ENERGY AND ANGULAR DISTRIBUTIONS OF PHOTONEUTRONS PRODUCED BY 70-MEV. X-RAYS

1955 ◽  
Vol 33 (12) ◽  
pp. 785-796 ◽  
Author(s):  
W. R. Dixon
Keyword(s):  
High Energy ◽  
Zinc Sulphide ◽  
Angular Distributions ◽  
X Rays ◽  
Evaporation Process ◽  
Light Elements ◽  
Energy Distributions ◽  
High Energy Tail ◽  
Nuclear Temperature ◽  
Energy And Angular Distributions

The angular distributions of the photoneutrons produced by 70-Mev. X-rays in seven elements have been measured with a zinc sulphide – lucite scintillation detector. For the heavy elements the distributions are essentially isotropic, indicating the predominance of the evaporation process, while for the light elements there is also an anisotropic component peaked at 90°. The energy distributions of the photoneutrons produced in copper and lead targets have been determined with nuclear emulsions. It is shown that most of the neutrons can be attributed to an evaporation process which is governed by a constant nuclear temperature, the temperature found for copper being 1.2 Mev., and for lead being 1.0 Mev. A high-energy tail on the energy distributions is attributed to direct interactions.

scholarly journals Nuclear disintegrations produced by cosmic rays

1949 ◽  
Vol 196 (1046) ◽  
pp. 325-343 ◽  
Keyword(s):  
Cosmic Radiation ◽  
High Energy ◽  
Energy Spectra ◽  
Angular Distributions ◽  
Excitation Energies ◽  
Wide Range ◽  
High Energy Tail ◽  
Energy And Angular Distributions ◽  
Photographic Emulsions ◽  
Α Particles

Measurements have been made on the energy and angular distributions of the charged particles from disintegration ‘stars’ produced in the silver and bromine nuclei of photographic emulsions exposed to cosmic radiation. The observations extended over a wide range of excitation energies (100 to 700 MeV). The energy spectra and angular distributions of the protons can be explained in all cases by simple evaporation theory. This energy distribution shows also a high-energy tail consisting of direct knock-on protons and slow mesons. At high excitation energies the α-particles exhibit collimation effects which are probably due to localized ‘boiling’ or a form of fission.

THE PHOTOPROTONS EMITTED FROM OXYGEN-16 NUCLEI

1956 ◽  
Vol 34 (10) ◽  
pp. 1022-1032 ◽  
Author(s):  
D. L. Livesey
Keyword(s):  
Excitation Function ◽  
Interference Effect ◽  
Proton Energy ◽  
Photographic Plate ◽  
Electric Quadrupole ◽  
High Energy ◽  
Angular Distributions ◽  
Energy Distributions ◽  
Plate Method ◽  
Oxygen Gas

The photographic plate method has been used to study photoprotons emitted from oxygen gas exposed to bremsstrahlung of maximum energies 30, 35, and 70 Mev. The proton energy distributions above 5 Mev. show maxima corresponding to peaks in the (γ, p) excitation function at 20.7, 21.9, and 24.0 Mev. The proton angular distributions are anisotropic, in general agreement with a sin2θ function, but the high-energy protons exhibit a degree of asymmetry about the 90° angle which may be due to a small electric-quadrupole interference effect.

scholarly journals Modelling the Soft X-ray Excess in E1615+061

1994 ◽  
Vol 159 ◽  
pp. 317-317
Author(s):  
M. Bałucińska-Church ◽  
L. Piro ◽  
H. Fink ◽  
F. Fiore ◽  
M. Matsuoka ◽  
...  
Keyword(s):  
Power Law ◽  
Column Density ◽  
High Energy ◽  
X Rays ◽  
Hard Component ◽  
X Ray ◽  
Simple Power ◽  
High Energy Tail ◽  
Photon Index ◽  
Best Fit

