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IX/20               The Fourth BATSE Burst Catalog       (Paciesas+ 1998)
============================================================================
The Fourth BATSE Burst Catalog
     Paciesas W.S., Meegan C.A., Pendleton G.N., Briggs M.S.,
     Kouveliotou C., Koshut T.M., Lestrade J.P., McCollough M.,
     Brainerd J.J., Hakkila J., Henze W., Preece R.D., Mallozzi R.S.,
     Fishman G.J.
    
============================================================================
ADC_Keywords: Gamma rays
Mission_Name: CGRO

Description:
    This is the fourth catalogue of the BATSE instrument on board of the
    Compton Gamma-ray Observatory, launched on April 5, 1991. It contains
    the locations and times for 1637 triggered gamma-ray bursts observed
    from 19 April, 1991 until 29 August, 1996.

File Summary:
-------------------------------------------------------------------------
  FileName      Lrecl  Records   Explanations
------------------------------------------------------------------------
ReadMe             80        .   This file
4b.dat             88     1637   Basic 4B catalogue.
4bcom.dat          86     2344   Comments table
4bdur.dat          52     1234   Duration table
4bexp.dat          51       37   BATSE exposure table
4bflux.dat        157     1292   Flux values for BATSE triggers
4bmax.dat          46      912   Cmaxmin table
4btric.dat         51       30   Trigger criteria table
4btris.dat         41       20   Exposure vs peak flux table
---------------------------------------------------------------------------

See also:
    http://cossc.gsfc.nasa.gov/cossc/batse/4Bcatalog/4b_catalog.html :
         4B Home page

Description of Table 4b.dat:
    This file specifies the locations and times for 1637 triggered
    gamma-ray bursts observed from 19 April, 1991 until 29 August, 1996.
    It therefore includes the data from the 3B catalog. The only revisions
    from the 3B catalog are improved locations for the triggers #741,
    2311, and 3155.

    Bursts since the end of the 1B catalog (March 1992) occurred when the
    GRO tape recorders were experiencing numerous errors. Consequently,
    there are gaps in the data of many bursts that preclude valid
    measurement of peak flux, peak rate, fluence, or duration. Peak rates
    on the 1 second timescale from each detector are almost always
    available. These data (called MAXBC rates) can be used to determine
    burst location. Previous difficulties with this data type have been
    largely removed, and we now believe that the systematic errors for
    MAXBC-located bursts are the same as for bursts located with other
    data types. It is still true however, that the MAXBC-located bursts
    usually have larger statistical errors than would be the case if
    another data type were available. The comments table provides "L"
    comments for MAXBC-located bursts. A number of CGRO and BATSE flight
    software changes have significantly reduced the problem of data gaps
    since March of 1993.

    The on-board software determines when a trigger occurs. When a burst
    trigger occurs, subsequent triggers are disabled for an accumulation
    period, during which the BATSE burst memories accumulate data. The
    accumulation period was 242 seconds until Dec 17, 1992, and from Jan
    8, 1996 to Feb 25, 1997. At all other times it has been 573 seconds.
    The stored burst data are then transmitted; the readout time for all
    triggers was 90 minutes until Dec 17, 1992. At that date, the flight
    software was revised to suspend readouts during telemetry gaps and to
    truncate readouts of weak events. This resulted in a variable readout
    time. During the burst data readout, the 64 ms threshold is revised to
    correspond to the maximum rate attained by the current burst, and
    triggering is disabled on the 256 ms and 1024 ms timescales. Bursts
    intense enough to trigger over this revised 64 ms value are termed
    "overwrites". They appear as triggers in this file, with the overwrite
    flag is set to 'Y'.

    The BATSE trigger numbers correlate all the files for this catalog.
    The trigger number is a running sequence of BATSE triggers which
    include cosmic bursts, solar flares and other events. The sequence
    begins with trigger 105 and ends with trigger 5586.
    Each burst has a unique catalog name. These BATSE catalog names later
    may be incorporated into a multi-spacecraft catalog with "GB" or "GRB"
    replacing this designation of "4B". The characters "4B " begin every
    BATSE catalog burst name, followed by the "yymmdd" of the burst.
    "yymmdd" is the two digit year, two digit month, and two digit day.
    When more than one gamma-ray burst occurs on one day, those bursts
    have a single letter suffix (B,C,D...), generally in order of
    intensity. Example: 4B 920503B refers to the second brightest burst
    that triggered BATSE May 3, 1992. The brightest burst on that day will
    have no suffix.

