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- Data
- Chandra
- HZ 43
- Sirius B
- GD 153
- Chandra
- Results
see papers
HZ43 Fitting Function
The Beuermann et al 2006 paper uses the TMAP white dwarf atmosphere model of Werner et al for fitting. For the purposes of calibration efforts, C. Markwardt developed a fitting function that can be used in place of the full atmosphere model. The fit was done in the 0.1 - 1 keV range. Note that Beuermann et al INCLUDE interstellar absorption in their model, so it is not necessary to provide an additional absorption component.
The model can be used in XSPEC using "mdefine" statements. The model is a modified blackbody spectrum, whose "energy" is a polynomial of several terms. The kT value is the white dwarf temperature in keV, and the norm is the expected norm. (Note that a 2021 version of XSPEC or later is required)
mdefine poly_hz43 e*(0.955968 + e*(-0.699684 + e*(0.555432 + e*(-0.292088 + e*0.069582))))+dummy
mdefine hz43 8.0525*poly_hz43(0.0)**2/kT**4/(exp(poly_hz43(0.0)/kT)-1.0)
and then defined as
model hz43
0.0130643 -0.0001(0.000130643) 0.01 0.01 0.02 0.02
0.0395467 0.001(0.000395467) 0 0 1e+20 1e+24
Here the temperature of ~0.013 keV is the best-fit temperature using this fitting function, and does not represent the true white dwarf temperature. The norm of ~0.039 is the best-fit norm, and again is physically meaningless other than as a fitting coefficient. Using this model results in the following curve in the photon spectrum. Solid is the Beuermann et al curve and dashed is the model. The residual panel below demonstrates that the worst-case error in this fitting function approximation is 1%.
Papers
- http://cdsads.u-strasbg.fr/abs/2006A%26A...458..541B Beuermann, K., Burwitz, V., Rauch, T. 2006: ''Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC'', A&A 458,541
- http://cdsads.u-strasbg.fr/abs/2008HEAD...10.0406K Kaastra, J. S., Lanz, T., Hubeny, I., Paerels, F. 2008: ''Establishing HZ43 A, Sirius B, and RX J185635-3754 as soft X-ray standards: a cross-calibration between the Chandra LETG+HRC-S, the EUVE spectrometer, and the ROSAT PSPC'', HEAD 10.0406
- http://cdsads.u-strasbg.fr/abs/2008A%26A...481..807R Rauch, T. 2008, ''Uncertainties in (E)UV model atmosphere fluxes'', A&A 481, 807
- http://cdsads.u-strasbg.fr/abs/2006A%26A...458..541B Kaastra, J. S., Lanz, T.. Hubeny, I.. Paerels, F. B. S. 2009, ''Effective area calibration of the reflection grating spectrometers of XMM-Newton. II. X-ray spectroscopy of DA white dwarfs'', A&A 497, 311
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