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Astron. Astrophys. 328, L13-L16

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Letter to the Editor

Early detection of the Optical Transient following
the Gamma-Ray Burst GRB 970228*

A. Guarnieri1, C. Bartolini1, N. Masetti1, A. Piccioni1, E. Costa2, M. Feroci2, F. Frontera3, D. Dal Fiume4, L. Nicastro4,
E. Palazzi4, A.J. Castro-Tirado5, and J. Gorosabel5

1 Dipartimento di Astronomia, Università di Bologna, via Zamboni, 33 I-40126 Bologna, Italy
2 Istituto di Astrofisica Spaziale, CNR, Frascati
3 Dipartimento di Fisica, Università di Ferrara
4 Istituto Tecnologie e Studio Radiazioni Extraterrestri, CNR, Bologna
5 Laboratorio de Astrofísica Espacial y Física Fundamental, INTA, Madrid

Received 13 May 1997 / Accepted 26 June 1997


The optical counterpart of the Gamma-Ray Burst GRB 970228, discovered by Groot et al. (1997a), is also detected in the B and R frames obtained $\sim$4 hours earlier at the Bologna Observatory. Our observations indicate a very likely rise of the optical emission within these 4 hours. The R luminosity of the transient at maximum was about 15 times that of an underlying extended object. Follow-up data show that the maximum optical emission was delayed of not less than 0.7 days with respect to the $\gamma$-ray peak and that no new big flares were seen after the main one. The optical transient became significantly redder once it has reverted to quiescence.

Key words: Gamma rays: bursts -- Methods: observational

*Based on observations obtained at the Osservatorio Astronomico di Loiano, Italy

Send offprint requests to: A. Guarnieri, adriano@astbo3.bo.astro.it

© European Southern Observatory (ESO) 1997

Online publication: November 24, 1997
Last change: March 26, 1998