Astron. Astrophys. Suppl. Ser. 138, 443-444

GRANAT/SIGMA observation of GRB 920723 soft gamma-ray afterglow

R.A. Burenin¹ - A.A. Vikhlinin¹ - O.V. Terekhov¹ - A.Yu. Tkachenko¹ - S.Yu. Sazonov¹ - M.R. Gilfanov^1,2 - E.M. Churazov^1,2 - R.A. Sunyaev^1,2 - P. Goldoni³ - A. Claret³ - A. Goldwurm³ - J. Paul³ - J.P. Roques⁴ - E. Jourdain⁴ - G. Vedrenne⁴ - P. Mandrou⁴

1 - Space Research Institute, Russian Academy of Sciences, Profsoyuznaya 84/32, 117810 Moscow, Russia
2 - Max-Planck-Institut für Astrophysik, Karl-Schwarzschild-Str. 1, 85740 Garching bei Munchen, Germany
3 - CEA, Centre d'Études de Saclay, France
4 - Centre d'Étude Spatiale des Rayonnements, Toulouse, France

Received January 21; accepted April 16, 1999

Abstract:

We present GRANAT/SIGMA observations of the soft gamma-ray afterglow immediately after the bright GRB 920723. After $\sim6\,$s, the burst light curve makes a smooth transition into an afterglow where flux decays as t^-0.7 for at least ${\sim}1000\,$s. At least ${\sim}20\%$ of main burst energy is emitted in the afterglow. The hardness of the afterglow spectrum corresponds to the power law spectral index $\approx 1$, which is significantly softer than the main burst.

Key words: gamma-rays: bursts