6. An EPIC Data Processing and Analysis Primer (Imaging Mode, Command Line)

So, you've received an XMM-Newton EPIC data set. What are you going to do with it? After checking what the observation consists of (see § 3.2), you should note when the observation was taken. If it is a recent observation, it was likely processed with the most recent calibrations and SAS, and you can immediately start to analyze the Pipeline Processed data (though reprocessing it with the current SAS will do no harm.) However, if it is more than a year old, it was probably processed with older versions of CCF and SAS prior to archiving, and the pipeline should be rerun to generate event files with the latest calibrations.

As noted in Chapter 4, a variety of analysis packages can be used for the following steps. However, as the SAS was designed for the basic reduction and analysis of XMM-Newton data (extraction of spatial, spectral, and temporal data), it will be used here for demonstration purposes. SAS will be required at any rate for the production of detector response files (RMFs and ARFs) and other observatory-specific requirements, though for the simple case of on-axis point sources the canned response files provided by the SOC can be used.

NOTE: For PN observations with very bright sources, out-of-time events can provide a serious contamination of the image. Out-of-time events occur because the read-out period for the CCDs can be up to $\sim6.3$% of the frame time. Since events that occur during the read-out period can't be distinguished from others events, they are included in the event files but have invalid locations. For observations with bright sources, this can cause bright stripes in the image along the CCD read-out direction.

It is strongly recommended that you keep all reprocessed data in its own directory! SAS places output files in whichever directory it is in when a task is called. Throughout this primer, it is assumed that the Pipleline Processed data are in the PPS directory, the ODF data (with upper case file names, and uncompressed) are in the directory ODF, the analysis is taking place in the PROC directory, and the CCF data are in the directory CCF.

If your data are recent, you need only to gunzip the files and prepare the data for processing (see §5. Feel free to skip the section on repipelining (§6.1 and proceed to later discussions. In any case, for simplicity, it is recommended that you change the name of the unzipped event file to something easy to type. For example, an MOS1 event list:

cp PPS/PiiiiiijjkkM1SlllMIEVLI0000.FTZ PROC/mos1.fits

where

iiiiiijjkk - observation number
lll - exposure number within the observation

Various analysis procedures are demonstrated in this chapter using the Lockman Hole SV1 dataset, ObsID 0123700101, which definitely needs to be repipelined. The following procedures are applicable to all XMM-Newton datasets, so it is not required that you use this particular dataset; any observation should be sufficient.

If you simply want to have a quick look at your data, the ESKYIM files contain EPIC sky images in different energy bands whose ranges are listed in Table 3.3. While the zipped FITS files may need to be unzipped before display in ds9 (depending on the version of ds9), they can be displayed when zipped using fv (fv is FITS file viewer available in the HEASoft package). In addition, the image of the total band pass for all three EPIC detectors is also provided in PNG format which can be displayed with a web browser. Also, the PP source list is provided in both zipped FITS format (readable by fv) and as an HTML file.

For detailed descriptions of PP data nomenclature, file contents, and which tasks can be used to view them, see Tables 3.2 and 3.3. For detailed descriptions of ODF data nomenclature and file contents, see Table 3.1.

6.1 Rerun the Pipeline

We assume that the data was prepared and environment variables were set according to §5. In the window where SAS was initialized, in your ``processing directory'' PROC, run emproc to produce calibrated photon event files for the MOS cameras, and epproc to do the same for the PN camera.

Emproc and epproc will automatically detect what mode the data were taken in.