    The burst trigger time is the end of the interval (64, 256 or 1024 ms)
    on which the burst triggered the detector.
    The error in angular location is the radius of a circle having the
    same area as the 68% confidence ellipse defined by the formal
    covariance matrix from a chi^2^ fit on the assumption of normal
    errors. The error is based solely on the Poisson uncertainty in the
    BATSE measurement of burst flux by each Large Area Detector. There is,
    in addition, an RMS systematic error of approximately 1.6 degrees.
    Adding 1.6 degrees in quadrature to the error in the table yields our
    estimate of the 68% confidence interval for the burst location error.
    The statistical error is believed to be Gaussian. The systematic error
    distribution has a more extended tail than a Gaussian.

Byte-by-byte Description of file: 4b.dat
----------------------------------------------------------------------------
   Bytes Format Units Label    Explanations
----------------------------------------------------------------------------
   1-  4  I4    ---   TrigNo   [105/5586] The BATSE trigger number
   6- 15  A10   ---   4B       The BATSE Catalog burst name, from obs. date
  19- 27  F9.1  d     JD       The Julian Date (TJD) of the trigger
  29- 37  F9.3  s     Time     The time in decimal seconds of day (UT)
                                 of the trigger
  39- 45  F7.3  deg   RAdeg    Right ascension (J2000) in decimal degrees
  47- 53  F7.3  deg   DEdeg    Declination (J2000) in decimal degrees
  55- 61  F7.3  deg   GLON     Galactic longitude in decimal degrees
  63- 69  F7.3  deg   GLAT     Galactic latitude in decimal degrees
  71- 76  F6.3  deg   PosErr   Radius in decimal degrees of positional error box
  78- 84  F7.3  deg   Angle    Angle in decimal degrees of geocenter (1)
      86  A1    ---   PrevFlag [YN] Overwrite flag: Y(true) if this burst
                                 overwrote an earlier, weaker trigger.
                                 N(false) otherwise
      88  A1    ---   NextFlag [YN] Overwritten flag: Y(true) if this burst was
                                   overwritten by a later, more intense trigger.
                                   N(false) otherwise
--------------------------------------------------------------------------------
Note (1): The angle between the burst and the nadir, as measured from the
          satellite
--------------------------------------------------------------------------------

Byte-by-byte Description of file: 4bcom.dat
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1-  4  I4    ---     TrigNo    [105/5586] BATSE trigger number
       6  A1    ---     Flag      [QAOLT] Comment flag (1)
   8- 86  A79   ---     Text      Comment
--------------------------------------------------------------------------------
Note (1): Q : comments on data quality
          A : additional observations by other instruments
          O : general comments
          L : comments on the gamma-ray burst coordinates
          T : comments on the gamma-ray burst duration
--------------------------------------------------------------------------------

Description of Table 4bdur.dat:
    This table contains values for T90 and T50, quantities related to
    burst duration, for 1234 gamma-ray bursts that triggered the BATSE LAD
    detectors between April 1991 and 29 August 1996. T90 and T50 are
    calculated using data summed over the 4 LAD discriminator channels and
    using data summed over only those detectors that satisfied the BATSE
    trigger criteria.

    Users must note that T90 and T50 are not available for those bursts
    which suffer from data gaps during the event; the integration
    procedure inherently fails in these cases. However, visual estimates
    of the burst duration are provided in the BATSE Comments table for
    those bursts with sufficient data coverage. Users may also find other
    pertinent comments concerning the calculated value of T90 and T50 in
    the BATSE COMMENTS table, and it is highly recommended that the
    COMMENTS table be consulted before any distribution selected on T90 or
    T50 is used.

    The measurements for trigger 148 were recalculated after errors in the
    3B values were brought to our attention by Jay Norris.

