Burst And Transient Source Experiment Data Research Articles

Effects of dead time losses on terrestrial gamma ray flash measurements with the Burst and Transient Source Experiment

Measurements from the Burst and Transient Source Experiment (BATSE) instrument on the Compton Gamma Ray Observatory (CGRO) are the only ones where characteristics of single terrestrial gamma ray flashes (TGFs) have been obtained thus far. However, it has been reported that the measurements suffer from significant dead time losses which complicates the analysis and raises question about earlier BATSE studies. These losses are due to the high‐intensity flux combined with limitations of the time resolution of the instrument. Since these losses will affect both the spectrum and the temporal distribution of the individual TGFs, results based on BATSE data need to be revisited, including our own. We have therefore developed a Monte Carlo method to study the effects of these dead time losses. We show that the energy spectrum of TGFs becomes softer as the dead time losses increase. We also show that the time delay between the light curves of hard (E > 300 keV) and soft (E < 300 keV) photons increases significantly as the dead time losses increase. The Monte Carlo approach also enables us to identify the BATSE TGFs where the dead time effects can be corrected. These are the short‐duration single‐peaked TGFs. Without correcting for dead time losses we find that these short single‐peak TGFs have a softer energy spectrum and larger time delay than the multipeaked TGFs. After correcting for dead time losses we perform a new analysis of production altitudes and find that the production altitude is reduced compared to analysis without dead time losses. The new production altitudes combined with dead time losses are also consistent with the apparent large time delays. Our method gives consistent results regarding production altitude and time delays and indicates that the corrected TGF intensities measured by BATSE are 3 to 4 times brighter than the uncorrected measurements would indicate. We also show that the production mechanism of these TGFs has a typical duration of 250 μs.

Study of Very Short Gamma-Ray Bursts: New Results from BATSE and Konus

Our recent studies of very short gamma-ray bursts (GRBs) of T90 ≤ 100 ms duration have indicated a significant angular asymmetry and a uniform V/Vmax distribution from the BATSE (Burst and Transient Source Experiment on the Compton Gamma Ray Observatory [CGRO]) data. Here we update these studies, and we extend our research to events observed with Konus, a GRB experiment from Russia on the International Solar Terrestrial Physics/Wind satellite, that gives us new insight into the spectra that was not possible with the BATSE data. Konus has observed 18 events with T90 ≤ 100 ms duration. These events display a considerable number of photons with energies above 1 MeV and have photons above 5 MeV in all cases. These appear to be some of the most energetic photons observed from any class of GRB to date.

Analysis Methods and Results of a Search for Weak Gamma‐Ray Bursts in the BATSE Data

We report initial results on the statistical properties of the dimmest gamma-ray bursts (GRBs) observed with the Burst and Transient Source Experiment (BATSE), using new ground-based methods to obtain a sample of GRBs from 502 days of BATSE data. Using the most sensitive ground-based detection of GRBs, the sample extends to GRBs much fainter than those detected by the onboard trigger, but because of the temporal resolution of the data, the sample is limited to GRBs of duration of at least 2 s. For each detected event, Bayesian probabilities are calculated for the event to belong to each of seven classes of differing physical origins. The sample of GRB candidates is defined by the requirement that the Bayesian probability for belonging to the GRB class is higher than 0.5. The intensity distribution of the GRB sample is corrected using a Monte Carlo simulation of the postflight detection efficiency. The sky distribution of the dimmest BATSE bursts is consistent with isotropy. The dimmest bursts are softer than the brightest triggered bursts.

BATSE Observations and Orbit Determination of the Be/X‐Ray Transient EXO 2030+375

The Be/X-ray binary transient pulsar EXO 2030+375 (Ps≈42 s) has been observed with the large-area detectors (LADs) of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO). Beginning in 1991 May, 22 outbursts were observed over 4 years. Thirteen outbursts between 1992 February and 1993 August occurred consecutively at intervals of ≈46 days, close to the orbital period determined by Parmar and colleagues using EXOSAT data. The pulse profiles from the BATSE data are double peaked and show no significant energy or luminosity dependence, unlike the EXOSAT observations of 1985 May-August. An exponential model was used to fit the observed hard X-ray energy spectra from the 13 consecutive outbursts. When EXOSAT discovered this pulsar during a giant outburst in 1985 May, the X-ray luminosity peaked at LX=1.0×1038 ergs s-1 (1-20 keV), assuming a 5 kpc distance to the source. The BATSE outbursts are found to be weaker, 0.3×1037 ≤ LX(1-20 keV) ≤ 3.0×1037 ergs s-1 after extrapolating the observed flux (20-50 keV) to the EXOSAT energy band. Pulse phases derived from the 13 outbursts were fitted to two different models to determine a binary orbit. The new orbit is used to estimate 95% confidence limits for the mean peak spin frequency change during the outbursts observed with BATSE. This and the mean peak flux are compared to the spin-up rates and fluxes determined by EXOSAT from the 1985 giant outburst, where disk accretion was thought to have occurred. It is unclear whether these normal outbursts were driven by wind or disk accretion.

