Gamma-ray Line Emission Research Articles

Deexcitation gamma-ray line emission from solar flare magnetic loops

A Monte Carlo simulation that follows individual ions throughout a solar flare magnetic loop is developed. Included are energy losses due to Coulomb collisions, removal by nuclear reactions, magnetic mirroring in the convergent flux tubes, and MHD pitch-angle scattering in the corona. Calculations are made of the depth distribution of nuclear deexcitation line production, the time dependence of the production of the lines, and the escape probability of the line photons from the solar atmosphere. It is found that the inclusion of mirroring and pitch-angle scattering leads to time profiles which are in good agreement with observations. This suggests that the decaying portions of the time profiles of gamma-ray emission observed from solar flares could be governed by transport and not by acceleration.

High-resolution observations of gamma-ray line emission from SN 1987A

Observations of SN 1987A made with a balloon-borne gamma-ray spectrometer comprising an array of high-purity germanium detectors on October 29-31, 1987 are presented. High resolution data, typically 2.5 keV at 1.33 MeV, were obtained for two transists of the supernova with interspersed background data. A preliminary estimation of line flux is presented. It is found that there is evidence of dynamical broadening of the 847 keV line. It is suggested that this line may be an emission from the first excited state of Fe-56 due to the radioactive decay of Co-56 providing evidence for nucleosynthesis in the supernova.

Gamma-ray line emission from SN1987A

The gamma-ray spectrometer (GRS) on NASA's Solar Maximum Mission satellite (SMM) has observed a significant (>5δ) net line flux at ˜847 keV in the background-subtracted spectrum of SN1987A—accumulated between 1 August and 31 October 1987. This is the energy of the strong gamma-ray line from decay of 56Co, which was predicted1,3 to be seen from supernovae. The inferred average line flux during this period is ˜(1.0±0.25) x 10−3 photons cm−2 s−1 at an energy of 843 ± 5 keV. This feature cannot be explained by any statistical or systematic fluctuations observed in the seven previous years of GRS data. There is also evidence for the 1,238-keV line from 56Co decay, with an average flux of ∼(6±2)xlO−4 photons cm−2 s−1 The quoted photon fluxes for both lines are preliminary. This observation confirms that 56Co is present in the supernova ejecta (as implied by the light curve4,5) and that nucleosynthesis took place during the explosion. The first appearance of the gamma-ray lines was roughly coincident with the first detections of X-rays by Ginga and MIR6,7.

The SEP matter sample and its correlation with gamma-ray observations

The current state of Solar Energetic Particle (SEP) observations above ∼ 1 MeV nucl.−1 is examined and compared to gamma-ray observations to assess the degree to which current understanding of the solar flare process can explain the observations and to delineate directions for future research. The particle acceleration appears to be due to either Fermi-type stochastic processes or flare-generated shock waves, but the available data can not yet distinguish between these two mechanisms. Large SEP events generally show no gamma-ray emission and may be examples of shock acceleration in the corona. The pre-accelerated matter, however, seems to be a mixture of hot (> 106 K) and cold ( 10). These enrichments may be due to thermal/ pressure gradient diffusion and neutral gravitational settling. Gamma-ray line emission events are often associated with small, ‘electron rich’ SEP events, some of which also include heavy ion enhancements. While time profiles of the gamma emission show that electrons and ions can be accelerated promptly (t < 1 s), comparison of the inferred flux of particles at the Sun with SEP observations in space indicate that few of these particles escape. The conditions for SEP release to interplanetary space have yet to be systematically detailed.

Prospects for gamma-ray line observations of individual supernovae

The gamma-ray line emission from individual type I and type II supernovae are studied using numerical simulations and photon propagation codes to predict the flux levels and line shapes. For both types, the gamma ray lines with the highest flux from an individual event are the 0.847 and 1.238 MeV lines from the Ni-56 to Co-56 to Fe-56 decay chain. For type I supernovae, the 0.847 MeV line peaks at about 70 days after event onset. The historical record indicates an approximate discovery rate of once in 10 years for balloon-borne instruments, once in two to three years for the Gamma-Ray Observatory, and once in one to two years for a proposed space mission. The 0.847 MeV line flux from type II supernovae peaks at about 600 days after event onset at a low level which restricts observations to the events in the Galaxy and its nearest neighbors. The expected line shape is narrower than for type I supernovae.

