A Complete Catalog of Swift GRB Spectra and Durations: Demise of a Physical Origin for Pre-Swift High-Energy Correlations - AstrophysicsReport as inadecuate




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Abstract: We calculate durations and spectral paramaters for 218 Swift bursts detectedby the BAT instrument between and including GRBs 041220 and 070509, including77 events with measured redshifts. Incorporating prior knowledge into thespectral fits, we are able to measure the characteristic $ u F { u}$ spectralpeak energy $E { m pk,obs}$ and the isotropic equivalent energy $E { m iso}$1-$10^4$ keV for all events. This complete and rather extensive catalog,analyzed with a unified methodology, allows us to address the persistence andorigin of high-energy correlations suggested in pre-Swift observations. We findthat the $E { m pk,obs}$-$E { m iso}$ correlation is present in the Swiftsample; however, the best-fit powerlaw relation is inconsistent with thebest-fit pre-Swift relation at >5 sigma significance. Moreover, it has a factor>~ 2 larger intrinsic scatter, after accounting for large errors on $E { mpk,obs}$. A large fraction of the Swift events are hard and subluminousrelative to and inconsistent with the pre-Swift relation, in agreement withindications from BATSE GRBs without redshift. Moreover, we determine anexperimental threshold for the BAT detector and show how the $E { mpk,obs}$-$E { m iso}$ correlation arises artificially due to partialcorrelation with the threshold. We show that pre-Swift correlations found byAmati et al.2002, Yonetoku et al. 2004, Firmani et al.2006 andindependently by others are likely unrelated to the physical properties ofGRBs and are likely useless for tests of cosmology. Also, an explanation ofthese correlations in terms of a detector threshold provides a natural andquantitative explanation for why short-duration GRBs and events at low redshifttend to be outliers to the correlations.



Author: Nathaniel R. Butler, Daniel Kocevski, Joshua S. Bloom, Jason L. Curtis

Source: https://arxiv.org/







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