Multiyear BATSE Earth Occultation Monitoring of NGC 4151

We report the results of nearly six years of continuous monitoring of the Seyfert galaxy NGC 4151 by the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory (CGRO). Continuous 2154 day (5.9 yr) light curves for NGC 4151 have been derived from Earth occultation analysis of CGRO BATSE data. Fluxes are calculated assuming a cutoff power-law model of the form F(E) = F(E0)(E/E0)-α exp (E0 - E/Ecutoff). Light curves for the 20-70 and 70-200 keV bands are shown and found to have an average flux of 11 × 10-3 and 2.3 × 10-3 photons cm-2 s-1, respectively. Evidence for intrinsic source variability is observed with a fractional variation ratio measured at Fvar = 0.2 in both the 20-70 and 70-200 keV bands. A systematic difference is found between OSSE 50-150 keV flux measurements of NGC 4151 and simultaneous BATSE flux measurements in the same energy range.

Effects of Spectral Shape on Cosmological Models of the BATSE Gamma‐Ray Burst Intensity Distribution

We have used the photon energy spectra of 100 bright gamma-ray bursts (GRBs) obtained from data from the Large Area Detectors of the Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory to examine the effects of spectral shape on cosmological models of the burst number-intensity distribution (log N – log P), where N is the number of bursts with peak photon flux greater than P. Since it has become common to use an assumed burst photon spectrum in computations of this type, we have examined the consequences of this assumption by using a range of observed burst spectra to create theoretical intensity distributions. We used a conventional Friedmann cosmology to create the models, and assumed that there is no burst source rate density evolution and that the sources are monoluminous (standard candles). This enabled us to focus on the effects of spectral shape on the log N – log P model parameters (peak luminosity and redshift). The shape of the burst spectrum has an influence on the maximum redshift consistent with the BATSE data. The variation in the burst photon spectra causes the model maximum redshifts to vary by an average of ~20%. However, the maximum redshift can differ among log N – log P models incorporating different spectra by more than a factor of 2. Thus, the use of an assumed burst spectrum in modeling the number-intensity distribution yields results that are moderately dependent upon the assumed spectral shape.

Is There Evidence for Repeating Gamma-Ray Bursters in the BATSE Data?

The possibility that classical gamma-ray bursts (GRBs) occasionally repeat from the same locations on the sky provides a critical test of GRB models. There is currently some controversy about whether there is evidence for burst repetition in the Burst and Transient Source Experiment (BATSE) data. We introduce a gamma-ray burst {open_quote}{open_quote}pair-matching{close_quote}{close_quote} statistic that can be used to search for a repeater signal in the BATSE data. The pair-matching statistic is built upon the reported position errors for each burst and is more sensitive than previously used statistics at detecting faint repeating bursts or multiple burst recurrences. It is also less likely to produce (false) evidence of burst repetition due to correlations in the positions that are inconsistent with repeating bursters. We find that the excesses in {open_quote}{open_quote}matched{close_quote}{close_quote} and {open_quote}{open_quote}antipodal{close_quote}{close_quote} pairs seen with other statistics are caused by an excess of pairs with a separation smaller than their error bars would indicate. When we consider all separations consistent with the error bars, no significant signal remains. We conclude that the publicly available BATSE 1B and 2B data sets contain no evidence for repeating gamma-ray bursters. {copyright} {ital 1996 The American Astronomical Society.}

