Forum Springer Astron. Astrophys.
Forum Whats New Search Orders

Astron. Astrophys. 332, L29-L32 (1998)

Previous Section Next Section Title Page Table of Contents

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 [FORMULA] 43 s (Costa et al. 1997b). The peak intensity was [FORMULA]  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 [FORMULA]  erg cm-2  s-1. The fluence of the event in 40-700 keV was [FORMULA]  erg cm-2 while in 2-10 keV it was [FORMULA]  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 [FORMULA] 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 [FORMULA] error radius was produced, centred at a position [FORMULA] apart from the centroid of the previous one (in 't Zand et al. 1997). The new position was R.A. = [FORMULA] and Decl.= [FORMULA] (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 [FORMULA] radius (99% confidence) (Heise et al. 1997), centred at R.A. = [FORMULA] and Decl.= [FORMULA]. This new region is contained within the previous one, but is centred about [FORMULA] apart.

[FIGURE] Fig. 1. BeppoSAX GRBM (40-700 keV) and WFC (2-26 keV) light curves of GRB970111

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.

Previous Section Next Section Title Page Table of Contents

© European Southern Observatory (ESO) 1998

Online publication: March 30, 1998