04/29/02
Boirin Laurence	ESTEC
postbus 299	SF2A- PCHE-
2200 AG	NOORDWIJK, PAYS-BAS

Presentation 1 : Oral
Strongly absorbed quiescent X-ray emission from the X-ray transient XTE J0421+56 observed by XMM-Newton
Boirin L., Parmar A., Oosterbroek T.
We have observed the X-ray transient XTE J0421+56 in quiescence with XMM-Newton. The observed spectrum is highly unusual being dominated by an emission feature at 6.5 keV. We fit the spectrum using a partially covered power-law and Gaussian line model, in which the emission is almost completely covered by material with an abundance consistent with solar and is strongly absorbed with an NH of 48x10^22 cm^-2. The Gaussian at 6.4 keV can be interpreted as a fluorescent emission line from iron. The spectra of X-ray transients in quiescence are normally modeled using advection dominated accretion flows, black-bodies, power-laws, or by the thermal emission from a neutron star surface. The strongly absorbed X-ray emission from XTE J0421+56 is therefore highly unusual and could result from the compact object being embedded within a dense circumstellar wind emitted from the supergiant B[e] companion star. The uncovered and unabsorbed component observed below 5 keV could be due either to X-ray emission from the supergiant B[e] star itself, or to the scattering of high-energy X-ray photons in an ionized corona or wind, such as observed in some low-mass X-ray binary systems.

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