False outliers of the E$_{p,i}$ - E$_{iso}$ correlation?

Abstract : Context. In the context of an in-depth understanding of GRBs and their possible use in cosmology, some important correlations between the parameters that describe their emission have been discovered, among which the “Ep,i – Eiso” correlation is the most studied. Because of this, it is fundamental to shed light on the peculiar behaviour of a few events, namely GRB 980425 and GRB 031203, that appear to be important outliers of the Ep,i – Eiso correlation.Aims. In this paper we investigate if the locations of GRB 980425 and GRB 031203, the two (apparent) outliers of the correlation, may be due to an observational bias caused by the lacking detection of the soft X-ray emissions associated with these GRBs, from respectively the Burst And Transient Source Experiment (BATSE) detector on-board the Compton Gamma-Ray Observer and INTEGRAL, that were operating at the epoch at which the observations were carried out. We analyse the observed emission of other similar sub-energetic bursts (GRBs 060218, 100316D and 161219B) observed by Swift and whose integrated emissions match the Ep,i – Eiso relation. We simulate their integrated and time-resolved emissions as would have been observed by the same detectors that observed GRB 980425 and GRB 031203, aimed at reconstructing the light curve and spectra of these bursts.Methods. We estimate the Ep,i and the Eiso parameters from the time-resolved and total integrated simulated spectra of GRBs 060218, 100316D and 161219B as observed by BeppoSAX, BATSE, INTEGRAL, and the Wide Field Monitor (WFM) proposed for the Large Observatory For X-ray Timing (LOFT) and enhanced X-ray Timing and Polarimetry (eXTP) missions.Results. If observed by old generation instruments, GRBs 060218, 100316D, and 161219B would appear as outliers of the Ep,i–Eiso relation, while if observed with Swift or the WFM GRB 060218 would perfectly match the correlation. We also note that the instrument BAT alone (15−150 keV) did measure GRB 060218 as an outlier.Conclusions. We suggest that if GRB 980425 and GRB 031203 would have been observed by Swift and by eXTP, they might have matched the Ep,i–Eiso relation. This provides strong support to the idea that instrumental biases can cause some events in the lower left corner of the Ep,i – Eiso plane to appear as outliers of the so-called Amati relation.Key words: gamma-ray burst: general / gamma-ray burst: individual: GRB 060218 / methods: data analysis
Type de document :
Article dans une revue
Astron.Astrophys., 2017, 608, pp.A52. 〈10.1051/0004-6361/201730704〉
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Soumis le : jeudi 21 décembre 2017 - 00:56:47
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Renato Martone, Luca Izzo, Massimo Della Valle, Lorenzo Amati, Giuseppe Longo, et al.. False outliers of the E$_{p,i}$ - E$_{iso}$ correlation?. Astron.Astrophys., 2017, 608, pp.A52. 〈10.1051/0004-6361/201730704〉. 〈hal-01669805〉



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