Journal Article

Time-resolved spectral correlations of long-duration γ-ray bursts

C. Firmani, J. I. Cabrera, V. Avila-Reese, G. Ghisellini, G. Ghirlanda, L. Nava and Z. Bosnjak

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 393, issue 4, pages 1209-1218
Published in print March 2009 | ISSN: 0035-8711
Published online February 2009 | e-ISSN: 1365-2966 | DOI:
Time-resolved spectral correlations of long-duration γ-ray bursts

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For a sample of long γ-ray bursts (GRBs) with known redshift, we study the distribution of the evolutionary tracks on the rest-frame luminosity-peak energy LisoEp diagram. We are interested in exploring the extension of the ‘Yonetoku’ correlation to any phase of the prompt light curve, and in verifying how the high-signal prompt duration time, Tf, in the rest frame correlates with the residuals of such correlation. For our purpose, we separately analyse two samples of time-resolved spectra corresponding to 32 GRBs with peak fluxes Fp > 1.8 phot cm−2 s−1 from the Swift-BAT detector, and seven bright GRBs from the Compton Gamma-ray Observatory (CGRO)-BATSE detector previously processed by Kaneko et al. After constructing the LisoEp diagram, we discuss the relevance of selection effects, finding that they could significantly affect the correlation. However, we find that these effects are much less significant in the Liso TfEp diagram, where the intrinsic scatter reduces significantly. We apply further corrections in order to reduce the intrinsic scatter even more. For the subsamples of GRBs (seven from Swift and five from CGRO) with measured jet break time, tj, we analyse the effects of correcting Liso by jet collimation. We find that (i) the scatter around the correlation is reduced, and (ii) this scatter is dominated by the internal scatter of the individual evolutionary tracks. These results suggest that the time-integrated ‘Amati’ and ‘Ghirlanda’ correlations are consequences of the time-resolved features, not of selection effects, and therefore call for a physical origin. We finally remark the relevance of looking inside the nature of the evolutionary tracks.

Keywords: gamma rays: bursts; gamma rays: observations

Journal Article.  7130 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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