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Astron. Astrophys. 317, L47-L50 (1997) 4. DiscussionWe previously found that a two-component model provides a good explanation of the energy-independent dipping in the Exosat ME band for X 1755-338, and proposed that this model may be able to explain all of the dipping sources. We now find that this model gives good fits to the Rosat PSPC data and allows the observed features of the PSPC data to be understood. Firstly there is no significant change in the LECO of the data
between non-dip and dip data. The LECO is determined by the power law
component and the spectral fitting results show there is no
significant change in
Secondly, the light curves show a clear decrease of count rate of
10% in the band 0.5 - 2.0 keV; in the lower band 0.1 - 0.5 keV there
is little evidence for dipping but a small residual level of dipping
of
The blackbody plus power law model was found to be a good fit to TTM data on X 1755-338 by Pan et al. (1995). However they were not able to find a best fit model, and several models fitted equally well including the above model and a multi-temperature disc plus power law. The latter model would allow the source to be a black hole candidate. Thus, the conclusion of Pan et al. that their results strongly support the black hole nature of the source does not seem to be justified. It is clear that the Rosat PSPC results support the
two-component model of the dippers. This model predicts that as
dipping is due to absorption of the blackbody it can not extend
indefinitely to energies much less than
© European Southern Observatory (ESO) 1997 |