Abstract. We analyze a preliminary sample of Swift GRBs with coinciding. BAT and XRT detections. We give a quantitative measure of the con- nection between ...
Direct comparison of GRB prompt and afterglow emission ´ter Veres1,2 , Zsolt Bagoly1 , Istva ´n Horva ´th2 , Pe ´zs3 and Andra ´s Kova ´cs1 Lajos G. Bala
1 E¨ otv¨os
University, Budapest 2 Bolyai Military University, Budapest 3 Konkoly Observatory, Budapest
Abstract We analyze a preliminary sample of Swift GRBs with coinciding BAT and XRT detections. We give a quantitative measure of the connection between the X-ray afterglow and the prompt GRB emission. We discuss count-to-flux converting techniques for the X-ray data. We argue that conversion using multiple spectra is better suited for assessing the connection of the two bands.
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Outline and discussion
We used various binning techniques for the data downloaded from the Swift archive and compared with Leicester (Evans et al., 2007) and Las Vegas (Zhang et al., 2007) data. For count-to-flux conversion we enter interval limits ”by hand” taking into account structures of the lightcurve. We have selected Swift GRBs with significant BAT emission at the time of the first XRT detection. This constraint yielded 80 GRBs and 171 bins. We measure the distance between the extrapolated γ-ray flux and the X-ray flux in the ”error-space” of the γ-ray flux. The majority of the distances are positive, meaning that, the extrapolated BAT flux is higher than the XRT flux. The bulk of the bins is between 0 and 6σ. (56%) For the bins outside of this range we must consider the
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BAT - XRT flux difference in sigma-space 50
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Figure 1: Histogram of distances. Filled bars are spectra with Cutoff power-law model, the rest is fitted with a simple Power-law model in the BAT range.
possibility that at least in some of the cases the spectral parameters -hence the flux- are different for the two bands. The Las Vegas conversion method gives a better match with our data, because it incorporates possible spectral evolution effects. In general, Leicester data gives a lower flux value at the beginning of the burst than both Las Vegas and our data. We conclude that converting the X-ray flux by integrating over the entire afterglow underestimates the X-ray flux. (both Las Vegas and our data yields a higher flux) The bulk of the distances between the BAT and the XRT data is centered between 0 and 6σ. This supports the interpretation, that the early X-ray afterglow and the end of the prompt phase have a common spatial origin, but there is a significant population outside this range. This research is supported by Hungarian OTKA grant K077795 and by the Bolyai Scholarship (I. H.).
References Evans, P. A., Beardmore, A. P., Page, K. L., et al. 2007, A&A, 469, 379 Zhang, B.-B., Liang, E.-W., & Zhang, B. 2007, ApJ, 666, 1002