To process the MOS data, type

emproc

Similarly, to process the PN data, type

epproc

If the dataset has more than one exposure, a specific exposure can be accessed using the withinstexpids and instexpids parameters, e.g.:

emproc withinstexpids=yes instexpids='M1S001 M2S001'

To create an out-of-time event file for your PN data, add the parameter withoutoftime to your epproc invocation:

epproc withoutoftime=yes

By default, these tasks do not keep any intermediate files they generate. Emproc and epproc designate their output event files with ``*ImagingEvts.ds''. In any case, you may want to name the new files something easy to type. For example, to rename one of the new MOS1 event files output from emproc's output reprocessing Lockman Hole data, type

mv 0070_0123700101_EMOS1_S001_ImagingEvts.ds mos1.fits

6.2 Create and Display an Image

To create an image in sky coordinates, type

evselect table=mos1.fits withimageset=yes imageset=image.fits \
$$ xcolumn=X ycolumn=Y imagebinning=imageSize ximagesize=600 yimagesize=600

where

table - input event table
withimageset - make an image
imageset - name of output image
xcolumn - event column for X axis
ycolumn - event column for Y axis
imagebinning - form of binning, force entire image into a given size or bin by a specified number of pixels
ximagesize - output image pixels in X
yimagesize - output image pixels in Y

The output file image.fits can be viewed by using a standard FITS display, such as ds9 (see Figure 6.1) :

ds9 image.fits &

Figure 6.1: The MOS1 image, displayed in ds9.

6.3 Applying Standard Filters the Data

The filtering expressions for the MOS and PN are, respectively:

(PATTERN $<=$ 12)&&(PI in [200:12000])&&#XMMEA_EM

and

(PATTERN $<=$ 4)&&(PI in [200:15000])&&#XMMEA_EP

The first two expressions will select good events with PATTERN in the 0 to 12 (or 0 to 4) range. The PATTERN value is similar the GRADE selection for ASCA data, and is related to the number and pattern of the CCD pixels triggered for a given event.The PATTERN assignments are: single pixel events: PATTERN == 0, double pixel events: PATTERN in [1:4], triple and quadruple events: PATTERN in [5:12].

The second keyword in the expressions, PI, selects the preferred pulse height of the event; for the MOS, this should be between 200 and 12000 eV. For the PN, this should be between 200 and 15000 eV. This should clean up the image significantly with most of the rest of the obvious contamination due to low pulse height events. Setting the lower PI channel limit somewhat higher (e.g., to 300 eV) will eliminate much of the rest.

Finally, the #XMMEA_EM (#XMMEA_EP for the PN) filter provides a canned screening set of FLAG values for the event. The FLAG value provides a bit encoding of various event conditions, e.g., near hot pixels or outside of the field of view. Setting FLAG == 0 in the selection expression provides the most conservative screening criteria and should always be used when serious spectral analysis is to be done on the PN. It typically is not necessary for the MOS.

It is a good idea to keep the output filtered event files and use them in your analyses, as opposed to re-filtering the original file with every task. This will save much time and computer memory. As an example, the Lockman Hole data's original event file is 48.4 Mb; the fully filtered list (that is, filtered spatially, temporally, and spectrally) is only 4.0Mb!

To filter the data, type

evselect table=mos1.fits withfilteredset=yes \
$$ expression='(PATTERN $<=$ 12)&&(PI in [200:12000])&&#XMMEA_EM' \
$$ filteredset=mos1_filt.fits filtertype=expression keepfilteroutput=yes \
$$ updateexposure=yes filterexposure=yes

where

table - input event table
filtertype - method of filtering
expression - filtering expression
withfilteredset - create a filtered set
filteredset - output file name
keepfilteroutput - save the filtered output
updateexposure - update exposure information in event list and in spectrum files
filterexposure - filter exposure extensions of event list with same time

6.4 Create and Display a Light Curve

Sometimes, it is necessary to use filters on time in addition to those mentioned above. This is because of soft proton background flaring, which can have count rates of 100 counts/sec or higher across the entire bandpass.

It should be noted that the amount of flaring that needs to be removed depends in part on the object observed; a faint, extended object will be more affected than a very bright X-ray source.

