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  • 1
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    BATSE gamma-ray burst line search. 1: Search for narrow lines in spectroscopy detector data (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Analysis of data from the Spectroscopy Detectors (SDs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (GRO) has found no convincing line features in the spectra of gamma-ray bursts (GRBs) in almost 3 years of operation, in contrast to expectations based on results from other experiments. In this Letter we discuss the visual search for narrow lines in the SD data. The search has examined 192 bursts, of which approximately 18 were intense enough that lines similar to those seen by instruments on the Ginga satellite would have been visible between approximately 20 and approximately 100 keV. A simplified calculation shows that the BATSE and Ginga results are consistent at the 13% level.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 2 - Letters (ISSN 0004-637X); 433; 2; p. L77-L80
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  • 2
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    Spectral evolution of a subclass of gamma-ray bursts observed by batse (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Among the gamma-ray bursts (GRBs) observed by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory we define a subclass of bursts based on similar morphology: a sharp rise followed by a longer decay time. About 7% of all the gamma-ray bursts observed by BATSE fall into this subclass. We study the spectral evolution of these bursts by fitting models to time-segmented burst spectra and find no clear distinction between the spectral evolutionary properties of this subclass and those of other bursts. Further, we study the high time resolution spectral evolution of this subclass of GRBs using their spectral hardness ratios. A majority of the bursts show hardness ratio leading the counting rate and also display a continuous hard to soft evolution. The time lag between the counting rate and the hardness ratio is found to be directly correlated with the rise time of the counting rate profile. We also find, for the first time, evidence for spectral variation in a timescale of 64 ms.
    Keywords: ASTRONOMY
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 426; 2; p. 604-611
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  • 3
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    The peak brightness of SN 1937C in IC 4182 and the Hubble constant (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: The light curve of the Type Ia supernova SN 1937C (in IC 4182) is important because Sandage et al. have measured a distance to the host galaxy by means of Cepheid variables and thus have derived the Hubble constant. However, the peak brightness of SN 1937C has only been derived with the relatively poor original comparison star brightnesses and without regard to a large body of data in the literature. In this paper, I will correct these and other procedural difficulties. I find that the late time photographic light curve appears to have a broken exponential decay with equivalent half-lives of 46 and 58 days with the break near 300 days after maximum. I also find that the peak B-magnitude was 8.71 +/- 0.14 on JD 2428770.0 +/- 1.0 at which time the B-V was -0.03 +/- 0.13. With these improved peak brightnesses, the distance modulus of Sandage et al., and peak absolute magnitudes in the center of the range of modern estimates, I derive the Hubble constant to be 50 km/s Mpc.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 426; 2; p. 493-501
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  • 4
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    BATSE spectroscopy catalog of bright gamma-ray bursts (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: This paper presents comprehensive results on the spectra of 30 bright gamma ray bursts (GRBs) as observed by the Spectroscopy Detectors (SDs) of the Burst And Transient Source Experiment (BATSE). The data selection was strict in including only spectra that are of high reliability for continuum shape studies. This BATSE Spectroscopy Catalog presents fluences, model fits (for five spectral models for three energy ranges), and photon spectra in a standard manner for each burst. Complete information is provided to describe the data selection and analysis procedures. The catalog results are also presented in electronic format (from the Compton Observatory Science Support Center) and CD-ROM format (AAS CD-ROM series, Vol. 2). These electronic formats also present the count spectra and detector response matrices so as to allow for independent study and fitting by researchers outside the BATSE Team. This BATSE Spectroscopy Catalog complements the catalog from BATSE Large Area Detector (LAD) data by Fishman et al. (1994).
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal Supplement Series (ISSN 0067-0049); 92; 1; p. 285-310
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  • 5
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    Optical transients and depth analysis (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Flaws of the depth analysis technique of distinguishing photographic plate defects are discussed. The method is shown to be unreliable in confirming or disproving the astrophysical nature of optical transients. The arguments of Greiner and of Zytkow to the contrary are criticized.
    Keywords: ASTRONOMY
    Type: In: Gamma-ray bursts - Observations, analyses and theories (A93-20206 06-90); p. 133-137.