Byte-by-byte Description of file: 4bdur.dat
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1-  4  I4    ---     TrigNo    [105/5586] The BATSE trigger number.
   6- 12  F7.3  s       T50       T50, interval covering 50% of the counts (1)
  14- 19  F6.3  s     e_T50       Uncertainty in T50
  21- 28  F8.3  s       T50start  The start time of the T50 interval, relative
                                   to the trigger time in table 4b.dat (2)
  30- 36  F7.3  s       T90       T90, interval covering 90% of the counts (3)
  38- 43  F6.3  s     e_T90       Uncertainty in T90
  45- 52  F8.3  s       T90start  The start time of the T90 interval, relative
                                   to the trigger time in table 4b.dat (4)
--------------------------------------------------------------------------------
Note (1): T50 measures the duration of the time interval during which
          25% to 75% of the total observed counts have been detected.
Note (2): The start of the T50 interval is defined by the time at which
          25% of the total counts have been detected, and the end of the
          T50 interval is defined by the time at which and 75% of the
          counts have been detected.
Note (3): T90 measures the duration of the time interval during which
          5% to 95% of the total observed counts have been detected.
Note (4): The start of the T90 interval is defined by the time at which
          5% of the total counts have been detected, and the end of the
          T90 interval is defined by the time at which 95% of the total
          counts have been detected.
--------------------------------------------------------------------------------

Description of Table 4bexp.dat:
    The exposure table specifies the fraction of the time that a burst at
    a particular point on the sky is detectable by BATSE, and accounts for
    earth blockage, SAA passages, times when the burst trigger is
    disabled, and times when a burst readout is in progress. It is a
    function of declination only. The burst is assumed bright enough to
    exceed the trigger threshold. A separate efficiency correction must
    also be included in analysis of burst rates as a function of peak
    flux. This efficiency is provided in a separate table; work is in
    progress to improve the efficiency calculation by including
    atmospheric scattering and handling of telemetry gaps. Due to the
    failure of the GRO tape recorders and the presence of telemetry gaps
    in the post-1B data, a different algorithm was used in preparing this
    table than was used for the 1B catalog. The new algorithm not only
    handles telemetry gaps, but is also more accurate in computing SAA
    passages. In addition, the old algorithm excluded time intervals
    during which the trigger thresholds were not at their standard
    settings of 5.5 sigma in each trigger timescale, while the current
    algorithm does not. A separate table is provided that specifies the
    history of the trigger thresholds. The recomputed 1B exposure is
    higher (0.42 versus 0.38), due primarily to the inclusion of times
    when thresholds were not at 5.5 sigma. The galactic dipole moment of
    the sky exposure has changed by about 0.005, due primarily to the more
    accurate accounting for the SAA. The change in the galactic quadrupole
    moment is negligible. In the exposure table below, the declination is
    given in degrees, and the exposure fraction at that declination is
    given for each of the cumulative catalogs (1B through 4B), and for
    each subset that was added to make the next catalog. In the previous
    exposure tables, the exposure was an average over a range of
    declinations of typically about 10 degrees. Here, the exposure applies
    to a specific declination. Additional statistics are provided at the
    end of the table. The average exposure is the average over the sky of
    the declination-dependent exposure fraction. Total time is the time
    between the start and the end of the catalog subset, in units of 10^6
    seconds. Total exposure, the product of the previous two numbers, is
    the total time, in units of 10^6 seconds and averaged over the sky,
    that BATSE was sensitive was sensitive to bursts for that catalog
    subset. The values of  and -1/3 are the
    galactic dipole and quadrupole moments of the exposure. The values of
     and -1/3 are the dipole and quadrupole moments
    in the equatorial coordinate system. The uncertainty in the exposure
    fractions are roughly estimated at about 4%. Possible sources of
    systematic error in the moments are currently under study, but are
    expected to be less than 0.003 for the galactic moments.

