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Astron. Astrophys. 364, L54-L61 (2000)

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2. Detection of the gamma-ray burst

GRB 000131 was observed by Ulysses, Konus/Wind, NEAR, and CGRO-BATSE on 2000 Jan. 31.624 UT. After 56 hours, it was localized via InterPlanetary Network (IPN) timing to two alternate 55 sq. arcmin error boxes (Hurley et al., 2000a), one of which was ruled out by the independent BATSE location (Kippen 2000). From the Ulysses, Konus/Wind, and NEAR data its 25-100 keV fluence was [FORMULA] erg/cm2.

BATSE detected the event (Trigger #7975) in a partial data gap, so the standard catalog data products such as flux, fluence, and duration are not available. However, by analyzing other data types from BATSE the relevant parameters could be estimated. The results are given in Table 1. The peak flux is in the top 5[FORMULA], and the fluence in the top 7[FORMULA] of all BATSE GRBs. The spectrum is well fit by a standard GRB model (Band et al. 1993) and shows a typical spectral evolution (Preece et al. 2000).


Table 1. Spectral data from BATSE

The BATSE light curve is shown in Fig. 1. The event consists of several spikes, most of which show a clear asymmetry, the leading edge being the steepest. A weak pulse lasting [FORMULA] 7 s is observed 62 s prior to the burst trigger. Its arrival direction is consistent (within a 12 degree error) with that of the main pulse. This spike is therefore most likely part of the burst. In this case the overall duration is about 170 s, i.e. significantly longer than measured by T90. The presence of this `precursor' is reminiscent of that displayed by GRB 991216 (Kippen et al. 1999; Hurley 2000a). However, in the case of GRB 000131, no long-lasting tail ([FORMULA]-ray afterglow) is observed.

[FIGURE] Fig. 1. Gamma-ray light curve of GRB 000131 recorded by the BATSE Large Area Detectors (LADs). b shows continuously recorded data with 1024 ms time resolution, a shows an enlargement of the most intense interval using triggered data with 64 ms time resolution. In both cases, data from the two most brightly illuminated LADs have been summed. Energy channels for the different data types and detectors have been chosen to approximately match (within a few percent) the energy range 60-320 keV.

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© European Southern Observatory (ESO) 2000

Online publication: December 15, 2000