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  • 1
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    Discovery of Correlated Behavior Between the Hard X-Ray and the Radio Bands in Cygnus X-3 (1999)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: Using Compton Gamma Ray Observatory BATSE hard X-ray (HXR) data and GHz radio monitoring data from the Green Bank Interferometer, we have performed a long-term study (approx. 1800 days) of the unusual X-ray binary Cyg X-3, resulting in the discovery of a remarkable relationship between these two wavelength bands. We find that during quiescent radio states, the radio flux is strongly anticorrelated with the intensity of the HXR emission. The relationship switches to a correlation with the onset of major radio flaring activity. During major radio flaring activity, the HXR drops to a very low intensity during quenching in the radio and recovers during the radio flare. Injection of plasma into the radio jets of Cyg X-3 occurs during changes in the HXR emission and suggests that disk-related and jet-related components are responsible for the high energy emission.
    Keywords: Space Radiation
    Type: Astrophysical Journal; Volume 517; 951-955
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  • 2
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    The Effect of Magnetic Fields on Gamma-Ray Bursts Inferred from Multi-Wavelength Observations of the Bursts of 23 January 1999 (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: Gamma-ray bursts (GRBs) are thought to arise when an extremely relativistic outflow of particles from a massive explosion (the nature at which is still unclear) interacts with material surrounding the site of the explosion. Observations of the evolving changes in emission at many wavelengths allow us to investigate the origin of the photons, and so potentially determine the nature of the explosion. Here we report the results of gamma-ray, optical, infrared, submillimeter, millimeter and radio observations of the burst ORB990123 and its afterglow. Our interpretation of the data indicates that the initial and afterglow emissions are associated with three distinct regions in the fireball. The peak flux of the afterglow, one day after the burst, has a lower frequency than observed for other bursts; this explains the short-lived radio emission. We suggest that the differences between bursts reflect variations in the magnetic-field strength in the afterglow-emitting regions.
    Keywords: Space Radiation
    Type: Nature; Volume 398; 394-399
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  • 3
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    The Identification of Two Different Spectral Types of Pulses in Gamma-Ray Bursts (1997)
    In:  Other Sources
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    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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  • 4
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    The Structure and Evolution of LOCBURST: The BATSE Burst Location Algorithm (1999)
    In:  Other Sources
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    Publication Date: 2011-08-23
    Description: The gamma-ray burst (GRB) location algorithm used to produce the BATSE GRB locations is described. The general flow of control of the current location algorithm is presented, and the significant properties of the various physical inputs required are identified. The development of the burst location algorithm during the releases of the BATSE IB, 2B, and 3B GRB catalogs is presented so that the reasons for the differences in the positions and error estimates between the catalogs can be understood. In particular, differences between the 2B and 3B locations are discussed for events that have moved significantly and the reasons for the changes explained. The locations of bursts located independently by the interplanetary network (IPN) are used to illustrate the effect on burst location accuracy of various components of the algorithm. IPN data and locations from other gamma-ray instruments are used to calculate estimates of the systematic errors on BATSE burst locations.
    Keywords: Space Radiation
    Type: Astrophysical Journal; Volume 512; 362-376
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  • 5
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    Temporal Characteristics of SGR 1806-20 and SGR 1900+14 Bursts (2001)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: We study the temporal properties of 268 bursts from SGR 1806$-$20 and 679 bursts from SGR 1900+14 all observed with the Rossi X-Ray Timing Explorer/Proportional Counter Array. Temporal parameters, such as T$_{90}$ durations and $\tau$$_{90}$ emission times are implemented. We find a lognormal distribution of burst durations, ranging over more than two orders of magnitude: T$_{90}$ $\sims$ 10$ {-2}$ to $\gtrsim$ 1 s, with a peak $\sim$ 0.1 s. The burst light curves tend to be asymmetrical, with more than half of all events showing rise times t$_{r}$ $〈$ 0.2 T$_{90}$. We find that there exists a correlation between the duration and fluence of bursts from both sources. We also find a significant anti-correlation between hardness ratio and fluence of SGR bursts. Finally we discuss possible physical implications of these results within the framework of the magnetar theory.
    Keywords: Space Radiation
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  • 6
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    The BATSE Gamma-Ray Burst E-Peak Distribution (2000)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: Gamma-ray burst observed by BATSE are found to have approximately the same characteristic energy, denoted as E_p. We examine whether instrumental effects can give rise to this observation. We simulate the derivation of E-p and determine that the values in the BATSE sample are accurate and complete above a minimum fluence. We simulate the triggering of BATSE on gamma-ray bursts, deriving the efficiency of detecting bursts as a function of characteristic energy. From this simulation, we model the observed E_p distribution function expected when the intrinsic distribution function is a power-law. We find that this distribution produces poor fits to the observations. We find that a log-normal intrinsic distribution with a power-law tail gives a good fit to the data. From these fits, we conclude that instrumental effects cannot produce the observed E_p distribution, and that the observed distribution is a consequence of a narrow intrinsic distribution of E_p in gamma-ray bursts.
