constraints on Source Properties and Host Galaxies of Cosmological Gamma-Ray Bursts  

Microsoft Academic Search

We discuss several constraints on the properties of gamma-ray bursts (GRBs) at cosmological distances. First we use the requirement that burst sources must be optically thin to a test photon for the process gamma + gamma --> e+ + e- in order to produce the observed nonthermal spectra. In particular, we derive probability distributions for the minimum Lorentz expansion factor

Eric Woods; Abraham Loeb

1995-01-01

431

Characteristics of Profiles of Gamma-Ray Burst Pulses Associated with the Doppler Effect of Fireballs  

Microsoft Academic Search

In this paper we derive in great detail the formula for count rates of gamma-ray bursts (GRBs) in the framework of fireballs, in terms of the integral of time, where the Doppler effect of the expanding fireball surface is the key factor concerned. Effects arising from the limit on the time delay due to the limited emitting areas on the

Yi-Ping Qin; Zhi-Bin Zhang; Fu-Wen Zhang; Xiao-Hong Cui

2004-01-01

432

Sensitive polarimetric search for relativity violations in gamma-ray bursts.  

PubMed

We show that the recent measurements of linear polarization in gamma rays from GRB 930131 and GRB 960924 constrain certain types of relativity violations in photons to less than parts in 10(37), representing an improvement in sensitivity by a factor of 100,000. PMID:17155222

Kostelecký, V Alan; Mewes, Matthew

2006-10-02

433

Gamma-ray bursts from internal shocks in a relativistic wind: temporal and spectral properties  

Microsoft Academic Search

We construct models for gamma-ray bursts in which the emission comes from internal shocks in a relativistic wind with a highly non-uniform distribution of the Lorentz factor. We follow the evolution of the wind using a very simplified approach in which a large number of layers interact by direct collisions but all pressure waves have been suppressed. We suppose that

F. Daigne; R. Mochkovitch

1998-01-01

434

Can Internal Shocks Produce the Variability in Gamma-Ray Bursts?  

Microsoft Academic Search

We discuss the possibility that gamma-ray bursts result from internal shocks in ultrarelativistic matter. Using a simple model, we calculate the temporal structure and estimate the efficiency of this process. In this model the flow of ultrarelativistic matter is represented by a succession of shells with random values of the Lorentz factor. We calculate the shocks that take place between

Shiho Kobayashi; Tsvi Piran; Re'em Sari

1997-01-01

435

The Neutron Component in Fireballs of Gamma-Ray Bursts: Dynamics and Observable Imprints  

Microsoft Academic Search

We analyze the dynamics of a neutron-proton relativistic wind, paying particular attention to fireballs of cosmological gamma-ray bursts (GRBs). Specific effects of the neutron component depend on whether the final Lorentz factor of a plasma wind exceeds some critical value or not. In the first case, velocity decoupling of the neutron and proton flows takes place, giving rise to an

E. V. Derishev; V. V. Kocharovsky

1999-01-01

436

“Seed” electrons from muon decay for runaway mechanism in the terrestrial gamma ray flash production  

Microsoft Academic Search

We describe a mechanism of enhanced terrestrial gamma ray flash production seeding via muon decay in the presence of high electric fields associated with lightning. Our model predicts 107 relativistic seed electrons per millisecond at about 15 km altitude with mean energy of 35 MeV and an avalanche multiplication factor of about 1010, in good agreement with Monte Carlo simulations.

Gerson S. Paiva; Antonio C. Pavăo; Cristiano C. Bastos

2009-01-01

437

Gamma-Ray Telescopes: 400 Years of Astronomical Telescopes.  

National Technical Information Service (NTIS)

The last half-century has seen dramatic developments in gamma-ray telescopes, from their initial conception and development through to their blossoming into full maturity as a potent research tool in astronomy. Gamma-ray telescopes are leading research in...

J. K. Cannizzo N. Gehrels

2010-01-01

438

Gamma-Ray Spectra of Fractionated Fission Products.  

National Technical Information Service (NTIS)

To determine the effects of fractionation on gamma-ray exposure rates in fission-product fields, spectra of gamma-rays emitted by fractionated products of thermal neutron fission of 235U were studied. Controlled fractionation was brought about by sweeping...

