Institut für Astronomie und Astrophysik
Abteilung AstronomieSand 1, D-72076 Tübingen, Germany
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Retrieving ROSAT data files
Analysis of ROSAT data is usually done using the ROSAT account on the AIT VAX cluster (username: ROSAT, ask the system manager for the password). On this account ESO MIDAS and the MPE EXSAS package can be used:
invoke MIDAS (November 1994 release):
The utilities described in this document (.prg, .cmd, .par files)
can be found in the directory
ROSAT calibration files are stored under the logical directory name
Archival data can be retrieved via WWW from the ROSAT public FTP archive. Select the directory of the requested ROSAT observation or use the archive browser to search for observations of your favourite object.
Download the files.
Unzip the files :
gzip -d *.*-gz
Depending on the date of (re)processing different file formats may be found and different EXSAS commands have to be used to transform the data into MIDAS/EXSAS format:
format | old MPE format | old US format | rationalized FITS ----------+----------------+----------------+------------------ extensions| .tfits | .cas | .fits | .ifits | .so | | .mt | .evr | | | ... | command | intape/rod | intape/usrod | intape/rdfMidas 002>
intape/usrod DISK <detector (HRI/PSPC)>
intape/rdf DISK <root name of disk files>
New PI data received on tape have to be read from DAT or EXABYTE tape using
Now you should have at least the following files:
events.tbl: photon event file,
eventrates.tbl: eventrates for photon and particle events,
attitude.tbl: spacecraft attitude information.
Binning an image: Use the
to get the image
image.bdf with 15'' pixels from
load/image image cuts=0,10
Identify your source by reading cursor coordinates:
get/coordinates equatorial 2000.0
Estimate detected counts in cursor rectangle:
statistics/image ? cursor
Measure image coordinates of object and possibly contaminating sources:
Select events in source and background areas and bin spectra using
select_spec.cmd command file: Insert the world coordinate
positions measured with
center/gauss into the command file at
select/ring center=(x,y) ...
-> raw spectrum, file name in this example:
Correct the spectrum for incomplete extraction of the point spread function,
deadtime losses, and spatial variations of the effective areas
(vignetting correction) using
correct_spec.par parameter file:
-> The resulting file (e.g.
a corrected effective area table, which has to be used later
for fitting a spectral model.
Perform rebinnig and background subtraction:
prepare/spectrum sourback spectrum
produces the binned countrate spectrum
During the run you are requested to specify channels to be omitted
and binning information,
the first 10 channels (<0.1 keV) should be omitted, the nominal energy
range of the PSPC ends at channel 240 (2.4 keV).
The channels of the detector response matrix have to be rebinned according
to the binning of the file
spectrum.tbl, for observations
prior to the 11th of October 1991
(PSPC gain change) use the DRM
for later observations use the file
bin/detector spectrum EXSAS_CAL:DRMPSPC drmb
-> binned DRM drmb.bdf
Fit a model to the spectrum:
Fitting a simple powerlaw using the parameter file
-> resulting file
pwlspec.tbl, contains countrate and
model photon spectrum,
fit parameters are stored in the descriptor header.
Plot the spectrum:
Or use the faster IDL program:
It is convenient to perform the necessary corrections already during the
selection process. This is done by switching the projection software
into correction mode:
-> correction mode is set, the specified files are used for vignetting correction and deadtime correction. Note that no PSF correction can be applied in correction mode.
Select source and background events and bin into lightcurve using
select_light.cmd and insert
your source coordinates and binsize.
prepare/lightcurve <table> <output-column>
-> background subtracted, corrected lightcurve in column <output-column>
-> start time of bins in column :S_TI
Plot the lightcurve:
plot/lightcurve <table> ? <output-column>
Writing the lightcurve as an ASCII file:
assign/print file <filename>
print/table <table> :S_TI
Hint: Due to the 400 second spacecraft wobble and the support structure of the PSPC entrance window the PSPC lightcurves show periodic dips. When highest precision of the lightcurve is required, use 400 sec binning in order to cover a full wobble period with each bin. Periodic features on timescales of tens of seconds to 400 seconds may be spurious.
make/projection correct command cannot be applied
to HRI data. Therefore the necessary corrections have to be applied
Selection of events:
As for the PSPC the
select_light.cmd command file may be used,
but due to the better angular resolution of the HRI a smaller
extraction radius (e.g. 50 sky pixel = 25'') is appropriate:
-> raw source and background light curves in table
Apply vignetting and deadtime correction using the parameter file
-> New column in table
lightcurve containing corrected source
light curve (column label
prepare/lightcurve lightcurve :lc
-> background subtracted, corrected lightcurve in column
Plotting and ASCII output:
see previous section PSPC lightcurves.
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Last modified 21 May 2008