Chandra Low Energy Transmission Grating Spectrum of SS Cygni in Outburst
Abstract
We have fitted the Chandra Low Energy Transmission Grating spectrum of SS Cygni in outburst with a single temperature blackbody suffering the photoelectric opacity of a neutral column density and the scattering opacity of an outflowing wind. We find that this simple model is capable of reproducing the essential features of the observed spectrum with the blackbody temperature Tbl = 250+/-50 kK, hydrogen column density NH = 5.0+2.9-1.5 x 1019 cm-2, fractional emitting area f = 5.6+60-4.5 x 10-3, boundary layer luminosity Lbl = 5+18-3 x 1033 erg/s, wind velocity v ~ 2500 km/s, wind mass-loss rate Mdotw ~ 1.1 x 1016 g/s, and arbitrary values of the wind ionization fractions of 20 ions of O, Ne, Mg, Si, S, and Fe. Given that in outburst the accretion disk luminosity Ldisk ~ 1 x 1035 erg/s, Lbl/Ldisk ~ 0.05+0.18-0.03, which can be explained if the white dwarf (or an equatorial belt thereon) is rotating with an angular velocity Omegawd ~ 0.7+0.1-0.2 Hz, hence Vrot sin i ~ 2300 km/s.
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