D. Sam L. R. Bunney

1971-01-01

439

Determination of intergalactic magnetic fields from gamma ray data  

Microsoft Academic Search

We report a measurement of intergalactic magnetic fields using combined data from Atmospheric Cherenkov Telescopes and Fermi Gamma-Ray Space Telescope, based on the spectral data alone. If blazars are assumed to produce both gamma rays and cosmic rays, the observed spectra are not sensitive to the intrinsic spectrum of the source, because, for a distant blazar, secondary photons produced along

Warren Essey; Shin’ichiro Ando; Alexander Kusenko

2011-01-01

440

Concept for a High-Energy Gamma-Ray Polarimeter.  

National Technical Information Service (NTIS)

We present a concept for an imaging gamma-ray polarimeter operating from approximately 50 MeV to approximately 1 GeV. Such an instrument would be valuable for the study of high-energy pulsars, active galactic nuclei, supernova remnants, and gamma-ray burs...

P. F. Bloser S. D. Hunter G. O. Depaola F. Longo

2003-01-01

441

Gamma ray bursts as probes of the first stars  

Microsoft Academic Search

The redshift where the first stars formed is an important and unknown milestone in cosmological structure formation. The evidence linking gamma ray bursts (GRBs) with star formation activity implies that the first GRBs occurred shortly after the first stars formed. Gamma ray bursts and their afterglows may thus offer a unique probe of this epoch, because they are bright from

James E. Rhoads

2001-01-01

442

Astrophysics with the 3-DTI Gamma-Ray Telescope  

NASA Astrophysics Data System (ADS)

Despite notable progress in gamma-ray astronomy, understanding the astrophysical sources of medium energy (MeV-range) gamma-rays still remains somewhat of a mystery. Medium-energy gamma-ray observations require diverse measurement techniques since the objects that produce these gamma- rays are both extended and point-like, transient and steady, and include both continuum and line emissions. The challenge is to develop a future gamma-ray instrument to survey the Galaxy with greatly improved sensitivity by increasing the overall aperture and effectively addressing background rejection. Clearly, this survey would be enhanced by observations at other wavelengths such as those from SWIFT and GLAST, and INTEGRAL. The ability to constrain the incident gamma-ray direction with highly precise imaging techniques and thus obtain dramatic improvements in sensitivity opens up the field of gamma-ray observations to many exciting new potential discoveries. We discuss the design of a Compton telescope with electron tracking and highlight some of the interesting MeV gamma-ray astrophysics questions that can be addressed by such a telescope.

Hunter, S. D.; Barbier, L. M.; Bloser, P. F.; et al.

443

Neutron and gamma-Ray Spectroscopy and Activation Analysis.  

National Technical Information Service (NTIS)

The objectives of this contract were to carry out basic research in the areas of neutron spectroscopy and dosimetry, gamma-ray spectroscopy and dosimetry, and activation analysis techniques. Early work in gamma-ray spectroscopy was done mostly with the be...

N. C. Rasmussen T. J. Thompson

1966-01-01

444

Towards a complete theory of Gamma Ray Bursts  

Microsoft Academic Search

Gamma Ray Bursts (GRBs) are notorious for their diversity. Yet, they have a series of common features. The typical energy of their $\\\\gamma$ rays is a fraction of an MeV. The energy distributions are well described by a ``Band spectrum'', with ``peak energies'' spanning a surprisingly narrow range. The time structure of a GRB consists of pulses, superimposed or not,

Arnon Dar; Alvaro De Rújula

2003-01-01

445

Solar Flares Fire Up Protons, Make Gamma Rays  

NASA Video Gallery

Solar flares produce gamma rays by several processes, one of which is illustrated here. The energy released in a solar flare rapidly accelerates charged particles. When a high-energy proton strikes matter in the sun's atmosphere and visible surface, the result may be a short-lived particle -- a pion -- that emits gamma rays when it decays. Credit: NASA's Goddard Space Flight Center

gsfcvideo

2012-06-11

446

Evaluation of Potash Grade with Gamma-ray Logs.  

National Technical Information Service (NTIS)

Potassium is an emitter of gamma-ray radiation, consequently deposits of potash can be detected and evaluated using gamma-ray logs. A method originally designed to evaluate uranium deposits in boreholes can also be applied to potash deposits. The method e...

