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MIT Kavli Institute Chandra X Ray Center MEMORANDUM November 24 2009 To Jonathan McDowell SDS Group Leader Ken Glotfelty DS Pipelines Tools Lead Dale Graessle DS Calibration Data Coordinator Brad Wargelin Calibration Scientist Ian Evans DS End to End Scientist From David P Huenemoerder SDS initial date Subject Interface Control Document HRC S P I Reference Data Algorithm Revision 1 4 URL http space mit edu cxc docs docs html hrcstgain File nfs cxc h3 dph CXC HRCS pifilt Doc hrcs spi icd 1 4 tex Overview of HRC S P I Computation 1 A new algorithm for computing the HRC S pulse height P I for Pulse Invariant Amplitude is documented in the memo A New Gain Map and Pulse Height Filter for the Chandra LETG HRC S Spectrometer by B J Wargelin P W Ratzlaff and M Juda 1 henceforth referred to as the Memo This algorithm can result in a reduction of HRC S background by about a factor of two There are two new parts to the processing 1 Computation of the P I for every event which requires a new Calibration Database CALDB file and algorithmic support in the tool hrc process events 1 http cxc harvard edu cal Letg GainFilter gain pdf November 25 2008 v1 4 changes small file name and header keyword changes to comply with CalCo s CALDB related requirements 2 Application of a position dependent filter before binning an LETGS spectrum which requires a new CALDB region file This memo will define the new CALDB files the processing algorithm for hrc process events and the filter application method 2 P I Computation The essence of the the P I computation is given by Equation 5 in the Memo rewritten slightly here as a1 Pn mij Dn norm bij Ci t Sij a0 1 We have changed the notation slightly to make the two dimensional nature of the calibration data explicit in detector raw coordinates by subscripts ij and we have removed explicit numerical values which are subject to calibration updates We use a row column notation in which row i is a RAWY index and column j indexes RAWX For HRC S the LETG dispersion is along RAWY In this equation the terms are Pn the desired value for P I for the nth event at detector raw pixel coordinate RAWX RAWY which will be mapped to calibration bin i j Dn represents the uncorrected event pulse height data value SAMP in Memo terms for the nth event Other terms are calibration data two of which are scalars an three are twodimensional maps m S and b and another is a time dependent term with one spatial dimension C For purposes of efficiency in CALDB representation and event processing we can collect terms into a more compact form Pn Gij0 Gij1 Dn Ci t 2 Gijk is the Gain Map with two spatial dimension i and j and one polynomial order dimension k Ci t is the time dependent gain



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