Byte-by-byte Description of file: 4bexp.dat
--------------------------------------------------------------------------------
   Bytes Format Units   Label     Explanations
--------------------------------------------------------------------------------
   1-  3  I3    deg     DEd       [-90/90] Declination (1)
   5- 11  F7.5  s       1B        1B exposure
  13- 19  F7.5  s       2B-1B     2B-1B exposure
  21- 27  F7.5  s       3B-2B     3B-2B exposure
  29- 35  F7.5  s       4B-3B     4B-3B exposure
  37- 43  F7.5  s       3B        3B exposure
  45- 51  F7.5  s       4B        4B exposure
--------------------------------------------------------------------------------
Note (1): Average Exposure:
 -----------------------------------------------------------------------
                             1B   2B-1B    3B-2B   4B-3B    3B     4B
 -----------------------------------------------------------------------
  Average Exposure
  factor                   0.425    0.478   0.507  0.494   0.477   0.483
  Total Time (10^6s)      27.9     31.1    49.1   61.36  108.1   171.5
  Total Exposure(10^6s)   12.05    14.9    24.9   30.31   51.6    81.9
  No. of bursts          260      325     537    515    1122    1637
              -0.008   -0.009  -0.009 -0.008  -0.009  -0.009
  -1/3         -0.004   -0.004  -0.004 -0.004  -0.004  -0.004
                 0.017    0.018   0.019  0.017   0.018   0.018
  -1/3        0.025    0.024   0.024  0.024   0.024   0.024
 ------------------------------------------------------------------------
--------------------------------------------------------------------------------

Byte-by-byte Description of file: 4bflux.dat
--------------------------------------------------------------------------------
   Bytes Format Units       Label     Explanations
--------------------------------------------------------------------------------
   1-  4  I4    ---         TrigNo    [105/5586] BATSE trigger number
   6- 15  E10.3 mW/m2       F1        Fluence for channel 1 (20-50 keV)
  17- 26  E10.3 mW/m2     e_F1        Error in F1 (1)
  28- 37  E10.3 mW/m2       F2        Fluence for channel 2 (50-100 keV)
  39- 48  E10.3 mW/m2     e_F2        Error in F2 (1)
  50- 59  E10.3 mW/m2       F3        Fluence for channel 3 (100-300 keV)
  61- 70  E10.3 mW/m2     e_F3        Error in F3 (1)
  72- 81  E10.3 mW/m2       F4        Fluence for channel 4 (E > 300 keV) (4)
  83- 92  E10.3 mW/m2     e_F4        Error in F4 (1)
  94-100  F7.3  ct/cm2/s    F64ms     Peak flux on the 64ms time scale (3)
 102-106  F5.3  ct/cm2/s  e_F64ms     Error in F64ms (1)
 108-114  F7.3  0.1s        T64ms     Time of F64ms (2)
 116-122  F7.3  ct/cm2/s    F256ms    Peak flux on the 256ms time scale (3)
 124-128  F5.3  ct/cm2/s  e_F256ms    Error in F256ms (1)
 130-136  F7.3  0.1s        T256ms    Time of F256ms (2)
 138-143  F6.3  ct/cm2/s    F1024ms   Peak flux on the 1024 time scale (3)
 145-149  F5.3  ct/cm2/s  e_F1024ms   Error in F1024ms (1)
 151-157  F7.3  0.1s        T1024ms   Time of F1024ms (2)
--------------------------------------------------------------------------------
Note (1): The errors are one sigma statistical errors.
Note (2): The peak flux times are expressed in decimal seconds relative
          to the burst trigger time for the end of the interval in which
          the flux was calculated.
Note (3): The peak flux energy range is 50-300 keV, coinciding with the
          energy range of the nominal BATSE on-board burst trigger.
Note (4): Since channel 4 is an integral channel, fluences given for
          this channel are quite sensitive to the assumed spectral form.
          Spectral analyses in this energy range should be performed with
          higher resolution data types. Many of the bursts between March
          1992 and March 1993 have significant gaps in the data and are
          not included in the table.
--------------------------------------------------------------------------------

Description of Table 4bmax.dat:
    This table specifies the peak count rate in units of the threshold
    count rate, and the threshold count rate. The table contains 912
    triggered bursts observed from launch until 29 August 1996. Many
    bursts are not included, particularly after March of 1992, since
    insufficient data exist to determine either the peak counts or the
    threshold.