To determine if our observation is affected by background flaring, we can examine the light curve:

evselect table=mos1.fits withrateset=yes rateset=mos1_ltcrv.fits \
$$ maketimecolumn=yes timecolumn=TIME timebinsize=100 makeratecolumn=yes [] fv mos1_ltcrv.fits &

where

table - input event table
withrateset - make a light curve
rateset - name of output light curve file
maketimecolumn - control to create a time column
timecolumn - time column label
timebinsize - time binning (seconds)
makeratecolumn - control to create a count rate column, otherwise a count column will be created

The output file mos1_ltcrv.fits can be viewed by using fv:

fv mos1_ltcrv.fits &

In the pop-up window, the RATE extension will be available in the second row (index 1, as numbering begins with 0). Select ``PLOT'' from this row, and select the column name and axis on which to plot it. The light curve is shown in Fig. 6.2.

Figure 6.2: The light curve, displayed in fv.

6.5 Applying Time Filters the Data

Taking a look at the light curve, we can see that there is a very large flare toward the end of the observation and two much smaller ones in the middle of the exposure.

There are many ways to filter on time: with an explicit reference to the TIME parameter in the filtering expression; by making a secondary Good Time Interval (GTI) file with the task tabgtigen, which will allow you to filter on TIME or RATE; or by making a new GTI file with the task gtibuild using TIME as the filter. All of these will get the job done, so which to use is a matter of the user's preference. All of these are demonstrated below.

Filter on RATE with tabgtigen

Examining the light curve shows us that during non-flare times, the count rate is quite low, about 1.3 ct/s, with a small increase at 7.3223e7 seconds to about 6 ct/s. We can use that to generate the GTI file:

tabgtigen table=mos1_ltcrv.fits gtiset=gtiset.fits timecolumn=TIME \
$$ expression='(RATE $<=$ 6)'

where

table - input count rate table
expression - filtering expression
gtiset - output file name for selected GTI intervals
timecolumn - time column

We can use evselect to apply it:

evselect table=mos1_filt.fits withfilteredset=yes \
$$ expression='GTI(gtiset.fits,TIME)' filteredset=mos1_filt_time.fits \
$$ filtertype=expression keepfilteroutput=yes \
$$ updateexposure=yes filterexposure=yes

where the parameters are as defined in §6.3.

Filter on TIME with tabgtigen

Alternatively, we could have chosen to make a new GTI file by noting the times of the flaring in the light curve and using that as a filtering parameter. The big flare starts around 7.32276e7 s, and the smaller ones are at 7.32119e7 s and 7.32205e7 s. The expression to remove these would be (TIME $<=$ 73227600)&&!(TIME IN [7.32118e7:7.3212e7])&&!(TIME IN [7.32204e7:7.32206e7]). The syntax &&(TIME $<$ 73227600) includes only events with times less than 73227600, and the "!" symbol stands for the logical "not", so use &&!(TIME in [7.32118e7:7.3212e7]) to exclude events in that time interval. Once the new GTI file is made, we apply it with evselect.

tabgtigen table=mos1_ltcrv.fits gtiset=gtiset.fits timecolumn=TIME \
$$ expression= \
$$ '(TIME $<=$ 73227600)&&!(TIME IN [7.32118e7:7.3212e7])&&!(TIME IN [7.32204e7:7.32206e7])' [] evselect table=mos1_filt.fits withfilteredset=yes \
$$ expression='GTI(gtiset.fits,TIME)' filteredset=mos1_filt_time.fits \
$$ filtertype=expression keepfilteroutput=yes \
$$ updateexposure=yes filterexposure=yes

where the parameters are as defined above.

