Journal Article

Peak energy of the prompt emission of long gamma-ray bursts versus their fluence and peak flux

L. Nava, G. Ghirlanda, G. Ghisellini and C. Firmani

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 391, issue 2, pages 639-652
Published in print December 2008 | ISSN: 0035-8711
Published online November 2008 | e-ISSN: 1365-2966 | DOI:
Peak energy of the prompt emission of long gamma-ray bursts versus their fluence and peak flux

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The spectral-energy (and luminosity) correlations in long gamma-ray bursts are being hotly debated to establish, first of all, their reality against possible selection effects. These are best studied in the observer planes, namely the peak energy Eobspeak versus the fluence F or the peak flux P. In a recent paper, we have started to investigate this problem considering all bursts with known redshift and spectral properties. Here, we consider instead all bursts with known Eobspeak, irrespective of redshift, adding to those a sample of 100 faint BATSE bursts representative of a larger population of 1000 objects. This allows us to construct a complete, fluence-limited, sample, tailored to study the selection/instrumental effects we consider. We found that the fainter BATSE bursts have smaller Eobspeak than those of bright events. As a consequence, the Eobspeak of these bursts is correlated with the fluence, though with a slope flatter than that defined by bursts with z. Selection effects, which are present, are shown not to be responsible for the existence of such a correlation. About six per cent of these bursts are surely outliers of the EpeakEiso correlation (updated in this paper to include 83 bursts), since they are inconsistent with it for any redshift. Eobspeak also correlates with the peak flux, with a slope similar to the EpeakLiso correlation. In this case, there is only one sure outlier. The scatter of the EobspeakP correlation defined by the BATSE bursts of our sample is significantly smaller than the EobspeakF correlation of the same bursts, while for the bursts with known redshift the EpeakEiso correlation is tighter than the EpeakLiso one. Once a very large number of bursts with Eobspeak and redshift will be available, we thus expect that the EpeakLiso correlation will be similar to that currently found, whereas it is very likely that the EpeakEiso correlation will become flatter and with a larger scatter.

Keywords: radiation mechanisms: non-thermal; gamma-rays: bursts; X-rays: general

Journal Article.  10417 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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