    The BATSE on-board software tests for bursts by comparing the count
    rates on the eight large-area detectors to threshold levels for three
    separate time intervals: 64 ms, 256 ms, and 1024 ms. A burst trigger
    occurs if the count rate is above threshold in two or more detectors
    simultaneously. The thresholds are set by command to a specified
    number of standard deviations above background (nominally 5.5{sigma}).
    Background rates are recomputed every 17 seconds. The thresholds
    exhibit a coarse quantization that results from truncating the square
    root of the 64 ms count rate. Since we require that rates be above the
    thresholds of at least two detectors, the trigger threshold is
    determined by the threshold of the second most brightly illuminated
    detector.

    When a burst trigger occurs, subsequent triggers are disabled during
    the accumulation period when the BATSE burst memories accumulate data.
    These data are then transmitted. During this readout period, the 64 ms
    threshold is revised to correspond to the maximum rate attained by the
    current burst, and triggering is disabled on the 256 ms and 1024 ms
    timescales. Bursts intense enough to trigger during this readout
    period are termed "overwrites". They are recognized in the table by
    the value of -999 in the threshold columns for 256ms and 1024ms.

Byte-by-byte Description of file: 4bmax.dat
--------------------------------------------------------------------------------
  Bytes Format Units  Label   Explanations
--------------------------------------------------------------------------------
  1-  4  I4    ---   TrigNo   [105/5586] BATSE trigger number
  6- 13  F8.3  s     CMax64   ?=-999.000 Maximum counts in the second most
                                brightly illuminated detector divided by the
                                threshold count rate on the 64 ms timescale
 15- 18  I4    ---   T64      ?=-999 Trigger threshold on the 64 ms timescale.
                                It is the number of counts in 64 ms required
                                to trigger the second most brightly illuminated
                                detector for this particular burst (1)
 20- 27  F8.3  s     CMax256  ?=-999.000 Maximum counts in the second most
                                brightly illuminated detector divided by the
                                threshold count rate on the 256 ms timescale.
 29- 32  I4    ---   T256     ?=-999 Trigger threshold on the 256ms timescale.
                                It is the number of counts in 256 ms required
                                to trigger the second most brightly illuminated
                                detector for this particular burst (1)
 34- 41  F8.3  s     CMax1024 ?=-999.000 Maximum counts in the second most
                                brightly illuminated detector divided by the
                                threshold count rate on the 1024 ms timescale.
 43- 46  I4    ---   T1024    ?=-999 Trigger threshold on the 1024ms timescale.
                                It is the number of counts in 1024 ms required
                                to trigger the second most brightly illuminated
                                detector for this particular burst (1)
--------------------------------------------------------------------------------
Note (1): Since a trigger can occur on any of the three timescales, there are
           often cases in which the maximum rate will be below threshold on one
           or two of the timescales. The value of V/Vmax can be determined for
           any burst by selecting the maximum of the three peak rates, raised to
           the -3/2 power. Many bursts have unknown counts or thresholds on one
           or more timescales. These are marked by a "-999" in the table.
           This can happen for one of the following reasons:
        1. If the trigger occurs on the 64 ms timescale during the peak 256 ms
            rate, then the peak 256 ms rate is not found.
        2. If the 64 ms peak rate never exceeds the 64 ms threshold, and it
            occurs before the trigger time, then the peak 64 ms rate is not
            found.
        3. If the 256 ms peak rate never exceeds the 256 ms threshold, and it
            occurs before the trigger time, then the peak 256 ms rate is not
            found.
        Note that items 2 and 3 do not affect V/Vmax, since these peak rates do
         not exceed threshold. Item 1 can on rare occasions lead to an
         overestimate of V/Vmax.
--------------------------------------------------------------------------------

Description of Table 4btric.dat:
    The BATSE instrument can trigger on various energy ranges and photon
    count rate thresholds. This provides an opportunity to selectively
    monitor for transient events with characteristic spectral properties.
    For instance, the instrument is most sensitive to gamma-ray bursts
    when the trigger energy covers 50 keV to 300 keV, and it is most
    sensitive to terrestrial gamma-ray flashes when the trigger energy is
    100 keV and above. Changes in count threshold can affect the
    triggering on event of a particular duration or characteristic peak
    flux. For instance, a high threshold on the 1024 ms timescale and a
    low threshold on the 64 ms timescale when triggering on the energy
    range 20 keV to 100 keV makes the instrument more sensitive to soft
    gamma-ray repeaters and less sensitive to solar flares. The table
    below gives the starting date and time for each trigger criterion used
    by the BATSE instrument.

