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J.P. Norris, J.T. Bonnell, D. Kazanas (NASA/GSFC), J.D. Scargle (NASA/ARC), J. Hakkila, T.W. Giblin (College of Charleston)
The number of free parameters required to model gamma-ray burst (GRB) pulsed emission must be at least of order the number of luminosity and total energy indicators (e.g., spectral lag, Epeak) that have been proposed, assuming parameter independence. The bright, usually complex bursts have many narrow pulses that are difficult to model due to overlap. However, the pulses in long-lag bursts are few in number, and ~ 100 times wider (10s of seconds) than pulses in the complex bursts, and therefore often have sufficient pulse definition for profitable study. Also, these simple bursts -- presumably having lower total energy, slower evolution, lower bulk Lorentz factor -- may have relatively simpler physics. In this work we analyze the temporal and spectral behavior of wide pulses in 24 long-lag bursts, using a pulse model with two shape parameters -- width and asymmetry -- and the Band spectral model with three shape parameters. We find that these five pulse descriptors are essentially uncorrelated for our long-lag sample, suggesting that at least ~ 5 parameters are needed to model burst temporal/spectral behavior. However, as anticipated, pulse width is strongly correlated with spectral lag; hence these two parameters may be viewed as mutual surrogates in formulations for estimating GRB luminosity and total energy.
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Bulletin of the American Astronomical Society, 36 5
© 2004. The American Astronomical Society.