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  • 6
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    Microsecond flares in gamma-ray bursts (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: It has been suggested that gamma-ray burst light curves may consist of many superposed flares with a duration shorter than 30/microsec. If true, the implications for the interpretation of burst data are enormous. With the launch of the Compton Gamma-Ray Observatory, four predictions of Mitrofanov's (1989) suggestion can be tested. Our results which contradict this suggestion are (1) the photon arrival times are not correlated between independent detectors, (2) the spectral hardness and intensity does not depend on the detector area, (3) the bursts seen by detectors which measure photon positions do not see microsecond flares, and (4) burst positions deduced from detectors with different projected areas are close to the positions deduced from time-of-flight differences between separated spacecraft. We conclude, therefore, that gamma-ray bursts are not composed of microsecond flares.
    Keywords: ASTROPHYSICS
    Type: Astrophysical Journal, Part 1 (ISSN 0004-637X); 404; 2; p. 673-677.
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  • 7
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    A ROSAT Wide Field Camera search for XUV bursts (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We have searched the ROSAT Wide Field Camera all-sky survey for shorttime-scale (less than 50 s) XUV bursts down to a limiting count of 5 x 10 exp -3 count/sq arcmin, corresponding to an incident flux of about 3 x 10 exp -10 erg/sq cm. In a total observation period of 171 d covering the entire sky, we found no evidence for such events. The present results are used to place limits on the log N-log S relation for gamma-ray bursts and constraints on the spectral shape of the previously reported ultrasoft X-ray transients.
    Keywords: ASTRONOMY
    Type: Royal Astronomical Society, Monthly Notices (ISSN 0035-8711); 260; 4; p. L25-L27.
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  • 8
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    Astronomy and the limits of vision (1993)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: Celestial visibility is the study of the limits of observability of objects in the sky, with application to deducing the truth about historical events or to the derivation of astronomical information of modern utility. This study is based on what is seen by ordinary humans, either in their everyday lives or at times of historical events. The results of such studies have more relevance to non-scientists than does any other area of astronomy. Celestial visibility is a young discipline in the sense that the number of interesting applications with simple solutions outnumber the solved problems; it is a broad interdisciplinary field that involves work with astronomy, meteorology, optics, physics, physiology, history, and archeology. Each of these disciplines contribute specialized mathematical formulations which quantify the many processes that affect light as it leaves a source, traverses the atmosphere, and is detected by the human eye. These formulas can then be combined as appropriate to create mathematical models for the visibility of the source under the conditions of interest. These model results can then be applied a wide variety of problems arising in history, astronomy, archeology, meteorological optics, and archeoastronomy. This review also presents a dozen suggestions for observing projects, many of which can be directly taken for individual study, for classroom projects, or for professional research.
    Keywords: ASTRONOMY
    Type: Vistas in Astronomy (ISSN 0083-6656); 36; p. 311-361
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  • 9
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    Lunar crescent visibility (1994)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: We report the results of five Moonwatches, in which more than 2000 observers throughout North America attempted to sight the thin lunar crescent. For each Moonwatch we were able to determine the position of the Lunar Date Line (LDL), the line along which a normal observer has a 50% probability of spotting the Moon. The observational LDLs were then compared with predicted LDLs derived from crescent visibility prediction algorithms. We find that ancient and medieval rules are higly unreliable. More recent empirical criteria, based on the relative altitude and azimuth of the Moon at the time of sunset, have a reasonable accuracy, with the best specific formulation being due to Yallop. The modern theoretical model by Schaefer (based on the physiology of the human eye and the local observing conditions) is found to have the least systematic error, the least average error, and the least maximum error of all models tested. Analysis of the observations also provided information about atmospheric, optical and human factors that affect the observations. We show that observational lunar calendars have a natural bias to begin early.
    Keywords: ASTRONOMY
    Type: ICARUS (ISSN 0019-1035); 107; 2; p. 388-403
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  • 10
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    Severe new limits on extragalactic models of gamma-ray bursts (1992)
    In:  Other Sources
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    Publication Date: 2011-08-24
    Description: A new and much more restrictive limit is imposed here on the distance of gamma ray bursts (GRBs) in extragalactic models of the bursts. This limit is based on the fact that deep optical and infrared surveys do not find any host galaxies in many GRB error boxes. It is shown that 10 of the brighter GRB sources must be farther than 1 gigaparsec and that eight of these must emit more than 10 exp 13 ergs during a burst. This result is about four orders of magnitude stricter in energy than the previous limit. Five of the sources have limits in that the energy must be greater than the binding energy of a neutron star.
    Keywords: ASTROPHYSICS
    Type: In: Gamma-ray bursts - Observations, analyses and theories (A93-20206 06-90); p. 107-112.
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