PHEBUS - Granat Phebus Gamma-Ray Bursts
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.
"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]
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).
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
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.
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.
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).
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
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%).
The error in the duration of the burst event, in seconds.
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.
The error in the Cmax/Cmin ratio.
This is a code indicating if the burst was observed independently by another
B - BATSE
D - DMS
E - EURECA
G - GINGA
K - KONUS
P - PVO
S - SIGMA
T - TGRS
U - ULYSSES
W - WATCH
Y - Yohkoh
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.
The error in the fluence or time-integrated energy flux,
in units of 10^-5 erg cm^-2.
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.
The error in the peak flux of the burst, in units of 10^-5 erg
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.
The error in the hardness of the integrated energy spectrum.
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
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
The reduced chi-squared of the best-fit model to the time-integrated burst
Questions regarding the PHEBUS database table can be addressed to the
HEASARC User Hotline.
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