Filter on TIME with gtibuild

This method requires a text file as input. In the first two columns, enter the start and end times (in seconds) that you are interested in, and in the third column, indicate with either a + or - sign whether that region should be kept or removed. Each good (or bad) time interval should get its own line, with any optional comments preceeded by a ``#''. In the example case, we would write in our ASCII file (named gti.txt):

0 73227600 + # Good time from the start of the observation... [] 7.32118e7 7.3212e7 - # but without a small flare here, [] 7.32204e7 7.32206e7 - # and here.

and proceed to gtibuild:

gtibuild file=gti.txt table=gti.fits

where

file - input text file
table - output GTI file

And we apply it in the usual manner:

evselect table=mos1_filt.fits withfilteredset=yes \
$$ expression='GTI(gtiset.fits,TIME)' filteredset=mos1_filt_time.fits \
$$ filtertype=expression keepfilteroutput=yes \
$$ updateexposure=yes filterexposure=yes

where the parameters are as described in §6.3.

Filter on TIME by Explicit Reference

Finally, we could have chosen to forgo making a secondary GTI file altogether, and simply filtered on TIME with the standard filtering expression (see §6.3). In that case, the full filtering expression would be:

(PATTERN $<=$ 12)&&(PI in [200:12000])&&#XMMEA_EM
$$ &&(TIME $<=$ 73227600) &&!(TIME IN [7.32118e7:7.3212e7])&&!(TIME IN [7.32204e7:7.32206e7])

This expression can then be used to filter the original event file, as shown in §6.3, or only the times can be used to filter the file that has already had the standard filters applied:

evselect table=mos1_filt.fits withfilteredset=yes \
$$ expression= \
$$'(TIME$<=$73227600)&&!(TIME IN [7.32118e7:7.3212e7])&&!(TIME IN [7.32204e7:7.32206e7])' \
$$ filteredset=mos1_filt_time.fits filtertype=expression keepfilteroutput=yes \
$$ updateexposure=yes filterexposure=yes

where the keywords are as described in §6.3.

6.6 Source Detection with edetect_chain

The edetect_chain task does nearly all the work involved with EPIC source detection. It can process up to three intruments (both MOS cameras and the PN) with up to five images in different energy bands simultaneously. All images must have identical binning and WCS keywords. For this example, we will perform source detection on MOS1 images in two bands (``soft'' X-rays with energies between 300 and 2000 eV, and ``hard'' X-rays, with energies between 2000 and 10000 eV) using the filtered event files produced here.

We will start by generating some files that edetect_chain needs: an attitude file and images of the sources in the desired energy bands, with the image binning sizes as needed according to the detector. For the MOS, the we'll let the binsize be 22.

The example uses the filtered event file produced in §6.5, with the assumption that it is located in the current directory.

First, make the attitude file by typing

atthkgen atthkset=attitude.fits timestep=1

where

atthkset - output file name
timestep - time step in seconds for attitude file

Next, make the soft and hard X-ray images with evselect by typing

evselect table=mos1_filt_time.fits withimageset=yes imageset=mos1-s.fits \
$$ imagebinning=binSize xcolumn=X ximagebinsize=22 ycolumn=Y yimagebinsize=22 \
$$ filtertype=expression expression='(FLAG == 0)&&(PI in [300:2000])'

and

evselect table=mos1_filt_time.fits withimageset=yes imageset=mos1-h.fits \
$$ imagebinning=binSize xcolumn=X ximagebinsize=22 ycolumn=Y yimagebinsize=22 \
$$ filtertype=expression expression='(FLAG == 0)&&(PI in [2000:10000])'

We will also make an image with both soft and hard X-rays for display purposes:

evselect table=mos1_filt_time.fits withimageset=yes imageset=mos1-all.fits \
$$ imagebinning=binSize xcolumn=X ximagebinsize=22 ycolumn=Y yimagebinsize=22 \
$$ filtertype=expression expression='(FLAG == 0)&&(PI in [300:10000])'

where the parameters are

table - event list
withimageset - flag to create an image
imageset - fits image name to be created
imagebinning - how to bin the image
xcolumn - table column to use for the X axis
ximagebinsize - binning in X axis
ycolumn - table column to use for the Y axis
yimagebinsize - binning in Y axis
filtertype - type of filtering
expression - filtering expression

