Update on the Low Energy Isolated Neutron Star and White Dwarf Cross-Calibration Standards

1. Update on the Low Energy Isolated Neutron Starand White DwarfCross-Calibration Standards Vadim Burwitz EPIC Calibration Meeting Nov. 6, 2007, Mallorca, Spain

2. Overview • Well calibrated Standards needed  for Absolute Calibration • Absolute Calibration Soft X-rays  dependant on model spectra of WDs and INs what models to use?, uncertainties? • Analysis of HZ 43A, Sirius B and RX J1856.5-3754 : XMM-Newton/Chandra  determine spectral parameters  improve instrumental response at low energies.

3. Simultaneous fit to RXJ1856 and the WDs

4. White Dwarfs • Objects • HZ 43 • Sirius B • Physical Models • White dwarf Atmosphere Models • Parameters (nH, eff. T, log(g), absolute Flux, abundance) •  nH well constrained  <1018 cm2 • Most up-to-date atmosphere codes used (Tübingen TMAP, TLUSTY Hubeny) • pure hydrogen good fit (very little Helium required) • better possibly stratified Hydrogen + Helium model  needs to tested • Instruments • ROSAT • EUVE • Chandra LETGS

5. White Dwarfs • Status of Models / Parameters for HZ43 and Sirius B • Available fits are done and complete see below: • Pease et al. SPIE, 2000  LETG effective area • Beuermann, Burwitz, Rauch A&A, 2006  corr. sugg. to LETGS eff area, ROSAT and EUVE • Kaastra et al. A&A, 2007 in prep.  independent check of Models • Done • Check differences Rauch / Hubeny model fluxes for Sirius B  differences in Theoretical models (beeing looked into) • To Do • Implement corrections for LETGS effective area. • EUVE: check why effective area is too low • ROSAT improvements to instr. params. need to implemented (Beuermann et al.)

7. NLTE pure H model spectrum of HZ43 Different bound-free and free-free absorption coefficients -- Seaton -- Karzas & Latter

8. Isolated Neutron Stars • Objects • RX J1856.5-3754 • Empirical Models • No NS Atmosphere Models fit the entire Spectrum from X-ray to optical • Best description of the full X-ray spectrum is given by a  2 component blackbody model • A single blackbody model provides a good description X-ray spectra above 0.2 keV • Parameters (nH, eff. T, absolute Flux, abundance) • nH is possibly an issue. Not all instruments can be used to contrain it. • Instruments • ROSAT, XMM, Chandra, SWIFT, SUZAKU • Chandra LETGS needed to constrain nH and low T component

9. Isolated Neutron Stars • Status of Models / Parameters for RXJ1856 • Early fits to LETGS and EPIC-pn with a single and two component blackbody model have been published: • Burwitz et al. 2002, 2004 • Drake et al. 2002 • Beuermann, Burwitz, Rauch A&A, 2006 (BBR06) • Fits to data from all listed instruments have started by Frank Haberl • To Do • Investigate independent measurement of nH • Compare BBR06 model to all instruments to see where improvements are need • Implement corrections for all relevant effective areas . • discuss next step • find a physical model

10. Simultaneous fit to RXJ1856 and the WDs

11. Parameters obtained from fit