Decay of the GRB 990123 optical afterglow: Implications for the fireball model

Alberto J. Castro-Tirado, María Rosa Zapatero-Osorio, Nicola Caon, Luz Marina Cairós, Jens Hjorth, Holger Pedersen, Michael I. Andersen, Javier Gorosabel, Corrado Bartolini, Adriano Guarnieri, Adalberto Piccioni, Filippo Frontera, Nicola Masetti, Eliana Palazzi, Elena Pian, Jochen Greiner, Renè Hudec, Ram Sagar, Anil K. Pandey, Vinay MohanRamakant K.S. Yadav, Nilakshi, Gunnlaugur Björnsson, Páll Jakobsson, Ingunn Burud, Frederic Courbin, Gaetano Valentini, Anna Piersimoni, Jésus Aceituno, Luz María Montoya, Santos Pedraz, Roland Gredel, Charles F. Claver, Travis A. Rector, James E. Rhoads, Fabian Walter, Jürgen Ott, Hans Hippelein, Victor Sánchez-Béjar, Carlos Gutiérrez, Alejandro Oscoz, Jin Zhu, Jiansheng Chen, Haotong Zhang, Jianyan Wei, Aiying Zhou, Sergei Guziy, Aleksei Shlyapnikov, John Heise, Enrico Costa, Marco Feroci, Luigi Piro

Research output: Contribution to journalArticlepeer-review

91 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)2069-2073
Number of pages5
Issue number5410
StatePublished - Mar 26 1999
Externally publishedYes

ASJC Scopus subject areas

  • General


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