OSO-8 Software:
Example 3 - Using Xspec

artist concept of OSO-8

A background sky position was found for the source used in Example 2. This background was chosen since it was relatively close to the source in location and in the time it was observed by OSO-8. The sky position is (R.A.(1950) = 72.310, Dec.(1950) = -3.820). OSO-8 observed this position on 6 September, 1975 from 02:09:45 to 04:10:35. Osofindfast will be used to determine the mission "good observing days" for the background and based on these days the raw PHA files and the response matrix closest in time need to be retrieved from the OSO-8 FTP area. Xspec will be used to perform the spectral fitting and background subtraction after the background spectrum has been modified slightly.

*Creating the source and background spectra This example begins the same way and the same source is used as in Example 2. Osofindfast is used for the background to determine the "good observing days" for this sky position. The appropriate raw PHA data spanning these days is retrieved from the archive and its filename is given in back_list as input to osopha.

*Using Xspec to perform spectral fitting and background subtraction The OSO-8 response matrices are normalized to unity in effective area. The correct effective area is calculated when a spectrum is extracted from the raw data using osopha. To use a spectrum as background in XSPEC, prior to entering XSPEC the AREASCAL value needs to be changed to match the AREASCAL value found in the source spectrum. This can be done using the tools fkeyprint to print the AREASCAL value in the source spectrum and fmodhead to insert the AREASCAL value in the background spectrum.

Calibrations in the past have shown that OSO-8 spectral fitting requires a systematic error of about 3% or 4% to be added to the data. This systematic error is introduced using the tool grppha.


% osopha
Equinox (d/f 1950)[1950.0] 
RA in hh mm ss.s or degrees[95.046] 
DEC in dd mm ss.s or degrees[-0.32] 
Rootname for generated spectral (+rates) output[a0620] source
Desired detector [1=B,2=C]:[2] 
Input listfile containing raw PHA files[a0620_list] 
Contaminating srces in FOV check?(d/f no)[no] 
Start PHA channel for broad-band light-curve (d/f 1)[1] 
End PHA channel for broad-band light-curve (d/f 63)[63] 
No. raw data integ. records (d/f=1 so B=40.96s ; C=12.98s)[1] 
Low int. threshold (c/s) for light-curve (d/f -10000)[-10000.0] 
High int. threshold (c/s) for light-curve (d/f 10000)[10000.0] 
Start PHA channel for soft-band light-curve [1-63] (d/f 5)[5] 
End PHA channel for soft-band light-curve [1-63] (d/f 14)[14] 
Start PHA channel for hard-band light-curve[1-63] (d/f 15)[15] 
End PHA channel for hard-band light-curve[1-63] (d/f 63)[63] 
Input observation start date (dd/mm/yy)[29/09/75] 
Input observation start time (hh:mm:ss)[00:00:00] 11:58:28
Input observation end date (dd/mm/yy)[03/10/75] 02/10/75
Input observation end time (hh:mm:ss)[00:00:00] 18:17:57
 
OSOPHA 1.0.0 start PHA + rates..
 
 OBJECT NAME                    source
 SOURCE RA and DEC (1950)   95.046  -0.320
 DETECTOR  2
 RAW DATA FILE LIST a0620_list
 PHASE RESTRICTION ? F
 FOV check for CONTAMINATING  SOURCES ? F
 START and END channels for LC creation    1  63
 Integration time (no. raw data records to integrate)     1
 INTENSITY CUT (cnts/sec)   -10000.000   10000.000
 CHANNEL BOUNDARIES  5 14 15 63
 Mean BROAD band BKGD level (c/s)        0.000
 Mean SOFT band BKGD level (c/s)        0.000
 Mean HARD band BKGD level (c/s)        0.000
 
 OBSERVATION START and STOP TIMES :
 START day (of 1975) and MILLISECS of that day : 272     7468000
 END day (of 1975) and MILLISECS of that day :  275     7557000
 
 
 Creating source.lc
 
 
 Creating source.spec
 
 
 MEAN RATE (+error) for PHA data (c/s/detarea) :     8.171     0.002
 HARDNESS RATIO for PHA  data :   0.020
 PHA ACCUMULATION TIME (secs) : 21294.285
 NET AREA of detector (sq. cm) : 65.80
 INTEGRATED RATE for PHA data (c/s) :  537.6695
 
