Astronomy and Astrophysics – Astronomy
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008aas...212.1603c&link_type=abstract
American Astronomical Society, AAS Meeting #212, #16.03; Bulletin of the American Astronomical Society, Vol. 40, p.210
Astronomy and Astrophysics
Astronomy
Scientific paper
Firmani et al. proposed a new Gamma Ray Burst (GRB) luminosity relation that showed a significant improvement over the Liso-Epeak relation. (Liso is the isotropic peak luminosity and Epeak is the photon energy of the spectral peak for the burst.) The new proposed relation simply modifies the Epeak value by multiplying it by a power of T0.45, where T0.45 is a measure of the GRB duration as originally proposed by Reichart et al. We begin by reproducing the results of Firmani for his 19 bursts. We then try switching in alternative Liso, T0.45 and Epeak values as reported in the literature for these same 19 GRBs, and find that the relation deteriorates substantially. We further test the relation by using 60 GRBs with measured spectroscopic redshifts, and again find a relation that has a somewhat larger scatter than the original Liso-Epeak relation. That is, a much larger sample of bursts does not reproduce the small scatter as claimed by Firmani et al. Finally, we investigate whether the Firmani relation is improved by the use of any of 31 alternative measures of duration (e.g., T90, T50, T90/Npeak, the fluence divided by the peak flux, T0.30, and T0.60) in place of T0.45. The quality of each alternative duration measure is evaluated with the root mean square of the scatter between the observed and fitted logarithmic Liso values. We find no substantially better duration measure than T0.45, whereas one of the best relations is where we simply assume that all bursts have a 10 second duration (which is equivalent to the original Liso-Epeak relation). Our results show that adding any duration to the Liso-Epeak relation does little more than add noise to the original relation.
Collazzi Andrew C.
Schaefer Bradley E.
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