Primary Γ-rays Research Articles

Stereoscopic observations of gamma rays at the Whipple observatory

Observations of photons at E ≥ 550 GeV from the Crab Nebula are presented and used to assess the potential of multi-telescope systems for γ-ray astronomy. The Whipple observatory 10 m and 8 m imaging atmospheric Čerenkov telescopes have been used to provide a stereoscopic view of air showers to make a more complete measurement of air shower parameters. Here we present a measurement of the spread in the arrival direction of primary γ-rays originating from a point source. The data show that the shower arrival direction can be reconstructed with an accuracy of σ = 0.°14.

Inverse Compton Scattering: Gap Parameters, Energy Loss of the Particles, and Possible Implications for Pulsar Radio Emission

The process of inverse Compton scattering (ICS) of high-energy particles off the photons above the pulsar polar cap is the dominant mechanism causing polar breakdown. In this paper, an approximate analytic description of the parameters of the two modes of the ICS namely, the ICS gap and the thermal ICS gap, are derived under the assumption of a multipolar magnetic field configuration in the neutron star's vicinity. For typical values of P, B, and T, the ICS usually has a lower height and smaller potential drop but results in larger factors for the secondary particles ejected from the gap. Above the polar the secondary particles do not keep the energy gained from the primary γ-rays, as expected. They will lose much of their energy via different mechanisms, among which the ICS process is dominant, as pointed out previously by different authors. We calculate the height-dependent factor decrease of the secondary particles via ICS above the gap. It is found that, for a certain polar cap temperature and a temperature of the whole neutron star surface, the particles will lose most of their energy as a result of the scattering within a not very high altitude (usually ~0.1-0.01 neutron star radii) after they escape from the then keep nearly unchanged energies for a long distance of several to a dozen stellar radii (the so-called platform), and then endure severe energy loss again, due to the nonresonant scattering dominant at higher altitudes. This effect has a direct implication for pulsar radiation theories, if pulsar radio emission comes from tens or hundreds of kilometers above the neutron star surface, which is just the height range of the Lorentz platform that we discuss. We caution that, if the polar cap temperature of a pulsar is relatively high, but not high enough to switch its to the thermal mode, the secondary particles will receive lower energies from the resonant ICS but endure severe energy loss above the so that their factors may be below the possible threshold for pulsar radio emission. In this case, the pulsar will null, or be radio-quiet. Some pulsars' nulling feature and Geminga's radio-quiet behavior may be a consequence of this effect.

What we can infer about the nuclear cosmic ray composition from the EAS longitudinal development

Abstract Results from a detailed Monte Carlo simulation for electromagnetic and hadronic cascades in the atmosphere, generated by primary γ-rays, p, O and Fe are provided in the primary energy range 10 12 –10 16 eV for vertical incident showers. In the simulation of the Extensive Air Showers (EAS) development, the CORSIKA (COsmic Ray SImulator for KAscade) code has been used to perform a full simulation of the electromagnetic and hadronic interactions. The main aims of this simulation are to obtain accurate information on the longitudinal development of the electromagnetic component, for both pure electromagnetic and hadronic cascades, for different primary cosmic rays. Results on the depencdence of the shower size and the photon number with primary energy are obtained. Ratios between the maximum development depth parameter and primary particle energy or the shower size have been studied and predicted values for the electron and photon content and fluctuations on these parameters have been determined at the maximum development depth of the EAS and at mountain altitude ( X = 800 g cm −2 ). We also seek to provide relations to interpret the experimental data, for those who do not have detailed simulation calculations available and also to provide material for a full and deep comparison of air shower Monte Carlo codes.

Method to infer about the nuclear UHE cosmic-ray composition from the EAS lateral development

Results from a detailed Monte-Carlo simulation for electromagnetic and hadronic cascades in the atmosphere, generated by primary γ-rays, p, O and Fe are provided in the primary energy range 10 12–10 16 eV for vertical incident showers. In the simulation of the Extensive Air Showers (EAS) development, the CORSIKA (COsmic Ray SImulator for KAscade) code has been used to perform a full simulation of the electromagnetic and hadronic interactions. The lateral development of the electromagnetic component, for both, pure electromagnetic and hadronic cascades have been deeply investigated and the NKG-type functions have been fitted to the lateral developments, to determine the lateral age parameters. Results on the variation of the shower size with the lateral age parameter and primary energy are obtained, as well as fluctuations on shower size at maximum development depth of the EAS and at mountain altitude ( X = 800 g cm −2). The main aim of this work is to obtain an accurate procedure to discriminate the nuclear composition of the UHE cosmic rays from the gamma rays background. We also seek to provide relations to interpret the experimental data, for those who do not have detailed simulation calculations available and also to provide material for a full and deep comparison of air shower Monte-Carlo codes.