P. H. Nelson

2007-01-01

447

Images of Simultaneous Gamma-Ray Burst Optical Counterpart  

NSDL National Science Digital Library

Astronomers have observed a visible light emitted at the same time as a gamma-ray burst for the first time on January 27, 1999. Six images of this gamma-ray burst are provided at the University of Michigan site.

1999-01-01

448

Gamma-ray Bursts - A Major League Puzzle  

NSDL National Science Digital Library

This site offers extensive information about gamma-ray bursts. The begins with an introduction of basic astronomy concepts and then moves onto gamma-ray properties, how they are detected, the fundamentals of ealy burst observations, theories, and speculations, and finally a summary of information collected from the BASTE project.

Horack, John

2005-06-07

449

On line gamma-ray spectrometry at open sea  

Microsoft Academic Search

Set up and application of a stationary monitoring network for measuring specific ?- activities in the Aegean Sea are described. Three NaI scintillator based spectrometers have been used to detect the gamma rays. The gross counting rate of each system was found to be nearly constant, when there was no rainfall. The volumetric activity of the natural gamma-ray emitter 40K

C. Tsabaris; D. Ballas

2005-01-01

450

Simulation of prompt gamma-ray emission during proton radiotherapy  

Microsoft Academic Search

The measurement of prompt gamma rays emitted from proton-induced nuclear reactions has been proposed as a method to verify in vivo the range of a clinical proton radiotherapy beam. A good understanding of the prompt gamma-ray emission during proton therapy is key to develop a clinically feasible technique, as it can facilitate accurate simulations and uncertainty analysis of gamma detector

Joost M Verburg; Helen A Shih; Joao Seco

2012-01-01

451

Very high energy gamma rays from X-ray binaries  

Microsoft Academic Search

We have reported the discovery of VHE gamma ray emission from the X-ray binary Cen X-3. We report further VHE observations of this object taken in 1998 and 1999. While these new data also show VHE gamma ray emission, no evidence of modulation at either the orbital or pulsar periods is found. .

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver

2000-01-01

452

Very high energy gamma rays from X-ray binaries  

Microsoft Academic Search

We have reported the discovery of VHE gamma ray emission from the X-ray binary Cen X-3. We report further VHE observations of this object taken in 1998 and 1999. While these new data also show VHE gamma ray emission, no evidence of modulation at either the orbital or pulsar periods is found.

P. M. Chadwick; K. Lyons; T. J. L. McComb; K. J. Orford; J. L. Osborne; S. M. Rayner; S. E. Shaw; K. E. Turver

2000-01-01

453

The University of Durham Mark 6 VHE gamma ray telescope  

Microsoft Academic Search

The operation of the University of Durham Mark 6 atmospheric Cerenkov telescope is discussed. The telescope has been used to detect gamma rays at energies >=150 GeV and to achieve good discrimination between gamma ray and hadron initiated showers, using both conventional imaging and novel fluctuation measures. The telescope was commissioned in 1995 and a description of its operation is

P. M. Chadwick; M. R. Dickinson; N. A. Dipper; J. Holder; T. R. Kendall; T. J. L. McComb; K. J. Orford; S. M. Rayner; I. D. Roberts; S. E. Shaw; K. E. Turver

1997-01-01

454

The Third BATSE Gamma-Ray Burst Catalog  

Microsoft Academic Search

The Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO) has triggered on 1122 cosmic gamma-ray bursts between 1991 April 19 and 1994 September 19. These events constitute the Third BATSE (3B) burst catalog. This catalog includes the events previously reported in the 2B catalog, which covered the time interval 1991 April 19 to 1993 March

Charles A. Meegan; Geoffrey N. Pendleton; Michael S. Briggs; Chryssa Kouveliotou; Thomas M. Koshut; John Patrick Lestrade; William S. Paciesas; Michael L. McCollough; Jerome J. Brainerd; John M. Horack; Jon Hakkila; William Henze; Robert D. Preece; Robert S. Mallozzi; Gerald J. Fishman

1996-01-01

455

Science with the new generation high energy gamma- ray experiments  

Microsoft Academic Search

This Conference is the fifth of a series of Workshops on High Energy Gamma- ray Experiments, following the Conferences held in Perugia 2003, Bari 2004, Cividale del Friuli 2005, Elba Island 2006. This year the focus was on the use of gamma-ray to study the Dark Matter component of the Universe, the origin and propagation of Cosmic Rays, Extra Large

