Astronomy and Astrophysics – Astrophysics
Scientific paper
Oct 1982
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1982ans..conf..246z&link_type=abstract
In its Accreting Neutron Stars p 246-249 (SEE N83-15179 05-88)
Astronomy and Astrophysics
Astrophysics
4
Gamma Ray Absorption, Gamma Ray Bursts, Magellanic Clouds, Astrophysics, Distance, Neutron Stars, Optical Thickness, Pair Production, Photon Density, Photons, Position (Location), Stellar Structure
Scientific paper
The coordinates of the 5 March, 1979 gamma-ray burst source coincide with those of the supernova remnant N49 in the Large Magellanic Cloud (LMC). The photon energies of the first impulsive phase of the burst extend above 511 KeV, the energy threshold in the center-of-momentum frame for the electron-position pair production by two photons. The rise time of this impulsive phase suggests that the size of the source is smaller than 75 km and requires that the source is smaller than 75 km and requires that the source be a compact object. This size and the 55 kpc distance of the LMC imply the density of photons of an order of magnitude of 1025 photons per cu cm, that is high enough to self-absorb all the gamma-photons in the pair production process. To avoid the attenuation inside the source, the models consisting of an emitting layer of a very small geometrical thickness placed above the neutron star surface were proposed. The optical depth due to the pair absorption of such a layer can be lower than unity, even if the source is in the LMC. However, because of the photon density near the source is still high, the photon absorption occurs above the source as well as inside it. The result of calculations of an optical thickness due to the gamma-gamma pair production process above the isotropically emitting burst source of a neutron star size excludes the thin layer model and suggests that either the emitted gamma-photons were strongly collimated or the burst source is much nearer than the LMC.
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