    Keywords: Space Radiation
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  • 7
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    The Error Distribution of BATSE Gamma-Ray Burst Locations (1999)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Empirical probability models for BATSE gamma-ray burst (GRB) location errors are developed via a Bayesian analysis of the separations between BATSE GRB locations and locations obtained with the Interplanetary Network (IPN). Models are compared and their parameters estimated using 392 GRBs with single IPN annuli and 19 GRBs with intersecting IPN annuli. Most of the analysis is for the 4Br BATSE catalog; earlier catalogs are also analyzed. The simplest model that provides a good representation of the error distribution has 78% of the probability in a "core" term with a systematic error of 1.85 deg and the remainder in an extended tail with a systematic error of 5.1 deg, which implies a 68% confidence radius for bursts with negligible statistical uncertainties of 2.2 deg. There is evidence for a more complicated model in which the error distribution depends on the BATSE data type that was used to obtain the location. Bright bursts are typically located using the CONT data type, and according to the more complicated model, the 68% confidence radius for CONT-located bursts with negligible statistical uncertainties is 2.0 deg.
    Keywords: Space Radiation
    Type: Astrophysical Journal Supplement Series; 122; 503-518
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  • 8
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    Average Emissivity Curve of Batse Gamma-Ray Bursts with Different Intensities (1999)
    In:  Other Sources
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    Publication Date: 2019-07-13
    Description: Six intensity groups with approximately 150 BATSE gamma-ray bursts each are compared using average emissivity curves. Time stretch factors for each of the dimmer groups are estimated with respect to the brightest group, which serves as the reference, taking into account the systematics of counts-produced noise effects and choice statistics. A stretching/intensity anticorrelation is found with good statistical significance during the average back slopes of bursts. A stretch factor approximately 2 is found between the 150 dimmest bursts, with peak flux less than 0.45 photons/sq cm.s, and the 147 brightest bursts, with peak flux greater than 4.1 photons/sq cm.s. On the other hand, while a trend of increasing stretching factor may exist for rise fronts for bursts with decreasing peak flux from greater than 4.1 photons/sq cm.s down to 0.7 photons/sq cm.s, the magnitude of the stretching factor is less than approximately 1.4 and is therefore inconsistent with stretching factor of back slope.
    Keywords: Space Radiation
    Type: Astrophysical Journal; 523; 610-616
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  • 9
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    Comparison of z-known GRBs with the Main Groups of Bright BATSE Events (2001)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: The small reference sample of six BATSE gamma-ray bursts with known redshifts from optical afterglows is compared with a comparison group of the 218 brightest BATSE bursts. These two groups are shown to be consistent both with respect to the distributions of the spectral peak parameter in the observer's frame and also with respect to the distributions of the frame-independent cosmological invariant parameter (CIP). Using the known values of the redshifts z for the reference sample, the rest-frame distribution of spectral parameters is built. The de-redshifted distribution of the spectral parameters of the reference sample is compared with distribution of these parameters for the comparison group after de-redshifting by the factor 1/(1+z), with z a free parameter. Requiring consistency between these two distributions produces a collective estimation of the best fitting redshifts z for the comparison group, z=1.8--3.6. These values can be considered as the average cosmological redshift of the sources of the brightest BATSE bursts. The most probable value of the peak energy of the spectrum in the rest frame is 920 keV, close to the rest mass of an electron-positron pair.
    Keywords: Space Radiation
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  • 10
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    Average Cosmological Invariant Parameters of Cosmic Gamma Ray Bursts (1998)
    In:  Other Sources
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    Publication Date: 2019-07-17
    Description: Average cosmological invariant parameters (ACIPs) are calculated for six groups of BATSE cosmic gamma-ray bursts selected by their peak fluxes on the 1.024s timescale. The ACIPs represent the average temporal and spectral properties of these events equally in the observer frame of reference and in the co-moving frames of outbursting emitters. The parameters are determined separately for rise fronts and for back slopes of bursts, defined as the time profiles before and after the main peaks, respectively. The ACIPs for the rise fronts are found to be different for different intensity groups, while the ACIPs for the back slopes show no significant dependence on intensity. We conclude that emitters of bursts manifest standard average properties only during the back slopes of bursts.
    Keywords: Space Radiation
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