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  • Other Sources  (10)
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  • 1
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    Implications of the BATSE data for a helocentric origin of gamma-ray bursts (1994)
    In:  Other Sources
    Details
    Publication Date: 2011-08-24
    Description: Several possible models have been suggested to explain the observed distribution of gamma-ray bursts: heliocentric distributions such as the Oort cloud, large galactic halos, and cosmological models. We report here on an investigation into the implications of the Burst and Transient Source Experiment (BATSE) gamma-ray burst distribution (Meegan et al. 1992a) data on the possible helocentric origin of gamma-ray bursts. We find no statistically significant anisotropy in the angular distribution of the bursts in a Sun-referenced coordinate system; there is no dipole moment in the direction of the Sun, and no quardrupole moment associated with the ecliptic plane. We have employed direct analytic calculations and Monte Carlo simulations of sources in the Oort cloud to constrain possible helicentric burst distributions. These can produce distributions consistent with the observed angular isotropy, the meal value of V/V(sub max), and the observed C/C(sub min) distribution of BATSE, and provide limits to burst energy of a few times approximately 10(exp 27) ergs. However, the agreement of the heliocentric C/C(sub min) distributions with the BATSE data is attributable to the relatively limited sampling of strong, nearby bursts. These bursts are known from observation to be homogeneously distributed, yet the density of sources in the Oort cloud is not constant in this region. Integral number-intensity distributions from the Oort cloud for larger numbers of bursts cannot reproduce the known homogeneity of the strong bursts without modification to the computed cometary number density and are therefore unlikely explanations of the gamma-ray burst distribution.
    Keywords: ASTROPHYSICS
    Type: The Astrophysical Journal, Part 1 (ISSN 0004-637X); 429; 1; p. 319-324
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  • 2
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    The Identification of Two Different Spectral Types of Pulses in Gamma-Ray Bursts (1997)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: It is shown in this study that two different types of spectral emission are generally produced in gamma-ray bursts. A subset of bursts is identified that exhibits a marked lack of fluence above 300 keV, and these bursts are shown to have luminosities about an order of magnitude lower than bursts with significant fluence above 300 keV. The bursts lacking emission above 300 keV exhibit an effectively homogeneous intensity distribution. In addition, it is shown that both types of emission are common in many bursts, demonstrating that a single source object is capable of generating both of them. These results strongly favor a gamma-ray burst source object that produces two different types of emission with varying degrees of superposition. The impact of this behavior is strong enough that it affects the properties of the burst intensity distribution, as well as the burst spectral characteristics.
    Keywords: Space Radiation
    Type: Astrophysical Journal; Volume 489; 175-198
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  • 3
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    Occultation analysis of BATSE data: Operational aspects (1992)
    In:  CASI
    Details
    Publication Date: 2013-08-31
    Description: The Burst and Transient Source Experiment (BATSE) large area detectors are being used to monitor hard x-ray/gamma ray sources on a daily basis for evidence of transient behavior. Flux measurements are performed using a simple earth occultation technique. Daily searches are also being performed to detect occultation steps of sources which are not being routinely monitored. Topics concerning the operational aspects of the occultation measurements are presented. Preliminary spectral results are also presented for several of the brighter sources.
    Keywords: SPACE RADIATION
    Type: NASA. Goddard Space Flight Center, The Compton Observatory Science Workshop; p 69-75
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  • 4
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    Discovery of intense gamma-ray flashes of atmospheric origin (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Observations have been made of a new terrestrial phenomenon: brief (approx. millisecond), intense flashes of gamma rays, observed with space-borne detectors. These flashes must originate at altitudes in the atmosphere above at least 30 km in order to be observable by orbiting detectors aboard the Compton Gamma-Ray Observatory (CGRO). At least a dozen events have been detected over the past 2 years. The photon spectra from the events are very hard and are consistent with bremsstrahlung emission from energetic (MeV) electrons. The most likely origin of these high energy electrons, while speculative at this time, is a rare type of high altitude electrical discharge above thunderstorm regions.
    Keywords: SPACE RADIATION
    Type: NASA-TM-110853 , NAS 1.15:110853
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  • 5
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    BATSE observations of 3C273 (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: The quasar 3C273 has been detected by all instruments on CGRO. The emission from this source is monitored continuously by BATSE using Earth occultation. We present results of a preliminary analysis of BATSE data, including light curves of the 3C273 flux covering approximately 150 days in the interval April-August 1991 and approximately 350 days in the interval July 1992-April 1993. The source intensity in the energy range 50-300 keV is typically approx. 0.002 ph cm(exp -2)s(exp -1). We find weak evidence for variations of as much as a factor of 3 in the intensity. We derive spectral parameters of 3C273 during the intervals TJD 8422-8435 (15-28 June 1991) and TJD 8532-8546 (3-17 October 1991) for comparison with other CGRO instruments.
