Bright Gamma-ray Bursts Research Articles

Search for a radio counterpart to GRB 940301 with westerbork

The COMPTEL instrument onboard theCompton Gamma-Ray Observatory imaged the bright gamma-ray burst GRB 940301 within 1.6 hours of the event, with a mean 1σ error radius of 1.5°. The error region was subsequently refined by combining the COMPTEL location with the arc derived from differences in the event arrival time at the Ulysses and BATSE detectors. Westerbork observations of the COMPTEL error region began on March 4 1994 at 21 cm, however coverage of the refined position was not obtained until 32 days after the GRB occurrence, by which time the operating wavelength had changed to 92 cm. We have constrained the level of variability of sources within the triangulation arc-COMPTEL 2σ error box region to be less than 40 mJy (5σ upper limit) at 92 cm 41 days after the burst.

On the stellar origin of gamma ray bursts

We show that our original suggestion that gamma-ray bursts (GRB) may be flares on Magnetically Active Stellar Systems (MASS) namely flare stars, RS CVn binaries and Cataclysmic variables agrees well with the new observations of CGRO. We make a multi component fit to the log(N) - log(S) distribution and the high degree of isotropy as observed by the previous generation of satellites as well as BATSE/CGRO using the second BATSE catalogue. We then discuss individual source association and optical transient observations and show that they favor the present suggestion. We discuss the physical mechanisms and gamma-ray production processes that can occur on such systems giving the GRB their characteristics. We predict increase of anisotropy in the BATSE/CGRO observations for bright GRB.

Photon-photon opacity constraints for relativistically expanding gamma-ray burst sources

Five bright gamma-ray bursts detected by BATSE have also been detected at higher energies by EGRET. Four are consistent with power-law spectra extending to energies as high as, in the case of GRB930131, 1 GeV. The fifth, and most recent, GRB940217, has a more complex spectrum, with one photon detected at 18 GeV, the most energetic GRB photon detection to date. The optical depth to photon-photon pair production in these sources is extremely large for distances more than about 10pc away if the radiation is emitted isotropically in the observer's frame. This optical depth can be dramatically reduced if the source is moving with a relativistic bulk Lorentz factor Γ, and recent calculations for this situation have been limited to cases of a beam with opening angle 1 Γ , or expansions of infinitely thin spherical shells. This paper presents our extension of the pair production optical depth calculation in relativistically expanding sources to more general geometries, including shells of finite thickness and arbitrary opening angle. We find that the minimum bulk Lorentz factors for the EGRET sources to be optically thin, i.e. display no spectral attenuation, is only moderately dependent on the shell thickness and its opening solid angle; these new limits on required velocity for given source geometries will aid in placing realistic constraints on GRB source models.

Duration distributions of bright and DIM BATSE gamma-ray bursts

We have measured the T(sub 90) and T(sub 50) durations of bright and dim gamma-ray bursts detected by the Compton Gamma-Ray Observatory's (CGRO) Burst and Transient Source Experiment (BASTE). The T(sub 90) T(sub 50) duration is defined as the interval over which 5% (25%) to 95% (75%) of the burst counts accumulate. Out of 775 bursts observed by BATSE 159 bursts were analyzed; bursts with durations shorter than 1.5 s were excluded. A Kolmogorov-Smirnov test yields a probability of 6 x 10(exp -5) that the T(sub 50) durations of the dim and bright samples are drawn from the same parent population. We find that the centroid and extent of the duration distribution for the dim sample are scaled by approximately a factor of 2 relative to those of the bright sample. The measured time-dilation factor is not sensitive to choice of energy band. These results are quantitatively consistent with previous tests for time dilation in a smaller sample of BATSE bursts. The sources of dimmer bursts, if cosmological, would lie at redshifts of order 2.

A search for the radio counterpart to the 1994 March 1 gamma-ray burst

We report on the results of a search for the radio counterpart to the bright gamma-ray burst of 1994 March 1. Using the Dominion Radio Astrophysical Observatory Synthesis Telescope sensitive, wide-field radio images at 1.4 GHz and 0.4 GHz were made of a region around GRB 940301. A total of 15 separate radio images were obtained at each frequency, sampling a near-continuous range of post-burst timescales between 3 and 15 days, as well as 26, 47, and 99 days. We place an upper limit of 3.5 mJy on a fading/flaring radio counterpart at 1.4 GHz and 55 mJy at 0.4 GHz. Unlike past efforts our counterpart search maintains high sensitivity over two decades of post-burst time durations. Time-variable radio emission after the initial gamma-ray burst is a prediction of all fireball models, currently the most popular model for gamma-ray bursts. Our observations allow us to put significant constraints on the fireball parameters for cosmological models of gamma-ray bursts.

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.

BATSE spectroscopy catalog of bright gamma-ray bursts

view Abstract Citations (59) References (33) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS BATSE Spectroscopy Catalog of Bright Gamma-Ray Bursts Schaefer, Bradley E. ; Teegarden, Bonnard J. ; Fantasia, Stephan F. ; Palmer, David ; Cline, Thomas L. ; Matteson, James L. ; Band, David L. ; Ford, Lyle A. ; Fishman, Gerald J. ; Meegan, Charles A. ; Wilson, Robert B. ; Paciesas, William S. ; Pendleton, Geoffrey N. ; Briggs, Michael S. ; Lestrade, John P. Abstract 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 a1. (1994). Subiect headings.. catalogs - gamma rays: bursts Publication: The Astrophysical Journal Supplement Series Pub Date: May 1994 DOI: 10.1086/191969 Bibcode: 1994ApJS...92..285S Keywords: Astronomical Catalogs; Astronomical Spectroscopy; Fluence; Flux Density; Gamma Ray Astronomy; Gamma Ray Bursts; Gamma Ray Spectra; Stellar Luminosity; Temporal Distribution; Background Noise; Gamma Ray Observatory; Scintillation Counters; Spectral Methods; Astrophysics; CATALOGS; GAMMA RAYS: BURSTS full text sources ADS | data products SIMBAD (53) NED (51) HEASARC (1)

The origin and location of the 5 March 1979 gamma-ray burst

Gamma-ray bursts (GRBs) have been controversial since their discovery, mainly because of the absence of counterparts at any other wavelength that would help identify the nature of the astrophysical object associated with them; this in turn could determine their distances and luminosities, providing some constraints on their physical parameters. The absence of identifiable counterparts, as well as certain spectral features attributed to red-shifted e+–e– annihilation radiation, has led to the conclusion that they occur on isolated neutron stars and hence their luminosities should not be far in excess of ˜1038ergs–1, the Eddington luminosity for a solar mass object. On this assumption, the observed fluxes of 10–5–10–6 erg cm–2 s–1 gave distance estimates of the order of a few kpc, although their isotropic distribution may be in conflict with such an assumption. Perhaps the most controversial GRB is that of 5 March 1979, precisely because there is an accurate positional identification of this burst1 with a known astronomical object, the supernova remnant N49 in the Large Magellanic Cloud (LMC). Such an association would fix the distance at 55 kpc, and with the observed flux (this is by far the brightest GRB observed to date), would require prodigious energy and luminosity from this GRB (l044erg and l044ergs–1 respectively), casting doubt, on theoretical grounds, on its distance and its physical association with the LMC. However, some Kosmos 856 observations2 may provide more direct evidence on energy released and hence give a decisive answer to this question.