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  • 1
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    OTS 1809+314 and the gamma-ray burst GB 790325b (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-12
    Description: Deep CCD images of the field containing the recurring Optical Transient Source (OTS) 1809+314 recently discovered on archival plates of the Sonneberg Observatory are presented. At the position of OTS 1809+314 no optical counterpart brighter than V = 24.0-24.5, r(Gunn) = 22.0-22.5, and I = 22.0-22.5 is found. In the zero proper motion limit our observations place severe constraints on possible quiescent counterparts. There is no compelling evidence to suggest an association between the historical optical transient source and the gamma-ray burst GB 790325b located about 5 arcmin to the east of OTS 1809+314.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 336; 889-895
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  • 2
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    Rapid searches for counterparts of GRB 930131 (1994)
    In:  Other Sources
    Details
    Publication Date: 2019-08-28
    Description: A fading counterpart to a gamma-ray burst (GRB) would appear as a point source inside a GRB error region soon after the burst which dims on a timescale from minutes to days. The favorable circumstances of the burst GRB 930131 allowed for an international campaign to search for fading counterparts starting 6.8 hr after the burst. We report observations from many optical sites, two radio telescopes, and archival ROSAT data, including deep Schmidt exposures 35, 44, and 64 hr after the burst. No fading counterparts were detected with our observations.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 422; 2; p. L71-L74
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  • 3
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    A provocative comment on the spatial distribution of gamma-ray bursters (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: It is shown that the four most intense bursts localized to date have a spatial distribution not inconsistent with the locations of the five weakest bursts. Both distributions are consistent with isotropy. As the burst intensities differ by a factor of about 5000 or more, one possible interpretation is that the sources are at distances which differ by a factor of about 70, yet no evidence of a disk distribution has appeared. The possible consequences for determining the burster distance scale are discussed.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts - Observations, analyses and theories (A93-20206 06-90); p. 183-187.
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  • 4
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    Gamma-ray bursts and neutron star field decay (1992)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: Assuming a Galactic origin of gamma-ray bursts, we use pulsar data to calculate the spatial distribution of neutron stars and determine the sampling depths of current detectors. Based on these distance limits, we calculate the corresponding age distribution of Galactic neutron stars and apply an exponential field decay model to test whether the observed high incidence rate of cyclotron lines is consistent with suggested field decay time scales of order 10 exp 7 years. We find that the properties of the observed population of gamma-ray bursts are inconsistent with the idea that bursts originate at arbitrary times on neutron stars whose fields decay on time scales shorter than about 10 exp 9 years. Possible interpretations of this inconsistency are discussed.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts - Observations, analyses and theories (A93-20206 06-90); p. 45-54.
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  • 5
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    Spectral evolution of gamma-ray bursts detected by the SIGNE experiment. 1: Correlation between intensity and spectral hardness (1994)
    In:  Other Sources
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    Publication Date: 2019-08-28
    Description: We study the continuum spectral evolution of 16 gamma-ray bursts detected by the Franco-Soviet SIGNE experiment in 1981-1982 by fitting time resolved (0.5 s) spectra in count space with simple thermal bremsstrahlung and synchrotron models. We find that there is no single characteristic of spectral evolution: we see hard-to-soft, soft-to-hard, luminosity-hardness tracking, and chaotic evolution. We perform correlation studies between instantaneous burst intensity and spectral temperature for seven bursts. While we basically confirm the existence of a correlation between these variables as originally claimed by Golenetskii et al. (1983) we find higher values and a broader range of correlation indices.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 422; 1; p. 260-268
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  • 6
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    Observational features of cosmic gamma-ray bursts: Evidence for Galactic versus extragalactic origin (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The recent observational data on gamma-ray bursts are reviewed. Burst time histories display features at the millisecond level which suggest a compact object origin. Lines in the energy spectra and spectral evolution point toward a Galactic neutron star origin, even though line features have not yet been confirmed in recent data. The Galactic distribution of burst sources, however, is both isotropic and sampled to its characteristic distance, making it unlikely that the sources are related to populations of Galactic neutrons stars we are familiar with. Counterpart searches, previously carried out years after the gamma-ray bursts, are now proceeding days after the events. Based on the current data, it is impossible to conclude whether bursters are Galactic, extragalactic, or both. Data being returned from current experiments, as well as data from new experiments to be launched in the next few years, may yet provide the answer.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 90; 2; p. 857-861
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  • 7
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    Do gamma-ray bursts originate from an extended Galactic Halo of high-velocity neutron stars? (1994)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: The gamma-ray burst brightness distribution is inhomogeneous and the distribution on the sky is nearly isotropic. These features argue against an association of gamma-ray bursts with those Galactic objects that are known to exhibit a strong concentration toward the Galactic center or plane. The observed statistical properties indicate a cosmological origin. Circumstantial evidence suggests that neutron stars are involved in the burst phenomenon. Here we consider Population II neutron stars in an extended Galactic Halo (EGH) as an alternative to cosmological scenarios. The Burst and Transient Source Experiment (BATSE) data indicate a small deviation from isotropy near the 2 sigma level of statistical significance. If confirmed for an increasing number of bursts, these anisotropies could rule out cosmological scenarios. On the other hand, EGH models require small anisotropies like those observed by BATSE. We consider simple distribution models to determine the generic properties such halos must have to be consistent with the observations and discuss the implications of the corresponding distance scale on burst models.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal Supplement Series (ISSN 0067-0049); 90; 2; 893-897
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  • 8
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    Neutron stars and the distance to gamma-ray bursters (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: Assuming that gamma-ray bursts originate from galactic neutron stars, an analytic method for studying their statistical properties is outlined. If a significant fraction of all neutron stars are born with space velocities of less than approximately 100 km/s, as suggested by studies of pulsar statistics, then the sampling distance to gamma-ray burst sources should be less than about several hundred pc. These results have important implications on theories of radio-pulsar evolution and magnetic-field decay.
    Keywords: ASTROPHYSICS
    Type: Astronomical Society of the Pacific, Publications (ISSN 0004-6280); 103; 774-776
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  • 9
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    X-ray echoes from gamma-ray bursts (1991)
    In:  Other Sources
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    Publication Date: 2019-07-12
    Description: The identification of an echo of reflected radiation in time histories of gamma-ray burst spectra can provide important information about the existence of binary companions or accretion disks in gamma-ray burst systems. Because of the nature of Compton scattering, the spectrum of the echo will be attenuated at gamma-ray energies compared with the spectrum of the primary burst emission. The expected temporal and spectral signatures of the echo and a search for such echoes are described, and implications for gamma-ray burst models are discussed.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 370; 341-344
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