SummaryWe report results of an international UV – X-ray campaign in 1990–1992 involving the IUE, Rosat and Ginga satellites to observe E1615+061, a Seyfert 1 galaxy with peculiar spectral and intensity behaviour over the last 20 years. The source has been found to be stable in its medium state during the observations. The Ginga (1–20 keV) spectrum of E1615+061 is adequately represented by a simple power law with a photon index α = 1.8 ± 0.1. However, α ∼ 2, as expected for the intrinsic power law component in a reflection model, cannot be ruled out statistically. The Rosat PSPC (0.1–2 keV) spectra collected during the All Sky Survey and the AO-1 phase can be well-described by a simple power law (α = 2.2 ± 0.1) with cold absorber (NH = 3.5 ± 0.3 · 10λ20 H/cmλ2). Both the photon index being significantly different than that obtained from the Ginga spectrum and the column density being smaller than the galactic column (NH ∼ 4.2 · 10λ20 H/cmλ2) give an indication of a soft excess over and above the hard component seen in the Ginga spectrum. E1615+061 has been observed with IUE in 1990 and in 1992. The source was stable and the colour excess E(B-V) derived from the data = 0.1 is in good agreement with that expected from the galactic absorption.To parameterise the soft excess we fitted the Rosat data with a two-component model consisting of a power law, and a blackbody or thermal bremsstrahlung, with a single galactic absorption term. The column density and the slope of the power law were kept constant. The blackbody temperature was 80 ± 6 eV and 63 ± 12 eV for photon index equal to 1.8 and 2.0, respectively, whereas the bremsstrahlung temperature was 220 ± 40 eV and 115 ± 30 eV for the two cases.An attempt to model the soft excess seen in the Rosat PSPC spectrum has been made assuming that the soft excess is the high energy tail of a disc spectrum which peaks in the UV part of the spectrum. Additionally it was assumed that there is a hard component contributing to the spectrum from UV to X-rays with parameters as described by the Ginga spectrum. The best fit parameters: the mass of the central source and the mass accretion rate were around 5 ± 1 · 10λ6 M⊙ and 0.2 ± 0.04 M⊙/yr, respectively.Our modelling shows that the soft X-ray excess can be described (χredλ2 < 1.2) as the high energy tail of an accretion disk spectrum if the intrinsic power law is quite steep (α = 2). The main contribution to the residuals in the Rosat PSPC range comes from 0.3–0.6 keV, with a tendency for these residuals to increase when the slope gets flatter. The accretion luminosity is ∼ 6.5 · 10λ44 erg/s for the best fit parameters, i.e. about the Eddington luminosity.

scholarly journals Comptonization by reconnection plasmoids in black hole coronae I: Magnetically dominated pair plasma

2021 ◽  
Author(s):  
Navin Sridhar ◽  
Lorenzo Sironi ◽  
Andrei M Beloborodov
Keyword(s):  
Black Holes ◽  
High Energy ◽  
Particle Energy ◽  
X Rays ◽  
Particle In Cell ◽  
Pair Plasma ◽  
Electron Positron ◽  
High Energy Tail ◽  
Hard State ◽  
Magnetic Tension

Abstract We perform two-dimensional particle-in-cell simulations of reconnection in magnetically dominated electron-positron plasmas subject to strong Compton cooling. We vary the magnetization σ ≫ 1, defined as the ratio of magnetic tension to plasma inertia, and the strength of cooling losses. Magnetic reconnection under such conditions can operate in magnetically dominated coronae around accreting black holes, which produce hard X-rays through Comptonization of seed soft photons. We find that the particle energy spectrum is dominated by a peak at mildly relativistic energies, which results from bulk motions of cooled plasmoids. The peak has a quasi-Maxwellian shape with an effective temperature of ∼100 keV, which depends only weakly on the flow magnetization and the strength of radiative cooling. The mean bulk energy of the reconnected plasma is roughly independent of σ, whereas the variance is larger for higher magnetizations. The spectra also display a high-energy tail, which receives ∼25 per cent of the dissipated reconnection power for σ = 10 and ∼40 per cent for σ = 40. We complement our particle-in-cell studies with a Monte Carlo simulation of the transfer of seed soft photons through the reconnection layer, and find the escaping X-ray spectrum. The simulation demonstrates that Comptonization is dominated by the bulk motions in the chain of Compton-cooled plasmoids and, for σ ∼ 10, yields a spectrum consistent with the typical hard state of accreting black holes.

Observation of Hot Electron Field Emission

2000 ◽  
Vol 621 ◽  
Author(s):  
Jonathan Shaw
Keyword(s):  
High Energy ◽  
Metallic State ◽  
Hot Electron ◽  
Many Body ◽  
Energy Distributions ◽  
Field Emitter Arrays ◽  
High Energy Tail ◽  
Electron Field ◽  
Gap States

ABSTRACTWe report energy distributions of silicon Field Emitter Arrays coated with 50A of ZnO. The distributions reflect changes in the ZnO conductivity induced by annealing in vacuum, temperature, and annealing in hydrogen. An additional coating of titanium performed in-situ produced large additional changes. Emission from the ZnO at energies near the Fermi level increased with gate voltage only after hydrogen annealing, when hot, and after Ti coating. In those same cases the emission distribution contained a tail at energies above EF. The highenergy emission tail is due to a many-body or Auger process whereby holes injected below EF create hot electrons. Although emission from ZnO occurred at energies up to 8eV below EF, no high-energy tail was observed in the normal case. Thus emission appears to occur from isolated electrons in ZnO gap states in cases where the distribution lacks a high-energy tail. Conversely, emission above EF suggests that emission occurred from a metallic state such as an accumulated conduction band.

scholarly journals Soft X-rays of AGN: Emission from Accretion Disks?

