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  • 1
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    Line strength variations in gamma-ray bursts GB870303 - Possible evidence of neutron star rotation (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-14
    Description: An exhaustive search of the Ginga data on gamma-ray burst GB870303 reveals two separate time intervals during which statistically significant line features are evident. One (previously unreported) interval shows a single prominent line feature at about 20 keV; a second, corresponding to the interval reported by Murakami et al. (1988), shows two line features at 20 and 40 keV. From model fits to the data, we find that both sets of lines are well-described by cyclotron resonant scattering in a magnetic field B around 1.8 x 10 exp 12 G, and that the differences in the line strengths between the two intervals are significant. The variations are qualitatively similar to those produced by a change in the viewing angle theta relative to the magnetic field. We conjecture that the change in theta is due to rotation of the neutron star, and derive limits of 45-180 sec on the rotation period P.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts; Proceedings of the Workshop, Univ. of Alabama, Huntsville, Oct. 16-18, 1991 (A93-40051 16-93); p. 211-215.
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  • 2
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    Self-collimated electromagnetic jets from magnetized accretion disks - The even-symmetry case (1990)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: This paper extends the previous treatment (Lovelace et al., 1987) of the origin of self-collimated EM jets to the case of even field symmetry, where the magnetic flux function Psi(r, z) is an even function of z. A viscous resistive accretion disk is assumed to surround a black hole with a force-free plasma outside of the disk. Inside the disk, the induction equation is solved for Psi(r, z) and the toroidal magnetic field. Outside the disk, previous results are used to study the formation of self-collimated EM jets. In contrast with the odd-symmetry case, for even symmetry the toroidal magnetic field acts to vertically compress the disk; a comparatively large toroidal magnetic field can exist inside the disk; and an appreciable fraction (possibly all) of the available accretion power can go into the jets.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 355; 38-43
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  • 3
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    Intrinsically asymmetric astrophysical jets (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Previous work on the origin of self-collimated electromagnetic jets is extended to the general case where there is no reflection symmetry of the magnetic field about the equatorial plane of the disk. The axisymmetric field structure inside the disk is obtained by solving for the magnetic flux function, and the toroidal magnetic field, from the generalized thin-disk induction equation, which is derived. The asymptotic (large-z) magnetic field structure outside the disk is obtained by solving the force-free Grad-Shafranov equation semianalytically. Jet solutions are found in which the power flow is carried mainly by the Poynting flux of the electromagnetic field and the angular momentum outflow from the disk is carried by the magnetic field. The ratio of jet luminosities (top/bottom) depends directly on the degree of asymmetry of the field and can easily be much greater than unity. It is argued that the degree of field asymmetry in the disk is determined by the asymmetry of the weak galactic field fed into the disk at large distances over long periods of time.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 390; 1 Ma; 46-65
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  • 4
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    Cyclotron resonant scattering in gamma-ray bursts - Line strengths and signature of neutron star rotation (1992)
    In:  Other Sources
    Details
    Publication Date: 2019-08-27
    Description: We explain the relative line strengths in gamma-ray bursts in terms of cyclotron resonant scattering. We describe the line signature of neutron star rotation and discuss the possibility that variations seen in the strengths and widths of the lines in GB780325 and GB870303 are due to rotation.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts - Observations, analyses and theories (A93-20206 06-90); p. 415-422.
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