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

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

A determination of the (He-3)/H ratio in the solar photosphere from flare gamma-ray line observations

The time dependence of the 2.223 MeV gamma-ray line emission from the capture of flare-produced neutrons in the solar photosphere provides a sensitive measure of the He-3 abundance there. Monte Carlo calculations have been made of this time dependence as a function of both He-3 abundance and observing angle for neutrons produced by thick-target interactions of flare-accelerated ions with a range of incident energy spectra and angular distributions. Assuming a mirroring distribution, suggested by other observations, it is found that the Solar Maximum Mission measurements of the time dependence of the 2.223 MeV line emission from the solar flare of June 3, 1982, imply a solar photospheric (He-3)/H ratio of (2.3 + or - 1.2) x 10 to the -5th at the 90 percent confidence level. 44 references.

Solar flare neutron production and the angular dependence of the capture gamma-ray emission

The depth dependence of the production of neutrons and capture gamma-ray line emission are calculated by Monte Carlo simulation of the nuclear processes taking place when flare-accelerated ions interact with the solar atmosphere. The calculations also give the heliocentric-angular dependence of the 2.223 MeV neutron capture line emission as a function of accelerated-ion energy spectrum and angular distribution. These results are compared with observations to determine the energy spectrum shape and total ion number for various flares.

Gamma-ray burst detection capabilities of comptel

The imaging gamma-ray telescope COMPTEL, capable of detecting gamma rays in the 1 to 30 MeV range, is one of four experiments onboard NASA's Gamma-Ray Observatory GRO. Besides its primary objectives COMPTEL will contribute to the understanding of cosmic gamma-ray bursts. Summarising, COMPTEL localises bursts (S (E > 1 MeV) ≥ 2.10 −6 erg/cm 2) within 1 sr FOV to better than 1° at medium gamma-ray energies, measures continuum energy spectra in the range 0.1 MeV to 20 MeV with fluence S ≥ 6.9 10 −7 erg/cm 2 (5 σ, E≥100 keV), measures gamma-ray lines with detector resolution 9.6% (at 0.5 MeV) and 7.0% (at 1.5 MeV) and determines time histories of both gamma-ray line and continuum emission with t ≥ 0.1 sec resolution.

Cosmic gamma-ray lines

We review recent observations of gamma-ray line emission from gamma-ray bursts, the interstellar medium, the Galactic Center, and solar flares, and we discuss the implications of these observations on high energy processes in these sources.

On the relation between solar-flare gamma-ray emission and proton escape into interplanetary space

It is shown that escaping of solar flare energetic protons into interplanetary space as well as their relation to the flare gamma-ray emission depend on the parameter β = 8πp/B 0 2 , where p is the pressure of hot plasma and energetic particles and B 0 is the magnetic field in a flaring loop. If β≪1, the bulk of the energetic protons escape to the loss cone because of diffusion due to small-scale Alfven-wave turbulence, and precipitate into the footpoints of the flaring loop. The flare then produces intense gamma-ray line emission and a weak flux of high energy protons in interplanetary space. If β>β*≃0.3-1.0, then fast eruption of hot plasma and energetic particles out of the flaring loop occurs, this being due to the flute instability or ‘magnetic-field-plasma’ nonequilibrium. The flare then produces a comparatively weak gamma-radiation and rather intense proton fluxes in interplanetary space. We predict a modulation of the solar flare gamma-ray line emission with a period ≲ 1 s during the impulsive phase that is due to the MHD-oscillations of the energy release volume. The time lag of the gamma-ray peaks with respect to the hard X-ray peaks during a simultaneous acceleration of electrons and protons can be understood in terms of strong diffusion.