    This table was last updated on May 1, 1997.

Byte-by-byte Description of file: 4btric.dat
--------------------------------------------------------------------------------
  Bytes Format Units   Label  Explanations
--------------------------------------------------------------------------------
  1-  8  A8 "DD/MM/YY" Date   Date on which the trigger was changed
 10- 16  I7    d       TJD    ? Julian day
     17  A1    ---     ---    [/] Separator
 18- 22  I5    s       SOD    ? Time of day for the trigger change
 24- 30  A7    ---     Chan   Channels used for triggering (1)
 32- 35  F4.1  ---     T64    ? Trigger threshold above the background count
                                 rate on the 64 ms timescales (2)
 37- 41  F5.2  ---     T256   ? Trigger threshold above the background count
                                 rate on the 256 ms timescales (2)
 43- 46  F4.1  ---     T1024  ? Trigger threshold above the background count
                                 rate on the 1024 ms timescales (2)
 48- 51  I4    ---     TrigNo ? First trigger occurring
                                 under the new criterion
--------------------------------------------------------------------------------
Note (1): The channel numbers correspond to the following energy bands:
     channel 1 is 20 keV to 50 keV
     channel 2 is 50 keV to 100 keV
     channel 3 is 100 keV to 300 keV
     channel 4 is 300 keV and above
Note (2): In units of standard deviation
--------------------------------------------------------------------------------

Description of Table 4btris.dat:
    BATSE will generate a burst trigger if the count rate in two or more
    detectors exceeds a threshold specified in units of standard
    deviations above background (nominally 5.5). The rates are tested on
    three time scales: 64 ms, 256 ms and 1024 ms. The energy range is
    nominally 50 keV to 300 keV. These efficiencies apply only to the
    nominal thresholds and energy range. A history of the thresholds and
    energy range settings is provided in the Trigger Criteria Table. The
    threshold in flux units depends on the background rate and the sky
    location relative to the detector normals. The following table gives
    the efficiency for generating a burst trigger as a function of peak
    flux on each of the three trigger time scales. An efficiency of 100%
    indicates that a burst will always generate a BATSE trigger if it is
    above the horizon and burst triggering is enabled. Corrections for
    earth blockage and other flux-independent effects can be made using
    the sky exposure map. The effects of atmospheric scattering are not
    included in this table. As a result, the efficiencies at low fluxes
    are underestimated. The thresholds are sensitive to the spectral shape
    of a burst. The threshold for a hard burst is lower than the threshold
    for a softer burst. The table assumes a power-law spectrum with an
    exponent of -1.5. For an exponent of -2.5, the lower thresholds
    increase by approximately 20%.

Byte-by-byte Description of file: 4btris.dat
--------------------------------------------------------------------------------
   Bytes Format Units       Label     Explanations
--------------------------------------------------------------------------------
   1-  5  F5.3  ct/cm2/s    T64       64 ms Threshold
   7- 13  F7.3  %           E64       64 ms Efficiency
  15- 19  F5.3  ct/cm2/s    T256      256 ms Threshold
  21- 27  F7.3  %           E256      256 ms Efficiency
  29- 33  F5.3  ct/cm2/s    T1024     1024 ms Threshold
  35- 41  F7.3  %           E1024     1024 ms Efficiency
--------------------------------------------------------------------------------

History: this catalog was copied from
   http://cossc.gsfc.nasa.gov/cossc/batse/4Bcatalog
   in February 1998.
================================================================================
(End)                                         Patricia Bauer  [CDS]  20-Feb-1998