SPI response functions

Formulation

A SPI event is characterised by an instrument direction, spanned by the telescope pointing direction \((\alpha_{\rm spix}, \delta_{\rm spix})\) and the pseudo-detector identifier DETID, and the measured energy \(E'\). The SPI response is stored in the form of FITS files that can be downloaded using

$ rsync -Lzrtv isdcarc.unige.ch::arc/FTP/arc_distr/ic_tree/prod/ $REP_BASE_PROD

where REP_BASE_PROD is the target repository where all SPI data will reside. Each SPI response FITS file contains the response functions for a given true energy \(E\). The response is presented in telescope coordinates, and gives for a given pseudo-detector identifier and true energy the effective area as a function of sky direction \((\alpha, \delta)\) with respect to the SPI telescope X axis

\[R(p',E',t'|p,E,t) = A_{\rm eff}(\alpha, \delta |{\tt DETID}, E)\]