ADVANCES IN THE RXTE PROPORTIONAL COUNTER ARRAY CALIBRATION: NEARING THE STATISTICAL LIMIT

During its 16 years of service, the Rossi X-Ray Timing Explorer (RXTE) mission has provided an extensive archive of data, which will serve as a primary source of high cadence observations of variable X-ray sources for fast timing studies. It is, therefore, very important to have the most reliable calibration of RXTE instruments. The Proportional Counter Array (PCA) is the primary instrument on board RXTE which provides data in 3-50 keV energy range with submillisecond time resolution in up to 256 energy channels. In 2009, the RXTE team revised the response residual minimization method used to derive the parameters of the PCA physical model. The procedure is based on the residual minimization between the model spectrum for Crab Nebula emission and a calibration data set consisting of a number of spectra from the Crab and the on-board Am-241 calibration source, uniformly covering the whole RXTE mission operation period. The new method led to a much more effective model convergence and allowed for better understanding of the PCA energy-to-channel relationship. It greatly improved the response matrix performance. We describe the new version of the RXTE/PCA response generator PCARMF v11.7 (HEASOFT Release 6.7) along with the corresponding energy-to-channel conversion table (version e05v04) and their difference from the previous releases of PCA calibration. The new PCA response adequately represents the spectrum of the calibration sources and successfully predicts the energy of the narrow iron emission line in Cas-A throughout the RXTE mission.