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Reading fits files from the AXAF simulator, MARX
At the current time (1997 Dec), the only AXAF files of general
interest are those produced by MARX via the MARX utility 'marx2fits'
and 'marx2img'. Although the MARX fits files conform to FITS
standards, there are two parameters in the events list fits header
which are written as reals whereas fits2qp expects integer format.
Therefore, we provide a script which fixes this incompatibility.
Note that future versions of MARX software may include changes that
will obviate the need for this work-around.
The following description tells how to produce a qpoe file from the
MARX fits file (events list format). We have tested the method only
to the extent of examining the qpoe file with 'xexamine', xexamine_r,
and rudimentary spectral functions like displaying PHA distributions.
Note also that if you want only spatial information, one can run the
MARX utility 'marx2img' which produces a fits file with a primary
image only. This can be read by the general IRAF task dataio.rfits to
produce an image file.
1) An event fits file is produced from MARX results by using the task
'marx2fits'
2) In IRAF, a PROS qpoe file can be created from this fits file.
>ncl
>xray
>xproto
>cd <your_working_directory>
xp> lpar marx2qpoe
inp_fits = input fits filename
out_qpoe = output qpoe filename
DetectorType = 1 Detector Type: (1)ASC-I (2)ASC-S (3)HRC-I (4)HRC-S
key_x = "chipx" index key for x coordinate
key_y = "chipy" index key for y coordinate
(axlen1 = 1024) dimension of qpoe axis #1
(axlen2 = 1024) dimension of qpoe axis #2
(display = 1) display level
(clobber = no) Okay to delete existing qpoe file?
(DeleteInterm = yes) Okay to delete intermediate file?
(fits_cards = "xdataio$fits.cards") definitions for fits cards
(qpoe_cards = "xdataio$qpoexrcf.cards") definitions for qpoe cards
(ext_cards = "xdataio$ext.cards") definitions for ext cards
(wcs_cards = "xdataio$wcsmarx.cards") definitions for wcs cards
(qp_pagesize = 16384) page size for qpoe file
(qp_bucketlen = 32767) bucket length for qpoe file
(flpar = no) flush pfile on assign?
(mode = "ql")
Note that besides choosing the proper detector, you must specify which coordinates
to use. For MARX VERSION: 2.04, the only non-zero coordinates are chip coordinates
(chipx, chipy) and tiled coordinates (tdetx, tdety). In the future, other options
will include detx, dety, and x, y (i.e. actual focal plane
coordinates).
At this stage, we suspect that most users will want to use the
spatial coordinates, tdetx, tdety. If you want the chip coordinates,
once you have the qpoe file, you will probably want to specify the
file as filename.qp[ccdid=n] where 'n' is the chip ID, as per figure
2.2 in the MARX manual. Note that in our tests, the four chips of the
ACIS I had to be rotated to recover the appearance of the source on
the sky. This is because the chip coordinates orientation differs
from instrument to instrument.
| Instrument |
Axlen |
Key |
| |
|
|
| ACIS-I |
1024 |
chipx,chipy |
| |
8192 |
tdetx,tdety |
| |
|
|
| ACIS-S |
1024 |
chipx,chipy |
| |
6144x1024 |
tdetx,tdety |
| |
|
|
| HRC-I |
16384 |
chipx,chipy |
| |
|
|
| HRC-S |
16384x4096 |
chipx,chipy |
| |
49152x4096 |
tdetx,tdety |
Notes:
HRC-I:
Chipx and tdetx are the same, as are chipy and tdety. It appears that
to recover the correct sky orientation, the image must be viewed from
'behind' with an additional rotation of 45 degrees. The choice of
TDET for HRC was a request from the HRC instrument team. The problem
is that we really need DETX, DETY (focal plane coords) and MARX
doesn't calculate them yet. The 'back to front' is because HRC-I is
wired up such that its native telemetry coordinate axes are a left
handed system.
For more details on coordinate systems, see:
http://hea-www.harvard.edu/ jcm/asc/coords/
then click on ... ASC Coordinate Systems, Version 4.2 memo
Once the parameters are chosen, run:
xp> marx2qpoe
Next: Viewing the qpoe file.
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rsdc@cfa.harvard.edu
1998-06-10