2. GRBM and WFC detection
On 1997 11 January, 09:43:59.99 UT the GRBM onboard BeppoSAX was triggered by an intense gamma-ray burst, showing a multipeak structure and lasting 43 s (Costa et al. 1997b). The peak intensity was erg cm-2 s-1 in the energy range 40-700 keV. This GRB was also detected by the WFC unit 2, with a similar time profile structure but a longer duration (see Fig. 1). The 2-10 keV peak flux was erg cm-2 s-1. The fluence of the event in 40-700 keV was erg cm-2 while in 2-10 keV it was erg cm-2. In Fig. 1 the gamma-ray (GRBM) and X-ray (WFC) light curves of the event are shown. Given that GRB970111 was one of the earliest X-ray transients detected in the WFC at the Quick Look Analysis, the position of the event was promptly distributed with a error radius (Costa et al. 1997b), somewhat worse than that obtainable from the instrinsic capabilities of the WFCs. After about 20 days a revised error box of the GRB970111 location with a error radius was produced, centred at a position apart from the centroid of the previous one (in 't Zand et al. 1997). The new position was R.A. = and Decl.= (equinox 2000.0). Very recently the WFC hardware team again improved the instrument calibration, further reducing the error box area to an irregular circle of radius (99% confidence) (Heise et al. 1997), centred at R.A. = and Decl.= . This new region is contained within the previous one, but is centred about apart.
The Interplanetary Network used the delay in the GRB arrival times between the interplanetary Ulysses mission and the ComptonGRO and BeppoSAX near-Earth satellites (Galama et al. 1997) to obtain a narrow strip of possible arrival directions in the sky. This allows the reduction of the GRB error box to a portion of the WFC error circle.
© European Southern Observatory (ESO) 1998
Online publication: March 30, 1998