Alberto J. Castro-Tirado,
15*
María Rosa Zapatero-Osorio,
2
Nicola Caon,
2
Luz
Marina Cairós,
2
Jens Hjorth,
3
Holger Pedersen,
3
Michael I. Andersen,
4
Javier Gorosabel,
5
Corrado Bartolini,
6
Adriano Guarnieri,
6
Adalberto Piccioni,
6
Filippo Frontera,
78
Nicola Masetti,
8
Eliana Palazzi,
8
Elena Pian,
8
Jochen Greiner,
9
Renè Hudec,
10
Ram Sagar,
11
Anil K. Pandey,
11
Vinay Mohan,
11
Ramakant K. S. Yadav,
11
Nilakshi,
11
Gunnlaugur Björnsson,
12
Páll Jakobsson,
12
Ingunn Burud,
13
Frederic Courbin,
13
Gaetano Valentini,
14
Anna Piersimoni,
14
Jesús Aceituno,
15
Luz María Montoya,
15
Santos Pedraz,
15
Roland Gredel,
15
Charles F. Claver,
16
Travis A. Rector,
16
James E. Rhoads,
16
Fabian Walter,
17
Jürgen Ott,
18
Hans Hippelein,
19
Victor Sánchez-Béjar,
2
Carlos Gutiérrez,
2
Alejandro Oscoz,
2
Jin Zhu,
20
Jiansheng Chen,
20
Haotong Zhang,
20
Jianyan Wei,
20
Aiying Zhou,
20
Sergei Guziy,
21
Aleksei Shlyapnikov,
22
John Heise,
23
Enrico Costa,
24
Marco Feroci,
24
Luigi Piro
24
Broad-band (ultraviolet to near-infrared) observations of the
intense gamma ray burst GRB 990123 started ~8.5 hours after the
event and continued until 18 February 1999. When combined with other
data, in particular from the Robotic Telescope and Transient Source
Experiment (ROTSE) and the Hubble Space Telescope (HST),
evidence emerges for a smoothly declining light curve, suggesting some
color dependence that could be related to a cooling break passing the
ultraviolet-optical band at about 1 day after the high-energy event.
The steeper decline rate seen after 1.5 to 2 days may be evidence for a
collimated jet pointing toward the observer.
1 Instituto de Astrofísica de
Andalucía, IAA-CSIC, Granada, Spain.
2 Instituto de Astrofísica de Canarias, La
Laguna, Tenerife, Spain.
3 Astronomical Observatory,
University of Copenhagen, Copenhagen, Denmark.
4 Nordic Optical Telescope, La Palma, Tenerife,
Spain.
5 Laboratorio de Astrofísica Espacial
y Física Fundamental, INTA, Madrid, Spain.
6 Dipartimento di Astronomia, Università di
Bologna, Bologna, Italy.
7 Dipartimento di Fisica,
Università di Ferrara, Ferrara, Italy.
8 Istituto Tecnologie e Studio Radiazioni
Extraterrestri, CNR, Bologna, Italy.
9 Astrophysikalisches Institut, Potsdam, Germany.
10 Astronomical Institute, CZ-251 65 Ondrejov,
Czech Republic.
11 U. P. State Observatory,
Manora Park, Naini Tal, 263 129 India.
12 Science
Institute, University of Iceland, Reykjavik, Iceland.
13 Institut d'Astrophysique et de
Géophysique de Liège, Université de Liège, 4000 Liege, Belgium.
14 Osservatorio Astronomico "V.
Cerulli," Teramo, Italy.
15 Calar Alto
Observatory, Almería, Spain.
16 Kitt Peak
National Observatory, Tucson AZ, 85726, USA.
17 Astronomical Observatory, University of Bonn,
Germany.
18 Radioastronomisches Institut, 53121 Bonn, Germany.
19 Max-Plank Institut für
Astronomie, Heidelberg, Germany.
20 Beijing
Astronomical Observatory, Chinese Academy of Sciences, Beijing 100080, and Beijing Astrophysics Center, Beijing 100871, China.
21 Nikolaev University Observatory, Nikolskaya, 24, 327030 Nikolaev, Ukraine.
22 Nikolaev Space
Research Group, Nikolaev Astronomical Observatory, 327030 Nikolaev,
Ukraine.
23 Space Research Organization
Netherlands, Utrecht, The Netherlands.
24 Istituto
di Astrofisica Spaziale, CNR, Frascati, Italy.
*
To whom correspondence should be addressed E-mail:
ajct{at}laeff.esa.es