Now we can run edetect_chain:

edetect_chain imagesets='mos1-s.fits mos1-h.fits' \
$$ eventsets='mos1_filt_time.fits' attitudeset=attitude.fits \
$$ pimin='300 2000' pimax='2000 10000' likemin=10 witheexpmap=yes \
$$ ecf='0.878 0.220' eboxl_list=eboxlist_l.fits \
$$ eboxm_list=eboxlist_m.fits eml_list=emllist.fits esp_withootset=no

where

imagesets - list of count images
eventsets - list of event files
attitudeset - attitude file name
pimin - list of minimum PI channels for the bands
pimax - list of maximum PI channels for the bands
likemin - maximum likelihood threshold
witheexpmap - create and use exposure maps
ecf - energy conversion factors for the bands
eboxl_list - output file name for the local sliding box source
$$ detection list
eboxm_list - output file name for the sliding box source detection in
$$ background map mode list
eml_list - output file name for maximum likelihood source detection list
esp_withootset - Flag to use an out-of-time processed PN event file,
$$useful in cases where bright point sources have left streaks in the PN data
esp_ooteventset - The out-of-time processed PN event file

The energy conversion factors (ECFs) convert the source count rates into fluxes. The ECFs for each detector and energy band depend on the pattern selection and filter used during the observation. For more information, please consult the calibration paper ``SSC-LUX-TN-0059'', available at the XMM-Newton Science Operations Center or see Table 8 in the 3XMM Catalogue User Guide. Those used here are derived from PIMMS using the flux in the 0.1-10.0 keV band, a source power-law index of 1.9, an absorption of $0.5\times10^{20}$ cm$^{-2}$.

We can display the results of eboxdetect using the task srcdisplay and produce a region file for the sources.

srcdisplay boxlistset=emllist.fits imageset=mos1-all.fits \
$$ regionfile=regionfile.txt sourceradius=0.01 withregionfile=yes

where

boxlistset - eboxdetect source list
imageset - image file name over which the source circles are to be plotted
includesources - flag to include the source positions on the display
regionfile - file name of output file containing source regions
sourceradius - radius of circle plotted to locate sources
withregionfile - flag to create a region file

Figure 6.3 shows the MOS1 event file overlayed with the detected sources.

Figure 6.3: MOS1 event file overlayed with the detected sources.

6.7 Extract the Source and Background Spectra

Throughout the following, please keep in mind that some parameters are instrument-dependent. The parameter specchannelmax should be set to 11999 for the MOS, or 20479 for the PN. Also, for the PN, the most stringent filters, (FLAG==0)&&(PATTERN<=4), must be included in the expression to get a high-quality spectrum.

For the MOS, the standard filters should be appropriate for many cases, though there are some instances where tightening the selection requirements might be needed. For example, if obtaining the best-possible spectral resolution is critical to your work, and the corresponding loss of counts is not important, only the single pixel events should be selected (PATTERN==0). If your observation is of a bright source, you again might want to select only the single pixel events to mitigate pile up (see §6.8 and §6.9 for a more detailed discussion).

In any case, you'll need to know spatial information about the area over which you want to extract the spectrum, so display the filtered event file with ds9:

ds9 mos1_filt_time.fits &

Select the object whose spectrum you wish to extract. This will produce a circle (extraction region), centered on the object. The circle's radius can be changed by clicking on it and dragging to the desired size. Adjust the size and position of the circle until you are satisfied with the extraction region; then, double-click on the region to bring up a window showing the center coordinates and radius of the circle. For this example, we will choose the source at (26188.5,22816.5) and set the extraction radius to 300 (in physical units).

