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 (10**17 cm-2) if such a column is not otherwise required.
To compute the integrated flux:
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