14580659
Gamma-Ray Spectral State Transitions of GRO J1719–24
We report the results of an in-depth study of the long-term soft gamma-ray (30 keV to 1.7 MeV) flux and spectral variability of the transient source GRO J1719-24 that was first discovered by BATSE and SIGMA in the fall of 1993. Our results were obtained from the JPL BATSE-EBOP database covering a 1000 day period between 1993 January 13 and 1995 October 10. During this period, the source underwent a major outburst in the fall of 1993 when the 35-100 keV flux rose from a quiescent state of less than 16 mcrab before 1993 September 17 to a level of 1.5 crab on October 3. The source remained in this high-intensity state over the next ~70 days, during which the 35-100 keV flux decreased monotonically by ~33% to ~1 crab on December 12, then decreased sharply to the pre-transition quiescent level of ~44 mcrab on December 21, where it remained until 1994 September 5. During a 400 day period between 1994 September 5 and 1995 October 10, the source again underwent a series of five transitions when the 35-100 keV flux increased to low-intensity levels of ~200-400 mcrab, a factor of 4-7 times lower than what was observed in 1993. The low- and high-intensity states were characterized by two different spectral shapes. The low-state spectra are described by a power law with a spectral index of ~2. The high-state spectra, on the other hand, have two components: a thermal Comptonized shape below ~200 keV with electron temperature kTe of ~37 keV and optical depth τ ~ 2.8, and a soft power-law tail with photon index of ~3.4 above 200 keV that extends to ~500 keV. The softer high-intensity spectrum and the harder low-intensity spectrum intersect at ~400 keV. The nonthermal power-law gamma-ray component in both the high- and low-intensity spectra suggests that the persistent nonthermal emission source is coupled to the hot and variable thermal emission source in the system. Furthermore, the correlation of the spectral characteristics with the high- and low-intensity states resembles that seen in two other gamma-ray-emitting black hole candidates, GRO J0422+32 and Cygnus X-1, suggesting that perhaps similar system configurations and processes are occurring in these systems. Possible scenarios for interpreting these behaviors are discussed.
118897112
Earth Occultation Imaging Applied to BATSE -- Application to a Combined BATSE-GBM Survey of the Hard X-Ray Sky
A combined BATSE-GBM hard X-ray catalog is presented based on Earth Occultation Imaging applied to a reanalysis of BATSE data. An imaging approach has been developed for the reanalysis of Earth Occultation analysis of BATSE data. The standard occultation analysis depends on a predetermined catalog of potential sources, so that a real source not present in the catalog may induce systematic errors when source counts associated with an uncatalogued source are incorrectly attributed to catalog sources. The goal of the imaging analysis is to find a complete set of hard X-ray sources, including sources not in the original BATSE occultation catalog. Using the imaging technique, we have identified 15 known sources and 17 unidentified sources and added them to the BATSE occultation catalog. The resulting expanded BATSE catalog of sources observed during 1991-2000 is compared to the ongoing GBM survey.
16708377
BATSE SOFT GAMMA-RAY OBSERVATIONS OF GROJ 0422 + 32
We report results of a comprehensive study of the soft gamma-ray (30 keV to 1.7 MeV) emission of GROJ0422+32 during its first known outburst in 1992. These results were derived from the BATSE earth-occultation database with the JPL data analysis package, EBOP (Enhanced BATSE Occultation Package). Results presented here focus primarily on the long-term temporal and spectral variability of the source emission associated with the outburst, which complement those reported earlier by BATSE The light curves with 1-day resolution in six broad energy-bands show the high-energy flux (>200 keV) led the low-energy flux (<200 keV) by ∼ 5 days in reaching the primary peak, but lagged the latter by ∼ 7 days in starting the declining phase. We confirm the " secondary maximum " of the low-energy (<200 keV) flux at ∼TJD 8970-8981, ∼ 120 days after the first maximum, reported earlier by the BATSE team (Harmon et al. 1993). Our data show that the " secondary maximum " was also prominent in the 200-300 keV band, but became less pronounced at higher energies. During this 200-day period, the spectrum evolved from a power-law with pho-ton index of 1.75 on TJD 8839, to a shape that can be described by a Comptonized model or an exponential power law below 300 keV, with a variable power-law tail above 300 keV. The spectrum remained roughly in this two-component shape until ∼ 9 November (TJD 8935) when the 35-429 keV luminosity dropped to below ∼ 20% of its peak value observed on TJD-8848. It then returned to the initial power-law shape with an index of ∼ 2 and stayed in this shape until the end – 3 – of the period. The correlation of the two spectral shapes (e.g.Compton/power law tail vs.power law) with the high and low luminosities of the soft gamma-ray emission is strongly reminiscent of that seen in Cygnus X-1, suggesting that similar processes are at work in both systems. We observed also four separate episodes of high-energy (400-1000 keV) emission during the first 84 days of the event. We interpret these results in terms of the Advection Dominated Accretion Flow (ADAF) model with possibly a " jet-like " region that persistently produced the non-thermal power-law gamma rays observed throughout the event.
118025925
CL$_s$ Method at Gaussian Limit to Present Searches
We describe a new method based on the CLs approach [1] to present results in searches of new physics under the condition that the relevant nuisance parameter space is continuous. Essentially, this method uses a Gaussian approximation for the distribution of a log-likelihood ratio test statistic used in a two-hypotheses testing problem, when the sample size is large. It leads to a simple way to form exclusion sets for the parameters of interest. This Gaussian CLs method can be seen as an alternative to the traditional method of setting confidence intervals based on p-values. And one advantage of the Gaussian CLs method is that, it requires a simple procedure that is applicable in many situations where the p-value method requires computationally-intensive Monte Carlo instead of a popular thresholding rule based on a Chi-square distribution. We illustrate this method in a problem of searching for a sterile neutrino. Specifically, we derive exclusion sets in the two-dimensional parameter space of (sin 2θ, |∆m|) based on the Gaussian approximation, and demonstrate that it provides adequately accurate results. Finally, we discuss the advantages and disadvantages of our method in comparison to the traditional methods of setting confidence intervals.