Nuclear levels in 187W

Levels in 187W have been studied up to 2.2 MeV with the ( d, p) and ( n, γ) reactions. The ( d, p) studies were performed at deuteron energies of 24 and 28 MeV and at two angles of 30° and 50° by using the high resolution Q3D spectrograph in Munich. Primary and secondary γ-rays and γ-γ coincidences were studied with Ge detectors. The combination of these results with the previously known ones allows us to extend the existing level scheme and refine some of its structure assignments. Most of the low-lying states have been classified in terms of the Nilsson model with the extension of some vibrational degrees of freedom. The possibility for the coexistence of triaxial or oblate shapes in 187W is observed in the form of anti-aligned states with a bandhead of 9 2 − at 364 keV. The polarization effects towards the triaxial shape produced by the odd neutron in specific Nilsson orbitals have been studied. The calculated polarization energies for some γ-driving orbitals are comparable with the prolate-oblate energy difference which indicates the possibility of the stabilization of triaxial or oblate shapes in these states.

Excitation study of high-lying states of differently shaped heavy nuclei by the method of two-step cascades

Recently obtained primary transition intensities from two-step gamma-ray cascade investigations of 14 heavy nuclei: 137,138,139 Ba, 146 Nd, 150 Sm, 156,158 Gd, 160 Tb, 164 Dy, 168 Er, 174 Yb, 181 Hf, 196 Pt and 198 Au are analysed. Experiments based on thermal neutron capture were undertaken mainly at the Frank Laboratory of Neutron Physics. Comparing these measured intensities and statistical model predictions, some properties of compound-state depopulation were derived. For the spherical nuclei of 137,138,139 Ba, 146 Nd, 196 Pt and 198 Au very intense cascades with high-energy primary transitions were observed. Rather different is the behaviour of the cascade intensity in the strongly deformed nuclei of 156,158 Gd, 160 Tb, 164 Dy, 168 Er and in the transitional nucleus of 150 Sm - where the intensity of primary γ-rays E 1 ∼ 2–3 MeV exceeds the calculated value.

Levels of 137Ba studied with neutron-induced reactions

The nucleus 137Ba has been studied via primary and secondary γ-rays as well as γγ-coincidences following thermal-neutron capture and inelastic neutron scattering. A level scheme was established up to 4.7 MeV consisting of 37 levels including 91 transitions. The neutron binding energy was determined to be 6905.59(8) keV. The thermal-neutron-capture cross section and isomer production of the 11 2 − state at 661.6 keV were determined to be 0.65 −0.04 +0.08 and 0.0098(4) b respectively. The experimental data on excitation energies and electromagnetic properties are compared with predictions of the SU(5) limit of the interacting boson-fermion model. A satisfactorily good agreement between experiment and theory can be stated.

Search for a high-energy γ-ray burst by an airborne experiment

A search for high-energy γ-ray bursts was carried out by an airborne experiment. We loaded a lead-glass-based electron-telescope onto a cargo airplane and measured secondary electrons at airplane altitude. The energy threshold of this method was 20 GeV for primary γ-rays; the angular resolution was 1.5 degrees. We searched for transient events from the same directions within various time windows. The total exposure time was 54.6 hours, and we set upper limits for the full-sky rates of high-energy γ-ray bursts.

Molecular dynamics simulations applied to the determination of nuclear lifetimes from Doppler-broadened γ-ray line shapes produced in thermal neutron capture reactions

Molecular dynamics simulation of slowing down of nuclei produced in thermal neutron capture reactions is used to deduce lifetime values of excited nuclear states in 36 Cl[τ=63±2 fs (E x=1.959 MeV) , 48±26 (2.49), 31±5 (2.68), 21±1 (2.86), 59±3 (3.60)], 49 Ti[29±2 (1.76), 79±4 (3.18), 16.2±0.7 (3.26)] , 54 Cr [112±22 (2.62), 10.3±0.5 (3.07), 24±2 (3.72)], 57 Fe [52±4 (1.63), 38±3 (1.73)] , 59 Ni [40±7 (2.89), 37±5 (3.18), 6.5±1.4 (4.14)], and 61 Ni [73±14 (2.12)] from Doppler-broadened γ-ray line shapes. It is characteristic for the line shapes that they are produced by emission of secondary γ-rays from nuclei recoiling at ultra-low velocities, below 10 5 m/s, the recoil energy being imparted to nuclei by emission of typically 5–10 MeV primary γ-rays. The novel method of analysis used in the deduction of the lifetime values is described. The relevance of interatomic potentials on the reliability of lifetime values is considered.

