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Astron. Astrophys. 321, 229-235 (1997)

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2. GRB 940301

On 1994, March 1st at [FORMULA] UT a strong gamma-ray burst occurred (GRB 940301), lasting [FORMULA] 40 s. The burst was recorded by BATSE and COMPTEL. With a fluence of [FORMULA] erg cm-2 (50-300 keV) it belongs to the 2 % brightest bursts detected with BATSE. The COMPTEL localization and the Inter Planetary Network (IPN) annulus (derived from the time difference between the detection on board of the Compton Gamma-Ray Observatory, CGRO, and the Ulysses spacecraft; the plotted IPN is an improved determination, Hurley, private communications) can be seen in Fig. 1.

[FIGURE] Fig. 1. Contour plot of the WSRT image at 325 MHz (April-June 1994) of the GRB 940301 field centered at [FORMULA] [FORMULA] [FORMULA], [FORMULA] [FORMULA] [FORMULA] (equinox B1950). Included are the 2 and 3 sigma COMPTEL error regions, the IPN triangulation annulus (radius + 3 [FORMULA] and radius -3 [FORMULA]), and the 21 cm fields 1, 2, 3, 4, 5, A and B at 20% response. Indicated are the positions of PSR B0655+64, the East source (B0637+6313) and the West source (B0635+6318). Contour levels are 15, 30, 60, 120, 240, 480, 960 and 1510 mJy. The increase in noise at the edge of the field is due to primary beam correction.

Because of the high declination of GRB 940301 it is a favorable target for the Westerbork Synthesis Radio Telescope (WSRT). Furthermore, GRB 940301 is located well out of the galactic plane: ([FORMULA].

GRB 940301 triggered an extensive multi-wavelength campaign with ground based optical and radio observatories from the BATSE/COMPTEL/NMSU Rapid Response Network (RRN; e.g., McNamara et al. 1995), of which Westerbork is a member.

The positional error box of this burst was also covered in observations by Frail et al. (1994; Penticton) and Koranyi et al. (1995; Cambridge) but no obvious candidate counterparts were reported by these authors. So far no identification of an optical or radio counterpart to the GRB 940301 has been made by the RRN (Harrison et al. 1995). The WSRT 325 MHz observations, which are an order of magnitude more sensitive than the low-frequency observations made with the Penticton (408 MHz) and Cambridge (151 MHz) arrays, revealed two variable radio sources. Preliminary results from the WSRT observations were presented in Hanlon et al. (1995).

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998