Alberto J. Castro-Tirado,
Javier Gorosabel,
Narciso Benítez,
Christian Wolf,
Ralf Fockenbrock,
Enrique Martínez-González,
Helmuth Kristen,
Adrick Broeils,
Holger Pedersen,
Jochen Greiner,
Enrico Costa,
Marco Feroci,
Luigi Piro,
Filippo Frontera,
Luciano Nicastro,
Eliana Palazzi,
Corrado Bartolini,
Adriano Guarnieri,
Nicola Masetti,
Adalberto Piccioni,
Marco Mignoli,
Magrethe Wold,
Mark Lacy,
Kurt Birkle,
Tom Broadhurst,
Søren Brandt,
Niels Lund
An optical transient within the error box of the gamma ray burst
GRB 970508 was imaged 4 hours after the event. It displayed a strong
ultraviolet excess, and reached maximum brightness 2 days later. The
optical spectra did not show any emission lines, and no variations on
time scales of minutes were observed for 1 hour during the decline
phase. According to the fireball and afterglow models, the intensity
should rise monotonically before the observed optical maximum, but the
data indicate that another physical mechanism may be responsible for
the constant phase seen during the first hours after the burst.
A. J. Castro-Tirado and J. Gorosabel, Laboratorio de
Astrofísica Espacial y Física Fundamental, INTA,
Madrid, Spain.
N. Benítez and E. Martínez-González, Instituto de
Física de Cantabria, Santander, Spain.
C. Wolf, R. Fockenbrock, K. Birkle, Max-Planck-Institut für
Astronomie, Heidelberg, Germany.
H. Kristen, A. Broeils, M. Wold, Stockholm Observatory, Saltsjobaden,
Sweden.
H. Pedersen, Copenhagen University Observatory, Copenhagen, Denmark.
J. Greiner, Astrophysikalisches Institut, Postdam, Germany.
E. Costa, M. Feroci, L. Piro, Istituto di Astrofisica Spaziale, CNR,
Frascati, Italy.
F. Frontera, Dipartimento di Fisica, Università di Ferrara,
Ferrara, Italy.
L. Nicastro and E. Palazzi, Istituto Tecnologie e Studio Radiazioni
Extraterrestri, CNR, Bologna, Italy.
C. Bartolini, A. Guarnieri, N. Masetti, A. Piccioni, Dipartimento di
Astronomia, Università di Bologna, Bologna, Italy.
M. Mignoli, Osservatorio Astronomico di Bologna, Bologna, Italy.
M. Lacy, Nuclear and Astrophysics Laboratory, Keble Road, Oxford, UK.
T. Broadhurst, Department of Astronomy, University of California,
Berkeley, CA 94720, USA.
S. Brandt, Los Alamos National Laboratory, Los Alamos, NM 87545, USA.
N. Lund, Danish Space Research Institute, Copenhagen, Denmark.
