SAX SPECTRAL SIMULATIONS

For a proper SAX proposal preparation the proposer should, as a minimum, execute the following operations:

a) estimate SAX NFI expected count rates for their sources;
b) estimate the telemetry rates for all NFI instruments/modes he/she wants to use.

For a better understanding of the expected results the proposer can also simulate SAX spectral data using XSPEC.

COUNT RATES:

To estimate count rates (and exposure times for a 5 sigma detection) we provide a WWW interface, based on the HEASARC PIMMS.

Alternatively, a command-driven version of PIMMS can be obtained from the anonymous FTP of legacy.gsfc.nasa.gov in the software/tools directory or from the SAX-SDC anonymous FTP (ftp.asdc.asi.it) in the pub/sax/software directory.

Click here for examples on how to use the command-driven version of PIMMS.

SIMULATING SPECTRA

The basic steps to simulate a spectrum in a SAX instrument with XSPEC are:

• read in the response matrix and effective area
• generate the appropriate background
• define a model
• generate the fake spectrum
• fit the spectrum

Response matrices and background files are available on the following anonymous ftp accounts:
www.asdc.asi.it
tesre.bo.cnr.it

Click here for examples on simulating spectra with XSPEC.

Macros are available to perform simulations of NFI instruments observations using XSPEC8.50 and XSPEC9.0:

• this is to simulate source+bgd spectra for LECS MECS and PDS (XSPEC8.50);
• this is to simulate source+bgd spectra for LECS MECS and PDS (XSPEC9.0);
• this is to simulate bgd and source+bgd spectra for LECS MECS and PDS (XSPEC8.50);
• this is to simulate bgd and source+bgd spectra for LECS MECS and PDS (XSPEC9.0);

• this is to simulate source+bgd spectra for LECS MECS PDS and HPGSPC (XSPEC8.50);
• this is to simulate source+bgd spectra for LECS MECS PDS and HPGSPC (XSPEC9.0);
• this is to simulate bgd and source+bgd spectra for LECS MECS PDS and HPGSPC (XSPEC8.50);
• this is to simulate bgd and source+bgd spectra for LECS MECS PDS and HPGSPC (XSPEC9.0);

After copying the macros the user should change:

• The model, and the model parameters;
• the integration time (note that for PDS and HPGSPC used in the standard "rocking" mode half of the time is spent on source and half to monitor the bgd, therefore the integration time "on source" of the PDS and the HPGSPC should be half of the total, or of that of LECS and MECS);
• the file names.

A macro can be read in XSPEC by typing at the XSPEC prompt @macro.xcm

The macros will create the simulated spectra. Before fitting these spectra the user needs to rebin the LECS and MECS spectra to have at least 15-20 counts per channel (if he/she wants to use chi2 statistics in the fit). Rebinning can be done with the ftools GRPPHA.

Before fitting the simulated spectra the user also needs to "ignore" :
the first 12 channels for the LECS,
the first 20 channels for the MECS,
the first 20 channels for the HPGSPC