M. Alvarez; D. D'Armiento; G. Agnetta; A. Alberdi; A. Antonelli; A. Argan; P. Assis; E. A. Baltz; C. Bambi; G. Barbiellini; H. Bartko; M. Basset; D. Bastieri; P. Belli; G. Benford; L. Bergstrom; R. Bernabei; G. Bertone; A. Biland; B. Biondo; F. Bocchino; E. Branchini; M. Brigida; T. Bringmann; P. Brogueira; A. Bulgarelli; J. A. Caballero; G. A. Caliandro; P. Camarri; F. Cappella; P. Caraveo; R. Carbone; M. Carvajal; S. Casanova; A. J. Castro-Tirado; O. Catalano; R. Catena; F. Celi; A. Celotti; R. Cerulli; A. Chen; R. Clay; V. Cocco; J. Conrad; E. Costa; A. Cuoco; G. Cusumano; C. J. Dai; B. Dawson; B. De Lotto; G. De Paris; A. de Ugarte Postigo; E. Del Monte; C. Delgado; A. Di Ciaccio; G. Di Cocco; S. Di Falco; G. Di Persio; B. L. Dingus; A. Dominguez; F. Donato; I. Donnarumma; M. Doro; J. Edsjo; J. M. Espino Navas; M. C. Espirito Santo; Y. Evangelista; C. Evoli; D. Fargion; C. Favuzzi; M. Feroci; M. Fiorini; L. Foggetta; N. Fornengo; T. Froysland; M. Frutti; F. Fuschino; J. L. Gomez; M. Gomez; D. Gaggero; N. Galante; M. I. Gallardo; M. Galli; J. E. Garcia; M. Garczarczyk; F. Gargano; M. Gaug; F. Gianotti; S. Giarrusso; B. Giebels; N. Giglietto; P. Giommi; F. Giordano; A. Giuliani; J. Glicenstein; P. Goncalves; D. Grasso; M. Guerriero; H. L. He; A. Incicchitti; J. Kirk; H. H. Kuang; A. La Barbera; G. La Rosa; C. Labanti; G. Lamanna; I. Lapshov; F. Lazzarotto; S. Liberati; F. Liello; P. Lipari; F. Longo; F. Loparco; M. Lozano; P. G. Lucentini De Sanctis; J. M. Ma; M. C. Maccarone; L. Maccione; V. Malvezzi; A. Mangano; M. Mariotti; M. Marisaldi; I. Martel; A. Masiero; E. Massaro; M. Mastropietro; E. Mattaini; F. Mauri; M. N. Mazziotta; S. Mereghetti; T. Mineo; S. Mizobuchi; A. Moiseev; M. Moles; C. Monte; F. Montecchia; E. Morelli; A. Morselli; I. Moskalenko; F. Nozzoli; J. F. Ormes; M. A. Peres-Torres; L. Pacciani; A. Pellizzoni; F. Perez-Bernal; F. Perotti; P. Picozza; L. Pieri; M. Pietroni; M. Pimenta; A. Pina; C. Pittori; C. Pontoni; G. Porrovecchio; F. Prada; M. Prest; D. Prosperi; R. Protheroe; G. Pucella; J. M. Quesada; J. M. Quintana; J. R. Quintero; S. Raino; M. Rapisarda; M. Rissi; J. Rodriguez; E. Rossi; G. Rowell; A. Rubini; F. Russo; M. Sanchez-Conde; B. Sacco; V. Scapin; M. Schelke; A. Segreto; A. Sellerholm; X. D. Sheng; A. Smith; P. Soffitta; R. Sparvoli; P. Spinelli; V. Stamatescu; L. S. Stark; M. Tavani; G. Thornton; L. G. Titarchuk; B. Tome; A. Traci; M. Trifoglio; A. Trois; P. Vallania; E. Vallazza; S. Vercellone; S. Vernetto; V. Vitale; N. Wild; Z. P. Ye; A. Zambra; F. Zandanel; D. Zanello

