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arfgen (arfgen-1.104) [xmmsas_20230412_1735-21.0.0]


Generates an OGIP-compliant ([3]) ancillary response file (ARF). The ARF contains a table listing area values (the column SPECRESP) for a number of different energy ranges (the columns ENERG_LO and ENERG_HI). The ARF can be used in conjunction with the response matrix file (RMF, generated by rmfgen) to allow fitting of particular spectral models against the observed spectral data. The actual choice of fitting package is entirely up to the user, the only prerequisite is that it is OGIP-compliant. The most widely used package is expected to be Xspec.

Specifically, arfgen takes calibration information provided by the CAL, performs the necessary corrections for instrumental factors depending on the user's requirements, and the state of spectral data, and formats the output such that it is compliant with [3]. It is this operation that is described here; details of individual CCF constituents and how the CAL processes such data are beyond the scope of this document, and the reader should refer to the Calibration Access and Data Handbook for such information ([1]).

The following table summarises the factors used to generate the ARF, and the status of the corresponding code needed to model that factor in arfgen:

Description Status
1 Telescope Effective Area Implemented
2 Filter Transmission Implemented
3 Quantum Efficiency Implemented
4 Complex region selection Implemented
5 Spatial variation of source Implemented
6 Source position specification Implemented
7 Encircled energy correction (point source) Implemented
8 RMF dataset i/p optional Implemented
9 Pattern support Implemented
10 Flux loss due to pile-up Not implemented
11 Bad pixel correction Implemented
12 Bad column correction Implemented
13 CCD gaps Implemented
14 Out of FOV/observing window Implemented
15 Out-of-time event smearing (PN) Implemented

Item 10 is actually implemented within rmfgen for EPIC-pn spectra.

Whether a factor is taken into account by arfgen in the generation of the ARF can be controlled by individual parameters with the prefix model. For example, to correct for filter transmission, the parameter modelfiltertrans should be set to true.

XMM-Newton SOC -- 2023-04-16