PHEBUS - Granat Phebus Gamma-Ray Bursts

Overview

The PHEBUS database table is the Terekhov et al. (1994, 1995) and Tkachenko et al. (1998, 2002) Catalog of Cosmic Gamma-Ray Bursts Registered by the Phebus (or Phoebus) instrument on-board the GRANAT Observatory which operated from December 1989 to December 1996. One of the purposes of Phebus was to study cosmic gamma-ray bursts (GRBs) in the 100 keV to 100 MeV region of the spectrum. This catalog contains information on GRBs registered during the entire seven years of the mission, such as the energy fluxes observed at the GRB luminosity maxima and the time-integrated energy fluences in the energy range above 100 keV. The details of the Phebus detectors and other operational information, such as the criteria for burst detection, can be found in the Terekhov et al. and Tkachenko et al. papers which are listed in the References Section.

Catalog Bibcodes

1994AstL...20..265T
1995AstL...21...73T
1998AstL...24..722T
2002AstL...28..353T

References

"A Catalog of Cosmic Gamma-ray Bursts Registered by the PHEBUS Instrument
of the GRANAT Observatory, December 1989 - May 1991", Terekhov, O.V. et al.
1994, Astronomy Letters, vol. 20, p. 265. [66 GRBs]

"Catalog of Cosmic Gamma-ray Bursts Detected with the PHOEBUS Instrument
aboard the GRANAT Observatory between Jun 1991 and December 1992", Terekhov,
O.V. et al. 1995, Astronomy Letters, vol. 21, p. 73. [52 GRBs]

"A Catalog of Cosmic Gamma-ray Bursts Detected with the PHOEBUS/Granat:
January 1993-September 1994", Tkachenko, A.Yu.  et al. 1998, Astronomy Letters,
vol. 24, p. 722. [60 GRBs]

"A Catalog of Cosmic Gamma-ray Bursts Detected with the PHOEBUS Instrument on
the Granat Observatory: October 1994-December 1996", Tkachenko, A.Yu. et al.
2002, Astronomy Letters, vol. 28, p. 353. [32 GRBs]

Provenance

The original version of this database table was created by the HEASARC in the late 1990s. Later updates were made in February 2002 and March 2003, based on the HEASARC's transcription of Tables 1 and 2 of Terekhov et al. (1994), Terekhov et al. (1995) and Tkachenko, A.Yu. et al. (1998), and of Table 1 of Tkachenko, A.Yu. et al. (2002).

HEASARC Implementation

The HEASARC created this database table from the concatenation of tables in 4 separate papers. This resulted in a grand total of 210 entries. It should be noted that in the final paper of the series (Tkachenko et al. 2002), the authors state that "over the entire period of its operation, the Phebus instrument detected 206 cosmic GRBs", i.e., 4 less than are contained in this HEASARC table. The HEASARC has no explanation for this discrepancy.

Parameters

Name
The burst designation in the standard IAU nomenclature for designating time-specific phenomena: PB stands for `Phebus Burst' and the six digits are in the usual year-month-day (YYMMDD) format. Thus the burst with name PB 891218 is the GRB detected by Phebus on December 18 1989.

Number_Flag
The part of this parameter before the decimal point is the number of the GRANAT Observatory observing run in which the burst was detected, while the part after the decimal point is the activation number of the burst cell during the given run.

Time
The date and approximate time of the activation of the Phebus instrument burst cell in Universal Time (UT) in the standard HEASARC Browse time format and precision. This time was given to a precision of 1 millisecond in the original reference (see the activation_time parameter for the precise time).

Activation_Time
The time of the activation of the Phebus instrument burst cell in Universal Time (UT). The date on which the burst occurred is encoded in the Name parameter, remember.

Duration
The duration of the burst event, T90, in seconds. This characterizes the time interval during which 90% of all photons from the burst were registered (from 5% to 95%).

Duration_Error
The error in the duration of the burst event, in seconds.

Cmax_To_Cmin
The ratio of the maximal to the minimal count rate necessary to have detected the burst. This is related to the statistic V/Vmax by the equation V/Vmax = (Cmin/Cmax)^1.5, where, for a given burst, V is the volume of the minimal sphere containing the burst, and Vmax is the maximal spatial volume accessible for burst registration. V/Vmax is thus a measure of the homogeneity of the spatial distribution of the cosmic GRB sources. For a spatially homogeneous distribution of GRBs, the average value of V/Vmax would be 0.5. In fact, the actual averaged value for the GRBs in the PHEBUS database table is 0.336+/- 0.007, which differs by more than 23 standard deviations from the spatially uniform value. Cmax/Cmin values were calculated for each of the 6 Phebus detectors, and the second largest value of these was used to determine the mean V/Vmax value. This is because the count-rate threshold must be exceeded in at least two detectors for a burst to be registered. The trigger of the burst cell can be activated for two time scales (0.25 and 1 sec). Therefore, Cmax/Cmin values were calculated for both time scales and the greater of the two values was the one selected.

Cmax_To_Cmin_Error
The error in the Cmax/Cmin ratio.

Remarks
This is a code indicating if the burst was observed independently by another instrument:

   B - BATSE
   D - DMS
   E - EURECA
   G - GINGA
   K - KONUS
   P - PVO
   S - SIGMA
   Sc- SROSS-C
   T - TGRS
   U - ULYSSES
   W - WATCH
   Y - Yohkoh

Fluence
The fluence or time-integrated energy flux transported by burst photons in the range above 100 keV, in units of 10^-5 erg cm^-2. This was derived from information on the energy spectrum accumulated during the entire burst.

Fluence_Error
The error in the fluence or time-integrated energy flux, in units of 10^-5 erg cm^-2.

Flux
The maximum or peak energy flux of the burst in the range above 100 keV, in units of 10^-5 erg cm^-2 s^-1. This was derived from spectral data for the individual spectrum corresponding to the interval of maximum brightness for the given event.

Flux_Error
The error in the peak flux of the burst, in units of 10^-5 erg cm^-2 s^-1.

Hardness
The hardness of the integrated energy spectrum, defined as the ratio of counts registered in the 400 to 1000 keV range to those in the 100 to 400 keV range.

Hardness_Error
The error in the hardness of the integrated energy spectrum.

Spectral_Form
A code used to describe the best-fitting of three different spectral forms that were used to fit the time-integrated burst spectra: P stands for a power-law function, B for the bremsstrahlung radiation law for optically thin plasma, and S for the synchtrotron radiation law. For each burst, fits were made to the integrated spectrum using each of these functional forms and the best-fitting functional form was found from a comparison of their various reduced chi-squared values. For some bursts where the reduced chi-squared values exceeded unity by a considerable amount, this implies that the hypothesis that their spectra can be described by such simple models is incorrect.

Spectral_Parameter
The `shape' parameter from the best-fitting model to the time-integrated burst spectrum: For a power-law model (Spectral_Form = P), this is the (dimensionless) power-law slope, for a bremsstrahlung model (Spectral_Form = B), this is the temperature in keV, and for the synchrotrom model (Spectral_Form = S), this is the critical energy Ec in keV in the synchrotron law equation.

Red_Chi_Squared
The reduced chi-squared of the best-fit model to the time-integrated burst spectrum.

Contact Person

Questions regarding the PHEBUS database table can be addressed to the HEASARC Help Desk.

Page Author: Browse Software Development Team
Last Modified: Monday, 16-Sep-2024 17:32:57 EDT