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*xflux, hxflux* - Calculation of X-ray Flux

The conversion of count rate to flux depends on the intrinsic spectrum of the source, so xflux must be used in conjunction with fit. Fit generates a table of the best fit intrinsic spectrum (_int.tab extension). xflux uses this table to calculate either the integrated flux between two energy limits or the flux density at a specific energy. In order to calculate the flux of a source with only a few counts, or for Einstein or ROSAT HRI data, fit must be run with rebin=yes and the spectral model given as input leaving only the normalization as a free parameter. For IPC or PSPC sources with a sufficient number of counts the task fit should be run as before.

The distance required to calculate the luminosity can be given in kpc or redshift z. In order to compute the luminosity correctly using xflux, the SAME distance must be input to both fit and xflux. Note that the only way to input a distance/z to fit is to also specify an intrinsic absorbing column; it should be negligible ($\sim$10**17 cm^-2) if such a column is not otherwise required.

To compute the integrated flux:

1.

First run qpspec to obtain counts from desired region. This produces ``..._obs.tab'' file.

2.

Then run fit (with rebin=yes for low count or HRI data). This is where you specify the spectral shape: e.g. abs(21.51)*pow(0.85); for details. The output file is ..._int.tab, which contains the amplitude (``normalization'') corresponding to the number of net counts gathered by qpspec.

3.

Finally, run xflux, which will give you flux (or flux density) for a user-specified energy band from the model spectrum.

  xs> xflux
  spectrum intermediate file:  rp90
  energy or range of energies in keV:  0.1:2.4     # flux between 0.1 and 2.4 keV
  flux between 0.1 and 2.4 keV
  distance e.g., 5 kpc or 1.0z:  1.0 kpc              # this distance must be the
                                                      # same as that used in fit.


Output file:  rp90_flux.tab

To compute the flux density at 1 keV:

  xs>  xflux

  spectrum intermediate file (rp90):
  energy or range of energies in keV (0.1:2.4):  1.0
  distance e.g., 5 kpc or 1.0z (1.0kpc):

Output file:  rp90_fd.tab

Detailed spectral analysis is not possible for sources observed with the ROSAT HRI, because of the detector's poor energy resolution. However, fluxes for HRI sources may still be calculated, provided one assumes a spectral shape. The task hxflux executes qpspec, fit, and xflux, as described above, with all spectral parameters except normalization held fixed at values specified by the user.

   input files:	  rh0110267.qp

   output files:  rh110267_flux.tab or rh110267_fd.tab

xs> hxflux

source qpoe file (xdata$rh110267.qp): xdata$rh110267.qp
source region descriptor (c 2322 4408 60): 
background qpoe file (xdata$rh110267.qp): 
bkgd region descriptor (a 2322 4408 120 240): 
root name for output files [root_obs.tab, etc.] (rh110267): 
spectral model, e.g. abs(logNH)*pow(alpha) (abs(19.0)*ray(1.0 cosmic 100)): 
energy or range of energies in keV (0.1:2.4): 
distance or redshift e.g. 5kpc or 1.0z (0.047): 

ds:                     0
file:                   rh110267_obs.tab
scale:                  0.00
mission:                20
seqno:                  CA110267.N2
instrument:             ROSAT_HRI
sub-instrument:         0
no. pha channels:       1
mean off-axis angle
   of events (arcmin):  28.84
radius (arcmin):        0.50
filter:                 0
livetime (sec):         2153.14
x, y:                   2322.00, 4408.00
livetime corr:          0.99
src area (sq. pix.):    11277.00
cts_tot (count):        1993.00  
bkgd area (sq. pix.):   135692.00
ccts_bkg (count):       16.21  
net (count):            1976.79  
neterr (count):         45.67  
Output table file(s):  rh110267_obs.tab, rh110267_soh.tab, rh110267_boh.tab
Performing the Simplex minimization fit.
Found 1 free parameter(s). 
Found 1 dataset(s).

 Data set #1 from file: rh110267_obs.tab 

 PHA energy range   observed     error   predicted (pred-obs)/error 
 --- ------------   --------     -----   --------- ---------------- 
   1  0.01->2.57      1976.8 *    45.7      1976.8        0.0 
               * indicates use in Chi-square calculation. 

The fitted net counts are: 1976.79; with error: 45.67.

Chi-square =      0.000 
Predicted Data file: dummy_prd.tab
Intermediate Spectra file: rh110267_int.tab

Model: abs(19.000)*ray(1.000 cosmic 100.000)

Model Component 1: Raymond Thermal 
          Cosmic abundance at 100 percent.
          temperature = 1.000 (fixed) 
 normalization (log) = 12.2580032 (calculated) 
    galactic Nh (log) = 19.000 (fixed) 
    intrinsic Nh (log) = 0.000 (fixed) 
          redshift = 0.000 (fixed) 


Output file: rh110267_flux.tab
Model: abs(19.0000)*ray(12.2580 1.0000 cosmic 100)
Absorption type: Morrison & Maccammon
Units:
        flux (ergs/cm**2/s)
        luminosity (10**34 ergs/s)
        energy (keV)
        H_0 (km/s/Mpc)

Compute flux and luminosity for energy range :

  flux    unabs_f       L      lo_energy  hi_energy    D_kpc    z    H_0   q_0
  ----    -------      ---     ---------  ---------    -----   ---   ---   ---
3.52E-11  3.73E-11   9.86E-4      0.10       2.40     4.70E-2 INDEF  50.0  0.00