1997 ◽  
Vol 163 ◽  
pp. 805-806
Author(s):  
R. Staubert ◽  
T. Dörrer ◽  
C. Müller ◽  
P. Friedrich ◽  
H. Brunner
Keyword(s):  
Active Galactic Nuclei ◽  
Accretion Disks ◽  
Galactic Nuclei ◽  
High Energy ◽  
X Rays ◽  
X Ray ◽  
Sky Survey ◽  
High Energy Tail ◽  
Low Energies ◽  
Excess Component

Soft X-ray spectra of many Active Galactic Nuclei (AGN) show structure which suggests excess emission at low energies, mostly below 1 keV. This was confirmed by the ROSAT spectra (0.1–2.4 keV) AGN in our samples which generally have steeper power law spectra than the canonical index of 0.7. The soft excess component may be the high energy tail of the big blue bump which in turn may be due to the integrated emission from an accretion disk around the central black hole.We discuss results of our spectral analysis of two different samples of AGN: 1) QSO/Seyfert-I from the ROSAT All Sky Survey (RASS) and 2) radio-quiet QSO from ROSAT Pointed Observations. The ROSAT data are combined with UV Data from IUE and hard X-ray data from various hard X-ray missions.

scholarly journals An X-ray Spectral Survey of BL Lac Objects

1989 ◽  
Vol 134 ◽  
pp. 191-193 ◽  
Author(s):  
P. Barr ◽  
P. Giommi ◽  
A. Pollock ◽  
G. Tagliaferri ◽  
D. Maccagni ◽  
...  
Keyword(s):  
High Energy ◽  
Oxygen Absorption ◽  
X Rays ◽  
Bl Lac Objects ◽  
Synchrotron Source ◽  
X Ray ◽  
High Energy Tail ◽  
Bl Lac ◽  
Spectral Survey ◽  
Bl Lacs

A wide variety of X-ray spectral forms has been reported in BL Lac objects. Concave spectra, i.e. a steep soft X-ray spectrum with a flat high energy tail, have been reported in a few of the brightest BL Lacs (e.g Urry 1986). Conversely, convex spectra (steep hard X-rays, flat soft X-ray spectrum) have also been reported, sometimes in the same objects (Madejski 1985, Barr et al 1988, George et al 1988). The high energy tails have usually been invoked as a signature of synchrotron-self-Compton emission. Two conflicting interpretations of the convex spectra have been made. Urry et al (1986) suggest absorption by a partially ionised medium, probably intrinsic to the BL Lac object, following the identification of an Oxygen absorption trough in the Einstein OGS spectrum of PKS 2155-304 by Canizares and Kruper (1984). Conversely, Barr et al (1988) attribute the hard X-ray steepening to energy loss mechanisms operating on a synchrotron source.

scholarly journals 1,000,000 Giant Pulses from the Crab Pulsar

2017 ◽  
Vol 13 (S337) ◽  
pp. 380-381
Author(s):  
Mitchell B. Mickaliger ◽  
Ben W. Stappers ◽  
Cees G. Bassa ◽  
Aldus G. Fletcher
Keyword(s):  
Single Pulse ◽  
High Energy ◽  
Daily Basis ◽  
Large Set ◽  
Crab Pulsar ◽  
Energy Distributions ◽  
Giant Pulses ◽  
High Energy Tail ◽  
Insight Into ◽  
Shed Light

AbstractThe Crab pulsar was first detected soon after the discovery of pulsars, and has long been studied for its unique traits. One of these traits, giant pulses that can be upwards of 1000 times brighter than the average pulse, was key to the Crab’s initial detection. Giant pulses are only seen in a few pulsars, and their energy distributions distinguish them from normal pulsed emission. There have been many studies over a period of decades to measure the power-law slope of these energy distributions, which provide insight into the possible emission mechanism of these giant pulses.The 42-foot telescope at Jodrell Bank Observatory monitors the Crab pulsar on a daily basis. We have single-pulse data dating back to 2012, containing roughly 1,000,000 giant pulses, the largest sample of Crab giant pulses to date. This large set of giant pulses allows us to do a range of science, including pulse-width studies and in-depth studies of giant-pulse energy distributions. The latter are particularly interesting, as close inspection of the high-energy tail of the energy distribution allows us to investigate the detectability of extragalactic giant-pulsing pulsars. Also, by calculating rates from these energy distributions, we may be able to shed light on a possible link between Fast Radio Bursts and giant pulses.

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