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Astron. Astrophys. Suppl. Ser. 138, 401-402

The hardness evolution of gamma-ray burst pulses

A. Crider1 - E.P. Liang1 - R.D. Preece2 - M.S. Briggs2 - G.N. Pendleton2 - W.S. Paciesas2 - D.L. Band3 -
J.L. Matteson3

Send offprint request: A. Crider

1 - Department of Space Physics and Astronomy, 6100 S. Main, Rice University, Houston, TX 77005-1892, U.S.A.
2 - Department of Physics, University of Alabama in Huntsville, Huntsville, AL 35899, U.S.A.
3 - Center for Astrophysics and Space Sciences 0424, University of California at San Diego, La Jolla, CA 92093, U.S.A.

Received January 21; accepted April 21, 1999


We have analyzed the evolution of the spectral hardness parameter, $E_{\rm pk}$ (the maximum of the $\nu F_{\nu}$ spectrum) as a function of fluence in gamma-ray bursts. We fit 41 pulses within 26 bursts with the trend reported by Liang & Kargatis (1996) which found that $E_{\rm pk}$ decays exponentially with respect to photon fluence $\Phi (t)$. We also fit these pulses with a slight modification of this trend, where $E_{\rm pk}$ decays linearly with energy fluence. In both cases, we found the set of 41 pulses to be consistent with the trend.

Key words: gamma-ray: bursts, observations

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