The Goodness of Simultaneous Fits in ISIS
Rothschild, Richard E.; Fürst, Felix; Klochkov, Dmitry; Kretschmar, Peter; Pottschmidt, Katja; Staubert, Rüdiger; Wilms, Jörn; Dauser, Thomas; Ferrigno, Carlo; Kreykenbohm, Ingo; Martínez-Núñez, Silvia; Ballhausen, Ralf; Schwarm, Fritz-Walter; Nowak, Michael A.; Falkner, Sebastian; Kühnel, Matthias; Grossberger, Christoph; Torrejón, José Miguel
Germany, United States, Switzerland, Spain
Abstract
In a previous work, we introduced a tool for analyzing multiple datasets simultaneously, which has been implemented into ISIS. This tool was used to fit many spectra of X-ray binaries. However, the large number of degrees of freedom and individual datasets raise an issue about a good measure for a simultaneous fit quality. We present three ways to check the goodness of these fits: we investigate the goodness of each fit in all datasets, we define a combined goodness exploiting the logical structure of a simultaneous fit, and we stack the fit residuals of all datasets to detect weak features. These tools are applied to all RXTE-spectra from GRO 1008-57, revealing calibration features that are not detected significantly in any single spectrum. Stacking the residuals from the best-fit model for the Vela X-1 and XTE J1859+083 data evidences fluorescent emission lines that would have gone undetected otherwise.