Limits on Reported Transient Emission Events near 0.5 MeV from the Crab and 1E 1740.7-2942

view Abstract Citations (14) References (21) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Limits on Reported Transient Emission Events near 0.5 MeV from the Crab and 1E 1740.7-2942 Smith, D. M. ; Leventhal, M. ; Cavallo, R. ; Gehrels, N. ; Tueller, J. ; Fishman, G. Abstract The SIGMA coded-mask telescope aboard the Granat observatory has reported transient emission near 0.5 MeV lasting for about 1 day from three Galactic objects: the Crab, black hole candidate Nova Muscae 1991, and, on two occasions, black hole candidate 1E 1740.7-2942 (1E) near the Galactic center. Two of these events (the Crab and one from 1E) have occurred since the launch of the Compton Gamma Ray Observatory (CGRO). Jung et al. searched for the 1E transient of 1992 using the Oriented Scintillation Spectrometer Experiment on CGRO but did not confirm the result. We use the Burst and Transient Source Experiment (BATSE) on CGRO to search for both this event and the Crab transient. We find a 3 σ_upper limit of 1.7 x 10-3 photons s-1 cm-2 compared to the reported flux of (5.1±1.7) x 10-3 photons s-1 cm-2 for the Crab transient, and a 3 σ upper limit of 1.8 × 10-3 photons s-1 cm-2 versus (4.28+2.7-1.5) × 10-3 photons s-1 cm-2 reported for the 1E event. Therefore, we do not confirm the two 1 day SIGMA transients for which BATSE data are available. Publication: The Astrophysical Journal Pub Date: February 1996 DOI: 10.1086/176840 Bibcode: 1996ApJ...458..576S Keywords: GALAXY: CENTER; GAMMA RAYS: OBSERVATIONS; ISM: INDIVIDUAL NAME: CRAB NEBULA; X-RAYS: BURSTS; STARS: INDIVIDUAL CONSTELLATION NAME: NOVA MUSCAE 1991; STARS: INDIVIDUAL ALPHANUMERIC: 1E 1740.7-2942 full text sources ADS | data products SIMBAD (4) HEASARC (1)

Gross spectral differences between bright and DIM gamma-ray bursts

We find that dim gamma-ray bursts (GRBs) are softer than bright GRBs, as indicated on average by data from the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory. We show that this correlation is statistically significant with respect to variations due to random differences between GRBs. This effect is discernable using a variety of methods and data sets, including public domain data. We analyze several types of systematic errors and selection effects in the BATSE data and conclude that the observed effect is not dominated by any of them. We therefore assert that this dim/soft effect is a real property of GRBs. It is possible that this correlation is a consequence of the time dilation detected by Norris et al. (1994) and that this is additional evidence that burst sources are located at cosmological distances.

The intrinsic luminosity of γ-ray bursts and their host galaxies

THE Burst and Transient Source Experiment (BATSE) on the Compton Gamma-Ray Observatory has shown that, although γ-ray bursts are distributed isotropically on the sky, there is an apparent dearth of weak events compared to those expected from a homogeneous distribution of sources1,2. This suggests that the bursts originate either in an extended galactic halo3 (that is, locally) or at cosmological distances4,5. The intensity distribution of the bursts can be used to constrain their source properties and spatial distribution, and here we address this question by considering the BATSE data with those from the Pioneer Venus Orbiter, correcting for the different reponse of the two instruments. We show that the composite intensity distribution can after all be fitted by a simple, homogeneous model of γ-ray burst sources with identical intrinsic luminosities where the faintest BATSE events are at a redshift of z∼0.80±0.05. We obtain an upper limit of about −18 on the absolute magnitude of the host galaxies by assigning model-derived distances to the brightest extragalactic objects found15 within the error boxes of eight well localized γ-ray bursts. All but the faintest active galaxies are excluded as the source of the bursts. The bursts may instead be associated with normal galaxies, but only if the host-galaxy magnitudes are close to our upper limit.

Necessity of evolution in cosmological γ-ray bursts

RESULTS from the Burst and Transient Source Experiment (BATSE)1 on the Compton Gamma-Ray Observatory show a relative deficiency of faint γ-ray bursts without any detectable anisotropy. This gives strong support to suggestions that the bursts originate at cosmological distances2, such that cosmic expansion reduces the detectability of faint (and therefore distant) sources relative to a uniformly filled euclidean space. But the Pioneer Venus Orbiter (PVO) observations of brighter bursts show no such deficiency, indicating that the bursts that it sees are at redshifts less than about one. The best-fit cosmological model based on PVO data (peak luminosity L0 = 2 x 1050erg s-1) with no evolution of the source population predicts, when extrapolated to the fainter sources, a factor of 40 more events than BATSE sees. Even the 3a limit from PVO (L0 = 9.1 x 1051 ergs-1) is barely consistent with the BATSE result. Evolution of the cosmological γ-ray burst sources with epoch therefore seems necessary if the PVO and BATSE data are to be reconciled. The required evolutionary trend is for fewer or fainter bursts at larger redshift.