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XMM-Newton Science Analysis System Page: 1
eslewchain
Richard Saxton (XMM-SOC, rsaxton@sciops.esa.int)
21 October 2008
Abstract
The task eslewchain splits an EPIC slew into small sections, roughly one degree
in length and generates images and exposure maps for each section. It makes use of
the tasks atthkgen, attcalc, evselect and eexpmap.
1 Status
version (from VERSION ): 1.0.1
2 Change history
Revision no. Date Comments
1.0.1 21/10/08 Updated for extra warning message
1.0 16/05/08 original
3 Instruments/Modes
Instrument Mode
EPIC PN, MOS IMAGING
4 Use
pipeline processing yes
interactive analysis yes
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5 Description
5.1 General
The aim of eslewchain is to produce scientically useful products from an XMM-Newton slew. It is
designed to work with data from the EPIC-pn or EPIC MOS cameras.
eslewchain takes as input a slew event le and associated attitude les and produces a series of images
and exposure maps. The task divides the event set into chunks of 72000 sky pixels (roughly 1 degree)
in either the X or Y dimension, depending on the direction of the slew. These mini event les are then
attitude corrected to project them onto the local tangential plane and then used to create the products.
Data products are produced in a number of photon energy bands
1 = 0.2{0.5 keV
2 = 0.5{1.0 keV
3 = 1.0{2.0 keV
4 = 2.0{12.0 keV
5 = 0.2-2.0 keV
0 = 0.2-12.0 keV
5.2 How to use
eslewchain runs on a processed event list in the current directory. A typical processing sequence would
be:
1. Download the slew datale (SDF) into a clean directory and point to it with the environment
variable SAS ODF.
2. Run ccfbuild and point to the CCF with SAS CCF
3. Run odngest
4. Run epproc in a working directory
5. Set the SAS ATTITUDE environment variable to "RAF".
6. Run eslewchain in the directory containing the event le produced by epproc.
5.2.1 Interpreting the results
Slew data is particularly susceptible to problems caused by background ares, low-energy noise and halos
around bright sources. For a practical guide of the issues to be aware of when interpreting slew data
please see Saxton et al. 2008, A&A 480, 611.
A diagnostic le, I"rev" "obsid" "ra" "dec" wartsnall.ds is produced for each sub image position. This
is an unltered image, containing events with all energies, all patterns and all ags. In this image,
problems due to low-energy noise and optical loading can readily be seen. It is worth checking this image
for problems before interpreting interesting features in the scientic images.
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5.3 Examples
6 Parameters
This section documents the parameters recognized by this task (if any).
Parameter Mand Type Default Constraints
None
7 Errors
This section documents warnings and errors generated by this task (if any). Note that warnings and
errors can also be generated in the SAS infrastructure libraries, in which case they would not be docu-
mented here. Refer to the index of all errors and warnings available in the HTML version of the SAS
documentation.
odf (error)
SAS ODF environment variable does not exist or data directory invalid
evle (error)
The SAS ODF directory does not contain an event le. Has the chain/proc been run ?
TaskFailed (error)
The subtask called by the chain has failed
NoFtools (error)
The ftools aren't available to eslewchain
SortFailed (error)
The 'sort' routine failed
CopyFail (error)
Failed to copy le - diskspace problem ?
NoEVFILE (error)
evselect failed
EregFail (error)
eregionanalyse failed to run to completion
UseRAF (warning)
SAS ATTITUDE should be set to "RAF" when processing slew data
corrective action: continue processing
8 Input Files
The input les are those contained in a directory after odngest and an EPIC proc or chain have been
run on a slew data le (SDF). In particular the directory must contain:
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1. An EPIC event le (only one should be present in the directory).
2. A Raw Attitude File, "rev" "obsid" SCX00000RAS.ASC
3. A summary File, "rev" "obsid" SCX00000SUM.SAS
9 Output Files
1. EPIC images of name I"rev" "obsid" "ra" "dec" b"band".ds Where band is the energy
band: 1 = 0.2{0.5 keV
2 = 0.5{1.0 keV
3 = 1.0{2.0 keV
4 = 2.0{12.0 keV
5 = 0.2-2.0 keV
0 = 0.2-12.0 keV
2. EPIC exposure maps of name E"rev" "obsid" "ra" "dec" b"band".ds Only bands 0,4 and 5
are produced.
10 Intermediate Files
1. ltered event les of name lt "X" "Y".ts
11 Algorithm
Find an event file in SAS_ODF
Find the celestial position of the start of the slew
If (X range of event file > Y range) {
NRANGES = (XMAX - XMIN) / 72000 + 1
else
NRANGES = (YMAX - YMIN) / 72000 + 1
}
for i=1 to NRANGES
Calculate the minimum and maximum for the main axis:
ax1min = (XMIN or YMIN) + 72000 * (i-1)
ax1max = ax1min + 72000
find ranges in second axis which have value of ax1 between min and max
NB: There can be >1 range if the slew doubles back
for j=1 to Nranges_ax2
Filter the event file with this X and Y range:
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evselect table=eventfile
expression=(X in [$x1:$x2])&&(Y in [$y1:$y2])
withfilteredset=yes filteredset=
Attitude correct the filtered event file to the centre pixel:
attcalc eventset= refpointlabel=user
nominalra= nominaldec=
Find the X, Y range of the attitude-corrected event file
Get the RA, DEC of the centre of the filtered file
Create an image name stem from the central RA and DEC
Iname = I
Create an unfiltered image from this event file as a diagnostic:
evselect table= imageset=
Create images in each energy band
evselect table= imageset=
expression=(FLAG==0)&&(PI in [200:500])&&(PATTERN==0)
evselect table= imageset=
expression=(FLAG==0)&&(PI in [501:1000])&&(PATTERN<=4)
etc.
Make exposure maps
eexpmap imageset=Idel.fits eventset=
expimageset=$expb4 $expb5 $expb0",
"pimin=2000 200 200","pimax=12000 2000 12000"
Add together 0.2-0.5, 0.5-1.0, 1.0-2.0 and 2-12 keV images to
make the b0 and b5 images using "farith"
} End of Second Axis loop
} End of First axis loop
12 Comments
 Slews which are very curved can produce exhorbitantly large images which do not maintain
the at projection and hence contain points with increasingly inaccurate astrometry. This
happens in about 1% of slews.
 AT points of in ection the interpolation of the curve fails a bit. This produces errors of < 1
arcmin at the worst.
 NB: The slew images have very few photons (typically about 100 in half a square degree).
For reasons which are not fully understood the more recent versions of the source detection
chain produce a large number of spurious sources from these images. At the moment it is
recommended to use SAS 6.1 to source search slew images.
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13 Future developments
14 Developer's notes
14.1 CAL usage
Only within the tasks called by the chain script.
References
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