How to process EPIC slew data

Introduction This thread explains how to process slew data taken with the EPIC-pn camera. Expected Outcome At the end of this thread a set of filtered event files and images will have been created. These represent contiguous sections of the slew. SAS Tasks to be Used eslewchain Prerequisites It is assumed that a slew data file (SDF) has been unpacked into the current directory. The SDF may be obtained from the archive. SAS Startup Thread Produce EPIC event lists Useful Links A guide to the XMM-Newton slew source catalogue Caveats

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Procedure

• Set up your SAS environment (following the SAS Start-up Thread)


• Create an EPIC-pn event list from the slew data file. The procedure for this is identical to the initial processing of a pointed observation.
  Produce EPIC event lists.


• Tell the SAS to use the Raw Attitude File (RAF) for the attitude reconstruction of the slew by:
  1. csh: setenv SAS_ATTITUDE RAF
  2. sh: export SAS_ATTITUDE=RAF


• Run eslewchain
  
  This task does not need any parameters. It reads the EPIC-pn event list from the directory pointed to by the environment variable SAS_ODF and processes the whole slew (which can take several hours for a long slew) producing a set of output files.


• The output files are :
  
  
  1. Attitude corrected images of name PobsidPNS003IMAGE_biii.ds Where, obsid is the 10-digit observation number, b is the energy band identifier and iii is the image sequence number in hexadecimal which typically increments from 000 to 04A or so.
  
  
  2. Exposure maps of name PobsidPNS003EXPMAPbiii.ds
  
  
  3. Filtered event files for each image section of name: PobsidPNS003PIEVLI0iii.ds
  
  The band number b means:
  
  

  Band	Energy
  1	0.2-0.5 keV
  2	0.5-1.0 keV
  3	1.0-2.0 keV
  6	0.2-2.0 keV
  7	2.0-12.0 keV
  8	0.2-12.0 keV

Last Updated: 1 June 2010

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Caveats Instrument selection during a slew: Initially the EPIC-MOS collected scientific data during slews. These data were of poor quality because the frame time in the MOS detectors is long compared with the motion of the satellite during a slew (90 degrees per hour). MOS sources are hence stretched out into long streaks with a consequent increase in the background level and reduction in the signal-to-noise ratio. The EPIC-pn frame times are small and give a relatively small pertubation to the effective point spread function (PSF) of sources. Practical issues Slew data is particularly susceptible to problems caused by background flares, 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.

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