The origin of the continuum of Active Galactic Nuclei

The high-energy continuum of active galactic nuclei can be interpreted by nonthermal models in which electron-positron pairs play a crucial role. The produced primary γ-rays interact with softer photons in the inner, high photon density regions of the source. The created pairs are relativistic, and contribute to the emission, especially in the X-ray band. When the photon density is large enough, therefore for large values of the luminosity-to size ratio, the spectrum produced by the reprocessing due to pairs is predicted to have a characteristic spectral index of one. This power law continuum partly impinges on cold matter, possibly in an accretion disk. The resulting Compton reflected radiation contributes to the X-ray emission, and the predicted overall spectrum is in agreement with the observed shape of the high-energy continuum. The proposed model is easily testable: observations in the hard—X-ray band above (30÷50) keV are crucial to discriminate these nonthermal models against thermal ones.

Gamma-ray production from52Cr(n, xγ) reactions at 14.6 MeV

We study γ-ray production from52Cr(n, xγ) reactions at 14.6 MeV neutron incident energy. Measured data relevant to production cross-sections for discrete γ-rays, total γ-ray spectrum and average γ-ray multiplicities, are analyzed in terms of the advanced statistical model of nuclear reactions, including pre-equilibrium emission of primary particles and γ-rays. The latter proves useful in rough description of high-energy part of the γ-ray spectrum. We find that integral quantities and data involving sufficient averaging (such as total γ-ray production, average γ-ray energies, average γ-ray multiplicities) can be predicted with a good precision. This is valid also for strong discrete γ lines. Generally, however, discrete γ-ray production cross-sections cannot be safely predicted better than within a factor of two. Things may be even worse for particular portions of the total γ-ray spectrum. Our findings set limits on predictability of many requested γ-ray production data even by most carefully applied theoretical methods.

Observation of Coulomb excitation of unstable nuclei utilization of a secondary beam

An experimental technique to detect γ-rays from secondary-beam Coulomb excitation was developed. A secondary beam of 76Kr produced by the inverse reaction 9Be( 70Ge, 3n) was Coulomb excited by a 208Pb target. Weak γ-rays from the secondary-beam Coulomb excitation were discriminated from those of a primary beam by measuring triple coincidences of primary γ-rays, scattered particles and emitted γ-rays from the second target. Coulomb excitation of the unstable nucleus was observed for the first time in the medium heavy mass region. The observed yield of the 2 + → 0 + transition in 76Kr is consistent with that which is estimated from the known B(E2: 0 + → 2 +) for this nucleus.

A multidimensional analysis of the Cherenkov images of air showers induced by very high energy γ-rays and protons

A multidimensional analysis based on Bayes decision rules and nonparametric multivariate density estimation is proposed for classification of the Cherenkov light images of air showers registered by an air Cherenkov detector (ACD) with the multichannel light receiver. The differences in the angular size of the image, its orientation and position in the focal plane of the ACD and spectral composition of the Cherenkov light are used in the analysis to distinguish the showers induced by primary γ-rays from showers induced by background cosmic rays (CR). It is shown that the usage of several image parameters together with their correlations can lead to a reduction of the CR background rejection down to a few tenths of a percent while retaining about 50% of useful (γ-ray-induced) events.

The Heidelberg cosmic ray project - aims and status

A new type of Extensive Air Shower (EAS) array is proposed which is based on the measurement of individual cosmic ray tracks and muon identification. Air showers can be detected in the range from 10 12 eV up to the highest energies. The direction of the primary γ-ray will be reconstructed with accuracies typically in the range of 0.1° to 0.3°. The sensitivity for the detection of point sources will be improved by about a factor of 100 in comparison to existing conventional EAS arrays or Atmospheric Cerenkov Telescopes.

Cosmic ray tracking — A new approach to high-energy γ-astronomy

A new type of extensive air shower (EAS) array is proposed which is based on the measurement of individual cosmic ray tracks and muon identification. Air showers can be detected in the range from a few times 10 12 eV up to the highest energies. The direction of the primary γ-ray will be reconstructed with accuracies typically in the range of 0.1°–0.3°. The sensitivity for the detection of point sources will be improved by about a factor of 100 in comparison to existing conventional EAS arrays or atmospheric Cherenkov telescopes.

The age parameter of ultrahigh-energy cosmic γ-ray showers

The lateral-age parameter of EAS as a possible parameter for distinguishing between photonic- and nucleonic-initiated showers is investigated by Monte Carlo simulation. Contrary to what has been assumed by many workers in the past, we find that γ-ray-initiated showers tend to be younger at most observing levels, with the difference being outside experimental resolution at sea level. This makes difficult to understand some reported directional excesses of ultrahigh-energy cosmic-rays as arising from primary γ-rays.