To extract the source spectrum, type

evselect table='mos1_filt_time.fits' energycolumn='PI' withfilteredset=yes \
$$ filteredset='mos1_filtered.fits' keepfilteroutput=yes filtertype='expression' \
$$ expression='((X,Y) in CIRCLE(26188.5,22816.5,300))' \
$$ withspectrumset=yes spectrumset='mos1_pi.fits' spectralbinsize=5 \
$$ withspecranges=yes specchannelmin=0 specchannelmax=11999

where

table - the event file
energycolumn - energy column
withfilteredset - make a filtered event file
keepfilteroutput - keep the filtered file
filteredset - name of output file
filtertype - type of filter
expression - expression to filter by
withspectrumset - make a spectrum
spectrumset - name of output spectrum
spectralbinsize - size of bin, in eV
withspecranges - covering a certain spectral range
specchannelmin - minimum of spectral range
specchannelmax - maximum of spectral range

When extracting the background spectrum, follow the same procedures, but change the extraction area. For example, make an annulus around the source; this can be done using two circles, each defining the inner and outer edges of the annulus, then change the filtering expression (and output file name) as necessary.

To extract the background spectrum, type

evselect table=mos1_filt_time.fits energycolumn='PI' withfilteredset=yes \
$$ filteredset='bkg_filtered.fits' keepfilteroutput=yes filtertype='expression' \
$$ expression='((X,Y) in CIRCLE(26188.5,22816.5,1500))&&!((X,Y) in CIRCLE(26188.5,22816.5,500))' \
$$ withspectrumset=yes spectrumset='bkg_pi.fits' spectralbinsize=5 \
$$ withspecranges=yes specchannelmin=0 specchannelmax=11999

where the keywords are as described above.

6.8 Check for Pile Up

Depending on how bright the source is and what modes the EPIC detectors are in, event pile up may be a problem. Pile up occurs when a source is so bright that incoming X-rays strike two neighboring pixels or the same pixel in the CCD more than once in a read-out cycle. In such cases the energies of the two events are in effect added together to form one event. If this happens sufficiently often, 1) the spectrum will appear to be harder than it actually is, and 2) the count rate will be underestimated, since multiple events will be undercounted. To check whether pile up may be a problem, use the SAS task epatplot. Heavily piled sources will be immediately obvious, as they will have a ``hole'' in the center, but pile up is not always so conspicuous. Therefore, we recommend to always check for it.

Note that this procedure requires as input the event files created when the spectrum was made, not the usual time-filtered event file.

To check for pile up in our Lockman Hole example, type

epatplot set=mos1_filtered.fits plotfile=mos1_epat.ps useplotfile=yes \
$$ withbackgroundset=yes backgroundset=bkg_filtered.fits

where

set - input events file \
plotfile - output postscript file \
useplotfile - flag to use file name from "plotfile" \
withbackgroundset - use background event set for background subtraction? \
backgroundset - name of background event file

The output of epatplot is a postscript file, mos1_epat.ps, which may be viewed with viewers such as gv, containing two graphs describing the distribution of counts as a function of PI channel; see Figure 8.4.

A few words about interpretting the plots are in order. The top is the distribution of counts versus PI channel for each pattern class (single, double, triple, quadruple), and the bottom is the expected pattern distribution (smooth lines) plotted over the observed distribution (histogram). The lower plot shows the model distributions for single and double events and the observed distributions. It also gives the ratio of observed-to-modeled events with 1-$\sigma$ uncertainties for single and double pattern events over a given energy range. (The default is 0.5-2.0 keV; this can be changed with the pileupnumberenergyrange parameter.) If the data is not piled up, there will be good agreement between the modeled and observed single and double event pattern distributions. Also, the observed-to-modeled fractions for both singles and doubles in the 0.5-2.0 keV range will be unity, within errors. In contrast, if the data is piled up, there will be clear divergence between the modeled and observed pattern distributions, and the observed-to-modeled fraction for singles will be less than 1.0, and for doubles, it will be greater than 1.0.

Finally, when examining the plots, it should noted that the observed-to-modeled fractions can be inaccurate. Therefore, the agreement between the modeled and observed single and double event pattern distributions should be the main factor in determining if an observation is affected by pile up or not.

