NAME

ao -- Evaluates the geometrical variation of the scattered solar X-ray background

USAGE

ao obs iflag tlog1 scale1 tlog2 scale2

DESCRIPTION

Program AO uses the methods described in Snowden and Freyberg (1993, ApJ, 404, 403) to estimate the nominal scattered solar X-ray background observed by ROSAT. This program organizes the calculation of atmospheric column densities along the line of sight of the observation and the intensity of scattered solar X-rays from those column densities for pointed observations. It uses the subroutine SSX to calculate the scattered solar spectrum. It also calculates the count rates in the seven standard pulse-height bands. The count rates are not normalized but do tend to have required scale factors between 0.1 and 1. (The actual scale factor is derived using the program RATE_FIT.) AO is written to use the linear combination of two thermal spectra to model the solar spectrum. The output of AO is used by the program RATE_FIT to fit the observation light curve.

AO creates a list of nominal scattered solar X-ray background count rates on the 60-s sample interval of the orbit data extension of the RDF xxx_ANC.FITS file. The output is used in the program RATE_FIT in conjunction with the output of the program RATE to fit the scattered solar X-ray and long-term enhancement background contamination.

The input file:

ftp://heasarc.gsfc.nasa.gov/caldb/data/gen/bcf/solar_geophys_data_v1.fits

contains solar and geophysical data which are required for AO and TILT.

If the observation to be analyzed occurred after the range of time covered by the file (i.e., if the file has not been updated recently enough), AO will return a warning.

The AO package uses the following input files.

1)ancillary data fits file for the observation: xxx_ANC.FITS for RDF data

2) Other fixed input :

valid_times_all.dat The file valid_times.dat is an ascii file; each line in the file consists of a counter (an integer), begin time (an integer), and end time (an integer), where the times are given in terms of spacecraft clock time. This must be the same time selection as used with the programs CASTDATA, CASTEXP, CASTPART, and LTE.

3) In addition, AO reads the following FITS files from the CALDB database: On-axis effective area (EFFAAREA), Window transmission (WTRANS), Gas efficiency (DET_EFF), ROSAT energy grid (ENERGY_GRID), Solar-geophys-data file (SOLAR_GEOPHYS), Detector response matrix (MATRIX) and Raymond and Smith thermal spectra (1991 vintage)(RAYMOND_SPECTRA).

The output from the AO package are the following ASCII files.

1) AO_SSX_SC.OUT - nominal SSX count rates on 60-s intervals, used in the program RATE_FIT.

2) AO_COL.OUT - column densities of atmosphere constituents on 60-s intervals.

NOTES ON USAGE

Before running this task user needs to set the CALDB environment variable in order to access data from the Calibration Database. For information on accessing the CALDB, see http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/caldb_remote_access.html to access the HEASARC CALDB remotely, or http://heasarc.gsfc.nasa.gov/docs/heasarc/caldb/caldb_install.html for information on installing a version of the HEASARC CALDB locally.

PARAMETERS

(obs = "OBS") [string]

Observation identifier, which is the prefix for the filename xxxxxxxx_anc.fits. Currently obs is limited to 8 characters, so if (for example) you have downloaded the file rp900176n00_anc.fits from the ROSAT archive, you should rename it to rp900176_anc.fits before running AO.

(iflag = "1") [integer]

Mode control: IFLAG=1 for simple treatment, 2 for more complete treatment. The simple treatment assumes that the residual atmosphere of the observation geometry (both along the line of sight and between the Sun and positions along the line of sight) is optically thin. The more complete treatment uses a nearly complete radiative transfer approach; it considers absorption between the Sun and a scattering element along the line of sight and between the scattering element and the satellite. The simple treatment runs a couple of orders of magnitude faster and is probably sufficient for all ROSAT PSPC observations.

(tlog1 = "6.2") [real]

Temperature for the first solar component - the intrinsic solar X-ray spectrum is modelled as two-component thermal plasma emission, in this case, Raymond and Smith (1977) with the 1991 computer code update. The program requests the log_10 of the temperature and the scale factor for each component. These same temperatures and scale factors must also be used below in the program TILT for consistency.

(scale1 = "0.8") [real]

The scale factor for the first solar component.

(tlog2 = "5.7") [real]

Temperature for the second component - Scale factors which sum to one for temperatures near log_10 T of near 6 (e.g., 6.2 0.8 and 5.7 0.2) will give model count rates which are typically within a factor of a few to ten of the true values (determined later by the program RATE_FIT).

(scale2 = "0.2") [real]

The scale factor for the second solar component.

(caldbdir = " ") [string]

This should be left blank. If the fixed input FITS files are in a different location than CALDB then the directory structure can be defined using caldbdir. This is mostly for test purposes and should be left unchanged.

(calfexp = "caldb") [string]

Name of calibration information to be used.

(chatter = "9") [string]

Chatter flag level for the output.

EXAMPLES

1. For the input file test_anc.fits and for input parameters (6.2, 0.8) and (5.7, 0.2) (as the first and second temperatures and scale factors respectively), assuming simple treatment (iflag=1) the usage is

        ft>  ao test 1 6.2 0.8 5.7 0.2

BUGS

The "OBS" parameter must be limited to 8 characters. Versions prior to FTOOLS 4.3 required that the input files be in uppercase; this requirement was removed in FTOOLS 4.3. The solar_geophys_data_v1.fits only includes data up to 1995/09/30.

CATEGORY