X-ray Absorption in the ISM and IGM


  • Calibration of X-ray absorption in our Galaxy
    R. Willingale, R.L.C. Starling, A.P. Beardmore, N.R. Tanvir and P.T. O’Brien 2013, MNRAS pdf abstract

  • X-ray absorption in the ISM is parameterized by the total hydrogen column density, NHtot, and the solar abundances of high Z element w.r.t. this hydrogen. NHtot=NHI+2NH2 where NHI is the atomic gas column density and NH2 is the molecular hydrogen column density. The X-ray afterglows of GRBs seen by the Swift XRT can be used to calibrate the X-ray absorption in our Galaxy. NH2 is estimated using
    NH2=NH2max*[1-exp(-NHI*E(B-V)/Nc)]α
    
    For our Galaxy NH2max=7.3x1020 molecules cm-2, Nc=3.0x1020 atoms cm-2, α=1.1 and the abundances are within ±10% of those given by Wilms J., Allen A., McCray R., 2000, ApJ, 542, 914.

    NHI is given by the LAB 21 cm all-sky survey, Kalberla P. M. W., Burton W. B., Hartmann D., Arnal E. M., Bajaja E., Morras R., Poppel W. G. L., 2005, A&A, 440, 775.
    E(B-V) is derived from IRAS and COBE/DIRBE infra-red by Schlegel D. J., Finkbeiner D. P., Davis M., 1998, ApJ, 500, 525.
    E(B-V)/NHtot (the dust/gas ratio) correlates with the CO survey of the Milky Way, Dame T. M., Hartmann D., Thaddeus P., 2001, ApJ, 547, 792.
    The NHI, E(B-V) and WCO maps have been re-sampled on the same Aitoff projection grid to facilitate the analysis.

  • WEBTOOL to calculate NHtot for any position nhtot
  • NHTOT ftools application program to calculate NHtot for any position - source files and build using SUSE x86_64_Linux nhtot.tar.gz

  • X-ray absorption evolution in Gamma-Ray Bursts: warm-hot intergalactic medium or evolutionary signature of their host galaxies?
    R.L.C. Starling, R. Willingale, N.R. Tanvir, A.E. Scott, K. Wiersema, P.T. O’Brien, A.J. Levan and G.C. Stewart, 2013, MNRAS pdf abstract

  • The WHIM (warm IGM) and the Lyman alpha forest (cold IGM) can account for a significant fraction of the X-ray absorption seen in high redshift sources, z>4.

  • XSPEC models to calculate X-ray absorption from the WHIM and the Lyman forest at a specified redshift - source files xabs.tar.gz readme