The source used in our Lockman Hole example is too faint to provide reasonable statistics for epatplot and is far from being affected by pile up. For comparison, an example of a bright source (from a different observation) which is strongly affected by pileup is shown in Figure 6.5. Note that the observed-to-model fraction for doubles is over 1.0, and there is severe divergence between the model and the observed pattern distribution.

Figure 6.4: The output of epatplot for a very faint source without pileup. Note that in the lower plot, there are too few X-rays for epatplot to model.

Figure 6.5: The output of epatplot for a heavily piled source. In the lower plot, there are large differences between the predicted and observed pattern distribution at energies above $\sim$ 1000 eV.

6.9 My Observation is Piled Up! Now What?

If you're working with a different (much brighter) dataset that does show signs of pile up, there are a few ways to deal with it. First, using the region selection and event file filtering procedures demonstrated in earlier sections, you can excise the inner-most regions of a source (as they are the most heavily piled up), re-extract the spectrum, and continue your analysis on the excised event file. For this procedure, it is recommended that you take an iterative approach: remove an inner region, extract a spectrum, check with epatplot, and repeat, each time removing a slightly larger region, until the model and observed distribution functions agree. If you do this, be aware that removing too small a region with respect to the instrumental pixel size (1.1'' for the MOS, 4.1'' for the PN) can introduce systematic inaccuracies when calculating the source flux; these are less than 4%, and decrease to less than 1% when the excised region is more than 5 times the instrumental pixel half-size. In any case, be certain that the excised region is larger than the instrumental pixel size!

You can also use the event file filtering procedures to include only single pixel events (PATTERN==0), as these events are less sensitive to pile up than other patterns.

6.10 Determine the Spectrum Extraction Areas

Now that we are confident that our spectrum is not piled up, we can continue by finding the source and background region areas. This is done with the task backscale, which takes into account any bad pixels or chip gaps, and writes the result into the BACKSCAL keyword of the spectrum table. Alternatively, we can skip running backscale, and use a keyword in arfgen below. We will show both options for the curious.

To find the source and background extraction areas explicitly,

backscale spectrumset=mos1_pi.fits badpixlocation=mos1_filt_time.fits

backscale spectrumset=bkg_pi.fits badpixlocation=mos1_filt_time.fits

where

spectrumset - spectrum file
badpixlocation - event file containing the bad pixels

6.11 Create the Photon Redistribution Matrix (RMF) and Ancillary File (ARF)

Now that a source spectrum has been extracted, we need to reformat the detector response by making a redistribution matrix file (RMF) and ancillary response file (ARF). To make the RMF:

rmfgen rmfset=mos1_rmf.fits spectrumset=mos1_pi.fits

where

rmfset - output file
spectrumset - spectrum file

Now use the RMF, spectrum, and event file to make the ancillary file:

arfgen arfset=mos1_arf.fits spectrumset=mos1_pi.fits withrmfset=yes \
$$ rmfset=mos1_rmf.fits withbadpixcorr=yes badpixlocation=mos1_filt_time.fits

If we had not run backscale, we could set a keyword in arfgen to find the region area:

arfgen arfset=mos1_arf.fits spectrumset=mos1_pi.fits withrmfset=yes \
$$ rmfset=mos1_rmf.fits withbadpixcorr=yes badpixlocation=mos1_filt_time.fits \
$$ setbackscale=yes

where

arfset - output ARF file name
spectrumset - input spectrum file name
withrmfset - flag to use the RMF
rmfset - RMF file created by rmfgen
withbadpixcorr - flag to include the bad pixel correction
badpixlocation - file containing the bad pixel information; should be set to the event
$$ file from which the spectrum was extracted.
setbackscale - flag to calculate the area of the source region and
$$ write it to the BACKSCAL keyword in the spectrum header

At this point, the spectrum is ready to be analyzed, so skip ahead to prepare the spectrum for fitting (§13).