COMPTEL Observations of GRB 930309

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Session 74 -- Gamma-Ray Bursts
Oral presentation, Thursday, 2:30-4:00, Zellerbach Auditorium Room

[74.06] COMPTEL Observations of GRB 930309

J.M. Ryan, R.M. Kippen, M. McConnell, M. Varendorff (UNH), J. Greiner, V. Sch\"onfelder (MPE), W. Hermsen, L. Kuiper (SRON-Leiden), K. Bennett, L. Hanlon, C. Winkler (SSD/ESA), T. Spoelstra (Westerbork Radio Observatory), B. McNamara, T. Harrison (NMSU)

The Imaging Compton Telescope (COMPTEL) on the {\sl Compton Gamma-Ray Observatory} (CGRO) images gamma radiation in the 0.75-30 MeV energy range. On 1993 March 9 at 0307:58 UT COMPTEL detected emission from the intense gamma-ray burst GRB 930309. The event was of approximately 20 s duration in the COMPTEL data. The imaging analysis is preliminary and because of limited counts, the error in position is larger than the nominal COMPTEL resolution of 1{\deg}. The most likely position of the burst is (2000) R.A. 21h32m31s, dec. 54{\deg}39$'$00$''$. The four corners of the one sigma error box are (2000) 21h40m00s, 55{\deg}25$'$12$''$; 21h38m07s, 53{\deg}15$'$36$''$; 21h27m07s, 53{\deg}19$'$48$''$; 21h27m22s, 55{\deg}30$'$00$''$. Because of the proximity of the sun in early March, the field was poorly observable with optical instruments. Only radio observatories who expressed interest were notified as part of the COMPTEL/NMSU Rapid Burst Response Campaign. However, a possible radio counterpart was detected by Westerbork Observatory at RA(2000) = 21h32m39s, Dec(2000)= 54{\deg}38$'$34$''$. Radio observations of the GRB error box began on 12 March 1993 (at 49cm), with subsequent observations on 16 March (49cm) and 18 March (6cm). The source was initially observed to have a flux of (76 $\pm$ 3.6) mJy at 49cm. Three days later the flux had declined to (66 $\pm$ 2.9) mJy. The observation at 6cm gives an upper limit on the flux of 1 mJy, indicating that the source has an unusually steep spectral slope. Monitoring at 49cm is still in progress.

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