Displaying the FEF Regions Covered by a Source
[CIAO 3.4 Science Threads]
OverviewLast Update: 1 Dec 2006 - reviewed for CIAO 3.4: no changes Synopsis: The RMF used to analyze a source depends on what part of the chip the source falls on. As described in the mkrmf help page, the RMF is calculated using information stored in a FEF file. Since the information in the FEFs changes over the chip - the exact regions over which a particular FEF is valid depend on the chip and the focal-plane temperature - it is sometimes useful to see how the source photons are distributed with respect to this grid (this is particularly true for extended sources). Purpose: To view the distribution of source photons on the FEF grid. Read this thread if: you are working with an ACIS observation (imaging or grating) and intend to create an RMF with mkrmf. This thread does not apply to users running mkacisrmf, since that tool uses a different format of calibration file in place of the FEF files. Related Links:
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Contents
Download regions.sl
The most recent version of regions.sl is v1.2 (17 July 2003):
unix% grep Id $ASCDS_CONTRIB/share/slsh/local-packages/regions.sl % $Id: regions.sl,v 1.2 2003/07/17 18:48:39 dburke Exp $
Note that $ASCDS_CONTRIB/share/slsh/local-packages/ is the default path in the standard CIAO scripts installation; see the Scripts page for more information. Please check that you are using the most recent version before continuing. If you do not have the script installed or need to update to a newer version, please refer to the Scripts page.
Getting Started
Sample ObsID used: 459 (HETG/ACIS-S, 3C 273)
File types needed: evt2
The script provides a S-Lang function (display_fef_regions()) which requires an event file containing the source photons; it will accept the DM virtual-file syntax for filtering on-the-fly. The input file should only contain photons falling on a single ACIS chip, so it will be necessary to include a filter such as "ccd_id=<number>" if the source region covers more than one chip. It should also contain a TIME column, as the first entry is used to find out the focal plane temperature at the time of the observation.
For this example, we use the 3C 273 source and background regions defined in the Extract ACIS Spectra for Pointlike Sources and Make RMFs and ARFs thread, namely:
unix% cat 3c273.reg # Region file format: CIAO version 1.0 rotbox(4148.125,4043.625,7.58978,22.338761,44.516094) unix% cat 3c273_bg.reg # Region file format: CIAO version 1.0 circle(4119,4014.75,10) circle(4077,4025.75,10) circle(4186.5,4023.25,10) circle(4196.25,4064.5,10)
Run the script
The S-Lang script must be loaded into ChIPS (or Sherpa) before it can be run (this step is only necessary once per ChIPS/Sherpa session):
chips> () = evalfile( "regions.sl" )
or by loading the code using the --slscript option:
unix% chips --slscript regions.sl
First we shall look at the source region:
chips> display_fef_regions( "acisf00459N002_evt2.fits[sky=region(3c273.reg)]" ) # Reading points from acisf00459N002_evt2.fits[sky=region(3c273.reg)] # Chip is ACIS-7 # Focal Plane temperature = -110 C # Number of photons in region = 736 # Region Num Fraction # chipx chipy photons 0257:0288 0353:0384 344 0.4674 0289:0320 0353:0384 187 0.2541 0257:0288 0385:0416 151 0.2052 0289:0320 0385:0416 52 0.0707 0257:0288 0321:0352 1 0.0014 0289:0320 0321:0352 1 0.0014
Figure 1 ![[Link to Image 1: Source distribution across the FEF tiles]](../../imgs/imageicon.gif){kind=small}
shows the plot. The
output tells us that almost half of the source photons fell
in the region CHIPX=257:288,
CHIPY=353:384.
Looking at the background region, we get:
chips> display_fef_regions( "acisf00459N002_evt2.fits[sky=region(3c273_bg.reg)]" ) # Reading points from acisf00459N002_evt2.fits[sky=region(3c273_bg.reg)] # Chip is ACIS-7 # Focal Plane temperature = -110 C # Number of photons in region = 216 # Region Num Fraction # chipx chipy photons 0257:0288 0417:0448 39 0.1806 0289:0320 0321:0352 31 0.1435 0257:0288 0289:0320 25 0.1157 0289:0320 0385:0416 25 0.1157 0289:0320 0417:0448 18 0.0833 0257:0288 0321:0352 16 0.0741 0257:0288 0449:0480 13 0.0602 0321:0352 0321:0352 12 0.0556 0289:0320 0353:0384 11 0.0509 0257:0288 0385:0416 8 0.0370 0289:0320 0289:0320 7 0.0324 0321:0352 0353:0384 3 0.0139 0225:0256 0449:0480 3 0.0139 0321:0352 0385:0416 2 0.0093 0289:0320 0449:0480 2 0.0093 0225:0256 0417:0448 1 0.0046
Figure 2 shows the plot.
History
| 04 Jan 2005 | updated for CIAO 3.2: this thread does not apply to the mkacisrmf tool |
| 16 Dec 2005 | reviewed for CIAO 3.3: no changes |
| 01 Dec 2006 | reviewed for CIAO 3.4: no changes |
