Gamma-ray Line Observations Research Articles

Nuclear line spectroscopy of solar flares

The study of nuclear line spectra from solar flares holds a rich promise for elucidating the properties of both the accelerated particles and the interaction or target region. We review the observations and the analysis of the large nuclear line rich flare which occurred near the west limb starting at 08:03 UT on 27 April, 1981. The observed spectrum from this flare contains three intense and isolated gamma-ray lines which can be analyzed in a model independent way. The measured energies are 1.628 ± 0.008, 4.430 ± 0.011, and 6.147 ± 0.022 MeV, identifying them as the de-excitation lines of 20Ne (1.634 MeV), 12C (4.438 MeV), and 16O (6.129 MeV). Elemental abundances of the ambient gas at the site of gamma-ray line production in the solar atmosphere are deduced using these gamma-ray line observations. The resultant abundances are different from local galactic abundances which are thought to be similar to photospheric abundances.

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.

Nuclear processes in the jets of SS 433

view Abstract Citations (22) References (11) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Nuclear processes in the jets of SS 433. Ramaty, R. ; Kozlovsky, B. ; Lingenfelter, R. E. Abstract The very narrow gamma-ray lines observed at 1.495 and 6.695 MeV from SS 433 which are blueshifted 1.369 and 6.129 emissions from deexcitations of (24)Mg-asterisk and (16)O-asterisk in grains moving with the jets and inelastically excited by interactions with the ambient medium are discussed. Energetic particle interactions in grains produce very narrow gamma ray lines from deexcitation of nuclear levels whose lifetimes are long enough that the excited nuclei stop before deexcitation. The presence of grains in the jets resolves hitherto discussed difficulties of inelastic excitation models for gamma ray production in SS 433, the very narrow widths of the observed lines and the absence of other strong lines, expected from abundant elements. A model is proposed which could be distinguished from a previously proposed fusion model by gamma ray line observations. Publication: The Astrophysical Journal Pub Date: August 1984 DOI: 10.1086/184322 Bibcode: 1984ApJ...283L..13R Keywords: Astrophysics; Gamma Ray Astronomy; Gamma Ray Bursts; Jets; Nuclear Astrophysics; Plasma Jets; Astronomical Models; Atomic Excitations; Energy Spectra; Particle Interactions; Astrophysics full text sources ADS | data products SIMBAD (1)

Advances in gamma-ray line astronomy

Recent gamma-ray line observations and their interpretations are reviewed and prospects for future line detections are discussed.

Statistical evaluation of gamma-ray line observations

view Abstract Citations (5) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Statistical evaluation of gamma-ray line observations Cherry, M. L. ; Chupp, E. L. ; Dunphy, P. P. ; Forrest, D. J. ; Ryan, J. M. Abstract The statistical reliability of reported positive observations of solar and cosmic gamma-ray lines has been evaluated. The relative probability that each measurement is due to a real source rather than to an accidental fluctuation in the background has been determined, and it is found that the results are statistically compelling in only a small fraction of the reported observations. At present, extreme caution must be exercised in drawing astrophysical conclusions from reports of the detection of cosmic gamma-ray lines. Publication: The Astrophysical Journal Pub Date: December 1980 DOI: 10.1086/158556 Bibcode: 1980ApJ...242.1257C Keywords: Cosmic Rays; Gamma Ray Spectra; Line Spectra; Solar Spectra; Astronomical Spectroscopy; Gamma Ray Astronomy; Statistical Analysis; Astrophysics full text sources ADS |

HEAO 1 observations of gamma-ray lines from a solar flare

HEAO 1 observed gamma radiation, including the 2.223 MeV line of deuterium and the 4.43 MeV line of C-12, from a white-light solar flare of 1978 July 11. Line strengths over a 4 minute integration were 1.00 + or - 0.29 and 0.18 + or - 0.07 photons/sq cm s, respectively, and the continuum in the 1-5 MeV range fitted a spectrum 10 E to the -3rd photons/sq cm s keV. The 2.2 MeV line lagged 94 + or - 30 s behind the gamma-ray continuum, which itself was delayed about 20 s from the hard X-ray (not less than 40 keV) and microwave fluxes. This is the second flare for which both MeV-range lines and continuum have been observed, and the first for which simultaneous white-light observations exist. The prompt gamma-ray line (4.43 MeV) can be directly interpreted as an energy deposition of not greater than 7 x 10 to the 26th ergs per sec by energetic protons at photospheric depths. This is insufficient to maintain the white-light continuum by normal photospheric emission mechanisms.

Sources of excitation of the interstellar gas and galactic structure

The excitation of the interstellar gas is discussed in the light of recent evidence from gamma-ray, molecular, and 21-cm line observations. Previous studies of the excitation of the interstellar gas have not taken into account the substantial density contrast that exists between spiral arms and interarm regions. We examine the role played by the galactic distribution of three sources of excitation (supernovae, OB stars, and ultraviolet stars) in determining the physical state of the interstellar gas in arm and interarm regions.