Inelastic Scattering of γ-Rays byK-Shell Electrons of Metallic Copper and Iron. I. Scattering byA2-Term

Theoretical study of γ-ray inelastic scattering by K -shell electrons for the case of q a ∼1 is presented, where \(\hbar q\) is the momentum transfer of the primary γ-ray and a is the orbital radius of the K -shell electron. Details of calculation for the contribution of A 2 -term to the scattering, A being the vector potential, are given a using a single orthogonalized plane wave for the wave function in the scattering state. The present theoretical result is compared with the experimental one obtained by Namikawa and Hosoya (NH) (Phys. Rev. Lett. 53 (1984) 1606): scattering of 59.57 keV γ-rays by K -shell electrons of Cu and Fe. The C peak and R peak found experimentally by NH are reproduced theoretically though the height of the R peak is 1/3 of that of the experimental result by NH.

On the Inelastic Scattering of γ-Rays by Deeply Bound Electrons

The inelastic scattering of γ-rays by a bound electron is investigated theoretically for the case of ka ∼1, where \(\hbar k\) is the momentum transfer of the primary γ-ray and a is the orbital radius of the bound electron, respectively. By tire use of orthogonalized plane wave (OPW) for an electron wave function in the scattering state, the result of calculation is compared with that of the experiment obtained by Namikawa and Hosoya (Phys. Rev. Left. 53 (1984) 1606): scattering of 59.57 keV γ-rays by K -shell electrons of Cu. The C peak and R peak in the experimental spectrum are obtained theoretically, but the height of the R peak is approximately 1/3 that of the experirnental result.

Average resonance capture studies of 185, 187W: The Nilsson model and the SU(3) Bose-Fermi symmetry scheme

Complete sets of low-lying 1 2 − and 3 2 − levels in 185W and 187W have been obtained using measurements of primary γ-rays following average resonance neutron capture at mean incident neutron energies of 2 and 24 keV. The results are discussed in terms of both the Nilsson model and the SU(3) boson-fermion symmetry scheme appropriate to this region. The data highlights the advantages and deficiencies of both frameworks, and shows that neither is able to describe the complete spectrum of low-lying low-spin energy levels. The two approaches are outlined and compared and the role of the missing degrees of freedom in each is discussed.

Energetic Radiation from Rapidly Spinning Pulsars. II. VELA and Crab

view Abstract Citations (427) References (25) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Energetic Radiation from Rapidly Spinning Pulsars. II. VELA and Crab Cheng, K. S. ; Ho, C. ; Ruderman, M. Abstract The growth of charge-depleted regions (gaps) in the outer magnetosphere of rapidly spinning magnetized neutron stars is limited by e± production. In the Vela pulsar a pair of e+ and e- created within the gap (primaries) are accelerated in opposite directions to extreme relativistic energies. The primary e-/e+ produce primary γ-rays through inverse Compton scattering on IR photons. Primary γ-rays are sufficiently energetic to produce (secondary) e± pairs in collisions with this same IR photon flux. Secondary synchrotron radiation by these pairs gives crossed fan beams of γ-rays and weaker ones of X-rays. Collisions of the hard secondary γ-rays with the secondary crossed beam soft X-rays give a large flux of lower energy e± (tertiary) pairs which fill much of the outer magnetosphere. It is the (tertiary) IR synchrotron radiation from tertiary pairs through the outer gap which initiates the entire series of pair production processes. For Vela, the calculated observable consequences include (a) twin cusped γ-ray pulses with photon spectrum F(ω) ≍ ω-3/2 ln (3 GeV/hω) from 3 GeV to about 102 KeV; (b) total fan beam radiated power 10-2 the pulsar spin-down energy loss rate; (c) an X-ray spectrum F(ω) ≍ ω-2/3 below 102 KeV; (d) weak, more closely spaced twin optical pulses from the tertiary radiation with power 10-5 that of the secondary γ-rays; (e) and e± outflow of 1036 s-1; (f) a double pulse of 1012 - 1013 eV γ-rays with about 10-2 the γ-ray power. Model Crab pulsar emissions are considered with emphasis on differences from those of Vela. Crab primary outer gap e+/e- lose most of their energy to curvature γ-rays, which convert to e± pairs in collisions with X-rays. These X-rays come from the synchrotron (secondary) emission from such (secondary) pairs created beyond the gap boundary. Inverse Compton scattering of secondary e± on the secondary X-rays boosts a fraction to γ-rays. The combination of secondary synchrotron and inverse Compton emission into twin fan beams gives the Crab pulsar spectrum from optical to GeV energies. Other mechanisms give the Crab's double pulsed radio and 1012 - 1013 eV emission and the possibility of 1015 eV nucleon beams. Publication: The Astrophysical Journal Pub Date: January 1986 DOI: 10.1086/163830 Bibcode: 1986ApJ...300..522C Keywords: HYDROMAGNETICS; PULSARS; RADIATION MECHANISMS; STARS: NEUTRON full text sources ADS | data products SIMBAD (3) Related Materials (1) Part 1: 1986ApJ...300..500C