SIMULTANEOUS FITS IN ISIS ON THE EXAMPLE OF GRO J1008–57

M Kühnel,R Staubert,B T Dauser,S Müller,J Wilms,D Klochkov,R E Rothschild,F.-W Schwarm,C Grossberger,K Pottschmidt,I Kreykenbohm Kreykenbohm,C Ferrigno,M A Nowak

doi:10.14311/ap.2015.55.0123

Abstract

<p>Parallel computing and steadily increasing computation speed have led to a new tool for analyzing multiple datasets and datatypes: fitting several datasets simultaneously. With this technique, physically connected parameters of individual data can be treated as a single parameter by implementing this connection directly into the fit. We discuss the terminology, implementation, and possible issues of simultaneous fits based on the Interactive Spectral Interpretation System (ISIS) X-ray data analysis tool. While all data modeling tools in X-ray astronomy in principle allow data to be fitted individually from multiple data sets, the syntax used in these tools is not often well suited for this task. Applying simultaneous fits to the transient X-ray binary GRO J1008–57, we find that the spectral shape is only dependent on X-ray flux. We determine time independent parameters e.g., the folding energy E<sub>fold</sub>, with unprecedented precision.</p>

Highlights

Implementation, and possible issues of simultaneous fits based on the Interactive Spectral Interpretation System (ISIS) X-ray data analysis tool.While all data modeling tools in X-ray astronomy in principle allow data to be fitted individually from multiple data sets, the syntax used in these tools is not often well suited for this task
Applying simultaneous fits to the transient X-ray binary GRO J1008–57, we find that the spectral shape is only dependent on X-ray flux
Before we describe the technical realization of simultaneous data analysis in ISIS, we introduce new notations used by the implemented functions

Summary

Motivation

Most data analysis in X-ray astronomy concentrate on describing single datasets or on characterizing samples with the results of fits of individual datasets. Instead of going back to the data analysis and fitting this dependency directly to enhance the precision of the parameter or to break degeneracies (feasible through reduced degrees of freedom), the dependency is analyzed on its own. In another way, the former analysis is repeated but with this parameter fixed according to the dependency that has been discovered. We discuss questions and issues, which arise by comparing advantages and disadvantages of simultaneous fits (Table 1)

Implementation into ISIS

Terminology

Applications

The Example GRO J1008–57

Outlook