A&A submitted. absorption from a distribution of column density (Locatelli, Ponti and Bianchi, 2021) ====================================================================================================== disnht: modeling X-ray absorption from distributed column densities ====================================================================================================== ADC_Keywords: Spectroscopy ; Interstellar medium Keywords: ISM: abundances - X-rays: diffuse background - X-rays: ISM - Galaxy: halo Abstract: Collecting and analysing X-ray photons over either spatial or temporal scales encompassing varying optical depth values requires knowledge about the optical depth distribution. In the case of sufficiently broad optical depth distribution, assuming a single column density value leads to a misleading interpretation of the source emission properties, nominally its spectral model. We present a model description for the ISM absorption in X-ray spectra at moderate energy resolution (CCDs), extracted over spatial or temporal regions encompassing a set of independent column densities. The absorption model (named disnht) approximates the distribution with a log-normal one and is presented in table format (readable by xspec). The solution table is made available and can be further generalised or tailored for arbitrary optical depth distributions encompassed by the extraction region. The disnht absorption model presented and its generalised solution are expected to be relevant for present and upcoming large angular scale analyses of diffuse X-ray emission (e.g. eROSITA, Athena missions). Description: We provide the tabulated optical depth values as a function of energy in the range 0.03-60 keV, computed for distributions of hydrogen column densities. The table parameters describe the column desnity distribution, assumed to be log-normal, through an average value AVG and a standard deviation STD (in dex units of cm^2). AVG and STD parameters are in the ranges 19.5-25.5 dex and 0.0-1.0 dex respectively. The .fits tables can be directly interpreted from the XSPEC X-ray spectral analysis software as a multiplicative model through the command etable{}. In this way the spectrum is multiplied by a factor exp(-TAU), where TAU is the tabulated value per energy bin. Energy bins have been fixed on a grid that oversamples the moderate energy resolution of current CCD X-ray spectrometers, by dividing the 0.03-60 keV band in 5000 log-spaced channels. TAU spectra are also provided as flat ascii tables for all AVG and STD values. Flat ascii and .fits tables are provided for different values of assumed ISM metal abundances: Anders, E. & Grevesse, N. (1989); Asplund et al. (2009) and Lodders et al. (2003). File Summary: ------------------------------------------------------------------------------------------------------ FileName Lrecl Records Explanations ------------------------------------------------------------------------------------------------------ ReadMe . . This file energy_bins.dat 29 9996 ascii table: Lower and upper bounds of spectral energy bins disnht_angr.dat.tar.gz 45000 15310000 ascii table: Absorption spectrum from log-normal hydrogen column density distribution; abundances from Anders, E. & Grevesse, N. (1989) disnht_angr.fits.tar.gz . . archive: fits table: Absorption spectrum from log-normal hydrogen column density distribution; abundances from Anders, E. & Grevesse, N. (1989) disnht_aspl.dat.tar.gz 45000 15310000 ascii table: Absorption spectrum from log-normal hydrogen column density distribution; abundances from Asplund, M., Grevesse, N., Sauval, A. J., & Scott, P. (2009) disnht_aspl.fits.tar.gz . . archive: fits table: Absorption spectrum from log-normal hydrogen column density distribution; abundances from Asplund, M., Grevesse, N., Sauval, A. J., & Scott, P. (2009) disnht_lodd.dat.tar.gz 45000 15310000 ascii table: Absorption spectrum from log-normal hydrogen column density distribution; abundances from Lodders et al. (2003) disnht_lodd.fits.tar.gz . . archive: fits table: Absorption spectrum from log-normal hydrogen column density distribution; abundances from Lodders et al. (2003) ------------------------------------------------------------------------------------------------------ Byte-by-byte Description of energy_bins.dat tables: -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 15 E9.8 keV ENERG_LO lower bound of energy bin 15 S1 --- delimiter [,] 16- 30 E9.8 keV ENERG_HI upper bound of energy bin -------------------------------------------------------------------------------- Byte-by-byte Description of disnht_*.dat.tar.gz tables: -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 E6.5 --- AVG average value of the log-normal column density distribution 12 S1 --- delimiter [,] 13- 24 E6.5 --- STD standard deviation of the log-normal column density distribution 24 S1 --- delimiter [,] 25- ... TAU ... ...- ... E6.5, S1 --- TAU ... ...- 60000 E6.5, S1 --- TAU absorption spectrum: optical depth value as function of energy (tabulated according to the energy bins in energy_bins.dat). 4998 E6.5 values separated by S1 [,] delimiters -------------------------------------------------------------------------------- Byte-by-byte Description of disnht_*.fits.tar.gz tables: Head-Data Unit 0 : -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- Head-Data Unit 1 : -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 S12 --- NAME name of parameter of column density log-normal distribution 12- 16 I4 --- METHOD flag for interpolation method 16- 20 F3.1 --- INITIAL initial parameter value for XSPEC fit task 20- 24 F3.1 --- DELTA parameter step value 24- 28 F3.1 --- MINIMUM minimum available value for parameter fit 28- 32 F3.1 --- BOTTOM lower bound for parameter prior 32- 36 F3.1 --- TOP higher bound for parameter prior 36- 40 F3.1 --- MAXIMUM maximum available value for parameter fit 40- 44 I4 --- NUMBVALS number of values for the parameter 44- 288 I4 --- VALUE array of NUMBVALS values of the parameter -------------------------------------------------------------------------------- Head-Data Unit 2 : -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1 S1 --- delimiter [(] 2- 13 E9.8 keV ENERG_LO lower bound of energy bin 13 S1 --- delimiter [,] 14- 25 E9.8 keV ENERG_HI upper bound of energy bin 26 S1 --- delimiter [)] -------------------------------------------------------------------------------- Head-Data Unit 3 : -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 4 F3.1 --- AVG average value of the log-normal column density 4- 8 F3.1 --- STD standard deviation of the log-normal column density 9- 44982 E9.8 --- TAU absorption spectrum: optical depth value as function of energy. 4998 E9.8 values --------------------------------------------------------------------------------