    Keywords: ASTRONOMY
    Type: NASA-CR-196185 , NAS 1.26:196185
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  • 6
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    Gamma-Ray Burst Spectral Indices: Evidence for Deceleration of Synchrotron Shocks (2000)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: The current scenario for gamma-ray bursts (GRBs) involves internal shocks for the prompt GRB emission phase and external shocks for the afterglow phase. Assuming synchrotron emission from energetic shocked electrons. GRB spectra observed with a low-energy power-law spectral index greater than -2/3 (for positive photon number indices E(sup alpha) indicate a problem with this model. The remaining spectra can test the synchrotron shock model prediction that the emission from a single distribution of electrons, cooling rapidly, is responsible for both the low-energy and high-energy power-low portions of the spectra. We find that the inferred relationship between the two spectral indices of observed GRB spectra is inconsistent with the constraints from the model, posing another problem for the synchrotron shock emission model. To overcome this problem, we describe a model where the average of -1, rather than the value of -3/2 predicted for cooling electrons. Situations where this might arise have been discussed in other contexts, and involve deceleration of the internal shocks during the GRB phase.
    Keywords: Space Radiation
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  • 7
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    The Identification of Two Different Spectral Types of Pulses in Gamma-Ray Bursts (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: It is shown in this study that two different types of spectral emission are generally produced in gamma-ray bursts. A subset of bursts is identified that exhibits a marked lack of fluence above 300 keV, and these bursts are shown to have luminosities about an order of magnitude lower than bursts with significant fluence above 300 keV. The bursts lacking emission above 300 keV exhibit an effectively homogeneous intensity distribution. In addition it is shown that both types of emission are common in many bursts, demonstrating that a single source object is capable of generating both of them. These results strongly favor a gamma-ray burst source object that produces two different types of emission with varying degrees of superposition. The impact of this behavior is strong enough that it is affecting the properties of the burst intensity distribution, as well as the burst spectral characteristics.
    Keywords: Space Radiation
    Type: Astrophysical Journal
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  • 8
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    On the Consistency of Gamma-Ray Burst Spectral Indices with the Synchrotron Shock Model (2002)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: The current scenario for gamma-ray bursts (GRBs) involves internal shocks for the prompt GRB emission phase and external shocks for the afterglow phase. Assuming optically thin synchrotron emission from isotropically distributed energetic shocked electrons, GRB spectra observed with a low-energy power-law spectral index greater than -2/3 (for positive photon number indices E(exp alpha) indicate a problem with this model. For spectra that do not violate this condition, additional tests of the shock model can be made by comparing the low- and high-energy spectral indices, on the basis of the model's assertion that synchrotron emission from a single power-law distribution of electrons is responsible for both the low-energy and the high-energy power-law portions of the spectra. We find in most cases that the inferred relationship between the two spectral indices of observed GRB spectra is inconsistent with the constraints from the simple optically thin synchrotron shock emission model. In this sense, the prompt burst phase is different from the afterglow phase, and this difference may be related to anisotropic distributions of particles or to their continual acceleration in shocks during the prompt phase.
    Keywords: Astrophysics
    Type: The Astrophysical Journal; 581; 1248-1255
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  • 9
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    The Identification of Two Different Spectral Types of Pulses in Gamma-Ray Bursts (1997)
    In:  Other Sources
    Details
    Publication Date: 2019-07-17
    Description: It is shown in this study that two different types of spectral emission are generally produced in gamma-ray bursts. A subset of bursts is identified that exhibits a marked lack of fluence above 300 keV, and these bursts are shown to have luminosities about an order of magnitude lower than bursts with significant fluence above 300 keV. The bursts lacking emission above 300 keV exhibit an effectively homogeneous intensity distribution. In addition, it is shown that both types of emission are common in many bursts, demonstrating that a single source object is capable of generating both of them. These results strongly favor a gamma-ray burst source object that produces two different types of emission with varying degrees of superposition. The impact of this behavior is strong enough that it affects the properties of the burst intensity distribution, as well as the burst spectral characteristics.
    Keywords: Space Radiation
    Type: Astrophysical Journal; 489; 175
    Format: text
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  • 10
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    Discovery of Intense Gamma-Ray Flashes of Atmospheric Origin (1994)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Detectors aboard the Compton Gamma Ray Observatory have observed an unexplained terrestrial phenomenon: brief, intense flashes of gamma rays. These flashes must originate in the atmosphere at altitudes above at least 30 kilometers in order to escape atmospheric absorption and reach the orbiting detectors. At least a dozen such events have been detected over the past 2 years. The photon spectra from the events are very hard (peaking in the high-energy portion of the spectrum) and are consistent with bremsstrahlung emission from energetic (million-electron volt) electrons. The most likely origin of these high- energy electrons, although speculative at this time, is a rare type of high-altitude electrical discharge above thunderstorm regions.
    Keywords: Geophysics
    Type: NASA-TM-112018 , NAS 1.15:112018 , Science; 264; 1313-1316
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