 
 **** OSOPHA 1.0.0   **** finished


% osofindfast
Equinox [ 1950 ]: 
Source RA [ 0 ]: 72.310
Source Dec. [ 0 ]: -3.820
Output listing filename: back
Output orbit file lists ? (y/n): n
Precessed RA and DEC values to 1975 epoch : 
              72.6213442716368 -3.7780690928163 
Opening output list for C detector : back_c 
 
 ** OSOFINDFAST.PL 1.0.0 finished **

% cat back_c
oso8_csxabc_248.fits
oso8_csxabc_249.fits
oso8_csxabc_973.fits

% cat back_list
cpha_176_375.fits
cpha_776_973.fits

% osopha
Equinox (d/f 1950)[1950.0] 
RA in hh mm ss.s or degrees[72.310] 
DEC in dd mm ss.s or degrees[-3.820] 
Rootname for generated spectral (+rates) output[back] 
Desired detector [1=B,2=C]:[2] 
Input listfile containing raw PHA files[back_list] 
Contaminating srces in FOV check?(d/f no)[no] 
Start PHA channel for broad-band light-curve (d/f 1)[1] 
End PHA channel for broad-band light-curve (d/f 63)[63] 
No. raw data integ. records (d/f=1 so B=40.96s ; C=12.98s)[1] 
Low int. threshold (c/s) for light-curve (d/f -10000)[-10000.0] 
High int. threshold (c/s) for light-curve (d/f 10000)[10000.0] 
Start PHA channel for soft-band light-curve [1-63] (d/f 5)[5] 
End PHA channel for soft-band light-curve [1-63] (d/f 14)[14] 
Start PHA channel for hard-band light-curve[1-63] (d/f 15)[15] 
End PHA channel for hard-band light-curve[1-63] (d/f 63)[63] 
Input observation start date (dd/mm/yy)[29/09/75] 06/09/75
Input observation start time (hh:mm:ss)[11:58:28] 02:09:45
Input observation end date (dd/mm/yy)[02/10/75] 06/09/75
Input observation end time (hh:mm:ss)[18:17:57] 04:10:35
 
OSOPHA 1.0.0 start PHA + rates..
 
 OBJECT NAME                      back
 SOURCE RA and DEC (1950)   72.310  -3.820
 DETECTOR  2
 RAW DATA FILE LIST back_list
 PHASE RESTRICTION ? F
 FOV check for CONTAMINATING  SOURCES ? F
 START and END channels for LC creation    1  63
 Integration time (no. raw data records to integrate)     1
 INTENSITY CUT (cnts/sec)   -10000.000   10000.000
 CHANNEL BOUNDARIES  5 14 15 63
 Mean BROAD band BKGD level (c/s)        0.000
 Mean SOFT band BKGD level (c/s)        0.000
 Mean HARD band BKGD level (c/s)        0.000
 
 OBSERVATION START and STOP TIMES :
 START day (of 1975) and MILLISECS of that day : 249     1305000
 END day (of 1975) and MILLISECS of that day :  249     2075000
 
 
 Creating back.lc
 
 
 Creating back.spec
 
 
 MEAN RATE (+error) for PHA data (c/s/detarea) :     0.132     0.004
 HARDNESS RATIO for PHA  data :   1.784
 PHA ACCUMULATION TIME (secs) :    77.906
 NET AREA of detector (sq. cm) : 90.91
 INTEGRATED RATE for PHA data (c/s) :   11.9760
 
 
 **** OSOPHA 1.0.0   **** finished


% fkeyprint source.spec AREASCAL
 
# FILE: source.spec
# KEYNAME: AREASCAL
 
# EXTENSION:    0
 
# EXTENSION:    1
AREASCAL=                65.80 / Area scaling factor

% cat area.txt
AREASCAL  65.80 / Area scaling factor

% fmodhead back.spec area.txt

% grppha source.spec sourcesys.spec comm="systematic 1-63 0.03 & exit"
 
