Interpretations of gamma-ray burst spectroscopy

II. Bright BATSE bursts

¹ Stockholm Observatory, AlbaNova University Center, 106 91 Stockholm, Sweden e-mail: felix@astro.su.se
² Department of Physics and Astronomy, Rice University, Houston, TX 77005, USA
³ Laboratory for Information Technology, Eötvös University, Budapest 1117, Hungary
⁴ Uppsala Astronomical Observatory, Box 515, 751 20 Uppsala, Sweden
⁵ Astronomical Institute of the Charles University, 180 00 Prague 8, V Holešovičkách 2, Czech Republic

Received: 30 June 2004
Accepted: 8 November 2004

Abstract

We analyze the spectral lags of a sample of bright gamma-ray burst pulses observed by CGRO BATSE and compare these with the results of high-resolution spectroscopical investigations. We find that pulses with hard spectra have the largest lags, and that there is a similar, but weaker correlation between hardness-intensity correlation index, η, and lag. We also find that the lags differ considerably between pulses within a burst. Furthermore, the peak energy mainly decreases with increasing lag. Assuming a lag-luminosity relation as suggested by Norris et al., there will thus be a positive luminosity–peak-energy correlation. We also find that the hardness ratio, of the total flux in two channels, only weakly correlates with the spectral evolution parameters. These results are consistent with those found in the analytical and numerical analysis in Paper I. Finally, we find that for these bursts, dominated by a single pulse, there is a correlation between the observed energy-flux, F, and the inverse of the lag, : . We interpret this flux-lag relation found as a consequence of the lag-luminosity relation and that these bursts have to be relatively narrowly distributed in z. However, they still have to, mainly, lie beyond , since they do not coincide with the local super-cluster of galaxies. We discuss the observed correlations within the collapsar model, in which the collimation of the outflow varies. Both the thermal photospheric emission as well as non-thermal, optically-thin synchrotron emission should be important.