2007-01-01

456

Discovery of Intense Gamma-Ray Flashes of Atmospheric Origin  

Microsoft Academic Search

Detectors aboard the Compton Gamma Ray Observatory have observed an unexplained terrestrial phenomenon: brief, intense flashes of gamma rays. These flashes must originate in the atmosphere at altitudes above at least 30 kilometers in order to escape atmospheric absorption and reach the orbiting detectors. At least a dozen such events have been detected over the past 2 years. The photon

G. J. Fishman; P. N. Bhat; R. Mallozzi; J. M. Horack; T. Koshut; C. Kouveliotou; G. N. Pendleton; C. A. Meegan; R. B. Wilson; W. S. Paciesas; S. J. Goodman; H. J. Christian

1994-01-01

457

GAMMA-RAY SENSITIVITY OF SILVER CHLORIDE EMULSIONS  

Microsoft Academic Search

Silver chloride emulsions were prepared in three different ; conipositions, and their gamma-ray sensitivity and light sensitivity were studied. ; It is suggested that the gamma-ray sensitivity of the emulsions depends to some ; extent upon the sensitivity in the higher light exposure region. It was also ; demonstrated that latent image fading of silver chloride emulsions depends on the

Tomoda

1958-01-01

458

A large-area balloon-borne gamma ray detector  

Microsoft Academic Search

A gamma ray detector sensitive to gamma rays about 10 MeV and having an effective area of about 1 sq m at 8% efficiency is described. A multiwire proportional counter provides data on the direction of secondary electrons, from which the direction of the initiating photons is inferred. The system consists of an array of seven converter plates alternating with

T. Jenkins; P. Albats; G. M. Frye Jr.; R. Kolman; S. Schindler; R. Schreiner; G. B. Thomson; O. B. Mace

1974-01-01

459

Comets, X-ray bursts, and gamma-ray bursts  

Microsoft Academic Search

The proposal, revived by Tremaine and Zytkow (1985), that accretion of comets by neutron stars may be the origin of gamma-ray bursts is considered. This mechanism has difficulty accounting for the observed gamma-ray spectrum and optical counterparts of the bursts. The survival of comets near supernovae is investigated. Ablation rates and the thermal structure of an ablating surface layer are

J. I. Katz

1986-01-01

460

SCATTERING OF GAMMA RAYS BY A STATIC ELECTRIC FIELD  

Microsoft Academic Search

In an effort to observe Delbruck scattering the absolute differential ; cross sections for the elastic scattering of 1.33-Mev gamma rays by lead, tin, ; and uranium and of 2.62-Mev gamma rays by lead and tin have been measured for ; angles between 15 and 105 degrees. The observed scattering is the coherent sum ; of Delbruck, Rayleigh, and nuclear

A. M. Bernstein; A. K. Mann

1958-01-01

461

Gamma-Ray Bursts from Decompressing Neutron Star Material()  

Microsoft Academic Search

We explore the possibility that decompressing neutron star material may be a source for the isotropic gamma-ray bursts observed by the Compton Gamma Ray Observatory. Such material might be ejected during the collision or tidal disruption of a neutron star in a binary sytem or as a result of neutron star seismic activity. Without gravitational confinement, this extremely neutron-rich material

G. J. Mathews; M. B. Aufderheide; M. T. Ressell; R. D. Rogers; B. S. Meyer; D. N. Schramm

1992-01-01

462

Competition of prompt neutrons and. gamma. rays from fission fragments  

Microsoft Academic Search

We have evaluated the effects of competition of neutrons and ..gamma.. rays from the fragments of fissioning nuclei. We discuss the question of deviation of the shape of the spectrum of prompt fission neutrons from a statistical point of view. For a separated fragment we carry out a calculation of the energy carried away by ..gamma.. rays when the excitation

A. E. Savelev; V. P. Gorelov; B. M. Dzyuba

1976-01-01

463

Pore Pressure Detection From the MWD Gamma Ray  

Microsoft Academic Search

Formation pore pressure abnormalities can be detected and evaluated by many known methods. These abnormalities may be identified by drilling parameters, formation log properties, mud analyses, etc. The natural gamma ray intensity, a formation property, can also be used for pressure detection and evaluation. Using the Measurements Whilee Drilling Gamma Ray Log, pore pressure can be interpreted at the well-site,

W. A. Zoeller

1983-01-01

464

Diagram of the Apollo 15 & 16 Gamma-ray Detector  

NSDL National Science Digital Library

This is a diagram of the Apollo 15 & 16 Gamma-ray Detector from the NASA website. Primarily intended to study the Moon's radioactivity, it made measurements of the cosmic gamma-ray background during its trip. It shows measurements in millimeters.