  -------------------------
  MANDATORY KEYWORDS/VALUES
  -------------------------
  --------------------------------------------------------------------
  --------------------------------------------------------------------
  EXTNAME   - SPECTRUM        Name of this BINTABLE
  TELESCOP  - OSO-8           Mission/Satellite name
  INSTRUME  - GCXSE           Instrument/Detector
  FILTER    -                 Instrument filter in use
  EXPOSURE  - 21294.          Integration time (in secs) of PHA data
  AREASCAL  - 65.800          Area scaling factor
  BACKSCAL  - 1.0000          Background scaling factor
  BACKFILE  - NONE            Associated background file
  CORRSCAL  - 0.00000E+00     Correlation scaling factor
  CORRFILE  - NONE            Associated correlation file
  RESPFILE  - NONE            Associated redistribution matrix file
  ANCRFILE  - NONE            Associated ancillary response file
  POISSERR  - FALSE           Whether Poissonian errors apply
  CHANTYPE  - UNKNOWN         Whether channels have been corrected
  TLMIN1    - 1               First legal Detector channel
  DETCHANS  - 63              No. of legal detector channels
  NCHAN     - 63              No. of detector channels in dataset
  PHAVERSN  - 1.1.0           OGIP FITS version number
  STAT_ERR  - TRUE            Statistical Error
  SYS_ERR   - FALSE           Fractional Systematic Error
  QUALITY   - TRUE            Quality Flag
  GROUPING  - FALSE           Grouping Flag
  --------------------------------------------------------------------
  --------------------------------------------------------------------
 ...... exiting, changes written to file : sourcesys.spec
 ** grppha 2.8.1 completed successfully

% xspec

               XSPEC 10.00 18:59:42 18-Aug-99
http://legacy.gsfc.nasa.gov/docs/xanadu/xspec/u_manual.html

d Plot device not set, use "cpd" to set it

 Type "help" or "?" for further information
XSPEC> data sourcesys.spec
 Net count rate (cts/s) for file   1   537.7    +/-   6.382
   1 data set is in use
XSPEC> back back.spec
 *WARNING*: Data and background channel type
 (UNK,PHA) for file  1
 Net count rate (cts/s) for file   1   525.7    +/-   6.394    
                                             ( 97.8% total)
   using background file...           back.spec
XSPEC> resp c260.rsp
 *WARNING*:  Response and data file channel type mismatch
 (PHA,UNK) for file   1

XSPEC> ign 0-5 24 32-**
XSPEC> mo wa diskbb pow
........
... enter parameters and fits 
........
XSPEC> show
 19:04:22 18-Aug-99
 Auto-saving is done after every command.
 Fit statistic in use is Chi-Squared
 Minimization technique is Lev-Marq
 Convergence criterion =   1.000000000000000E-002
 Querying enabled
 Prefit-renorming enabled
 Solar abundance table is angr

 Information for file   1
  belonging to plot group   1, data group   1
 telescope = OSO-8 , instrument = GCXSE , channel type = UNK
  Current data file: sourcesys.spec
  Background file  :back.spec
  No current correction
  Response (RMF) file    : c260.rsp
  Auxiliary (ARF) file    : none
 Weighting method is standard
  Noticed channels     6 to    23
  Noticed channels    25 to    31
  File integration time    2.1294E+04
     and effective area     65.80
  File observed count rate     487.7    +/- 6.2896     cts/s
  Model predicted rate :    7.434

  mo = wabs[1]( diskbb[2] + powerlaw[3] )
  ----------------------------------------------------------------------
  ----------------------------------------------------------------------
  mo = wabs[1]( diskbb[2] + powerlaw[3] )
  Model Fit Model Component  Parameter  Unit   Value
  par   par comp
    1    1    1   wabs       nH       10^22   0.3000     frozen
    2    2    2   diskbb     Tin      keV     0.6971     +/-  0.6636E-02
    3    3    2   diskbb     norm             1.2516E+05 +/-   9986.
    4    4    3   powerlaw   PhoIndex         3.616      +/-   1.391
    5    5    3   powerlaw   norm            15.03       +/-   46.94
  ----------------------------------------------------------------------
  ----------------------------------------------------------------------
 Chi-Squared =      17.38118     using    25 PHA bins.
 Reduced chi-squared =     0.8276750     for     21 degrees of freedom
 Null hypothesis probability = 0.688

spectrum


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