Iron K Spectra from L-Shell Ions in Photoionized Plasmas Work in Progress Duane Liedahl Physics and Advanced Technologies Lawrence Livermore National Laboratory Motivations:Si K  fluorescence from L-shell ions in HMXBs spectroscopic diagnostic potential high spectral resolution at Fe K provided by Astro-E 2 Focus:resonant Auger destruction Applications:stellar winds in HMXBs accretion disks in AGN and X-ray binaries

ASCA data from Vela X-1 motivated a wind model based on spherically symmetric mass loss See Sako et al., ApJ, 1999 contours of log ionization parameter  =L/nr 2 Model accounts for emission from H-like and He-like ions of several elements Does not account for fluorescence lines that were observed Si charge state distribution

From wind model we can predict high-ionization component of high-resolution Chandra spectrum

Chandra spectrum Vela X-1data shows entire Si L-shell K  spectrum Several charge states are separated, although each ionic component is a blend Mg-F O N C B Be

Same features are observed in other X-ray binaries

Broad range of silicon charge states suggests that fluorescence from iron L-shell ions should be observed

Fabian, et al., 2000, PASP Iron K lines are used to probe black hole accretion disks Nandra, et al.,1999, ApJ

Models used to fit relativistic Fe K line involve 6.4 keV “near-neutral line” or H-like and He-like lines – no K  from Fe L Where are the K lines from Fe L-shell ions? It was suggested that resonant Auger destruction is responsible. (Ross, Fabian, & Brandt 1996, MNRAS; see also Band et al. 1990, ApJ) How does silicon observed in HMXBs respond to this process?

Resonant Auger destruction is simply line scattering with a high destruction probability per scatter Since destruction probability is high, a good approximation is to zero out all K lines from Fe L-shell ions – right? mechanism operates for F-like to Li-like ions (for K  need vacancy in n=2 shell)

We use an escape probability method to model resonant Auger destruction geometric setup P esc vs. line center optical depth

line optical depth depends on fractional population of lower level Calculation of line optical depths requires knowledge of level population distribution appropriate to local plasma conditions

Many iron K  transitions terminate on excited levels Example: Be-like Fe XXIII Calculations performed with the HULLAC atomic physics package

This line terminates on ground Fe XXIII illustrates the selective action of resonant Auger destruction four lines to levels 6, 7, 8 models folded through  E fwhm = 6 eV gaussian resolution kernel

Define an effective fluorescent yield to account both for atomic physics and resonant Auger destruction

A better assessment of resonant Auger destruction accounts for level population distributions We have demonstrated the effect of Fe RAD for the “nebular case,” that is, only ground levels are significantly populated Should be adequate for most HMXB environments, not so for disks

Consistent treatment requires population kinetics model for pre-ionization charge state (cf., Jacobs et al. 1989, Phys Rev A)

Photoionization out of excited levels provides access to different autoionizing levels, resulting in a different K spectrum line fluorescence yield high yield lines low yield lines

We include a bright EUV radiation field to drive the level populations schematic of ion layer in an accretion disk atmosphere level populations for 9 lowest Be-like levels for kT = 80 eV Planckian

low yield lines high yield lines Level population distribution can make a big difference in both fluorescence line spectra and ion fluorescence yield Comparison of Fe XXIV spectra in “zero-D” showing effect of different level population distributions

Resonant Auger destruction modifies the outgoing spectrum but does not entirely quench emission

Disk environment leads to enhancement of effective fluorescent yield for this ion – even with resonant Auger destruction

Li-like iron is not an exception – similar results are found for three other charge states

Calculation by Mario Jimenez-Garate; figure provided by Chris Mauche Vertical disk structure calculations show that column densities of Fe L ions are each a few times cm -2 (see also Nayakshin & Kallman 2001, ApJ)

K  emission from Fe L boosts theoretical “Fe line” equivalent widths for expected accretion disk parameters ionic equivalent widths Li-like through F-like Fe summed equivalent width suggested range of column density found in accretion disk atmosphere

AGN models predicting relativistic O VIII emission should include Fe L K  calculations for consistency

Summary and Comments Focus of this work is on assessing spectroscopic effects of resonant Auger destruction Conclude that it is not valid to “turn off” K  lines from L-shell ions when modeling disks That L-shell ions are not required in fits to AGN spectra remains puzzling but will be better tested with Astro-E 2 Fe K lines from L-shell ions should be observed in some HMXBs Connection between HMXBs and AGN in this context? HMXB spectra can be used to exercise spectral models by providing constraints based on observations – feed back into disk models Resonant Auger destruction can be turned into a new class of plasma diagnostic