The names of non-triggered events are given in the format NTB YYMMDD.FF, where NTB stands for "Non-Triggered Burst" and YYMMDD.FF specifies the approximate date and time the event was recorded. YY are the last 2 digits of the year, MM indicates the month, and DD.FF gives the day (with fractional part FF/100).
The acronym, TJD, stands for "Truncated Julian Date", which is the day numbering scheme used in BATSE operations. It is a modification of the standard astronomical Julian Date (JD). The TJD is obtained from the JD or the Modified Julian Date (MJD) as follows:
TJD = JD - 2440000.5 = MJD - 40000.0Note that dates in the TJD system begin at Greenwich mean midnight, while those on the JD and MJD system begin at Greenwich mean noon.
The acronym, SOD, stands for "Seconds of Day". This indicates the time of the event (in seconds) on the given TJD. Since the TJD begins at Greenwich mean midnight, the SOD correponds (in seconds) to Universal Time (UT).
The two detectors most brightly illuminated by the burst.
The direction to the source for each event in the GRO spacecraft coordinate system. The GRO azimuthal angle (Az) is given in decimal degrees, and refers to an angle measured in the GRO X-Y plane, from the GRO +X axis. The GRO elevation angle (El) is given in degrees. It is the usual elevation angle, given as 90 degrees minus the angle with the GRO +Z axis.
The right ascension (RA) and declination (Dec) corresponding to the source direction are given in decimal degrees, referred to J2000.0.
The uncertainty in the estimated source direction, given in degrees.
The angle between the source direction and the direction to the center of the earth is given in degrees. (Note that the daily DISCLA FITS files contain a field with the tag 'GEO_EL' and the description 'Geocenter Elevation'; this field actually contains a zenith angle, that is, an angle with the GRO +Z axis.)
The angle between the source direction and the direction to the center of the sun is given in degrees.
The geographic position of GRO at the time of the event.
Cmax is an abbreviation for the maximum count rate achieved during a burst on a given time scale (here, 1.024 s, 4.096 s, and 8.192 s). Cmin is an abbreviation for the minimum count rate required for that event to be detected by our off-line search algorithm. Here we give the value of Cmax/Cmin and Cmin. Values of 0.0 or -1.0 indicate that the event was not detected in DISCLA channels 2 and 3 on the corresponding time scale.
The peak flux of an event is the estimated photon number flux (integrated over DISCLA channels 2 plus 3) corresponding to the DISCLA time bin with the most counts above background. Since the DISCLA data have a time resolution of 1.024 s, our peak flux is really a peak "fluence" integrated over 1.024 s. The units of peak flux are photons per square centimeter per second.
To estimate peak flux, the differential peak flux (photons per square centimeter per second per keV) is integrated over the energy range covered by channels 2 and 3 in the detector most brightly illuminated by the event. This range is roughly 50-300 keV, although the channel boundaries in the individual detectors vary by roughly 20 percent. A power-law form is assumed for the differential peak flux.
The fluence of an event is estimated using the formula F = cTPE, where c is a conversion factor from keV to ergs, T is the time over which the fluence is estimated, P is the mean photon number flux during the time T, and E is the mean photon energy over the energy range covered by DISCLA channels 2 and 3 (about 50-300 keV). Since the spectra of some bursts show evolution, the fluences for bursts longer than 4.096 s are estimated by adding up the fluences from individual 4.096 s slices of the burst.
The duration of an event is estimated using the T50 and T90 measures. T50 is the time interval during which the accumulated counts from the burst increase from 25% to 75% of the total counts. Likewise, T90 is the time interval during which the accumulated counts increase from 5% to 95% of the total counts.
Any notable features of the event.
| May 5, 1998 | Back to Non-triggered Burst Home Page | Author: Jeff Kommers |