With XSPEC12, it is now possible to produce fake spectra output in OGIP Type II format.  It is also possible to enter in Type II file information (for background, arf, corfile) simply by adding a row specifier in curly brackets to the file name (see examples below).  Type II file information can be entered even if the fake output is to be in Type I format, and vice versa.  See the discussion below on Type I vs. Type II output for a detailed description.  When prompted for exposure time and corrscale however, the values entered will apply to all the spectra in a type II file.  At present, it is not possible to specify different exposure time and corrscale values for each of the spectra in a type II faked output file.

With the addition of OGIP type II file handling capabilities, the possible options for the fakeit output format grows more complex.  Backwards compatibility is maintained though, so any fakeit commands used with type I files in previous versions of Xspec will still work the same, placing all the output in type I files.  Fakeit determines whether to place its fake spectra and background data into type I or type II files based on the following rules:

The simplest case is for fake spectra that are based on currently loaded spectra.  Fakeit will then just use the format of the currently existing files for its output, for both the PHA spectra and background spectra if applicable.  For example:  Assume 3 spectra are currently loaded, spectrum 1 from file typeIdata.pha and spectra 2 and 3 from file typeIIdata.pha.  Then,

XSPEC12> fakeit

will produce 3 fake spectra in 2 output files with names prompted from the user.  The first file will be type I, the second containing 2 spectra in type II.  The same is true for any background files produced. 

If the user asks for more fake spectra to be created than the number of spectra currently loaded,  for example by typing the following when the same 3 spectra above described are loaded:

XSPEC12> fakeit 5

then fake spectra 1-3 will be placed in the two files as before.  For the additional fake spectra (4 and 5), fakeit uses the following rule:  If any of the originally loaded spectra were in a type II file, then all of the additional fake spectra will be placed in 1 type II file.  Otherwise, they will each be placed in a separate type I file.  In this example, since a type II file was originally loaded (typeIIdata.pha) when fakeit was called, spectra 4 and 5 will be placed together in a type II output file, in addition to the type I and type II files for the first 3 fake spectra. 

For cases where fakeit is used and there is no currently loaded spectra, it will produce output in type I format UNLESS either of the following situations exist:  1.  The user has entered any type II background files on the command line, indicated by row specifiers in brackets.  2.  The format of the FIRST response file used clearly belongs to a format associated with type II data, such as with SPI/Integral with its multiple RMF format (see section on SPI/Integral usage).

Overall, though the method of determining output format for additional spectra may seem quite complicated, it can be easily summed up:  Fakeit will place all additional spectra and backgrounds (ie. those not based on already loaded data) in type I output files, UNLESS it detects ANY evidence of type II file usage amongst the user specified input, in which case it will produce type II output. 

Note For SPI/Integral Format:

Since the SPI/Integral format builds its responses from a combination of multiple RMFs and ARFs, it must use a different scheme than the OGIP type I and II formats for storing RMF and ARF file location information.  This information is stored in a FITS extension, named “RESPFILE_DB” , added to the PHA file.  Therefore, when fakeit prompts the user for the location of the response file, simply enter the name of a FITS file which contains a RESPFILE_DB extension pointing to the RMFs and ARFs to be applied.  When prompted for an ARF name, enter nothing. 

The prompts will only appear for the first spectrum in the data set, and the ARFs will be assigned row by row 1 to 1 with the spectra.   For example, if no data is currently loaded, to create 3 fake SPI spectra from the RMFs and ARFs named in the RESPFILE_DB extension of the file “realSpiData.pha”:

XSPEC12> fakeit 3

// ...(various prompts will follow)...

For fake spectrum #1 response file is needed:  realSpiData.pha

// ...and ancillary file:  <Ret>

// ...(more fakeit prompts)...

This will create 3 fake spectra, each making use of the same RMFs/ARFs, spectrum 1 using the first row of the ARFs, spectrum 2 using the second etc. 

*** CAUTION – SPI/Integral ***

As currently implemented, the RESPFILE_DB method of storing ARF locations does not retain specific row information.  The assumption is that the rows in the ARF correspond 1 to 1 with the rows in the spectral data extension.  Therefore, much confusion can arise when the row numbers of the loaded spectra do not match that of the fake spectra.   For example:

XSPEC12> data my_spi_data.pha{3-4}

// my_spi_data.pha contains a RESPFILE_DB table pointing to arf1.fits,

// arf2.fit, arf3.fits.

// ...(fit to some model(s))...

XSPEC12> fakeit

This will produce 2 fake spectra generated from the model*response operation, where the model has parameters based on a fit to the original spectra in rows 3 and 4 of my_spi_data.pha, which used ROWS 3 AND 4 of the 3 arf files for their own responses.  However, the responses used above to generate the 2 fake spectra will use ROWS 1 AND 2 of the 3 arf files.  This is necessary since the fake spectra will be placed in rows 1 and 2 of their fakeit output file.

            Type II files:

            Assume four spectra with no backgrounds have been loaded from one type II file:

XSPEC12> data original_type2_data.pha{5-8}

Then, after model(s) have been entered and a fit:

XSPEC12> fakeit

This will produce 4 fake spectra in rows 1 to 4 of one type II output file, with responses and arfs taken from the columns of original_type2_data.pha.

XSPEC12> fakeit ,,backb{1-3}

This produces 5 fake spectra in two type II output files, and 3 fake background spectra also placed in two type II output files:

            The first 4 fake spectra are placed in one output file since that is how the 4 spectra they were based on were originally organized.  The default numerical data for this file are taken from the original spectra.  Fake spectra 3 and 4 now have backgrounds, based on backb{1} and backb{2} respectively.  These will generate 2 fake background spectra, placed in rows 3 and 4 of the first output fake background file.  Rows 1 and 2 of this file will just consist of zeros since the first 2 spectra have no backgrounds.

            The fifth fake spectrum will be placed in the second type II PHA file.  Response and numerical data will not be based on the existing loaded spectra.  A fake background will be generated from backb{3} and placed in row 1 of the second type II fake background file.

            Now assume no data is currently loaded:

XSPEC12> fakeit 2 backb{1}

2 fake spectra in one type II output file are produced, as is a corresponding fake background file with 2 rows.  The fact that the user has entered a type II background file on the command line tells fakeit to produce type II output.  The first fake spectrum will have no associated background, so row 1 in the fake background file will be all zeros.  Row 2 will consist of the fake background generated from backb{1}.