COMPTEL OBSERVATIONS OF THE STRONG GAMMA-RAY BURST GRB-940217

The imaging MeV gamma-ray telescope COMPTEL on board the Compton Gamma -Ray Observatory has observed a very strong (S[> 0.3 MeV] = 2.03 x 10( -4) erg cm(-2)), complex, and long lasting (162 s) gamma-ray burst on February 17, 1994 (GRB 940217). The burst consists of several peaks. T emporal fluctuations occur on timescales as short as 100 ms. Hard-to-s oft spectral evolution has been observed during the burst emission and also within individual peaks. The photon spectra obtained within the peaks can be modelled by single power law spectra and by broken power laws with break energies at around 1 MeV. The best-fit power law slope s vary between 1.1 and 3.5 throughout the event. The spectra are consi stent within COMPTEL's different observing modes and also agree very w ell with contemporaneous EGRET and BATSE measurements. No significant line emission is detected in any of the recorded spectra. Precise loca tion ([alpha(2000), delta(2000)] = [29.5 degrees, 3.8 degrees], with a 3 sigma error radius of about 1 degrees) has been obtained through di rect COMPTEL MeV imaging in combination with timing analysis by the In terplanetary Network. Four hours after the event, the position derived by COMPTEL was distributed to a network of multi-wavelength observers . No detection of a fading or quiescent counterpart has so far been re ported at any wavelength. During a 20 minute time interval starting si milar to 90 minutes after the burst event, the EGRET instrument on boa rd the Compton Gamma-Ray Observatory reported ''post-burst'' emission at high energies (up to GeV). COMPTEL does not detect any significant ''post-burst'' emission at low energies (0.3 - 30 MeV), and our upper limits are marginally consistent with the EGRET detections. Using high energy spectral and temporal information, distance limits to GRB 9402 17 between 145 AU and 11.7 kpc have been derived assuming homogenous a nd isotropic emission. If GRB 940217 is at cosmological distances (e.g . at 1 Gpc) the lower limit on the relativistic bulk Lorentz beam fact or is >18. This implies that our observed breaks at around 1 MeV are e ither too low in energy to be produced by gamma-gamma interaction (via e(+)e(-) - pair creation), or GRB 940217 is closer than 1 Gpc.