A comparison of the fluences and photon peak fluxes for the Swift and RHESSI gamma-ray bursts

arXiv:1009.1770v1 [astro-ph.HE] 9 Sep 2010 A comparison of the fluences and photon peak fluxes for the Swift and RHESSI gamma-ray bursts D. Huja1, J. ˇR´ıpa1 and A. M´esz´aros1 1 Charles University, Faculty of Mathematics and Physics, Astronomical Institute, Prague, Czech Republic Abstract Fluences and photon peak fluxes of the gamma-ray bursts (GRBs) detected by the Swift and RHESSI satellites are graphically compared. The Swift-BAT data set consists of the T90 GRB durations, fluences at range 15-150 keV, peak fluxes (fluxes) at the same energy range and covers the period Nov. 2004 Feb. 2009 with 429 events. The RHESSI data set consists of the T90 durations, count fluences at range 25-1500 keV, fluxes at the same range and covers the period Feb. 2002 Nov. 2007 with 425 events. In these two databases 25 GRBs were detected by both satellites with known fluxes and fluences. The relationship between the RHESSI fluxes (counts/s) and the Swift fluxes (ph cm−2s−1), and the relationship between the RHESSI fluences (counts) and the Swift fluences (10−7 erg cm−2) are plotted in fig. 1. There is no simply relation to convert the RHESSI count fluxes/fluences to the Swift fluxes/fluences in energy units, but there exists a very strong correlation between them. The Swift fluxes of the short and the long GRBs are on average approximately the same, but for the RHESSI data the fluxes of the short GRBs are on average higher than for the long ones. In the case of fluences, for both samples, the long GRBs have on av- erage higher values than the short ones. Also the gradient of the best-fitted straight line in the fluence-T90 dependency is very similar for both data sets. 1 Figure 1: Top left: Duration vs. fluxes: Fluxes measured by Swift are on average the same for the short and long GRBs, the gradient of the best-fitted straight line is -0.0656 [1], but RHESSI fluxes are on average higher for the short GRBs than for the long ones. The gradient of this relation is -0.3255 [1]. Top right: Duration vs. fluences: Fluences measured by Swift are on average higher for the long GRBs than for the short ones, the gradient is 0.6077 [1]. Fluences obtained by RHESSI for the long GRBs are on average higher than for the short ones with similar gradient: 0.5930 [1]. Bottom left: The relationship between fluxes detected by RHESSI and Swift for the common 25 GRBs. The correlation coefficient is 0.5840 [2], t-coeff. is 3.450 (in the null case of no correlation like Student’s t-distribution with 25-2=23 dof), probability of no correlation is not higher than 0.2 %. Bottom right: The relationship between the RHESSI and Swift fluences for the common 25 GRBs. The correlation coeff. is 0.8511 [2], t-coeff. is 7.776, probab. of no correlation is not higher than 7x10−6 %. We acknowledge support of the grants GAUK 46307, GAˇCR 205/08/H005, MSM0021620860, and OTKA K077795. References [1] TRUMPLER R. J. AND WEAVER H. F., Statistical Astronomy, (Uni- versity of California Press, Berkeley) 1953. [2] PRESS H. W. ET AL., Numerical Recipes in Fortran, (Cambridge Uni- versity Press) 1994, chapter 14.5.

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