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J.J. Bloch (LANL), C. Akerlof (UMich), R. Balsano (LANL), S. Barthelmy, P. Butterworth (GSFC), D. Casperson (LANL), T. Cline (GSFC), S. Fletcher (LANL), F. Frontera (USF), G. Gisler (LANL), J. Heise (SRO), J. Hills (LANL), R. Kehoe, B. Lee (UMich), S. Marshall (LLNL), T. McKay (UMich), R.S. Miller (LANL), L. Piro (IAS), W. Priedhorsky, J. Szymanski, J. Wren (LANL)
Since their discovery more than 25 years ago (Klebesadel et al, 1973), the origin of gamma-ray bursts (GRBs) has been profoundly enigmatic. This situation improved radically in 1997 when coordinates provided by the BeppoSAX satellite enabled the delayed detection of faint optical afterglows associated with GRBs which demonstrated that these phenomena are at truly cosmological distances. However the brief duration of gamma-ray bursts has hitherto precluded optical detection while the burst was still in progress. We report here the first discovery of such a signal from GRB 990123, a remarkably bright and distant event. The light curve was sampled 7 times in the interval between 22 and 600 seconds following the burst onset. Over this time span, the brightness increased by 3 magnitudes to mv ~9 in 25 seconds and then waned by 5 magnitudes 8 minutes later before falling below detection threshold. The absolute magnitude of this object at peak brightness is \leq -36.4, about 6 \times 106 times as bright as a type Ia supernova, making this the most luminous object ever detected.
The discovery reported here was performed with ROTSE-I, a four-fold array of 35 mm camera telephoto lenses coupled to large format CCD imagers mounted on a rapidly slewing platform and having a composite FOV of 16\arcdeg \times 16\arcdeg. The instrument is directly connected to the GRB Coordinates Network (GCN). The apparatus is installed at Los Alamos National Laboratory in northern New Mexico.
This talk will describe the details and implications of this remarkable detection and the instrumentation used to obtain it.
This work was supported by NASA and the Department of Energy.
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