Search for gamma-ray line emission from SS 433

view Abstract Citations (8) References (17) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Search for gamma-ray line emission from SS 433. MacCallum, C. J. ; Huters, A. F. ; Stang, P. D. ; Leventhal, M. Abstract A balloon-borne germanium gamma ray telescope was flown over Palestine, TX to search for Doppler-shifted nuclear lines recently reported from the extraordinary object SS 433. The resolution of a veto circuit problem is described, and the data analysis method is discussed. No gamma ray line activity from SS 433 was detected at any energy. If present at the reported time-averaged intensities, the reported lines would have been detected at the 2-3 sigma level. Publication: The Astrophysical Journal Pub Date: April 1985 DOI: 10.1086/163089 Bibcode: 1985ApJ...291..486M Keywords: Emission Spectra; Gamma Ray Astronomy; Stellar Radiation; X Ray Binaries; Balloon Flight; Counting Circuits; Doppler Effect; Heao 3; Visible Spectrum; Astrophysics full text sources ADS | data products SIMBAD (1)

Time Histories of Gamma- and Hard X-Ray Emissions from Solar Flares

The Hinotori gamma-ray spectrometer observed time histories of gamma-ray line and electron bremsstrahlung X-ray emissions from four solar flares. The time histories of impulsive flares require that both nuclei and electrons are rapidly accelerated to energies >10 MeV/nuc and >1 MeV respectively in a time scale of <10 s, and the gamma-ray line peak is coincident with the electron bremsstrahlung peak in <4 s. The gradual flare shows the gamma-ray line peak is apparently delayed by tens of seconds with respect to the electron bremsstrahlung peak. The gamma-ray line peak delay is attributed either to the simultaneous acceleration of nuclei and electrons in one step and a longer life time of the nuclei against the injection, the propagation and the slowing down in the flare region or to the second phase (step) acceleration of nuclei.

Gamma-ray line emission, nuclear destruction and neutron production in hot astrophysical plasmas. The deuterium boiler as a gamma-ray source

Gamma-ray line emission, nuclear destruction and neutron production in hot astrophysical plasmas. The deuterium boiler as a gamma-ray source

HEAO 3 observations of the Crab pulsar

view Abstract Citations (39) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS HEAO 3 observations of the Crab pulsar. Mahoney, W. A. ; Ling, J. C. ; Jacobson, A. S. Abstract The Crab pulsar (PSR 0531+21) is the only pulsar which has been observed throughout almost the entire electromagnetic spectrum from 0.5 keV to over 2000 GeV. In general, the emission from the Crab nebula and its pulsar has been remarkably constant in time (except for the pulsations). However, several recent observations, especially of gamma-ray line emission, indicate possible time variations. The present investigation is concerned with the data obtained with the HEAO C-1 experiment. The data have been studied with the hope of finding information regarding a number of questions, taking into account the existence of line emission from the pulsar, the variation of the shape of the light curve with time, and the spectral variations as a function of pulsar phase. The spectrum of the total phase-averaged pulsed emission is found to be consistent with a single power-law spectrum from 50 keV to 10 MeV. Publication: The Astrophysical Journal Pub Date: March 1984 DOI: 10.1086/161848 Bibcode: 1984ApJ...278..784M Keywords: Crab Nebula; Gamma Ray Spectra; Heao 3; Light Curve; Pulsars; Stellar Spectra; Compton Effect; Monte Carlo Method; X Ray Spectroscopy; Astrophysics full text sources ADS | data products SIMBAD (2)

Point-like gamma-ray sources

Various models are examined, which could give rise to point-like gamma-ray sources, at the present time indistinguishable, experimentally, from true point sources. These models involve energetic processes associated with interstellar clouds, e.g. supernova-cloud interactions, neutron star accretion inside interstellar clouds, cloud collisions, etc. The dynamical evolution of such systems is discussed and physical processes are described in a mathematical framework which can be solved. Statistical arguments are presented, where possible, on the likelihood that the scenarios may actually occur in our Galaxy. The visibility of the systems at other wavelengths, e.g. infrared, X-ray, radio etc., and further consequences, e.g. gamma-ray line emission, special radio emission line features, absorption features etc. are also discussed. Finally, a limited attempt at identification of some ‘gamma-ray objects’ is made based on the theoretical predictions.

