Question ID = 0156
Question ID = 0156
Assigned Member (担当者)2012-05-02 M.Nakajima 2012-05-13 Y.TeradaName and Institute (質問者/機関)Miss Chandreyee MaitraQuestion (質問)We would like to bring to your notice some anomaly that we havenoticed in the XIS response. The iron emission lines in some sources show large systematic residuals (please see the attached file gx1+4_residual.ps). The structure of the residual hints that the fitted line is broader than that observed with the XIS. Further investigations indicate that the energy resolution given in the XIS (all three instruments) response matrices are poorer (wider0 than what is observed in some sources. While trying to fit the spectrum of some sources with strong iron emission lines (GX 1+4 in the example below) we have encountered this problem. The source has very strong and narrow K alpha and K beta lines of Fe. While trying to fit the K alpha line, it appears that the line in the response matrix has a poorer resolution than what is observed in the source with the XIS detectors. We are aware that the gain and the resolution of the detectors have changed with time and we have used the latest CALDB versions relevant to the date of observation. We have also performed an exercise of fitting the Fe k alpha line observed in the spectrum outside XSPEC with a Gaussian to measure the width. Further we simulated a spectrum (with fakeit command in XSPEC) with the same parameters as GX 1+4 (including a narrow iron line at 6.4 keV) and the same exposure time, & using the same corresponding response matrix. It appears that the width is larger for the Iron line generated by the response matrix. The attached figure gx1+4_fe_line_comp.ps shows the observed spectum (in red) and the spectrum simulated with a narrow iron line (in green). I am using HEASOFT 6.11 in Ubuntu 10.04 and XSPEC V 12.7. Observation & Data reduction details: ************************************************************************* Obs id 405077010. extracted spectra with both the cleaned event files with standard criteria as well as by reprocessing the unfiltered events. No change in spectrum observed. ************************************************************************ Details of CALDB files used for response matrix generation for GX 1+4 obs: 1. quantum efficiency file ver 20080616 2. rmf param file ver 20080901 3. makepi file ver 20091202 ************************************************************************** ------------- ----------------------------------------------------------- resolution observed by the instrument || resolution simulated XIS0 167 eV 213 eV XIS1 248 eV 270 eV XIS3 169 eV 199 eV --------------------------------------------------------------------------- We have found similar evidences for some other sources with strong iron line like in GX 301-2 spectrum observed with Suzaku. Answer from(回答の文責)the XIS teamAnswer (答え)The following two files you use are too old to reproduce the XIS spectra after 2009.
For reference, the difference of energy resolution with the rmfparam of 2008 and 2011 are plotted in the PDF file attached. Numerically, the rmfparam 20080901 produce the response file with energy resolutions of 206 and 282 eV for FI and BI, respectively, whereas rmfparam 20110708 show 184 eV and 249 eV for FI and BI, respectively. Those two values seems to be consistent with your reports. Status （詳細なステータス）2012-05-02 Accept2012-05-13 assigned 2012-05-16 circulated to the XIS team 2012-05-17 ans from XIS team 2012-05-27 Closed 
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