2010-05-05

465

Fundamental Physics with GEV Gamma Rays  

NASA Astrophysics Data System (ADS)

Can we learn about New Physics with astronomical and astro-particle data? Understanding how this is possible is key to unraveling one of the most pressing mysteries at the interface of cosmology and particle physics: the fundamental nature of dark matter. Rapid progress may be within grasp in the context of an approach which combines information from high-energy particle physics with cosmic-ray and traditional astronomical data. I discuss how modifications to the pair annihilation cross section of dark matter with enhanced rates at low relative velocities can lead to a burst of annihilation in the first dark matter halos. I then introduce a novel approach to particle dark matter searches based on the complementarity of astronomical observations across the electromagnetic spectrum, from radio to X-ray and to gamma-ray frequencies.

Profumo, S.

2010-12-01

466

Perspectives on Gamma-Ray Pulsar Emission  

SciTech Connect

Pulsars are powerful sources of radiation across the electromagnetic spectrum. This paper highlights some theoretical insights into non-thermal, magnetospheric pulsar gamma-ray radiation. These advances have been driven by NASA's Fermi mission, launched in mid-2008. The Large Area Telescope (LAT) instrument on Fermi has afforded the discrimination between polar cap and slot gap/outer gap acceleration zones in young and middle-aged pulsars. Altitude discernment using the highest energy pulsar photons will be addressed, as will spectroscopic interpretation of the primary radiation mechanism in the LAT band, connecting to both polar cap/slot gap and outer gap scenarios. Focuses will mostly be on curvature radiation and magnetic pair creation, including population trends that may afford probes of the magnetospheric accelerating potential.

Baring, Matthew G. [Department of Physics and Astronomy, MS-108, Rice University, P. O. Box 1892, Houston, TX 77251-1892 (United States)

2011-09-21

467

Gamma-ray bursts and cosmology.  

PubMed

I review the current status of the use of gamma-ray bursts (GRBs) as probes of the early Universe and cosmology. I describe the promise of long GRBs as probes of the high redshift (z>4) and very high redshift (z>5) Universe, and several key scientific results that have come from observations made possible by accurate, rapid localizations of these bursts by Swift. I then estimate the fraction of long GRBs that lie at very high redshifts and discuss ways in which it may be possible to rapidly identify-and therefore study-a larger number of these bursts. Finally, I discuss the ways in which both long and short GRBs can be made 'standard candles' and used to constrain the properties of dark energy. PMID:17301023

Lamb, D Q

2007-05-15

468

Supernovae and Gamma-ray Bursts  

NASA Astrophysics Data System (ADS)

The properties of the Supernovae discovered in coincidence with long-duration Gamma-ray Bursts and X-Ray Flashes are reviewed, and compared to those of SNe for which GRBs are not observed. The SNe associated with GRBs are of Type Ic, they are brighter than the norm, and show very broad absorption lines in their spectra, indicative of high expansion velocities and hence of large explosion kinetic energies. This points to a massive star origin, and to the birth of a black hole at the time of core collapse. There is strong evidence for gross asymmetries in the SN ejecta. The observational evidence seems to suggest that GRB/SNe are more massive and energetic than XRF/SNe, and come from more massive stars. While for GRB/SNe the collapsar model is favoured, XRF/SNe may host magnetars.

Mazzali, Paolo A.

2012-09-01

469

The Gamma-Ray Burst - Supernova Connection  

NASA Astrophysics Data System (ADS)

A preponderance of evidence links long-duration, soft-spectrum gamma-ray bursts (GRBs) with the death of massive stars. The observations of the GRB-supernova (SN) connection present the most direct evidence of this physical link. We summarize 30 GRB-SN associations and focus on five ironclad cases, highlighting the subsequent insight into the progenitors enabled by detailed observations. We also address the SN association (or lack thereof) with several sub-classes of GRBs, finding that the X-ray Flash (XRF) population is likely associated with massive stellar death whereas short-duration events likely arise from an older population not readily capable of producing a SN concurrent with a GRB. Interestingly, a minorit