Recurrent pulse trains in the solar hard X-ray flare of 1980 June 7

This study presents a detailed examination of the solar hard X-ray and gamma-ray flare of 1980 June 7 as seen by the Hard X-Ray Burst Spectrometer on SMM. The hard X-ray profile is most unusual in that it is characterized by an initial pulse train of seven intense hard X-ray spikes. However, the event is unique among the 6300 events observed by HXRBS in that the temporal signature of this pulse train recurs twice during the flare. Examinations of the hard X-ray data in conjunction with radio and gamma-ray observations show that the 28-480 keV X-ray emission is simultaneous with the 17 GHz microwave fluxes within 128 ms and that the 3.5-6.5 MeV prompt gamma-ray line emission is coincident with secondary maxima of the microwave and X-ray fluxes. Although the absence of spatially resolved hard X-ray observations leaves other possibilities open, a parameterization of the event as a set of seven sequentially firing loops is presented that offers many satisfying explanations of the observations.

Diffuse galactic gamma-ray line emission from nucleosynthetic Fe-60, Al-26, and Na-22 - Preliminary limits from HEAO 3

Data obtained during a two-week period in the fall of 1979 with the HEAO 3 gamma-ray spectroscopy experiment have been searched for diffuse galactic plane gamma-ray line emission expected t4 result from the decay of nucleosynthetic Fe-60, Al-26, and Na-22. With the possible exception of the 1809 keV line from Al-26 decay, for which a 2.6-omicron cosmic excess of (6.0 + or - 2.3) x 0.0001 photons/sq cm per sec per rad was measured, no positive detection was made. However, new limits ranging from 1.8 to 11 times 0.0001 photons/sq cm per sec per rad, at the 3-omicron level of confidence, have been placed on diffuse emission in these lines from the vicinity of the galactic center (between -30 and 30 deg). These limits are lower than some theories predict and thus place new constraints on the yields of these radionuclides in explosive nucleosynthesis and on the present rate of galactic nucleosynthesis.

X-ray and gamma-ray observations of a white-light flare

HEAO-1 observed hard radiations (X- and gamma-rays) from a major solar flare on 11 July 1978. The observations showed gamma-ray line and continuum emission extending to the highest energy observed. The lines are identified with the 2.2 MeV line of deuterium formation and the 4.4 MeV line of inelastic scattering on 12C, both previously observed in the flares of August 1972 [1]. The 11 July flare was identified as a white-light flare by observations at Debrecen [2]. It thus provides the first opportunity for a detailed examination of white-light flare theories that depend upon proton heating of the photosphere. The line strength over a four-minute integration at 2.2 MeV was 1.00 ± 0.29 ph(cm 2 sec) −1, and the gamma-ray emission (excluding the 2.2 MeV line which was appreciably delayed) lagged by less than 20 sec approximately after the hard X-ray and microwave fluxes. We conclude that the “second-stage” acceleration of high-energy solar particles must commence promptly after the impulsive phase.

The HEAO 3 gamma-ray spectrometer

The Third High Energy Astronomy Observatory (HEAO 3), successfully launched into low earth orbit on 20 September 1979, carries a large high resolution gamma-ray spectrometer designed for cosmic nuclear spectroscopy. This Gamma-Ray Spectrometer (the HEAO C-1 experiment) consists of a cluster of four coaxial high purity germanium detectors, each with a volume of approximately 100 cm 3. Surrounding the germanium detectors is a 6.6 cm thick CsI shield operating in active anticoincidence with the central detectors and defining a field of view of about 30° fwhm. An initial energy resolution of 3 keV fwhm at 1.46 MeV was achieved for each detector. All valid events in the germanium detectors are individually analyzed by an 8192 channel pulse area analyzer and transmitted at a maximum rate of 15.6 events/s for each detector. During a 6 month mission, the experiment will perform a complete sky survey for narrow cosmic gamma-ray line emission to the sensitivity level of about 10 −4 photons/cm 2 s over an operating energy range of 0.05–10 MeV.